Oceans and Estuaries
Oceans and Estuaries
A view of the earth from a satellite shows an azure planet composed almost entirely of water. According to Tom S. Garrison, in Oceanography: An Invitation to Marine Science (2005), the ocean covers over two-thirds of the earth's surface to an average depth of 12,451 feet (or almost 2.3 miles). The U.S. Geological Survey (USGS), in Where Is Earth's Water Located? (August 28, 2006, http://ga.water.usgs.gov/edu/earthwherewater.html), notes that the earth contains 97% of the planet's water. It has a profound influence on the earth's environment. The ocean has subdivisions that are recognized as the Atlantic Ocean, the Pacific Ocean, the Indian Ocean, and the Arctic Ocean.
The terms ocean and sea are sometimes used interchangeably, but they are terms used out of tradition. According to Garrison, the ocean is "the vast body of saline water that occupies the depressions of the Earth's surface" and includes all the oceans and seas. For convenience sake, the ocean is subdivided into artificial compartments and given names that include the Atlantic, Pacific, and Indian oceans and the Mediterranean, Red, and Black seas.
Origin of the Ocean
Research suggests that the ocean is about four billion years old and that both the atmosphere on Earth and the ocean were formed through a process called outgassing of the earth's deep interior. According to this scientific theory, the ocean originated from the escape of water vapor from the melted rocks of the early Earth. The vapor rose to form clouds surrounding the cooling planet. After the earth's temperature had cooled to a point below the boiling point of water, rain began to fall and continued falling for millions of years. As this water drained into the huge hollows of the planet's cracked surface, the oceans were formed. The force of gravity kept this water on Earth. The oceans are still forming today at an extremely slow pace. According to Garrison, about 0.025 cubic miles is added to the ocean each year.
Why Is the Ocean So Salty?
The salinity (saltiness) of the ocean is due to the presence of a high concentration of dissolved inorganic solids in water, primarily sodium and chloride (the components of table salt). Table 6.1 shows the principal constituents of ocean water. Early in the life of the planet, the ocean probably contained little of these substances. However, since the first rains descended on the young Earth billions of years ago and ran over the land, the rain has eroded the soil and rocks, dissolving them and transporting their inorganic solids to the ocean. Rivers and streams also carry dissolved inorganic solids and sediments and discharge them into the ocean. In Why Is the Ocean Salty? (1993, http://www.palomar.edu/oceanography/salty_ocean.htm), Herbert Swenson estimates that U.S. rivers and streams discharge 225 million tons of dissolved solids (salts) and 513 million tons of suspended sediment into the ocean each year. Throughout the world, rivers annually transport about four billion tons of dissolved salts to the ocean.
Over billions of years the ocean has become progressively more salty. The activity of the hydrological cycle concentrates the ocean salts as the sun's heat evaporates water from the surface of the ocean, leaving the salts behind. (See Figure 6.1.) There is so much salt in the ocean that if it could be taken out and spread evenly over the earth's entire land surface, it would form a layer more than five hundred feet thick—about the height of a forty-story building. (See Figure 6.2.)
Swenson notes that the salinity of the ocean is currently about thirty-five pounds per thousand pounds of ocean water, or thirty-five parts per thousand (ppt). This is similar to having a teaspoon of salt added to a glass of drinking water. By contrast, the U.S. Environmental Protection Agency (EPA), in In Condition of the Mid-Atlantic Estuaries (November 1998, http://www.epa.gov/emap/html/pubs/docs/groupdocs/estuary/assess/cond_mae.pdf), indicates that freshwater has less than 0.5 ppt. Salinity in estuaries varies from slightly brackish (0.5 to 5 ppt) at the freshwater end to moderately brackish (5 to 18 ppt), to highly saline (19 ppt or more) near the ocean. An estuary is a body of water where a river meets the ocean and fresh- and saltwater mix.
|Principal constituents of seawater|
|Chemical constituent||Content (parts per thousand)|
|Source: Herbert Swenson, "Principal Constituents of Seawater," in Why Is the Ocean Salty? U.S. Geological Survey, 1993|
|Total dissolved solids (salinity)||35.079|
Ocean as Controller of Earth's Climate
The ocean plays a major role in the earth's weather and long-term climate change. It has a huge capacity to store heat and can affect the concentration of atmospheric gases that control the planet's temperature. In Environmental Health: Ecological Perspectives (2005), Kathryn Hilgenkamp indicates that the top eight feet of the ocean hold as much heat as the entire atmosphere, making the ocean's ability to distribute heat an important factor in climate changes. For example, the occurrence of a southward-flowing current of warm water off the coast of western South America (El Niño), which is caused by a breakdown of trade wind circulation (steady winds blowing from east to west above and below the equator) can disrupt global weather patterns.
The ocean plays a crucial role in the cycle of carbon dioxide, a process affecting global warming. For example, the National Oceanic and Atmospheric Administration (NOAA) reports in "After Two Large Annual Gains, Rate of Atmospheric CO2 Increase Returns to Average, NOAA Reports" (NOAA Magazine, March 31, 2005), that the ocean stores some of the seven billion tons of carbon dioxide added each year to the atmosphere by natural sources and humankind's burning of fossil fuels. The ocean, trees, plants, and the soil serve as reservoirs for about half of all the human-produced carbon dioxide emitted each year since the Industrial Revolution, whereas the other half is accumulating in the atmosphere.
According to the Population Reference Bureau (2006, http://www.prb.org/Content/NavigationMenu/PRB/Journalists/FAQ/Questions/Coastal_Population.htm), approximately 3 billion people worldwide, about half the world's population, live within 200 kilometers (about 125 miles) of a coastline. This living preference places huge segments of the world population at risk from coastal hazards, such as hurricanes, tidal waves, and flooding and increases pollution of both the ocean and estuaries.
|Leading states in coastal population growth, 1980–2003|
|State||Total change (million persons)||State||Percent change|
|Source: Kristen M. Crossett et al., "Table 2. Leading States in Coastal Population Growth, 1980–2003," in Population Trends Along the Coastal United States: 1980–2008, National Oceanic and Atmospheric Administration, National Ocean Service, September 2004, http://marineeconomics.noaa.gov/socioeconomics/assessment/population/pdf/2_national_overview.pdf (accessed February 5, 2007)|
|New Jersey||1.2||New Hampshire||46|
In Population Trends along the Coastal United States: 1980–2008 (September 2004, http://marineeconomics.noaa.gov/socioeconomics/assessment/population/pdf/1_front_matter_intro.pdf), Kristen M. Crossett et al. state that in 2003 an estimated 53% of the U.S. population (occupying only 26% of the total U.S. land mass) lived in coastal counties. From 1980 to 2003 the total coastal population of the United States increased by 27%, which is consistent with the nation's rate of increase as a whole. However, some coastal communities increased in population much more than others. Table 6.2 shows the leading states in coastal population growth, from 1980 to 2003. California had the greatest number of people move into the state, but Florida had the highest percentage growth.
The most common coastal hazard is the threat of the huge ocean storms that come ashore, generally during the warmer months of the year, and cause devastating damage to property and human life. These storms go by different names in different parts of the world. They are called hurricanes or tropical storms in the North Atlantic, the eastern North Pacific, and the western South Pacific. Typhoon is used for storms in the China Sea and the western North Pacific, whereas cyclone is used for storms in the Arabian Sea, the Bay of Bengal, and the South Indian Ocean.
In August 2005 Hurricane Katrina hit the U.S. Gulf Coast, causing widespread devastation in cities such as New Orleans, Louisiana; Mobile, Alabama; and Gulfport, Mississippi. Katrina was one of the strongest storms to reach the U.S. coast in the last 100 years with sustained winds during landfall of 125 miles per hour. Since 1900, it was the third deadliest hurricane (killing 1,833 people) and was by far the costliest hurricane. (See Table 6.3 and Table 6.4.)
|The deadliest mainland United States hurricanes, 1900–2006|
|Note: Hurricanes, or tropical cyclones, were not named until the 1950s.|
|aThis figure could be as high as 10,000 to 12,000.|
|bOver 500 lost on ships at sea, 600-900 estimated deaths.|
|cMoving more than 30 miles per hour.|
|dOf the total lost 344 were lost on ships at sea.|
|Source: Adapted from Jerry D. Jarrel et al., "Table 2. The Thirty Deadliest Mainland United States Tropical Cyclones 1900–2000," in The Deadliest, Costliest, and Most Intense United States Hurricanes from 1900 to 2000, National Oceanic and Atmospheric Administration, National Weather Service, October 2001, http://www.aoml.noaa.gov/hrd/Landsea/deadly/Table2.htm (accessed January 9, 2007)|
|1||Unnamed (TX, Galveston)||1900||4||8,000a|
|2||Unnamed (FL, Lake Okeechobee)||1928||4||1,836|
|3||Katrina (Eastern LA, western MS)||2005||3||1,833|
|4||Unnamed (FL, Keys)||1919||4||600b|
|5||Unnamed (New England)||1938||3c||600|
|6||Unnamed (FL, Keys)||1935||5||408|
|7||Audrey (Southwest LA, inland TX)||1957||4||390|
|9||Unnamed (LA, Grand Isle)||1909||4||350|
|10||Unnamed (LA, New Orleans)||1915||4||275|
|11||Unnamed (TX, Galveston)||1915||4||275|
Tsunamis are another coastal threat. A tsunami is an ocean wave—which may reach enormous dimensions—produced by a submarine (undersea) earthquake, landslide, or volcanic eruption. A December 2004 tsunami, triggered by a massive earthquake in the Indian Ocean, killed over two hundred thousand people and caused massive damage in Indonesia, Sri Lanka, India, Thailand, and many small islands in the region. The true death toll from the tsunami may never be known, and the devastation was so overwhelming that it is difficult to attach a dollar figure to it.
Much research is targeted at understanding and predicting coastal storms and tsunamis so that coastal residents can be warned of an impending event. Besides increasing the amount of property at risk, coastal population growth has created potentially life-threatening problems with storm warnings and evacuation. It has become increasingly difficult to ensure that the ever-rising numbers of residents and visitors can be evacuated and transported to adequate shelters during storm events. Sometimes hurricane evacuation decisions must be made well in advance of issuing hurricane warnings to mobilize the appropriate manpower and resources needed for the evacuation. Also, when a significant percentage of the coastal population has not experienced an event such as a hurricane, people are less likely to prepare and respond properly before, during, and after the event. However, following the 2004 tsunami, government officials and scientists began working to create a new tsunami warning system for that region.
|The costliest U.S. hurricanes, 1900–2006|
|Rank||Hurricane||Year||Category||Damage in billions of dollars|
|aCosts normalized to 2002 dollars using gross national product (GNP) Inflation/Wealth Index.|
|bCosts unadjusted for inflation.|
|Source: Compiled in January 2007 by Sandra Alters for Thomson Gale, 2007, from Jerry D. Jarrel et al., "Table 3. Costliest U.S. Hurricanes 1900–2000 (unadjusted)," in The Deadliest, Costliest, and Most Intense United States Hurricanes from 1900 to 2000, National Oceanic and Atmospheric Administration, National Weather Service, October 2001, http://www.aoml.noaa.gov/hrd/Landsea/deadly/Table3.htm (accessed January 10, 2007) and "1980–2005 Billion Dollar U.S. Weather Disasters," in Billion Dollar U.S. Weather Disasters, National Oceanic and Atmospheric Administration, National Climatic Data Center, January 2007, http://www.ncdc.noaa.gov/img/reports/billion/disasterssince1980.pdf (accessed January 10, 2007)|
|1||Katrina (eastern LA, western MS coastlines)a||2005||3||$125|
|2||Andrew (southeast FL and LA)a||1992||5||36|
|3||Rita (TX-LA border coastlines)a||2005||3||16|
|4||Wilma (southwest FL)a||2005||3||16|
|5||Charley (FL, SC)a||2004||4||15|
|8||Frances (FL, GA, SC, NC, NY)a||2004||2||9|
|9||Jeanne (east central FL)a||2004||3||7|
|10||Agnes (FL, northeast U.S.)b||1972||1||8.6|
|11||Betsy (southeast FL and LA)b||1965||3||8.5|
|12||Camille (MS, southeast LA, VA)b||1969||5||7|
|13||Georges (FL Keys, MS, AL)a||1998||2||6.6|
|14||Floyd (mid atlantic & northeast U.S.)a||1999||2||6.5|
|15||Alicia (north TX)a||1983||3||5.9|
|17||Diane (northeast U.S.)b||1955||1||5.5|
|18||Isabel (NC, VA, MD)a||2003||2||5|
|19||Frederic (AL, MS)b||1979||3||5|
|20||Unnamed (New England)b||1938||3||4.7|
|21||Opal (northwest FL, AL)a||1995||3||3.6|
|22||Carol (northeast U.S.)b||1954||3||3.1|
|24||Carla (north & central TX)b||1961||4||2.6|
|25||Donna (FL, eastern U.S.)b||1960||4||2.4|
|27||Elena (MS, AL, northwest FL)a||1985||3||2.4|
|28||Bob (NC, northeast U.S.)a||1991||2||2.1|
|29||Celia (south TX)b||1970||3||2|
|30||Dennis (FL, AL, GA, MS, TN)a||2005||3||2|
|31||Hazel (SC, NC)b||1954||4||1.9|
|32||Unnamed (FL, MS, AL)b||1926||4||1.7|
|33||Unnamed (north TX)b||1915||4||1.5|
|34||Dora (northeast FL)b||1964||2||1.5|
|35||Eloise (northwest FL)b||1975||3||1.5|
|36||Gloria (eastern U.S.)b||1985||3||1.5|
|37||Unnamed (northeast U.S.)b||1944||3||1.2|
|38||Beulah (south TX)b||1967||3||1.1|
|39||Bonnie (eastern NC & VA)a||1998||3||1.1|
CORAL REEFS—A SPECIAL OCEAN HABITAT
A coral reef is a submerged ridge near the surface of the water made up not only of colonies of coral animals that secrete hard skeletons but also of other aquatic organisms such as algae, mollusks, and worms. Coral reefs are among the richest marine ecosystems in terms of beauty, species, productivity, biomass (the amount of living matter), and structural complexity. They are dependent on intricate interactions between the coral, which provides the structural framework, and the organisms that live among the coral. Most reefs form as long narrow ribbons along the edge between shallow and deep waters, and their assets are many: fisheries for food, income from tourism and recreation, materials for new medicines, and shoreline protection from coastal storms.
Coral Reef Structure
Corals are simple, bottom-dwelling organisms related to the sea anemone and jellyfish. The basic building block of coral is a polyp, a tiny animal that has a common opening used to take in food and excrete wastes and is surrounded by a ring of tentacles. The weak stinging cells of the tentacles are used to capture small zoo-plankton (minute floating aquatic animals) for food. Each polyp sits in its own tiny bowl of calcium carbonate (its skeleton), which the coral constantly builds as it grows up from the ocean floor. Reef-building corals live in large colonies formed by the repeated divisions of genetically identical polyps, although many species of coral animals are represented within the reef. The colonies can take a wide variety of shapes, including branched, leafy, or massive forms, which may grow continuously for thousands of years.
Inside the sac of each coral polyp lives a single-celled algae. The algae give off oxygen and nutrients the coral uses to grow, and the coral gives off carbon dioxide and other substances the algae uses. Such a living situation is called symbiosis—the living together of two dissimilar organisms with mutual benefit.
Because of their dependence on symbiotic algae, coral reefs can grow only under conditions favoring the algae. Coral reefs are confined to tropical waters because the algae require warm, shallow, well-lit waters that are free of turbidity and pollution.
Coral Reefs—Ecosystems at Risk
The proximity of coral reefs to land makes them particularly vulnerable to the effects of human actions. Because they depend on light, coral reefs can be severely damaged by silt, which leads to an overgrowth of seaweed and other factors that reduce water clarity and quality. Sport diving and overfishing for food and the aquarium trade can deplete species and damage coral, resulting in disruption to the intricate interactions among reef species, as well as coral decline. (Overfishing means that so many fish are harvested that the natural breeding stock is depleted.) Introduction of exotic species through human activity can be devastating as the new predators consume the living reefs.
NOAA notes in "Major Reef-Building Coral Diseases" (January 23, 2007, http://www.coris.noaa.gov/about/diseases/) that along with becoming infected by bacteria or developing diseases of unknown causes, corals may respond to stress and damage with a condition known as coral bleaching. The coral expels the microscopic algae that normally live within its cells and provide the coral with their color, their ability to rapidly grow skeleton, and much of their food. The bleached coral turns pale, transparent, or unusual colors and then starves because it is unable to feed or reproduce. Increased bleaching is an early warning sign of deteriorating health and can be caused by extremes of light, temperature, or salinity.
Natural events, such as hurricanes, can also damage coral reefs. Healthy reefs generally recover from such damage, but unhealthy reefs often do not. In "Hazards to Coral Reefs" (January 23, 2007, http://www.coris.noaa.gov/about/hazards/), NOAA warns, "Current estimates note that 10 percent of all coral reefs are degraded beyond recovery. Thirty percent are in critical condition and may die within 10 to 20 years. Experts predict that if current pressures are allowed to continue unabated, 60 percent of the world's coral reefs may die completely by 2050."
Coral Reefs in the United States
The EPA notes in the 2000 National Water Quality Inventory (August 2002, http://www.epa.gov/305b/2000report/chp4.pdf) that coral reefs are found in only three places in the United States: Florida (primarily in the Florida Keys), throughout the Hawaiian archipelago, and in the offshore Flower Gardens of Texas. The Florida reef system is part of the Caribbean reef system, the third largest barrier-reef ecosystem in the world. Five U.S. territories—American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands—also have lush reef areas. Figure 6.3 shows that the northwestern Hawaiian Islands make up 69% of the country's coral reef areas, by far the largest percentage in the United States and its territories.
Many U.S. coral reefs have been designated as marine sanctuaries with varying degrees of protection. The full extent and condition of most of these coral reefs is only beginning to be studied as a special area of focus.
In September 2002 NOAA released the first national assessment of the condition of coral reefs in the United States. The report, The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2002 (http://www.nccos.noaa.gov/documents/status_coralreef.pdf), was prepared under the auspices of the U.S. Coral Reef Task Force and established a baseline that is used for biennial reports on the health of coral reefs in the United States. NOAA also released the report A National Coral Reef Action Strategy (September 2002, http://www.coris.noaa.gov/activities/actionstrategy/) to Congress outlining specific action to address thirteen major goals, including the continuation of mapping and monitoring, to protect coral reefs.
According to the State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States, there are an estimated 7,607 miles of U.S. reefs and a range of 4,479 to 31,470 miles of reefs off the Freely Associated States. (The United States and Freely Associated States refer to fourteen jurisdictions that contain coral reef ecosystems, which are listed in Figure 6.4.) The report notes that an estimated 27% of the world's shallow water coral reefs may already be beyond recovery, and about 66% are severely degraded. The report also indicates that in all areas some coral reefs in the United States are in good to excellent health. However, every reef system is suffering from both human and natural disturbances. These reefs suffer from the same problems as do reefs all over the world, especially those resulting from rapidly growing coastal populations. The report states that 10.5 million people now live in U.S. coastal areas next to shallow coral reefs, and every year about 45 million people visit the areas.
Florida and the U.S. Caribbean were considered to be in the most unfavorable condition, mainly because of nearby dense populations and the effects of hurricanes, disease, overfishing, and a proliferation of algae. The NOAA report indicates that live coral cover in the Florida Keys has declined 37% since 1997. Since 1982, white-band disease has killed nearly all the elkhorn and staghorn corals off the coasts of St. Croix (U.S. Virgin Islands), Puerto Rico, and southeastern Florida.
In August 2005 NOAA released the second national assessment of the condition of coral reefs in the United States, The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2005, (http://ccma.nos.noaa.gov/ecosystems/coralreef/coral_report_2005/CoralReport2005_C.pdf), which was edited by Jenny E. Waddell. Waddell notes progress in building a mapping and monitoring system. She also indicates that many local action strategies have been developed to counter threats to coral reefs, especially in priority threat areas. In separate chapters, each reporting area describes in quantitative detail the state of the coral reefs in their area. This differs from the more general qualitative (descriptive) nature of the first report.
A summary of a comparison between the 2002 and 2004 perceived levels of threat to coral reef ecosystems is shown in Figure 6.4. The rows compare each jurisdiction for all threat categories for 2002 and 2004. In Florida, for example, the threat level in each threat category remained the same from 2002 to 2004, except for the "other" category. Thus, the composite trend rose by one point from 2002 to 2004, as shown in the far right column, resulting in a increase of threat overall (arrow).
The columns compare each threat category for all jurisdictions for 2002 and 2004. For example, climate change, diseases, tropical storms, and fishing increased in threat level over those two years across all jurisdictions. However, eight of fourteen threat categories were perceived to have decreased in severity since 2002.
Nearshore waters are shallow waters a short distance from the shore in lakes, rivers, estuaries, and the ocean. Depending on the size of the water body, the nearshore waters may be minimal in size (a small lake) or large (the coastal waters of the Atlantic Ocean). They reflect the conditions and activities within the watershed. A watershed is an area in which water, sediments, and dissolved materials drain to a common outlet, such as a lake, river, estuary, or the ocean.
Whether marine, estuarine, or fresh, nearshore waters serve a variety of functions. They are the prime recreational waters, providing opportunities for swimming, boating, diving, surfing, snorkeling, and fishing. Nearshore waters are intimately linked with wetlands and sea grasses and provide a unique habitat for a variety of plants and animals. According to the EPA, in "Nearshore Waters and Your Coastal Watershed" (July 1998, http://www.epa.gov/owow/oceans/factsheets/fact3.html), these waters are the source of food and shelter for many species of fish and shellfish and provide habitat for 80% of the fish species in the United States. Nearshore waters also provide many opportunities for education and research for students, naturalists, and scientists.
Because of their proximity to the shoreline, nearshore waters are particularly vulnerable to pollution. As a result, water quality in most confined waters and some nearshore waters is deteriorating, which in turn affects the plant and animal life. Besides pollution, nearshore waters are vulnerable to the everyday (and to all appearances, harmless) activities of people. For example, swimming has been restricted in some shallow lagoons with coral reefs and beautiful beaches because heavy use by swimmers resulted in chemical concentrations of suntan oil and sunblock lotion in the water that was high enough to kill or impair the coral reefs. Wakes from recreational powerboats in high-use areas have been shown to increase wave action, resulting in increased shoreline erosion. Increased pollutant levels from boat paints, spills during refueling, and leaks of gas and oil from recreational boat engines in areas of high recreational use affect both plants and animals. Private pier and boathouse construction result in shading of water, which contributes to sea grass decline. Balancing the need to accommodate the public's desire to enjoy water-related activities and ownership of waterfront property and the need to protect nearshore waters is a difficult management issue.
Estuaries are places of transition, where rivers meet the sea. An estuary is a partially enclosed body of water formed where freshwater from rivers flows into the ocean, mixing with the salty seawater. As mentioned earlier, salinity in estuaries varies from slightly brackish (0.5 to 5 ppt) at the freshwater end to moderately brackish (5 to 18 ppt), to highly saline (19 ppt or more) near the ocean. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by reefs, barrier islands, or fingers of land, mud, or sand that make up their seaward boundary. Estuaries come in all shapes and sizes. Examples include the Chesapeake Bay, Puget Sound, Boston Harbor, San Francisco Bay, and Tampa Bay. In "The National Estuary Program: A Ten Year Perspective" (October 4, 2006, http://www.epa.gov/owow/estuaries/aniv.htm), the EPA states that there are approximately 130 estuaries in the United States.
The tidal sheltered waters of estuaries support unique communities of plants and animals that are specially adapted for life under a wide range of conditions. Estuarine environments are incredibly productive, producing more organic matter annually than any equal-sized area of forest (including rain forests), grassland, or cropland. A wide range of habitats exists around and in estuaries, including shallow open water, tidal pools, sandy beaches, mud and sand flats, freshwater and salt marshes, rocky shores, oyster reefs, mangrove forests, river deltas, wooded swamps, and kelp and sea grass beds.
NATIONAL ESTUARY PROGRAM
The Water Quality Act of 1987 created the National Estuary Program (NEP) to help achieve long-term protection of living resources and water quality (the basic "fishable/swimmable" goal of the Clean Water Act) in estuaries. To improve an estuary, the NEP brings together community members to define program goals and objectives, identify estuary problems, and design action plans to prevent or control pollution, while restoring habitats and living resources such as shellfish. This approach results in the adoption of a comprehensive conservation and management plan for implementation in each estuary. This integrated watershed-based, stakeholder-oriented, water resource management approach has led to some significant local environmental improvements since its founding. The EPA notes in "National Estuary Program" that in 1987 the NEP consisted of six estuary programs located throughout the nation; in 2006 there were twenty-eight estuary programs in eighteen states and Puerto Rico.
In "National Estuary Program Success Stories" (December 12, 2006, http://www.epa.gov/owow/estuaries/success.htm), the EPA mentions several NEP successes. Two examples of environmental improvement resulting from the NEP can be found in the Leffis Key and Corpus Christi projects. The Leffis Key restoration project in Sarasota Bay, Florida, resulted in thirty acres of productive intertidal habitat being created and planted with more than fifty thousand native plants and trees at a cost of $315,000. In Corpus Christi Bay, Texas, treated biosolids were applied to a twenty-five-acre plot of aluminum mine tailings, resulting in plant growth promotion, wildlife habitat, and improved water quality. Biosolids are composed of sewage sludge that has been properly treated and processed to make a nutrient-rich material that can be safely recycled and applied as fertilizer.
CHESAPEAKE BAY PROGRAM
According to the Chesapeake Bay Program Office (August 19, 2003, http://www.chesapeakebay.net/info/bayfaq.cfm#big), the Chesapeake Bay (the Bay) is the largest estuary in North America and one of the most productive estuaries in the world. It has a sixty-four-thousand-square-mile watershed that encompasses six states and the District of Columbia. Its watershed is home to more than fifteen million people and thirty-six hundred species of plants and animals. The Bay has over 11,600 miles of shoreline and averages 21 feet deep, with hundreds of thousands of acres of shallow water. It is two hundred miles long and thirty-five miles wide at its widest point.
The first estuary in the United States to be targeted for restoration and protection, the Bay is protected under its own federally mandated program, separate from the NEP. The Chesapeake Bay Program (2007, http://www.chesapeakebay.net/) began in 1983 with a meeting of the governors of Maryland, Pennsylvania, and Virginia; the mayor of the District of Columbia; and the EPA administrator. These individuals signed the Chesapeake Bay Agreement committing their states and the District of Columbia to prepare plans for protecting and improving water quality and living resources in the Chesapeake Bay. The Chesapeake Bay Program evolved as the institutional mechanism to restore the Bay and to meet the goals of the Chesapeake Bay Agreement.
Although great progress has been made in the Chesapeake Bay restoration, much remained to be done by early 2007. The editorial "A Cleaner Bay, a Step at a Time" (Salisbury Daily Times, February 8, 2007) notes that increased population growth in the Chesapeake Bay area is contributing to ongoing problems in the estuary. The editorial sums up the work still needed to meet a 2010 cleanup deadline:
- About 1 million failing septic tanks across the regional watershed need to be dug up and repaired.
- Farmers—some 80,000 of them—would have to make expensive and radical changes to the way they manage their land and their fertilizer application.
- Hundreds of municipal and private sewage plants would have to be overhauled, costing millions of dollars each.
- In all, about $28 billion would have to be spent, or double the $14 billion already being devoted toward the restoration effort.
CONDITION OF THE NATION'S ESTUARIES
The EPA, NOAA, the USGS, the U.S. Fish and Wildlife Service, coastal states, and the National Estuary Programs coordinate efforts to produce the National Coastal Condition Report, which describes the ecological and environmental conditions in U.S. coastal waters, including estuaries. The most recent report is the National Coastal Condition Report II (2005) (December 2004, http://www.epa.gov/owow/oceans/nccr/2005/downloads.html). Figure 6.5 is a summary graphic from this report and shows the overall national coastal condition for estuaries.
The report uses five indicators of estuarine condition. (See Figure 6.5.) For each indicator, researchers assessed the condition at 2,073 estuary sites in the "lower 48" states between 1997 and 2000. The second step was to assign a regional rating. The water quality index consists of indicators such as nitrogen and phosphorus levels, water clarity, and level of dissolved oxygen. The sediment quality index refers to the level of contamination of the sediment with toxic chemicals. The benthic index refers to organisms that live at the bottom of estuaries. A good benthic index is one in which a wide variety of benthic species are found, of which there are few pollution-tolerant species and several pollution-sensitive species that are found. The coastal habitat index is an assessment of the loss of wetland areas (the terrestrial-aquatic interface) of estuarine ecosystems. The fish tissue index refers to levels of chemical contaminants within fish.
The National Coastal Condition Report II states that "the overall condition of estuaries in the United States is fair." The report also notes that estuaries in the Northeast have poorer water quality conditions than those in other regions of the country. The sediment quality index is poor in the estuaries of the Great Lakes, the Northeast, and Puerto Rico. The benthic index is also poor in the Northeast and Puerto Rico. For estuaries along the northeastern coast, only the coastal habitat index has a good rating.
Figure 6.6 shows percentages of estuary area in the United States (excluding the Great Lakes) that is impaired, threatened, or unimpaired for human or aquatic life uses. Impaired human use means that fish are contaminated in those waters and are not acceptable to eat. Impaired aquatic life use means that the benthic index is poor. Threatened use correlates with a fair condition. Twenty-one percent of estuaries are unimpaired for human and/or aquatic life uses. Forty-four percent is threatened for both uses. Fifteen percent are impaired for both uses.
The EPA, states, tribes, and other federal agencies are collaborating on a new process to monitor the nation's waterways. Following the publication of the 2000 National Water Quality Inventory, the EPA entered a transition period in the gathering and analysis of water quality data in nationally consistent, statistically valid assessment reports. The EPA article "Schedule for Statistically Valid Surveys of the Nation's Waters" (December 5, 2005, http://www.epa.gov/owow/monitoring/guide.pdf) details its new reporting schedule.
In the 2000 National Water Quality Inventory, the EPA reports that fourteen of the twenty-seven coastal states and territories had rated the water quality of some of their coastal waters in 2000. The states had assessed 14% of the 22,618 miles of national coastline excluding Alaska, or 5.5% (3,221 miles) of ocean shoreline (including Alaska's 36,000 miles of coastline). Of the 14% of ocean waters assessed, 79% fully supported their designated uses, 14% were impaired, and 7% were supporting uses but threatened. Designated uses (such as fishing and drinking water supply) are the beneficial water uses assigned to each water body by a state as part of its water quality standards.
The EPA reports in the 2000 National Water Quality Inventory that bacteria (pathogens, which are disease-causing organisms) were identified as the leading contaminants of ocean shoreline waters, followed by oxygen-depleting substances and turbidity (cloudiness) in 2000. (See Figure 6.7.) Bacteria provide evidence of possible fecal contamination that may cause illness. States use bacterial indicators to determine if oceans are safe for swimming or secondary contact recreation, such as waterskiing. Figure 1.5 in Chapter 1 shows the pathways of bacteria to surface waters. The most common sources of bacteria are urban runoff, inadequately treated human sewage, and runoff from pastures and feedlots (nonpoint sources), all of which were identified by several states as leading sources of ocean shoreline impairment. (See Figure 6.8.)
Turbidity, which is a measure of the relative clarity of water, is caused by suspended matter or other impurities that make the water look cloudy. These impurities may include clay, silt, finely divided organic and inorganic matter, plankton, and other microscopic organisms. It interferes with the transmission of light to underwater grasses and other plant life in need of this light. If the transmission of light is reduced because of heavy silt in the water, this can smother bottom-dwelling organisms such as oysters. Turbidity was responsible for more than 10% of the impaired ocean shoreline miles reported to the EPA in 2000. (See Figure 6.7.) Three of the leading sources of ocean impairment are also contributors to turbidity: runoff from highly developed urban areas, agricultural activities (nonpoint sources), and construction projects. (See Figure 6.8.)
The EPA reports in the 2000 National Water Quality Inventory that most of the ocean waters assessed supported the five general-use categories shown for estuaries: aquatic life support, fish consumption, shellfishing, primary contact, and secondary contact. These categories represent summaries of the designated uses and their achievement provided by the states to the EPA. Waters that either support their designated uses only part of the time or do not support their uses at all are considered impaired. Good water quality supports primary contact (swimming without risk to public health) in 85% of the assessed ocean waters (the same percentage for use support in estuaries) and fish consumption (fish safe to eat) in 91% (compared with 52% of use support in estuaries).
In 94% of the waters assessed, the water was considered of good quality and capable of supporting aquatic life (suitable habitat for protection and propagation of desirable fish, shellfish, and other aquatic organisms). In the shellfish harvesting summary (water quality supports a population of bivalves free from toxicants and pathogens that can pose a health risk to people who eat them), 86% of the ocean waters assessed had good water quality that supported this use. In addition, good water quality in 91% of the ocean waters assessed supported secondary contact recreation (people can perform water-based activities such as waterskiing and boating without risk of adverse human health effects).
Beach closings take place hundreds of times each year to protect the public from possible exposure to pathogens. The bacteria that cause the closings are generally harmless, but they are present in large numbers in human and animal sewage. Their presence indicates the possible presence of disease-causing organisms.
The most common problem caused by swimming in contaminated water is gastroenteritis, which is contracted by swallowing water while swimming and can result in diarrhea, nausea, vomiting, and cramps. Even though gastroenteritis is generally not harmful to healthy adults, it can cause serious illness in children, the elderly, and people with autoimmune diseases, such as the human immunodeficiency virus and the acquired immunodeficiency syndrome.
The EPA established the Beaches Environmental Assessment and Coastal Health (BEACH) Program in 1997 to help reduce the risk of waterborne illness at the nation's beaches and recreational waters through improvements in water protection programs and risk communication. Three years later, the BEACH Act of 2000 was signed into law. This law was an amendment to the Clean Water Act and required:
- The EPA to issue new or revised water quality criteria for pathogens and pathogen indicators.
- Coastal states to adopt these new or revised water quality standards.
- The EPA to award grants to states and local governments to develop and implement beach monitoring and assessment programs.
The BEACH Act also required the EPA to prepare a progress report for Congress every four years. The first report was Implementing the BEACH Act of 2000: Report to Congress (October 2006. http://www.epa.gov/water science/beaches/report/full-rtc.pdf).
In Implementing the BEACH Act, the EPA determines that the major pollution sources responsible for beach closings and advisories in 2002 included runoff of storm water following rainfall (21%), sewage spills or overflows from various sources (13%), and unknown sources (43%). (See Figure 6.9.)
Table 6.5 shows the number of beaches surveyed for closings and advisories from 1997 through 2004. The number of beaches in the survey grew voluntarily from 1,021 in 1997 to 2,823 in 2002. Beginning in 2003, however, coastal states were required to report beach information to the EPA. Thus, the number surveyed in 2004 grew to 3,574.
Table 6.5 shows that from 1997 through 2004 approximately 26% of U.S. beaches were affected by advisories or closings. Nevertheless, the EPA notes in Implementing the BEACH Act that most of the advisories or closings lasted only one or two days. In 2004, for example, only 4% of possible open beach days were lost to advisories or closings.
As a result of the BEACH Act, the EPA has improved its Beach Advisory and Closing On-line Notification Web site (http://oaspub.epa.gov/beacon/beacon_national_page.main), which provides data to the public on beach advisories and closings. Along with collecting more comprehensive data and strengthening water quality standards, the EPA is also working to improve pollution control efforts at the nation's beaches.
|Numbers and percentages of beaches affected by advisories or closings, 1997–2004|
|Voluntary survey||Required reporting|
|*Incomplete data from 11 states; Environmental Protection Agency is working to complete data set.|
|Source: "Table 3.2. National Health Protection Survey of Beaches Trends, 1997–2004," in Implementing the BEACH Act of 2000 Report to Congress, U.S. Environmental Protection Agency, October 2006, http://www.epa.gov/waterscience/beaches/report/full-rtc.pdf (accessed February 6, 2007)|
|Number of beaches||1,021||1,403||1,891||2,354||2,445||2,823||1,857*||3,574|
|Number of beaches affected by advisories or closings||230||353||459||633||672||709||395||942|
|Percentage of beaches affected by advisories or closings||23||25||24||27||27||25||21||26|
OCEAN POLLUTANTS—SOURCES AND EFFECTS
Any number of human-made materials or excessive amounts of naturally occurring substances can adversely affect marine and estuarine waters and their inhabitants. Because water is such an effective solvent and dispersant, it is difficult to track and quantify many pollutants known to have been discharged into marine and estuarine waters, and in many cases the source of pollution may be unknown. Some pollutants, such as oil spills, are easily detected the moment they enter the water. Others, such as toxic chemicals, are less obvious, and their presence may remain undetected until they cause extensive damage.
Oil is one of the world's most important fuels. Its uneven distribution on the planet, however, forces its transport over the ocean, through pipelines, and over land. This inevitably results in accidents, some massive and some small, during drilling and transporting. In March 1967 the 118,285-ton supertanker Torrey Canyon, carrying oil from Kuwait, caused the world's first massive marine oil spill off the coast of England.
Oil spills are a dramatic form of water pollution—visible, immediate, and sometimes severe. The sight of dead and dying otters and birds covered with black film arouses instant sympathy, and the bigger the spill, the more newsworthy it is. Even though it is true that oil can have a devastating effect on marine life, the size of the spill itself is often not the determining factor in the amount of damage it causes. Other factors include the amount and type of marine life in the area and weather conditions that can disperse the oil. Despite the drama that tanker spills create, worldwide pollution from them is a relatively minor source of marine pollution. Tanker spills represent a small fraction of the oil released to the environment worldwide when compared with industry sources, nontanker shipping releases, and oil seepage from natural sources.
According to the EPA (March 9, 2006, http://www.epa.gov/oilspill/exxon.htm), when the supertanker Exxon Valdez ran into a reef in Prince William Sound, Alaska, in March 1989, more than eleven million gallons of oil spilled into one of the richest and most ecologically sensitive areas in North America. The Exxon Valdez Oil Spill Trustee Council (2007, http://www.evostc.state.ak.us/History/PWSmap.cfm) states that a slick (spill area) of approximately eleven thousand square miles—the size of Rhode Island and Maryland combined—threatened fish and wildlife. Otters died by the thousands, despite efforts by trained environmentalists and local volunteers to save them. Oil-soaked birds lined the shores, only to be eaten by larger predator birds, which then succumbed to dehydration and starvation because the ingested oil destroyed their metabolic systems.
OCEAN POLLUTION ACT OF 1990
In response to the Exxon Valdez disaster, Congress passed the Oil Pollution Act of 1990 (OPA). Most of the OPA provisions were targeted at reducing the number of spills and reducing the quantity of oil spilled. Among its provisions were the creation of a $1 billion cleanup-damage fund (the money comes from a tax on the petroleum industry), advance planning for controlling spills, stricter crew standards, and the requirement that new tankers have double hulls. When the exterior hull of a double-hulled tanker is punctured, the interior hull holding the oil may still remain intact. (The Exxon Valdez was not double-hulled.) The law requires older tankers to be fitted with double hulls by 2010. The OPA also:
- Compels the use of escort tugboats in certain harbors to assist tankers.
- Requires standards for tank levels and pressure-monitoring devices to detect leaks in cargo tanks.
- Requires the U.S. Coast Guard to establish minimum standards for overfill devices to prevent overfill oil spills. (An overfill oil spill is the result of too much oil being pumped into a tanker during a transfer from a facility to a tanker or between two tankers. On occasion, overfill spills have involved large quantities of oil.)
DECLINES IN OIL SPILLS
Declines in oil spills are being seen on a global scale. The International Tanker Owners Pollution Federation reports that between 1970 and 1979 the average incident rate for large spills (over 700 metric tons or approximately 215,000 gallons) from the worldwide tanker industry was 25.2 spills per year. (See Figure 6.10.) Between 1980 and 1989 the average rate dropped to 9.3 spills per year. From 1990 to 1999 the global spill rate declined further to 7.8 spills per year and from 2000 through 2006 to 3.7 spills per year. Larger spills, such as these, are most often caused by collisions and groundings. Smaller spills most often occur because of routine operations, such as loading in ports or at oil terminals.
The decline in oil spills in U.S. waters is even more dramatic. Figure 6.11 shows the number of oil spills over one thousand gallons in U.S. waters from 1973 to 2004. Most spills are not shown on this graph because they are smaller than one thousand gallons. According to the report U.S. Coast Guard Polluting Incident Compendium: Cumulative Data and Graphics for Oil Spills 1973–2004 (2006, http://www.uscg.mil/hq/gm/nmc/response/stats/Summary.htm), 88% of all spills from 1973 to 2004 were between one and one hundred gallons. Spills over one hundred thousand gallons have not occurred in U.S. waters since 1996, and before that, since 1990.
Although oil tanker spills are highly visible cases of pollution entering the ocean, the U.S. Department of the Interior's Minerals Management Service reports in OCS Oil Spill Facts (September 2002, http://www.mms.gov/stats/PDFs/2002OilSpillFacts.pdf) that the largest input of oil into marine environments is natural seepage (naturally occurring oil in the ground that moves through the soil and into the water). In North America natural seepage contributes 63% of the total marine oil input. Twenty-two percent of the oil found in the marine waters off the coast of North America is due to municipal and industrial waste and runoff. Marine transportation is responsible for only 3%, although worldwide, it is responsible for 33%.
NOAA (March 27, 2007, http://marinedebris.noaa.gov/whatis/welcome.html) defines marine debris as "any man-made object discarded, disposed of, or abandoned that enters the coastal or marine environment. It may enter directly from a ship, or indirectly when washed out to sea via rivers, streams and storm drains." The effects of marine debris can be both costly to coastal communities and dangerous to humans and aquatic life. Certain types of marine debris, such as broken glass and medical waste, can pose a serious threat to public health, causing beach closures and swimming advisories and robbing coastal communities of significant tourism dollars.
In December 2006 the Marine Debris Research, Prevention, and Reduction Act became law. The purpose of the act was to create a Marine Debris Research, Prevention, and Reduction Program within NOAA and the Coast Guard to help identify, determine sources of, assess, reduce, and prevent marine debris and its adverse impacts on the marine environment and navigation safety.
CRUISE SHIP WASTE
Laurie Asseo reports in "Cruise Line Fined Millions for Dumping" (Milwaukee Journal Sentinel, July 22, 1999) that in 1999 the Royal Caribbean, one of the world's largest cruise lines, pleaded guilty in federal court to dumping oil and hazardous chemicals in U.S. waters and lying about it to the Coast Guard. It agreed to pay a record $18 million fine for polluting waters. This was besides the $9 million in criminal fines the company agreed to pay in a previous plea agreement. Asseo notes that six other cruise lines have pleaded guilty to illegal waste dumping since 1993 and have paid fines of up to $1 million. These cases focus attention on the difficulties of regulating the expanding cruise line industry, because most major ships sailing out of U.S. ports are registered in foreign countries.
In "Cruise Ship Water Discharges" (March 23, 2007, http://www.epa.gov/owow/oceans/cruise_ships/), the EPA reports that there are more than 230 cruise ships operating worldwide. Feeding and housing thousands of people on each of these vessels means that a great deal of waste is generated while at sea. The EPA notes that "some of the waste streams generated by cruise ships include bilge water (water that collects in the lowest part of the ship's hull and may contain oil, grease, and other contaminants), sewage, graywater (waste water from showers, sinks, laundries and kitchens), ballast water (water taken onboard or discharged from a vessel to maintain its stability), and solid waste (food waste and garbage)."
The EPA is conducting a variety of activities to address the problem of cruise ship waste. Among these activities the agency is assessing the need for additional standards for waste discharge from cruise ships operating in Alaska and is preparing a cruise ship waste assessment report (September 14, 2006, http://www.epa.gov/owow/oceans/cruise_ships/disch_assess.html). The assessment report will characterize cruise ship waste, analyze existing programs for managing those wastes, and determine whether better management of those wastes is needed.
Plastics such as bags, containers, bottle caps, and beverage carriers are dumped daily from oceangoing vessels, commercial and recreational fishing boats, offshore oil and gas platforms, and military ships. Other types of plastic debris—factory wastes, sewer overflows, illegal garbage dumping, and human littering—come from land sources. Thousands of seabirds and marine animals die each year as a result of ingesting or becoming entangled in this plastic.
Another concern is commercial fishing nets. Once made of natural materials, these nets are now made mainly of durable, nondegradable plastic. When they are lost or discarded in the ocean, they pose a floating hazard to seals, dolphins, whales, and diving birds, which can become entangled in the nets. In 1988 thirty-one nations ratified an agreement making it illegal for their ships to dump plastic debris, including fishing nets, into the ocean. As part of that agreement, the United States enacted the Marine Plastics Pollution Research and Control Act, which went into effect in 1989. Among other regulations, the act imposes a $25,000 fine for each violation.
Plastic pellets are the raw materials that are melted and molded to create plastic products. According to Paul Watson, in "The Plastic Sea" (July 24, 2006, http://www.seashepherd.org/editorials/editorial_060724_1.html), sixty billion pounds of resin pellets are manufactured in the United States annually. The two primary ways that these pellets enter the ocean are direct spills during cargo handling operations at ports or spills at sea, and storm water discharges that carry the pellets from industrial sites. Plastic pellets may persist in the water environment for years, depending on the resin type, the amount and types of pellet additives, and how the pellets react to sunlight, wave action, and weathering. Although pellets have been found in the stomachs of wildlife, primarily seabirds and sea turtles, their effects have not been clearly demonstrated to be harmful.
Since 1991 the Society of Plastics Industries (SPI), the major national trade association for manufacturers who make plastic products in the United States, has been working with the EPA to identify and minimize the sources of plastic pellet entry into the ocean. In July 1991 the SPI instituted Operation Clean Sweep (http://www.opcleansweep.org/), an industry-wide education campaign to encourage members to adopt the SPI 1991 Pellet Retention Environmental Code and the 1992 Processor's Pledge aimed at committing the U.S. plastics industry to total pellet containment.
Another important problem is ghost fishing. This is the entrapment of fish and marine mammals by lost or abandoned nets, pots, fishing line, bottles, and other discarded objects. When marine creatures are entangled in old six-pack beverage binders or caught in abandoned fishing nets, they suffer and may die.
In 1972 Congress enacted the Marine Protection, Research, and Sanctuaries Act (also known as the Ocean Dumping Act) to prohibit the dumping into the ocean of material that will unreasonably degrade or endanger human health or the marine environment. The act applies to waters within two hundred miles of the U.S. coast and was amended in 1988 to prohibit dumping industrial waste and sewage sludge into the ocean. As a result, the only ocean dumping allowed as of early 2007 was dredged material from the bottom of water bodies to maintain navigation channels and berthing areas. To dump dredged material in the ocean, a permit must be obtained from the EPA.
Algae are plantlike organisms that manufacture their own food via photosynthesis. Most algal species in U.S. coastal waters are not harmful and serve as the energy producers at the base of the food chain. However, sometimes algae may grow fast and bloom, creating dense, visible patches near the water surface. Red tide is a common name for events in which certain algae containing reddish pigments bloom so that the water appears to be red. Often, these particular species are toxic to humans and wildlife, but not all species of algae are toxic, nor do all species impart color to the water during blooms.
Eutrophication and Hypoxia
Algal blooms often occur because an abundance of plant nutrients, such as nitrates and phosphates, have entered the water. Thick layers of algae block the sunlight from reaching the algae and other plant life below, so those organisms die. (See Figure 6.12.) When the nutrients run out, much of the rest of the algae die. Bacteria and other decomposers feed on the dead algae, using oxygen in the water as they break down the tissues. This process, in which an overenrichment of a water body with nutrients results in an excessive growth of organisms and a resultant depletion of oxygen concentration, is called eutrophication. The deficiency of oxygen in the water is called hypoxia, and it is a condition that can have severe effects on local ecosystems.
Hypoxia kills most of the sessile (permanently attached) bottom-dwelling benthic organisms in a body of water, such as oysters and clams; aquatic animals that swim or crawl, such as fish, shrimp, and crabs, either leave the area or die as shown in Figure 6.12. For this reason, areas where hypoxic conditions exist are frequently referred to as dead zones. Hypoxia is a worldwide problem that often occurs where rivers carrying large amounts of agricultural runoff empty into lakes, estuaries, and the ocean.
In 1998 Congress passed the Harmful Algal Bloom and Hypoxia Research Act. The act requires the formation of a federal multiagency task force to investigate the problem and report back to Congress with a plan and recommendations to address harmful algal blooms and hypoxia. The Harmful Algal Bloom and Hypoxia Amendments Act of 2004 reauthorized the 1998 act.
EUTROPHICATION AND HYPOXIA IN THE GULF OF MEXICO
One location in the United States where hypoxia occurs is the Gulf of Mexico, off the Louisiana coast. According to the USGS in the fact sheet "Restoring Life to the Dead Zone: Addressing Gulf Hypoxia, a National Problem" (June 2000, http://www.nwrc.usgs.gov/factshts/016-00/016-00.htm), the Gulf's hypoxic zone is comparable to the largest hypoxic areas in the world, such as those in the Black and Baltic seas. The Gulf of Mexico hypoxic zone is approximately six to seven thousand square miles of water where the oxygen level is below two ppm. Under normal conditions dissolved oxygen levels would be five to six ppm.
The zone is caused by harmful algal blooms that are believed to be the result of the discharge of nutrients from the Mississippi River watershed into the Gulf of Mexico. The nutrients (nitrogen and phosphorus) come from fertilizers, animal waste, and domestic sewage. The nitrate-nitrogen level in the main stem of the Mississippi River, which drains thirty-one states, has doubled since the 1950s. Figure 6.13 shows the Mississippi Basin watershed and the states whose rivers drain into it.
To correct the situation and as a requirement of the Harmful Algal Bloom and Hypoxia Research Act, the EPA, six other federal agencies, nine states, and two Native American tribes developed an action plan to reduce nutrient loads reaching the Gulf: the Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (January 2001, http://www.epa.gov/msbasin/taskforce/pdf/actionplan.pdf). It has the goal of reducing the size of the hypoxic zone by over 68% no later than 2015. The plan also calls for implementation of nutrient management strategies to achieve a 30% reduction in the amount of nutrients reaching the Gulf of Mexico. Reducing nutrients in the water, particularly nitrogen and phosphorus, will help reverse the hypoxia. This is accomplished primarily by implementing farming practices that reduce fertilizer runoff, restoring wetland areas, and restoring riverbanks. Information generated through the research and monitoring portions of the plan will be used to modify future goals and actions as necessary. As of early 2007, the Basin Expert Review report was expected to be completed in the spring or summer of 2007, with a revised action plan due in 2008 (January 22, 2006, http://www.epa.gov/msbasin/taskforce/pdf/timeline_process01_06.pdf).
Exotic species are plants, animals, and microbes that have been carried from one geographic region to another, either intentionally or unintentionally. Unintentional introduction includes transport in ballast water of ships or as pests on imported fruits, vegetables, and animals or animal products. Before modern times, movement from one geographical region to another was infrequent and slow, allowing time for the ecology to absorb and counterbalance the newcomers.
However, because of rapid transport, organisms can now move across continents in a matter of hours or days. Once removed from their natural ecological system, where eons of evolution have established predator-prey relationships, competitive species, and other devices to maintain balance, exotic species may reproduce unchecked in their new locations because they have no natural competitors or predators.
Both estuarine and ocean habitats have suffered from exotic species introduction. In the Chesapeake Bay, MSX (Haplosporidium nelsoni ) and Dermo (Perkinsus marinus ), two oyster diseases that have ravaged oyster populations, came to the Bay with oysters introduced from other regions. The coral reefs in the Northern Mariana Islands are being decimated by the introduction of the crown-of-thorns starfish. The green crab introduced from the Baltic Sea to the shores of New England occurs in such high numbers that the crab is believed to be eating young scallops and other valuable seafood.
Passage of the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 was a first step in attempting to prevent species migration. This legislation authorized the Fish and Wildlife Service and NOAA to adopt regulations to prevent the unintentional introduction of aquatic nuisance species. In 1999 the Invasive Species Council was created by presidential executive order to oversee efforts to control unwanted exotic species. The council is chaired jointly by the secretaries of interior, agriculture, and commerce. Council members include the secretaries of state, treasury, and transportation, and the administrator of the EPA. To date, a variety of laws have been enacted and legislation has been introduced to help research this problem and find ways to abate and control it. The Northeast Midwest Institute, in "Biological Pollution" (February 20, 2007, http://www.nemw.org/biopollute.htm), provides a listing of the proposed and enacted legislation.
The oceans are great interconnected bodies of salt water that cover 71 percent of Earth’s surface, a total of 139,400,000 square miles (361,100,000 square kilometers). They contain 97 percent of all the water on Earth, a total volume of 329,000,000 cubic miles (1,327,000,000 cubic kilometers).
Oceanography, the science of the oceans, officially started in the 1870s when the British ship Challenger began its career of oceanic exploration. The findings of this expedition took twenty years to analyze and are published in fifty thick volumes. Another research vessel, the Meteor, equipped with electronic equipment, began exploration in 1925 and discovered great mountains and trenches on the sea floor. Only since the 1930s have people entered the deeper regions. The deepest spot, the Mariana Trench in the Pacific Ocean, was not reached until 1960. New information continues to be discovered all the time about how oceans work and what lives in them.
There are three main reasons why water covers so much of our planet. First, millions of years ago as Earth was forming, many active volcanoes released water vapor into the atmosphere in the form of steam. Second, Earth’s gravity did not allow the water vapor to escape into space. It collected, along with other gases, to form clouds. Third, as Earth cooled, the moisture in those clouds condensed (turned from vapor to water), falling to Earth as rain. The rain filled the low areas in Earth’s crust, and the cooler temperatures allowed much of this water to remain in liquid form. Over time, enough water accumulated to create a great ocean. If all of these factors had not been at work over 200 million years ago, our Earth might be dry, barren, and lifeless much like the moon.
|WORDS TO KNOW|
|Bathypelagic zone: An oceanic zone based on depth that ranges from 3,300 to 13,000 feet (1,000 to 3,000 meters).||Mesopelagic zone: An oceanic zone based on depth that ranges from 650 to 3,300 feet (200 to 1,000 meters).|
|Coriolis Effect: An effect on wind and current direction caused by Earth’s rotation.||Neap tides: High tides that are lower and low tides that are higher than normal when the Earth, sun, and moon form a right angle.|
|Epigelagic zone: An oceanic zone based on depth that reaches down to 650 feet (200 meters).||Neritic zone: That portion of the ocean that lies over the continental shelves.|
|Fast ice: Ice formed on the surface of the ocean between pack ice and land.||Pack ice: A mass of large pieces of floating ice that have come together on an open ocean.|
|Hadal zone: An oceanic zone based on depth that reaches from 20,000 to 35,630 feet (6,000 to 10,860 meters).||Spring tides: High tides that are higher and low tides that are lower than normal because the Earth, sun, and moon are in line with one another.|
|Littoral zone: The area along the shoreline that is exposed to the air during low tide; also called intertidal zone.||Thermocline: Area of the ocean’s water column, beginning at about 1,000 feet (300 meters), in which the temperature changes very slowly.|
Scientists named the original great ocean Panthalassa (pan-thah-LAHS-uh). More than 220 million years ago, only one large continent existed in this vast, primitive ocean. This land mass was named Pangaea (pan-GEE-uh). As time passed, Pangaea began to pull apart, and the ocean flowed into the spaces created between the land masses.
The breakup of Pangaea was caused by heat forces welling up from deep within Earth. Earthquakes split the ocean floor, creating fracture zones, or faults. Magma (molten rock) from below Earth’s crust flowed into the fractures. As the magma cooled, it solidified, creating basins and ridges. After millions of years of repeated earthquakes and welling up of magma, the upper parts of Earth’s crust were pushed farther apart. About 50 million years ago, the continents and the oceans took the basic shapes and positions of their current location.
The sea floor is still spreading at a rate of about 2 inches (5 centimeters) a year. This means the shapes of the continents and oceans are still changing.
All the oceans considered together are called the World Ocean. The World Ocean is divided by the continents into three major oceans; the Atlantic, the Pacific, and the Indian. The Atlantic lies to the east of North and South America, and the Pacific lies to the west. The Indian Ocean lies to the south of India, Pakistan, and Iran. Some scientists consider the water surrounding the North Pole as a fourth ocean, the Arctic; most consider it part of the Atlantic.
The Pacific Ocean is the world’s largest at 59,000,000 square miles (153,000,000 square kilometers). The next in size is the Atlantic at 32,000,000 square miles (83,000,000 square kilometers). The smallest of the three is the Indian Ocean at 26,000,000 square miles (67,000,000 square kilometers). The Atlantic is divided into North Atlantic and South Atlantic regions, and the Pacific into North Pacific and South Pacific.
About 6 million years ago Baja (BAH-hah), California, split away from Mexico to form the Gulf of California. This splitting continues, and Baja is moving westward at a rate of about 2.5 inches (6 centimeters) a year.
The terms ocean and sea are often used interchangeably. However, an ocean is generally larger and deeper than a sea, and the physical features along its floor may be different. Seas are either contained within a larger ocean or connected to it by means of a channel. For example, the Sargasso, the Mediterranean, and the Caribbean Seas are all part of the Atlantic Ocean.
Even smaller bodies of water, called gulfs and bays, lie along the oceans’ margins. A gulf is partly surrounded by land and it usually joins the ocean by means of a strait, which is a narrow, shallow channel. The Gulf of Mexico lies at the point where the Atlantic curves in between Mexico and Florida. It connects to the Atlantic by the Straits of Florida. A bay is partly enclosed by land, but it joins the ocean by means of a wide mouth or opening. The Bay of Bengal, which lies between India and Myanmar, is an example.
The water in an ocean, exclusive of the sea bed or other landforms, is referred to as the water column. The average depth of the World Ocean’s water column is 12,175 feet (3,711 meters).
The term sea level refers to the average height of the sea when it is halfway between high and low tides and all wave motion is smoothed out. Sea level changes over time. Between 1930 and 1950, sea level along the east coast of the United States rose about 0.25 inches (1 centimeter) per year.
Every element known on Earth can be found in the ocean. Ocean water is 3.5 percent dissolved salts by weight, including primarily chloride, sodium, sulfur (sulfate), magnesium, calcium, and
|SEAS, GULFS, AND BAYS OF THE OCEANS|
|Atlantic Ocean||Indian Ocean||Pacific Ocean|
|Baltic Sea||Andaman Sea||Bering Sea|
|Barents Sea||Arabian Sea||Celebes Sea|
|Mediterranean Sea||Phillipine Sea||Coral Sea|
|Black Sea||Red Sea||East China Sea|
|Norwegian Sea||Sea of Okhotsk||Java Sea|
|Sargasso Sea||Sea of Japan|
|North Sea||South China Sea|
|Scotia Sea||Timor Sea|
|Weddell Sea||Yellow Sea|
|Greenland Sea||Gulf of Aden|
|Gulf of Guinea||Gulf of California|
|Gulf of St. Lawrence||Bay of Bengal|
|Labrador Sea||Great Australian Bight (bay)|
potassium. The measure of these salts determines the ocean’s salinity (saltiness). One cubic mile (4.1 cubic kilometers) of sea water contains enough salt to cover all the continents with a layer 500 feet (153 meters) deep. These salts make sea water heavier than fresh water.
Most of the oceans’ salts come from the weathering of rocks and the materials released by volcanoes. The level of saltiness has been increased by millions of years of evaporation and precipitation (rain, snow, and sleet) cycles. The water closest to the surface is usually less salty because of rainfall and fresh water flowing in from rivers. One of the saltiest bodies of water is the Red Sea, which receives little fresh water from rivers. One of the least salty is the Baltic Sea, which receives inflow from many rivers.
The temperature of the oceans varies. In general, temperature changes are greatest near the surface where the heat of the sun is absorbed. In the warmest regions, this occurs to depths of 500 to 1,000 feet (152 to 305 meters). Near the equator, the average surface temperature is about 77°F (25°C). The warmest surface water is found in the Pacific Ocean. In February, off the coast of Australia, the surface temperature is about 81°F (27°C).
Taking the Salt from Sea Water
Water, water, everywhere, and all the boards did shrink;
Water, water, everywhere, nor any drop to drink.
The mariners (sailors) in Samuel Taylor Coleridge’s (1772–1834) “Rime of the Ancient Mariner,” were in trouble because they were out of fresh water. Sea water is not safe to drink because its high salt content causes illness and, eventually, death. In some areas with few fresh water sources, the salt can be removed from ocean water. This is process is called desalination.
There are several methods for desalination. In one method, the water is heated until it evaporates. As the water vapor condenses, it is collected as fresh water and the salts are left behind. In a second method, an electric current is passed through the water. The salts collect on strips of metal called electrodes. In a third method, the water is frozen and the salt crystals are separated from the ice crystals. The ice crystals are then melted back to water.
The average surface temperature of the ocean near the poles is about –28°F (–2°C). Sea water grows colder more slowly than fresh water because of its salt content. In the Arctic, the water column is permanently covered with ice. Pack ice (a mass of large pieces of floating ice that have come together) forms on open water. Fast ice is ice formed between pack ice and the land.
The range of annual temperatures on land can vary more than 100°F (47°C). In the ocean, temperatures vary only about 15°F (7°C) annually. Most of the ocean (about 95 percent) is so deep it is unaffected by the sun and seasonal changes. At a depth of about 1,650 feet (500 meters) begins an area called the thermocline, where temperatures change very slowly. Close to the ocean floor, the average water temperature is between 32° and 41°F (0° and 5°C) throughout the World Ocean.
Zones in the ocean
Different parts of the ocean have different features, and different kinds of creatures live in them. These different parts are called zones. Some zones are determined by the amount of light that reaches them. Others are based on depth and the life forms present. The different zones overlap and interact with one another.
Zones determined by light penetration
The surface waters of the ocean receive enough light to support photosynthesis in plants. Photosynthesis is the process by which plants use the energy from sunlight to change water and carbon dioxide (from the air) into the sugars and starches they use for food. These surface waters are called the sunlit zone, which reaches down as far as 660 feet (200 meters) below the surface.
The next level is the twilight zone, which ranges from 660 to 3,000 feet (200 to 914 meters). Only blue light can filter down to this level, where it is too dark for plant life, but where at least 850 species of fish make their home. These twilight dwellers have large eyes and often travel to the sunlit zone at night to feed.
In the deepest region of the oceans, from 3,000 to 36,163 feet (914 to 11,022 meters), there is no light. This is called the dark zone. It is not known if any fish that live here travel upward at night, but their eyes are usually tiny and many are blind.
Zones determined by depth
Based on depth, the zone closest to the surface of the sea is called the epipelagic zone. It reaches down to 660 feet (200 meters) and corresponds to the sunlit zone. The next zone is the mesopelagic zone, and it corresponds to the twilight zone. It ranges from 660 to 3,000 feet (200 to 914 meters). The zones of darkness follow. First is the bathypelagic zone, which covers from 3,000 to 9,843 feet (914 to 3,000 meters). Then comes the abyssopelagic zone, ranging from 9,843 to 19,685 feet (3,000 to 6,000 meters). At the very bottom is the hadal zone. It reaches from 19,685 feet (6,000 meters) to the very bottom of the Mariana Trench, the deepest spot on Earth at 35,840 feet (10,924 meters).
Zones determined by sea life
The entire water column of the ocean is a vast ecosystem (an environment in which all organisms living within are dependent on other living and nonliving organisms for survival and continued growth) called the pelagic zone. Most life forms that live in it are concentrated near the surface where light is available. The neritic zone is the portion of the ocean that lies over the continental shelves (extensions of the continent that taper gently into the sea). The littoral zone refers to the area along the shoreline that is exposed to the air during part of the day as tides flow in and out.
The oceans are constantly, restlessly moving. This movement takes the form of tides, waves, surface currents, vertical currents, and eddies and rings.
Tides are rhythmic movements of the oceans that cause a change in the surface level of the water, noticeable particularly along the shoreline. When the water level rises, it is called high tide. When it recedes (drops), it is called low tide. Some tides, such as those in the Mediterranean Sea, are barely measurable. In the Bay of Fundy in Nova Scotia, the difference between high and low tide may be as much as 52 feet (16 meters). High and low tides occur in a particular place at least once during each period of 24 hours and 51 minutes.
The great icecap over the North Pole has shrunk in size during different prehistoric periods, adding its water to the oceans. This added water has raised sea level as much as 660 feet (200 meters). During cooler periods the icecap has always been restored to an even larger size.
Tides are caused by a combination of the gravitational pull of the sun and moon, and Earth’s rotation. The gravitational pull from the sun or moon causes the water to bulge outward. At the same time, the centrifugal force created by Earth’s rotation causes another bulge to occur on the opposite side of Earth. These areas experience high tides. Water is pulled from the areas in between, and those areas experience low tides.
When the Earth, sun, and moon are lined up, the gravitational pull is stronger. Then, high tides are higher and low tides are lower than normal. These are called spring tides. When the Earth, sun, and moon form a right angle, the gravitational pull is weaker. This causes high tides to be lower and low tides to be higher than normal. These are called neap tides.
Wind-driven surface waves
Waves are rhythmic rising and falling movements of the water. Although waves make the water appear as if it is moving forward, forward movement is actually very small. Most surface waves are caused by wind. Their size is due to the speed of the wind, the length of time it has been blowing, and the distance over which it has traveled. As these influences grow stronger, the waves grow larger, and storm waves can produce waves over 100 feet (31 meters) high. When the ocean’s surface can absorb no more energy, instead of growing in size, the waves collapse. Hurricanes, with wind speeds of 106 miles per hour (170 kilometers per hour), rarely raise waves higher than 43 feet (13 meters).
Once set in motion, waves can move for long distances. Over time, they become more regular in appearance and direction, forming a swell. By studying the movement of the swell, experienced ocean travelers can determine where a distant storm has occurred.
In shallow areas, such as along a shoreline, the bottom of a wave is slowed down by friction as it moves against the sea floor. The top of the wave is not slowed down by friction and moves faster than the bottom. When the top finally gets ahead of the bottom, the wave tumbles over on itself and collapses causing a breaker and sending a mass of swirling, bubbling foam tumbling onto the shore.
A type of surface wave called a tsunami (soo-NAH-mee) is caused by undersea earthquakes. When the ocean floor moves during the quake, its vibrations create a powerful wave that travels to the surface. The tsunami is barely noticeable in mid-ocean, but as it approaches bays, channels, or sloping shorelines, its power is concentrated. Suddenly its height increases, sometimes forming a towering crest that can reach a height of 200 feet (61 meters) as it crashes onto the land. A tsunami that struck eleven countries bordering the Indian Ocean in 2004 was 50 feet (15 meters) high and killed over 130,000 people.
Most tsunamis do not create walls of water but appear as sudden upwellings (rising of the water level). They are seldom just one wave. A dozen or more that vary in strength often travel in succession. Tsunamis can move as fast as an airplane—440 miles (700 kilometers) per hour—and can travel thousands of miles from their source before sweeping onto the land. As they recede back to sea, they make a loud sucking noise.
When tsunamis strike inhabited areas, they can destroy entire towns and kill many people. Some people drown as the wave washes inland; others are pulled out to sea when the tsunami recedes. Hawaii is very vulnerable to tsunamis because of its position in a Pacific region known for frequent volcanic activity and earthquakes. The Pacific Ocean experiences, on average, two life-threatening tsunamis each year. They are monitored by the Pacific Tsunamis Warning Center (PTWC).
Currents are the flow of water in a certain direction. They can be both large and strong. For example, the Gulf Stream, a current that lies off the eastern coast of the United States, and the Kuroshio (koo-ROH-shee-oh) near Japan, travel at 2.5 to 4.5 miles per hour (4 to 7 kilometers per hour). Usually, surface currents do not extend deeper than a few hundred yards (183 meters). The Florida Current and the Gulf Stream extend to depths of 6,560 feet (2,000
Storm at Sea
The large and usually violent tropical cyclones that form over oceans are called hurricanes in the Atlantic and eastern Pacific, and typhoons in the western Pacific. Their wind speeds are at least 75 miles (120 kilometers) per hour and may reach 180 miles (300 kilometers) per hour. A single storm may cover an area up to 2,000 miles (3,200 kilometers) in diameter and release up to 10 inches (25 centimeters) of rain a day.
Hurricanes and typhoons require very moist air to supply their energy, and only very warm air contains enough moisture. As a result, they only form over water at temperatures of at least 80°F (27°C). As they move over cooler regions, their power diminishes and they break up.
The forceful, rotating winds created by tropical storms cause much damage, especially when they reach land, as do the waves that batter the shoreline. Many people lose their lives each year in tropical storms. After 1944, airplanes were used to help spot and keep track of these storms. Weather satellites in orbit around Earth now monitor their growth and movement.
meters). They are caused by the wind, the rotation of Earth, and the position of continental landmasses. They contain about 10 percent of the World Ocean water.
The Sea State Scale
The heights of waves are measured on the sea state scale in number values from zero to nine. A sea state of zero means calm, smooth water. A sea state of nine means waves over 45 feet (14 meters) high.
Effects of wind
Winds directly affect only the upper zone of the ocean down to about 660 feet (200 meters). The currents created by the wind may reach depths of more than 3,000 feet (914 meters). Wind-driven currents move horizontally (parallel to Earth’s surface).
Winds over the oceans tend to follow a regular pattern, generally occurring in the same place and blowing in the same direction. At the equator are the doldrums, very light winds that create little water movement. Both north and south of the equator to about 30° latitude are the trade
winds, which blow primarily east. (Latitude is a distance north or south of Earth’s equator, measured in degrees.) At about 60° latitude are the westerlies. Near the poles, the polar easterlies occur. These three wind patterns create three basic systems of ocean currents: the equatorial system, the subtropical gyre (JYR), and the subpolar gyre. (A gyre is a circular or spiral motion.)
The Coriolis effect
The rotation of Earth influences the patterns of the wind and the ocean’s currents. This is called the Coriolis (kohree-OH-lus) Effect. In the Northern Hemisphere, the Coriolis Effect causes air masses moving south to veer westward. Just the opposite happens in the Southern Hemisphere. Air masses moving north veer eastward. Currents north of the equator move in a clockwise direction. Currents south of the equator move counterclockwise. The Coriolis Effect is greater near the poles and causes the currents on the western sides of ocean basins to be stronger than those on the eastern sides.
Effect of landmasses
Currents are affected by the presence of obstacles such as the continents and large islands. In the North Pacific, for example, currents moving west are deflected northward by Asia and southward by Australia. The same currents then move east until North and South America send them back toward the equator.
Upward and downward movements occur in the ocean. These vertical currents are primarily the result of differences in water temperature and salinity.
At the North and South Poles, the surface water often freezes, due to its lower salt content. As a result, the salts become more concentrated in the water below the surface, causing this water to remain unfrozen and become heavier. This heavy, cold water then sinks and travels along the ocean floor toward the equator. At the same time, near the equator, the sun warms the surface water, which travels toward the poles. As this cycle repeats itself, the water is continually circulating. Warm surface water flows toward the poles, cools, sinks, and flows back toward the equator. Vertical currents help limit the depth of horizontal currents.
Tides of Fire
In 1964, an earthquake struck Alaska, causing great damage. A pipeline carrying oil was broken and the oil caught fire. A tsunami three stories high followed the quake, surging inland. Because oil floats on water, the burning oil was carried overland in a tide of fire. The fires reached the railroad yards, where the iron tracks soon glowed red from the heat. More tsunamis followed and flowed over the tracks. The sudden cooling made the tracks rise up and curl like giant snakes
Ben Franklin Speeds the Mail
In 1770, Benjamin Franklin (1706–1790) was postmaster general for the American colonies. At that time, the colonies depended upon sailing ships to carry the mail back and forth between England and America. A constant complaint from postal customers was that mail going east to England always arrived weeks sooner than mail moving west to the colonies. Puzzled, Franklin decided to investigate.
Franklin’s cousin, Timothy Folger, was a ship’s captain. He told Franklin about the presence of the Gulf Stream. He explained that when they traveled to England, the ships moved with the current, which added to their speed. When they returned to America, they had to fight the current, which slowed them down.
Luckily, the Gulf Stream was only about 62 miles (100 kilometers) wide. Franklin believed it could be avoided and mapped a new route. He named the current the Gulf Stream because it flowed out of the Gulf of Mexico.
In some coastal areas, strong wind-driven currents carry warm surface water away. An upwelling of cold water from the deep ocean occurs to fill the space. This is more common along the western sides of the continents. These upwellings bring many nutrients from the ocean floor to the surface.
Eddies or rings
Eddies or rings are whirlpools that move in a circular motion against the flow of a main surface current. Eddies are probably caused when the speed and intensity of a current increases to such a point that the current becomes unstable. The eddy allows the excess speed and intensity to be distributed into the surrounding water.
Effect of the water column on climate and atmosphere
The World Ocean is responsible for much of the precipitation (moisture) that falls on land. Ocean water evaporates in the heat of the sun, forms clouds, and falls elsewhere in the form of rain, sleet, or snow.
The ocean absorbs and retains some of the sun’s heat. In the winter, this heat is released into the atmosphere, helping to keep winter temperatures warmer inland. In summer, when the water temperature is cooler than the air temperature, winds off the ocean help cool coastal areas.
Pools of warmer or cooler water within the ocean influence storms in the atmosphere. The El Niño flow of warmer water, which affects the storm systems in North and South America, is an example. This warm current causes changes in winds and air pressure, bringing severe storms and droughts (very dry periods). How El Niño’s effect comes about is still not clearly understood.
The oceans help regulate the levels of different gases in the atmosphere, such as oxygen and carbon dioxide. About one-half of the carbon dioxide that is produced by burning forest fires and other causes is captured by the oceans. Too much carbon dioxide in the atmosphere contributes to warmer global temperatures. The ocean’s presence helps moderate such undesirable changes.
The ocean floor is that area of Earth’s crust covered by ocean water. It is divided into the continental margins and the deep-sea basins.
The continental margin is the part of the seafloor at the edges of the continents and major islands where, just beyond the shoreline, it tapers gently into the deep sea. The continental margin includes the continental shelf, the continental slope, and the continental rise.
The continental shelf is that part of the margin that begins at the shoreline. It is flat and its width varies. Off the coast of Texas the shelf is 125 miles (200 kilometers) wide. The continental shelf is usually less than 660 feet (200 meters) below sea level. It receives much rich sediment (soil and other particles) from rivers that flow to the sea and, being in the sunlit zone, it supports many forms of ocean life.
At the end of the continental shelf there is a steep drop. This is the continental slope, which descends to depths of 10,000 to 13,000 feet (3,000 to 4,000 meters) and ranges from 12 to 60 miles (20 to 100 kilometers) in width. In many places, the slope is cut by deep underwater canyons that may have been formed by prehistoric rivers.
Beyond the continental slope is the continental rise, where sediments drifting down from the continental shelf collect. These deposits may extend as far as 600 miles (914 kilometers) into the ocean where the deep-sea basin begins.
The deep-sea basins begin at the edge of the continental rise. These vast, deep basins in the ocean floor contain underwater mountain ranges (ridges), volcanoes, deep trenches, and wide plains.
The mid-ocean ridge
A long chain of submerged (underwater) mountains called the mid-ocean ridge runs through the World Ocean. This ridge was formed when rifts (cracks) were created in the sea floor by earthquakes and volcanic action. Hot lava seeped or poured out of these cracks, spreading apart the sea floor. As the seafloor spread, it buckled, forcing Earth’s crust upward and forming a chain of mountains about 40,000 miles (65,000 kilometers) long. This ridge was discovered at different locations by different scientists who did not realize it was one chain and who gave it different names, such as mid-Atlantic ridge or West Chile Rise.
|LANDFORMS OF THE OCEAN’S BASINS|
|Atlantic Ocean Basin||Indian Ocean Basin||Pacific Ocean Basin|
|Falklands Escarpment||Central Indian Ridge||Aleutian Trench|
|Mid-Atlantic Ridge||Java Trench||East Pacific Rise|
|Puerto Rico Trench||Ninetyeast Ride||Emperor Seamount Chain|
|Sandwich Trench||Hawaiian Ridge|
|Scotia Ridge||Japan Trench|
|Walvis Ridge||Kermadec-Tonga Trench|
|West Chile Trench|
The mid-ocean ridge usually rises 0.6 to 1.8 miles (1 to 3 kilometers) above the surrounding sea floor. Those peaks that break the surface of the water form volcanic islands. Iceland is an example. The highest submerged mountain is 29,520 feet (8,997 meters) and is found between Samoa and New Zealand.
Deep valleys often cut into the mid-ocean ridge, and are frequently the site of volcanic and earthquake activity.
Some isolated volcanoes that do not reach the surface of the ocean, called seamounts, form alongside the mid-ocean ridge but are separate from it. Seamounts have steep slopes and may be as high as 13,000 feet (5,000 meters).
On the deep ocean floor in highly volcanic zones, jets of hot water (up to 716°F [380°C]), called smokers, have been discovered. These water jets are composed of ordinary seawater that enters clefts (splits) in hot volcanic rock where it heats up, expands, and escapes. In its passage through the rock, the hot water absorbs large quantities of dissolved minerals that make it look cloudy and smokelike as it reenters the surrounding ocean. Sometimes the dissolved minerals are deposited around the vents (openings) through which it is expelled, forming hollow black chimneys as high as 33 feet (10 meters).
As the sea floor spreads, it meets the edges of the continents, which resist its movement. This results in an area of extreme pressure called a subduction zone. In the subduction zone, this enormous pressure forces the expanding sea floor down and under the continental margin, often causing a deep, V-shaped trench to form. The greatest depths in the oceans are found in these trenches, and the deepest trenches are located in the Pacific. The Mariana Trench is the deepest at 35,840 feet (10,924 meters).
Ocean trenches are much deeper than any valley on the continents. The Grand Canyon in Arizona, for example, is about 1 mile (1.6 kilometers) deep. The Mariana Trench in the Pacific is about 6.8 miles (11 kilometers) deep. If Mt. Everest, the tallest mountain on Earth, could be put into the Mariana Trench, more than 6,800 feet (2,073 meters) of ocean would still cover it.
Islands and atolls
Continental islands were once part of a nearby continent. As the continent drifted, the island broke away. These islands may include hills and mountains similar to those on the continent.
Oceanic islands are those that rise from the deep-sea floor. Volcanoes, some of which are still active, formed most of the islands. At first, volcanic islands lack any form of life except possibly bacteria. Seeds and plant spores (single cells that grow into a new organism) arrive on the wind or are carried there by ocean waves or visiting animals. Gradually, an ecosystem tailored to each particular island is formed.
The Newborn Island, Surtsey
In 1963, a baby island was born off the coast of Iceland. It has been named Surtsey. The product of an underwater volcano, Surtsey was formed of cooled magma. A similar island may be forming on the seabed southeast of Hawaii.
Atolls are ring-shaped coral reefs that have formed around a lagoon. A coral reef is created by small, soft, jellylike animals called corals. Corals attach themselves to hard surfaces and build a shell-like external skeleton. Many corals live together in colonies. Young corals build their skeletons next to or on top of older skeletons. Over hundreds, thousands, or millions of years, a wall, or reef, of these skeletons is formed. The mountain peak in the center gradually sinks or is washed away and only the reef remains.
Abyssal plains are the vast flat areas where light does not penetrate. They make up the largest portion of the ocean floor. The abyssal plain is deepest in the Pacific Ocean at 20,000 feet (6,098 meters) and shallowest in the Atlantic Ocean at 10,000 feet (3,048 meters).
Where the ocean floor remains uncovered by sediment, a hard rock called basalt is visible. Elsewhere, the floor is covered by sediments that have drifted down from the continental margins, from volcanic activity, from dead marine life, from coal-burning ships, and even from dust carried by the wind and deposited on the water’s surface. These sediments build up until they create a flat surface.
Sediments are of two types. Those formed from the waste products and dead tissues of plants and animals are called ooze. Usually, ooze is found only in temperate (having moderate temperatures) and tropical (hot and humid) regions where it may become hundreds of yards (meters) thick. Other sediments are usually red clay. About 1 inch (2.5 centimeters) of red clay is deposited on the ocean floor every 2,500 years. In parts of the ocean floor, the sediment layer is more than 3,000 feet (7,000 meters) thick.
Plants that live in the sea are surrounded by water at all times. For this reason, they have no need to develop the special tissues and organs for conserving water that are needed by plants on land. Seaweeds, for example, use their rootlike structures called holdfasts to anchor them in one spot. They do not use them to draw water from the soil.
The Web of Life: Alien Algae
In 1984, an alien was discovered in the Mediterranean Sea. Although probably not from outer space, its origin remains unknown and it is gradually taking over. It is a species of green algae that usually grows only in aquariums. Somehow it found its way into the sea where it grows aggressively with no natural enemies. It is smothering anything from the beach to a depth of about 150 feet (46 meters). It has no scientific name, but some researchers believe it is derived from Caulerpa taxifolia. Others are in favor of calling it C. Godzilla for obvious reasons.
This species reproduces by fragmentation; small pieces that break off grow into new plants. Any attempt to dig it up or mow it down fails, because millions of potentially new plants are created in the process. Pesticides are too toxic and dangerous for wildlife. The only hope for saving the Mediterranean from the algae seems to be the use of bio-controls (natural means of controlling pests). Scientists are searching for an animal, such as a snail or slug that will eat the algae. Bio-controls can cause other problems. Sometimes the new animal turns up its nose at the pest plant and eats other, more desirable plants. Then, instead of one problem, there are two. Until a remedy is found, many countries, including the United States, are prohibiting the importation of this type of algae for use in aquariums.
The water offers support to ocean plants. Giant underwater plants do not require tough woody stems like land plants to remain upright; the water holds them up. Instead, sea plants have soft and flexible stems, allowing them to move with the current without breaking.
Many species of plants live in the oceans; however, all species are not found in all oceans. Species of plants found in the Indian Ocean, for example, are seldom found in the Atlantic. Most plants live along the continental margins and shoreline, not in mid-ocean.
Ocean plants can be divided into two main groups: plantlike algae (AL-jee) and green plants.
It is generally recognized that algae do not fit neatly into the plant category, but they have some characteristics similar to true plants.
Algae are found extensively in the oceans. Most algae have the ability to make their own food by means of photosynthesis (foh-toh-SIN-thih-sihs). Others absorb nutrients from their surroundings.
The types of algae commonly called seaweed resemble green plants, but they have no true leaves, stems, or roots. Some are so tiny they cannot be seen with the naked eye. Others are massive and live in vast underwater forests. Many algae, such as kelp, have soft, jellylike cell surfaces. Other types, such as diatoms, form shells, scales, or stony coverings.
Some algae float freely in the water, allowing it to carry them from place to place. These are called plankton (a Greek word meaning “wanderers”). Kelp anchors itself to the sea floor, and belongs to the benthic species. (Benthos in Greek means “seafloor.”)
Phytoplankton are tiny plants that usually cannot be seen without the aid of a microscope. They float on the water’s surface, always within the sunlit zone, and are found near the coast and in mid-ocean. They are responsible for about 90 percent of the photosynthesis carried out in the oceans, helping to supply Earth’s atmosphere with oxygen as a result.
Two forms of phytoplankton are the most common, diatoms and dinoflagellates (dee-noh-FLAJ-uh-lates). Diatoms have simple, geometric shapes and hard, glasslike cell walls. They live in colder regions and even within Arctic ice. Dinoflagellates have two whiplike attachments that make a swirling motion to help them move through the water. They live in tropical zones (regions around the equator).
Both land and sea plants contain chlorophyll, the green pigment in which they turn energy from the sun into food. As long as light is available, ocean plants can grow, even in the Arctic. In some algae, the green of chlorophyll is masked by orange-colored pigments, giving them a red or brown color.
Most algae grow in the sunlit zone where light is available for photosynthesis. Algae require other nutrients that must be found in the water, such as nitrogen, phosphorus, and silicon. In certain regions, upwelling of deep ocean waters during different seasons brings more of these nutrients to the surface. This results in greater numbers of algae during those times. These increases are called algal blooms. When the upwelling ceases, their numbers decrease.
Nitrogen and phosphorus are in the shortest supply in most oceans, which limits plant growth. When these elements are added to a body of water by sewage or by runoffs from farmland, there is a sudden burst of algae growth in these regions.
Algae may reproduce in one of three ways. Some split into two or more parts, each part becoming a new, separate organism. Others produce spores. A few reproduce sexually; cells from two different plants unite to create a new plant.
Green plants do not grow in mid-ocean. Instead, various types of seagrasses live in protected areas along the continental shelf where their roots can find soil and nutrients. Some marine animals use them for food and for hiding places.
The Colors of Kelp
Kelp must absorb sunlight in order for photosynthesis to take place. For this reason, kelp are found in the sunlit zone in fairly shallow water. Different species are found at different depths, and these species vary in color. This color difference is due to the filtering effect of the water. As sunlight penetrates deeper, different colors in it are filtered out. Near the surface, kelp is green. Farther down, the brown varieties grow. Red and blue species are found where there is the least amount of light.
The oceans swarm with life and are the largest animal habitats on Earth. More life forms are found in the oceans than in tropical rain forests. Most species live along the continental margins. Some of those enter mid-ocean regions when they migrate to different areas in search of food or for breeding purposes. The numbers that live in mid-ocean permanently are fewer. The Gulf Stream, for example, supports so few species it is almost like a desert.
Living organisms must maintain a balance of body fluids and salt levels in their blood. Animals that live in the sea have developed ways to cope with its high salinity. Naked animals or those with thin skins or shells usually have high levels of salt in their blood and do not need to expel any excess. Others, such as most fish, have special organs that remove the extra salt from their bodies and release it into the water.
The water offers support to marine (ocean) animals as it does to plants. For example, giant whales could not exist on land because of their body weight. The effect of gravity would be too great. But ocean water allows them to float and swim effortlessly. Many marine animals have special chambers in their bodies that allow them to adjust their buoyancy (BOY-un-see; ability to float) so that they can change their depth. Some, such as seals, have fins to make swimming easier. Others, such as octopi, forcefully eject water in a kind of jet stream to help them move.
Distribution of animals in the oceans depends primarily on the food supply. Tropical seas, which are rich in nutrients, have many more life
forms than polar seas. The lack of sudden temperature changes in the oceans makes the environment comfortable for most marine animals.
Marine animals may be classified as microorganisms, vertebrates, and invertebrates. They are also classified according to their range of movement. Plankton drift in the currents and include both microorganisms and larger animals such as jellyfish. Many plankton move upward and downward in the water column by regulating the amount of gas, oil, or salt within their bodies. (Production of gas or oil and removal of salt causes the organism to rise; the reverse causes it to sink.) Many larger animals spend part of their young lives as plankton. Crabs, which float with the current in their larval (immature) form, are an example. Larger animals that swim without the help of currents, such as fish and whales, are called nekton. Benthos are animals that live on the ocean floor. These include snails, clams, and bottom-dwelling fish.
Microorganisms cannot be seen with the human eye without the aid of a microscope. Most microorganisms are zooplankton (tiny animals that drift with the current). They include foraminiferans, radiolarians, acantharians, and ciliates, as well as the larvae or hatchlings of animals that will grow much larger in their adult form.
Until 1998, it was believed that bacteria appeared in the ocean only where other organisms were decomposing (decaying). Scientists now agree that bacteria are found throughout the ocean and make up much of the dissolved matter in the mid-ocean water column. As such, they provide food for microscopic animals. Bacteria help decompose the dead bodies of larger organisms, and for that reason their numbers increase near the coastlines where the larger organisms are found.
Bacteria are found in the sediment on the dark ocean bottom and around the waterjet smokers created by deep-sea volcanic vents. These deep-sea bacteria obtain food and oxygen by means of chemosynthesis (kee-moh-SIHN-thuh-sihs), a process in which the organism creates food using chemical nutrients as the energy source instead of sunlight. The bacteria live in cooperation with animals unique to this region, providing them with important nutrients.
Some zooplankton eat phytoplankton and are preyed upon by other carnivorous zooplankton, such as arrow worms. Krill are shrimplike zooplankton that play an important part in the food web of the ocean. They feed upon plant-eating zooplankton and are eaten in turn by larger fish and mammals. The largest mammals of all, the great whales, consume tons of krill each day.
Animals without backbones are called invertebrates. Many species are found in the oceans. Crustaceans, invertebrates with hard outer shells such as lobsters and clams, are probably the most numerous and diverse group.
Invertebrates found in the oceans range from planktonic jellyfish to benthic worms and crabs.
Most crustaceans swim freely in the upper waters. Some, like the barnacle, attach themselves permanently to solid surfaces. Clams typically live in shallow water. At least one species has been found on the deep ocean floor near smokers where they have adapted to the warm, sulfur-rich water.
The Red Tide
Some species of dinoflagellates are poisonous. When enough of them are present, they color the water red, creating what is called red tide. Their toxic secretions kill many fish, and even humans are not immune. When the poison is released into the air by waves breaking on shore, people can develop irritation in their mouth and lungs.
Squid live along coastlines and in mid-ocean, in surface and deep waters. They can exist as plankton, drifting along with the current, or use a form of jet propulsion by squirting water in a forceful stream from a tube near their heads.
Giant tubeworms grow up to 8 feet (2.4 meters) long and live in clusters around deep-sea smokers. These worms have neither a mouth nor a digestive system. They survive because of bacteria that live around them and produce the nutrients they need by chemosynthesis.
Invertebrates may eat phytoplankton, zooplankton, or both. Some eat plants or larger animals. The sea anemone uses its stinging tentacles to paralyze shrimp and small fish that swim past. Other invertebrates, including lobsters and crayfish, roam along the ocean floor to feed on dead organisms. A species of hadal zone spider has no eyes and feeds by sticking a long tube into worms and other soft creatures and sucking out body juices.
Marine invertebrates reproduce in one of three ways:
- Eggs are laid and fertilized externally. A parent watches over the young in the early stages, and offspring number in the hundreds.
- Fertilization is internal. A parent cares for the young in the early stages, and offspring number in the thousands.
- Fertilization is external. The young are not cared for, and offspring number in the millions. Survival depends upon the absence of predators and the direction of currents.
Reptiles are vertebrates (animals having backbones). The body temperatures of reptiles changes with the temperature of their surroundings. In cold temperatures, they become sluggish, so they do not have to waste energy keeping their body temperatures up as do most mammals and birds.
The two types of reptiles found in the oceans are sea turtles and sea snakes. Sea turtles can be distinguished from land turtles by their paddle-shaped limbs called flippers, which enable them to swim. The largest marine turtle, the Atlantic leatherback, may weigh as much as 2.2 tons (2,020 kilograms) and measure 9 feet (3 meters) from the tip of one flipper to another. Sea turtles have glands around their eyes that remove excess salt from their bodies. This process makes them appear to cry.
At least thirty-two species of snakes live in tropical oceans, and all of these are found in regions around Australia and New Guinea. They look much like land snakes, having long bodies, some of which attain 9 feet (3 meters) in length. Unlike land snakes, they have salt glands that help them maintain a body fluid balance. Their tails are paddle shaped, which helps them move through the water, and some species are able to close their nostrils, which enables them to dive and remain submerged for hours. Sometimes, colonies of thousands can be seen floating on the surface of the water, basking in the sun.
Reptiles can survive for a long time without eating. When food is obtained they often eat large amounts. Turtles are omnivorous (eating both plants and animals). They eat soft plant foods as well as small invertebrates such as snails and worms. Turtles have no teeth. Instead, the sharp, horny edges of their jaws are used to shred food enough to swallow it.
Sea snakes are carnivorous (meat-eaters), feeding primarily on fish, including eels, that they find along the ocean floor in rocky crevices. They first bite their prey, injecting it with poison so it cannot escape.
Green sea turtles are typical of oceanic reptiles. They are migrators, traveling as far as 1,250 miles (2,000 kilometers) to return to a particular breeding area where they lay their eggs. Analysis of their brain structure suggests that they have a keen sense of smell and a built-in sense of direction that guide them to their particular breeding grounds. One green turtle was observed to travel 300 miles (480 kilometers) in ten days, which indicates it was moving quite quickly. Green sea turtles and the other six species of sea turtles are endangered.
Sea snakes are all venomous. The most dangerous is the beaded sea snake since just three drops of its venom can kill nine people. Very few human deaths occur from sea snake bites because the creatures are afraid of humans.
Both snakes and turtles lay eggs, and some types of snakes bear live young. Turtles lay their eggs in a hole on a sandy shore, which they then cover. After the nest is finished, the female abandons it and seems to take no interest in the offspring. Six weeks later, the eggs hatch and the young turtles run for the water and disappear into the ocean.
Some species of sea snakes come to shore during breeding season and lay their eggs on land. The remainder bear live young at sea.
The Sneaky Shark
The cookie-cutter shark, a dwarf species named because it bites a round, cookie-shaped chunk of flesh out of bigger animals, uses a sneaky method of attracting prey, The cookie-cutter’s underside glows, except for a large spot beneath its jaw. The ability to glow helps it blend in with the light filtering down from above. To another predator, the dark spot beneath its jaw may appear to be a smaller, innocent-looking fish. When a tuna or swordfish comes along, it spies the dark spot and thinks lunch is at hand. But when the big fish rushes upward for a bite, the cookie-cutter shark is the one that gets the meal.
The oceans are home to about 14,700 kinds of fish, about 60 percent of all fish species on Earth. Fish are primarily cold-blooded (temperature varies with the surroundings) vertebrates having gills and fins. The gills are used to draw in water from which oxygen is extracted. The fins are the equivalent to arms and legs and are used to help propel the fish through the water.
Mackerel sharks and tuna are examples of warm-bodied fish. They have a special system of blood circulation that allows them to keep their body temperature as much as 21°F (12°C) above the water temperature. This extra warmth gives them more muscle power and thus more speed.
Fish vary in size from the tiny goby of the Philippines that measures less than 0.5 inch (1 centimeter) in length to the giant whaleshark that can grow as long as 60 feet (18 meters). Most fish have long, streamlined bodies built to move swiftly through the water, but shapes vary greatly. Manta rays, for example, are flat and round. Seahorses are narrow and swim with their bodies in a vertical (upright) position.
Most fish species live in the sunlit zone. Approximately 855 species live in the twilight zone, including the hatchetfish, the dragonfish, the lanternfish, the lancet fish, and the viperfish. These fish often have large, upward-angled eyes designed to see in the murky depths. They may have rows of light organs on their undersides, which help them blend in with the more well-lit waters above them or help them attract mates. The light from these organs is produced by either bacteria or chemical reactions they produce themselves. Some species have stretchy bodies, huge jaws, and fanglike teeth that enable them to take in and digest prey as large or even larger than themselves. These features may help them survive in a region where food is scarce.
Fish living in the dark zone include the gulper eel, the anglerfish, the whalefish, and the tripod fish. Most are white and small and either have no eyes or have tiny eyes that are blind. They, too, may have stretchy bodies and huge mouths. Few have light organs, perhaps because these would not be very useful around other blind fish. Many twilight and dark-zone fish have sensory hairs on their bodies that detect motion or changes in water pressure. Some can also detect odors.
Typical mid-ocean fish include sharks and tunas. There are about 330 species of sharks. Most of these live in coastal waters. Only six species favor the mid-ocean. These include the crocodile, the whale, the blue, the shortfin mako, the oceanic whitetip, and the silvertip. Some live and travel alone; others move about in schools (large gatherings of fish). They are present in all oceans except the Antarctic. Sharks are most abundant in tropical and subtropical waters. They vary in size and behavior and are relatively free of disease. With the exception of other sharks, they have few enemies.
Some deep-ocean sharks must remain in constant movement in order to breathe. Their forward motion forces water through their gills from which they extract oxygen. Other species with more ordinary respiratory (breathing) systems can float or rest on the ocean bottom. Most sharks move leisurely, but some species are very fast. The blue shark can attain speeds of up to 40 miles (64 kilometers) per hour. A shark’s sensitive eyes can see well in dim light, which enables some species to hunt in the twilight zone. They have a highly developed sense of smell and can sense movement vibrations in the water, which makes it easy for them to find prey.
All sharks are carnivorous. The rare whale shark, the largest fish in the ocean at more than 50 feet (15 meters), feeds only on small fish and plankton. The real predator is the great white, which averages 20 feet (6 meters) in length but may grow much larger. The diet of a shark includes almost every animal in the oceans, including other sharks. During feeding frenzies, large numbers of sharks attack the same prey, tearing it to pieces. In their haste to eat they may rip into one another, and any unlucky wounded shark is eaten along with the rest of the meal. Sharks often go without food for long periods, during which time oil stored in their livers helps sustain them.
Compared to some other species of fish, sharks do not produce large numbers of young. They may have as few as two or almost one hundred. Some species lay eggs, while in others, the young develop much as mammals do inside the female and are born alive. Development of the egg or embryo (baby) may take from a few months to two years, depending on the species. The parents do not care for their young, which are completely developed at birth.
As humans probe farther into the oceans, they encounter sharks more frequently. Six species are known to attack humans: great whites, tigers, bulls, makos, hammerheads, and oceanic whitetips. In 2005 only about 58 unprovoked attacks occurred, and only a few were fatal. Most mid-ocean sharks live too far offshore to present much of a threat.
Tunas live in both temperate and tropical oceans; usually in the surface waters. They tend to be large fish, although their size varies from species to species. The largest species, the bluefin, may grow to more than 14 feet (4.2 meters) in length and weigh more than 1,400 pounds (680 kilograms). Their dark blue-green and silver coloring helps disguise them from predators. They are migrators and travel long distances in search of food and for breeding purposes. Skipjack tunas have been observed to travel as far as 16,000 miles (256,000 kilometers).
Like some species of sharks, tunas must be in constant motion in order to breathe. They are warm-bodied fish, which means their circulatory system enables them to maintain a body temperature warmer than that of the surrounding water. This gives them more power; they are fast swimmers, traveling at more than 30 miles (48 kilometers) per hour. Since their energy demands are great, they require a lot of food. They primarily eat other fish and squid.
Tunas are in great demand commercially as food for humans. For example, a bluefin tuna, which is endangered, can be worth as much as $60,000. To prevent overfishing, international agreements have been made to limit the number that can be caught and the areas where tuna fishing is allowed.
Most fish live near the continental margins where food is readily available. Some are plant eaters whose diets are primarily phytoplankton, algae, or sea grasses. Fish that must swim in search of prey have more streamlined bodies than those that burrow into the bottom sediments for it.
Fish that live primarily in the twilight zone often travel to the sunlit zone at night to feed. Their large eyes aid them in finding prey, which may not be able to see as well under low-light conditions. They often use a light organ to lure prey.
Fish that live in the deepest regions must depend on food that falls from above, such as particles of zooplankton or the dead bodies of other animals. Strict carnivores are rare in the dark zone, perhaps because there is too little prey. Many dark-zone fish have bodies that stretch to accommodate large meals when they can find them. Although most dark-zone fish are not luminous, the anglerfish has a light organ used to lure prey. This organ is positioned over its mouth like the bait on the end of a fishing pole. Another fish, drawn by the light to investigate, is snapped up for a meal. Some species of dark-zone fish travel at night to higher levels for food, but they do not travel as far as fish living in the twilight zone.
Most fish lay eggs, although many, such as certain species of sharks, bear live young. Some, such as the Atlantic herring, abandon their eggs once they are laid. Others build nests and care for the new offspring. Still others carry the eggs with them until they hatch, usually in a special body cavity or in their mouths.
Certain marine fish, such as sturgeons and Pacific salmon, are actually born in freshwater rivers but spend most of their lives at sea, often traveling thousands of miles. Years later they return to the river where they were born. There, they breed and then die. Atlantic freshwater eels leave American and European rivers to breed in the Sargasso Sea, where they, too, die. By some inherited means of guidance, their young return to those same rivers, and the cycle is repeated.
Male anglerfish, a dark-zone species, are dwarfs. Before the breeding season, the male bites into the skin of the female, and their circulatory systems become joined so that the male receives his nutrients from the female’s blood. (The circulatory system includes the heart, blood vessels, and lymphatics that carry blood and lymph throughout the body.) This may help assure that males and females can find one another at the appropriate time in this sparsely populated region. Some dark-zone fish are hermaphroditic. This means the reproductive organs of both sexes are present in one individual fish, and true mating is not necessary.
Most seabirds remain near land where they can nest during breeding season. A few species are known to travel great distances over the oceans in search of food and spend most of their lives doing so. The Arctic tern, for example, is the greatest long-distance migrator of all, traveling up to 20,000 miles (32,000 kilometers). These species are classified as oceanic birds. Many seabirds have adapted to marine environments by means of webbed feet and special glands for removing excess salt from their blood.
Many seabirds remain near the coastline and spend much of their time on land. A few species, such as the albatross, petrel, and tern are oceanic birds.
Albatrosses are wanderers, spending much of their lives over the open ocean. Some appear to follow established routes; others follow the wind. Albatrosses are very large birds with long, narrow wings that may span up to 12 feet (3.5 meters) from tip to tip. In 1998, a black-footed Laysan albatross was observed to have traveled 25,135 miles (40,216 kilometers) in seventynine days. Albatrosses sleep on the ocean’s surface, drink seawater, and feed on small fish and squid. Some species are scavengers and follow ships at sea, eating the garbage thrown overboard. Although they mate for life, the mated pair normally live thousands of miles apart and come together on land only during the breeding season.
Petrels, like albatrosses, spend most of their lives at sea. One species, called storm petrels, were once believed by sailors to signal the coming of bad weather. Storm petrels feed on plankton floating on the surface of the ocean. Some diving petrels can swim after prey underwater. Larger species eat carrion (dead animals). Like albatrosses, petrels come to land only to breed.
Terns plunge dive into the ocean to catch small fish. These sea birds encounter more hours of daylight each year than any other creature thanks to their migration patterns.
All seabirds are carnivorous. Most eat fish, squid, or krill, and they live where the food they prefer is in ready supply. Several species, such as cormorants and diving petrels, hunt underwater, using their wings to swim. Other species, such as gannets, spot their prey from high above and then dive-bomb into the water, bringing their catch to the surface to eat. Some, like gulls, swoop down on fish swimming close to the surface.
Seabirds tend to nest on islands where there are few land-dwelling predators. Some nest in huge colonies on the ground, others dig burrows, and still others prefer ledges on a cliff. Like other birds, seabirds lay eggs and remain on the nest until the young are able to
leave on their own. Some live in one area and migrate to another for breeding. The Arctic tern, for example, spends the winter months in Antarctica, then travels halfway around the globe to breed during the summer in the Arctic Circle.
The three most important mammals that are truly marine are whales, porpoises, and sea cows. They must remain in the water at all times. Other mammals, including seals and sea otters, spend much of their time in the water but are able to live on land, and do so especially at breeding time.
Common marine mammals
Whales and their cousins, porpoises and dolphins, are the primary deep-ocean mammals. Whales are found in all the world’s oceans, including the Antarctic. Most species migrate, some traveling as much as 14,000 miles (22,400 kilometers) during one breeding season. Their paths usually follow ocean currents and may depend upon available food supplies and water temperature. Most species travel in schools. Smaller species may live as long as thirty years. The larger species may live to be 100 years old.
Whales fall into two categories: toothed whales and baleen whales. Instead of teeth, baleen whales have a row of bony, fringed plates they use to filter plankton from the water. Baleen whales include the gray, the humpback, and the blue whale. Blue whales are the largest animal known to have lived. They grow to lengths of 100 feet (30 meters) and may weigh as much as 200 tons (180 metric tons). Toothed whales include killer, beluga, and sperm whales. These are all predators, feeding mainly on fish and squid.
A layer of dense fat, called blubber, surrounds the whale’s body directly under its skin. Whales are warm blooded and the main purpose of this fatty layer may be to help them maintain body temperature. Some species, such as the sperm whale, may dive to depths of more than 3,300 feet (1,006 meters) and stay underwater for up to an hour, but whales must return to the surface to breathe. The blowhole on the top of a whale’s head is actually the nostril. The spout, which looks like a stream of water the whale shoots in the air through its blowhole, is actually exhaled air. This exhaled air is usually warmer than the outside atmosphere and its moisture quickly condenses and looks like steam.
Whales occasionally jump out of the water, landing again with a huge splash. This is called breaching. The reason for it is unknown, but it may have something to do with the fact that they are very social animals. Almost all species of whales produce sounds such as whistles, squeals, and clicks. These sounds may have much to do with social behavior, and there is little doubt that they express certain emotional states such as fear or hunger.
The sea cow is the only plant-eating mammal that truly lives in the sea. Most marine mammals are carnivorous. Some, like the baleen
|DIVING ABILITIES OF DIFFERENT ANIMALS*|
|* These are distances that have been actually measured, depths may be much greater in some cases.|
|Sperm whale||5,280 feet (1,609 meters)|
|Weddell seal||1,968 feet (600 meters)|
|Blue whale||1,000 feet (305 meters)|
|Penguin||800 feet (244 meters)|
|Human with aqualung||260 feet (79 meters)|
|Porpoise||164 feet (50 meters)|
whales, feed primarily on zooplankton, especially krill. Others, like the porpoise, feed on fish and invertebrates such as squid and even clams or oysters.
Like other mammals, marine mammals bear live young. Most have only one offspring at a time. The young are nursed with milk produced by the mother’s body until they are able to find food on their own.
At one time sharks were plentiful; however, reduction in their food supply from commercial fishing and a growing interest in the sharks themselves for human food have reduced their numbers.
Most seabirds tend to be unafraid. Many are threatened by humans who use them for food or feathers when they come to land. On the open ocean, thousands are caught accidentally each year in fishing nets. Others suffer from pollution, pesticides, and the results of oil spills, which destroy the waterproofing effect of their feathers. The albatross population alone has declined 40 percent in the past thirty years.
Until the twentieth century and the introduction of factory whaling ships, the great whales were numerous. Beginning around 1864 and ending in the 1970s, commercial whaling reduced the numbers of many coastal species. In 1986, a number of nations suspended commercial whaling in order to allow populations to increase. Since then, a few countries allow limited hunting locally for food. The North Atlantic right whale, protected since the 1930s, has fewer than 500 specimens remaining.
The bluefin tuna has decreased to 10 percent of its population since 1975.
People do not live in the ocean environment for long periods of time, but the oceans have had an effect on all human life. Human life has its effect on the oceans too.
Impact of the ocean on human life
Without the oceans, there would be no life on Earth. Not only did the first life forms originate there, but
Sea Serpent Sightings
For centuries, people have wondered if strange, gigantic creatures lay hidden in the unexplored regions of the sea. Every now and then, someone reports seeing what they think is a sea serpent. So far, the sightings that could be checked have turned out to be creatures already known. For example, a sea serpent that was reportedly washed up on the California coast turned out to be the remains of a beached whale. Sharks or other predators had eaten part of the whale, and its skin was twisted in such a way that it appeared to have a very long neck. Large regions of the ocean are still unexplored, and gigantic animals may yet remain to be discovered. The larva of an enormous eel has been found in the Pacific, for example. If its parent ever turns up, it might just be the legendary sea serpent.
the oceans help sustain all life forms. Oceans regulate gases in the atmosphere, and the phytoplankton that grows in them provide oxygen. The oceans influence weather and help moderate temperature; they are largely responsible for the rain, sleet, and snow that fall on land. They are also a source of food, water, energy, minerals, and metals.
Food and water
Since prehistoric times, humans have depended upon the oceans for food, primarily fish. Some fish, such as orange roughy, are caught in deep waters, but most primary fishing areas are over the continental margins where the waters support more sea life.
To make up for the shortage of certain species of fish, fish farming has become popular. In fish farms, fish eggs are hatched and the young fish are fed and protected until they can be released into the ocean or sold for food. A few sea fish, such as salmon, are grown successfully in farms but their flesh lacks the high levels of nutrients found in wild salmon.
Algae are used for food and to make food products. Certain varieties of kelp are popular in Japan, where they are cultivated in sea farms and used as a vegetable. In the United States, algae are used primarily as thickeners in ice creams and puddings.
Sea salt is another food item taken from the oceans. Sea water isolated in shallow ponds along the shoreline is allowed to evaporate until a crust of crystals forms. The crystals are then collected, processed, and packaged.
Sea water is desalted and used by some desert countries for drinking and irrigation (a method of supplying water to dry land). This process, called desalination, is expensive and not very efficient. Only wealthy countries can afford to do it.
Millions of years ago, sediments from dead animal and plant life (fossils) formed on the ocean floor. Time, heat, and pressure from overlying rock have worked to turn these sediments into fossil fuels, primarily gas and oil. To obtain these resources, oil rigs (large platforms standing well above sea level but anchored to the sea bed) are built. From these platforms, drilling is done into the rock, releasing the gas and oil,
which are then pumped to shore through pipelines. Most gas and oil deposits have been obtained from offshore rigs. As these deposits are used up, ways of acquiring deposits in the deep sea are being explored.
Ocean surface waters absorb large quantities of solar energy (energy from the sun). A process known as Ocean Thermal Energy Conversion has been used to capture some of that energy for human use. Conversion plants are located in Hawaii and other tropical islands. Producing usable energy from ocean currents, waves, and tides is also being explored.
Minerals and Metals
Minerals and metals are other important oceanic resources. Rocks, sand, and gravel dredged from the sea floor, especially in the North Sea and the Sea of Japan, are used in construction. Bottom deposits of manganese, iron, nickel, and copper have been found in the deep ocean, but so far, extracting them is expensive and poses environmental problems. Some minerals, such as sulfur, can be pumped as liquids from beneath the ocean floor.
Since the first humans ventured out on the oceans in ships, the oceans have provided transportation routes. At least 40,000 years ago, people made the journey from Southeast Asia to Australia and New Guinea. Since then, seagoing routes have been used for trade, expansion, travel, and war.
Impact of human life on the oceans
The World Ocean surrounds us, so what one country does to it affects all countries. If one country over-fishes a species of fish, other countries may suffer.
Wrecks at Sea
Since people first began to travel on the open sea, there have been shipwrecks. Some areas, such as the Bermuda Triangle in the Atlantic, are famous for the number of ships lost in them.
The sea helps preserve wooden ships by covering them with sediment so that wood-eating animals that might attack them are kept away. Metal ships, however, rust easily in seawater. Animals, such as corals, grow on the outside of the ship, and others, such as fish and octopi, may use the interior for shelter.
The most famous wrecked ship is the Titanic, which sank in 1912 on its first voyage. The Titanic was supposedly unsinkable because it contained many water-tight compartments that should have kept it afloat. It struck an enormous iceberg and sank in less than three hours. Of the 2,228 people on board, 1,523 died.
Use of plants and animals
After World War II (1939–45) the technology of commercial fishing improved, and a growing population increased the demand for fish as a food source. Major food species such as herring, cod, haddock, sardines, and anchovies, had been greatly reduced. Marine fishing reached an all-time high in 1989, at about 98 million tons (89 million tonnes). Regulations now limit fishing for these species. Some scientists believe that by monitoring the number of fish in a certain species, and by adding more species of those used for human food, no species should be threatened with extinction.
Fish farms are a means of helping maintain certain species of commercially popular fish. Pacific salmon are raised in hatcheries (fish farms) in the United States and Norway; oysters are raised in the United States; and shrimp farms can be found in Mexico, Ecuador, and Taiwan. Japan has greatly increased its catch of fish by building artificial reefs along its coastline. These reefs attract algae, which in turn attract fish and other sea animals.
The great whales were hunted for centuries by people of many countries for their meat, which was used for food; their fat, which was used for oil and in making soap; and for other body parts, which were ground into animal feed or used to make such items as brushes. Whales are now protected, but some scientists believe certain species will never recover from their losses and may still face extinction.
The Stellar sea cow, which looked like a giant walrus, weighed up to 11 tons (10 metric tons) and was hunted into extinction in the 1700s.
Many sea plants and animals are popular as souvenirs or art objects. When seashells from dead animals are taken, no harm is usually done. However, many shells available commercially are taken from living animals and the animals are left to die.
Marine parks and reserves have been set up all over the world to protect endangered species. They include the Shiprock Aquatic Reserve in Australia and the Hervey Bay Marine Park in California. Species on the endangered lists include the leatherback sea turtle, humpback whale, green sea turtle, and the bowhead whale.
Large quantities of natural resources, such as oil and minerals, can be found in the oceans or beneath the ocean floor. These resources have not been used up because they are still too difficult or too expensive to obtain. As methods improve that may change.
The God of the Sea
To the ancient Greeks, Poseidon was the god of the sea. It was believed that he lived beneath the oceans’s depths and controlled the fate of those who ventured out upon the waters. Poseidon could summon tsunamis, which is how he brought down the ancient kingdom of Crete, home of the fearful mythical Minotaur who was half man, half bull.
Quality of the environment
For centuries, the oceans have been used as a garbage dump. Six million tons (5,442,000 metric tons) of litter are dumped into them each year from ships alone, while sewage and industrial wastes come from coastal cities. Discarded items, such as plastic bags and old fishing nets, pose a hazard for the animals that get caught in them. Oil spills from tanker ships carrying oil from one country to another are dangerous, as is oil from oil refineries and pipelines. Efforts by concerned nations have begun to correct some of these problems. In 1972, an agreement to prohibit dumping of toxic (poisonous) materials in open seas was signed by ninety-nine nations.
At one time, radioactive nuclear wastes, which are extremely toxic, were dumped into the ocean. The Irish Sea, where this occurred, is the most radioactive sea in the world. Dumping of nuclear waste is now banned. Some countries have begun to study the deepest areas of the sea as potential disposal sites for extremely dangerous wastes, such as waste from nuclear reactors. Whether this can be done successfully without harm to the ocean environment, and ultimately to humans, remains to be seen.
Humans have explored the surface of the seas since ancient times, going as far as their craft and their courage would take them. By 3200 BC the Egyptians had invented sails and were traveling by sea to different countries for trading purposes. The ocean depths are another matter; humans can go only so deep without special equipment.
During the 1600s, diving bells were designed that allowed divers to go as deep as 60 feet (18 meters). Lead-lined wooden barrels filled with air were lowered periodically to the bell and a leather tube was used to connect them with the divers. In the 1700s, compressed air (air forced into a metal container) and the development of metal helmets and flexible
diving suits made exploration easier. In 1943, Jacques Cousteau and Emile Gagnan made diving to a depth of 165 feet (50 meters) possible by perfecting the automatic aqualung. (An aqualung provides compressed air through a mouthpiece.) Diving deeper has proven difficult. The dark, the cold, and the high pressure created by the weight of the water overhead limit what humans can do without special pressurized suits and protective vehicles.
The Seven Seas
Centuries ago, people spoke of “sailing the seven seas.” The seas in question were those considered navigable at the time: the Atlantic, Pacific, Indian, and Arctic Oceans; the Mediterranean and Caribbean Seas; and the Gulf of Mexico. Now scientists only speak of three major oceans, the Atlantic, Pacific, and Indian. The remainder of the original seven are considered part of the Atlantic.
In 1960, the bathyscaphe (BATH-uh-skafe) Trieste, operated by the U.S. Navy, descended almost 6.8 miles (11 kilometers) into the Mariana Trench in the Pacific. A bathyscaphe is a small, submersible (underwater) vehicle that can accommodate several people and is able to withstand the extreme pressures of the deep ocean—more than 16,000 pounds (110,240 kilopascals) per square inch. Other manned submersibles, including the U.S. Alvin, the French Nautile, the Japanese Shinkai 6500, and the Russian Mir I and Mir II, have reached depths of 3.7 miles (6 kilometers) and have greatly added to our knowledge about the ocean floor. In 1996, the Japanese submersible Kaiko collected the first samples of sediment from the Challenger Deep, the lowest part of the Mariana Trench.
Safety and other considerations make manned exploration of the oceans difficult. For these reasons, remotely operated vehicles are often used for unmanned exploration. Some vehicles are about the size of a small car. They are attached by cables to a “mother” ship and may be equipped with video cameras, mechanical arms, and sensors that measure temperature, salinity, and other water conditions. New models are expected to go as deep as 13,120 feet (4,000 meters) and have cameras that can operate without lights. These newer models are not able to go as deep as previous models, like the Trieste, but they are more sophisticated and are meant for more elaborate studies.
Much exploration has been made using sonar equipment. Sonar is the use of sound waves to detect objects. Single pulses of sound are sent out by a machine at regular intervals and as the sound pulses are reflected back a “picture” is obtained of the surrounding area. Sonar has helped researchers map the mountains and valleys of the ocean floor.
The transfer of energy from organism to organism forms a series called a food chain. All the possible feeding relationships that exist in a biome make up its food web. In the ocean, as elsewhere, the food web consists of producers, consumers, and decomposers. These three types of organisms transfer energy within the oceanic environment.
Phytoplankton are the primary producers in the oceans. They produce organic materials from inorganic chemicals and outside sources of energy, primarily the sun.
Zooplankton and other animals are consumers. Zooplankton that eat only plants are primary consumers in the oceanic food web. Secondary consumers eat the plant-eaters. They include the baleen whale and zooplankton that eat other zooplankton. Tertiary consumers are the predators, like tunas and sharks. Humans are also tertiary consumers called omnivores, organisms that eat both plants and animals.
Decomposers feed on dead organic matter and include lobsters and large petrels. Bacteria help in decomposition.
Harmful to the oceanic food web is the concentration of pollutants and dangerous organisms. It was once thought that the ocean would dilute harmful chemicals, but just the opposite is true. They become trapped in sediments where life forms feed. These life forms are fed upon by larger organisms, and at each step in the food chain the pollutant becomes more concentrated. When humans eat contaminated sea animals, they are in danger of serious illness. The same is true of diseases such as cholera, hepatitis, and typhoid, which can survive and accumulate in certain sea animals and then be passed on to people.
The Indian Ocean
The Indian Ocean is the third largest in the world and covers about 20 percent of Earth’s water surface. Its volume is estimated to be about 62,780,380 cubic miles (261,590,400 cubic kilometers).
The Indian Ocean
Location: South of India, Pakistan, and Iran; east of Africa; west of Australia; north of the Antarctic Sea
Area: 28,000,000 square miles (73,000,000 square kilometers) Average Depth: 12,760 feet (3,890 meters)
The Indian Ocean contains many islands. During the prehistoric breakup of the continents, small pieces of continent were left behind in the Indian Ocean as undersea plateaus (high, level land areas). Some of these plateaus rise above the water and form islands, such as the Laccadives. Many other islands, such as Mauritius, are volcanic in origin. On the ocean’s eastern border lie the islands of Indonesia; on the western border lie Madagascar, Zanzibar, the Comoros, the Seychelles, the Maldives, and the Nicobar Islands. To the south are the Crozets and the Kerguelen. Coral reefs (undersea walls made from coral skeletons) can be found in areas of the ocean located in the tropics.
Running through the center of the Indian Ocean’s floor is part of the mid-ocean ridge in the form of an upside-down Y. Many peaks in this mountain chain are about 6,560 feet (2,000 meters) high. All along the chain are active volcanoes; earthquakes constantly occur, causing spreading of the sea floor. The Indian Ocean basin is expanding at a rate of about 1 inch (2.5 centimeters) each year.
The Java Trench is the only known trench in the Indian Ocean. It lies south of Indonesia and, at its lowest point, is 4.5 miles (7 kilometers) deep. To the north of the trench is another string of volcanoes, the most famous of which is Krakatoa, which exploded so violently in 1883 that it could be heard 1,860 miles (3,000 kilometers) away.
Several major rivers flow into the Indian Ocean bringing large quantities of sediment. These include the Indus and Ganges in India and the Zambesi in southern Africa. Over thousands of years, these sediment layers have formed vast fans that spread out over the nearby ocean floor.
Climatic conditions over most of the Indian Ocean are tropical. In its warmest part, the Arabian Sea, surface waters can reach 86°F (30°C). Near the Antarctic Sea, the temperature can drop to less than 54°F (12°C). Average annual rainfall is about 40 inches (102 centimeters). In the ocean’s northern reaches, rainfall is affected by the monsoons (rainy seasons) that drench the Asian continent. In the southern portion, trade winds blow from the southeast all year long.
Two major currents occur in the Indian Ocean. In the southwest, the Agulhas flows between Africa and Madagascar. At the equator, the North Equatorial Current occurs in the winter and flows west.
Where the Indian Ocean meets the Pacific Ocean in the region of the Philippines, marine life is very rich. In the open ocean marine life is scarce because the waters of the Indian Ocean are warm, and growth of phytoplankton is limited. As a result, the creatures that feed on phytoplankton are limited.
Among the species of invertebrate plankton that live in the Indian Ocean is the sea wasp jellyfish. Its poisonous sting produces large welts. A person with many stings can die in minutes. Crabs, lobsters, oysters, squid, and giant clams are found here.
The Indian Ocean supports many species of seabirds, especially around the shoreline where food is plentiful. The most common birds are noddies, boobies, terns, frigate birds, storm petrels, and albatrosses.
Species of mid-ocean fish include sharks, flying fish, tunas, marlins, and sunfish. The coelacanth, a species of fish surviving from prehistoric times, has been found off the Comoros Islands, where it is now protected.
Whales are plentiful in the Indian Ocean, especially in the cooler southern waters where food is abundant. Much of the Indian Ocean is now a protected area for whales. Other mammals include fur seals, elephant seals, and, in northern portions, sea cows. Sea cows have become endangered because they are easily caught in nets and killed for their meat and hides.
Commercial fishing in the Indian Ocean is limited to local needs. Over the centuries, the ocean’s greatest value has been for trade transport. Since the discovery of large oil deposits in the Middle East, it has been key to the shipment of petroleum extracted along the Persian Gulf.
The first Westerner to explore the Indian Ocean was Vasco da Gama (c. 1460–1524) of Portugal. In May 1498, da Gama reached India and, for the next century, Portugal claimed this ocean as part of its empire. The ocean was so vast that no one nation controlled the surrounding lands until England in the early 1800s. After World War II (1939–45), England withdrew from the area. Gradually, India, Russia, and the United States have become major influences. Countries bordering the ocean want it declared a peaceful zone where all people may travel the waters freely and safely.
The Sargasso Sea
The Sargasso (sar-GAS-oh) Sea is a clear, saucer-shaped area of water near the island of Bermuda in the Atlantic. It is formed by two main opposing ocean currents, the Gulf Stream to the north, and the North Equatorial Current to the south. Its waters are warm and, because of the action of the currents, they slowly revolve clockwise above much colder Atlantic depths. This rotation causes the water in the center to rise, and the level of the Sargasso is about 3 feet (1 meter) higher than the water surrounding it.
The Saragasso Sea
Location: Western North Atlantic
Area: 2,000,000 square miles (5,200,000 square kilometers) Average Depth: 3 miles (4.8 kilometers)
The name Sargasso comes from Sargassum, the type of brown algae that grows there in abundance. The algae are plankton, and they possess clusters of gas-filled chambers resembling grapes at the bases of their fronds that keep them afloat. Huge masses of the algae drift on the surface of the sea. These algae reproduce when pieces break off the main organism and begin to grow. Every piece can potentially grow into a new organism.
Many animals live in the Sargasso Sea that are ordinarily not found in mid-ocean because of the plentiful algae. Some animals, like tubeworms, attach themselves to the algae and sift the water for tiny organisms they use for food. Crabs, shrimp, and snails roam everywhere over the fronds. The leptocephalus (lep-TOH-sef-a-LOS) eel migrates to the Sargasso to breed but otherwise lives in freshwater rivers thousands of miles away.
Permanent species of fish include the sargassum fish, which lives only in the Sargasso. Its scientific name means “the actor;” an appropriate name because it spends its life pretending to be a sea weed frond. Its body has black and yellow-green blotches to match the algae. It has a pair of fins with fingerlike projections that allow it to attach to a frond and drift as the frond does. When it stalks its prey, it climbs over the weeds. One of its fingerlike projections resembles a bit of food, which it dangles in front of its mouth waiting for another fish to take the “bait.”
Italian explorer Christopher Columbus (1451–1506) reported on the Sargasso after his first voyage to the “Indies,” and he claimed to have found evidence of other voyagers there. It is possible that the Carthaginians, who lived in the city of Carthage on the North coast of Africa during ancient times, may have reached the Sargasso as early as 530 BC. Legends tell of ships being trapped in the weeds, but that likely never happened. Instead, ships set adrift may have been carried here because of the rotating current, and this may be the source of the myth.
The Black Sea
The Black Sea is the world’s largest inland body of water. It qualifies as a sea because it remains connected to the Sea of Marmara, the Aegean Sea, and finally to the Mediterranean Sea by means of the Bosporus Strait. Large European rivers including the Dnieper, the Danube, the Dniester, and the Don flow into it. The fresh water they bring makes it less salty than most seas.
The Black Sea
Location: North of Turkey, south of Russia and the Ukraine
Area: 162,000 square miles (419,580 square kilometers) Average Depth: 3,826 feet (1,166 meters)
Two currents flow through the 19-mile (30-kilometer) -long Bosporus Strait. A rapid surface current carries water from the Black Sea toward the Aegean and eventually into the Mediterranean. Beneath this current, a strong undercurrent travels in the opposite direction, bringing waters from the Mediterranean into the Black Sea. These currents create very choppy waters and help create the Black Sea’s unusual environment.
The water column in the Black Sea is layered. Salt water coming from the Mediterranean enters at a deep level and continues to sink. Fresh water from the rivers flows into the shallow coastal areas. Fresh water is lighter than salt water, so it floats on top of the salt water. The two layers mix very little. The bottom layer, which consists of almost 90 percent of the water column, receives little oxygen creating a dead zone. Nothing lives at the bottom of the Black Sea except a few species of bacteria. A form of sulfur dissolved in the deep water gives it the odor of rotten eggs.
The upper layer supports abundant life forms. About 300 species of algae live in the upper layer to a depth of about 65 feet (20 meters). These plants provide food for zooplankton, mollusks, and other sea life. Many kinds of fish live in the upper layer, including anchovies, bluefish, turbot, and sturgeon. The largest mammals in the Black Sea are dolphins. More than 1 million dolphins once lived there, but their numbers were greatly reduced by commercial fishing. Some countries have begun programs to protect the dolphins and other endangered species.
Countries surrounding the Black Sea once depended upon it financially for fish. Overfishing, the use of pesticides, industrial pollution, diversion of river waters for irrigation, and nuclear contamination from the Chernobyl reactor explosion in 1986 have caused fish populations to decrease. Lack of fresh river water has resulted in an increase in the size of the dead zone, which may eventually take over the entire Black Sea. If that happens, nothing will be able to live in it except bacteria.
In Greek legend, the Black Sea was the body of water on which Jason and the Argonauts sailed in search of the Golden Fleece. For centuries, the Black Sea was considered unfriendly for sailors because of its sudden storms and strong currents. These dark storms and heavy threatening fogs may have been what earned the sea its name.
The Pacific Ocean
The Pacific Ocean is the world’s largest ocean. Waters in its northern and southern halves seldom mix. In the north it is linked to the Arctic Sea by means of the Bering Strait. In the south it is bordered by the Antarctic Sea. Its volume is about 154,960,672 cubic miles (643,375,552 cubic kilometers).
The Pacific Ocean
Location: West of North and South America; east of Asia and Australia
Area: 64,000,000 square miles (1,666,000,000 square kilometers) Average Depth: 12,700 feet (3,870 meters)
The mid-ocean ridge cuts through the Pacific basin from Japan to Antarctica and attains a height of 13,000 feet (3,962 meters) in some places. Trenches along the continents often exceed 26,000 feet (7,925 meters) in depth. Deeper trenches are found along strings of islands, such as the Aleutians and the Philippines. The deepest trench in the world, the Mariana, is found in the Pacific near the Mariana Islands.
Islands are numerous in the Pacific, and most have been created by volcanoes. The famed “Ring of Fire,” an area of intense volcanic activity is found in the region of Indonesia. Islands near the equator usually have coral reefs.
Around the equator, the trade winds maintain a permanent current moving from east to west. As this current turns northward around the island of Japan, it is called the Kuroshio (koo-ROH-shee-oh) current. Like the Gulf Stream in the Atlantic, the Kuroshio is a strong, intense current.
The areas of the Pacific most abundant with plant and animal life are in the far north and far south where icy water circulating upward from the sea floor brings nutrients to the surface. Millions of tons of phytoplankton and zooplankton drift upon the waters in spring and summer, providing food for baleen (toothless) whales and basking sharks, as well as smaller animals. Species from one area seldom inhabit the other.
The Pacific is home to one of the most dangerous of the invertebrates, the little blue-ringed octopus, whose sting is highly poisonous and usually deadly. Another invertebrate, the Pacific lobster, lacks claws and uses its antennae instead for defense.
Several species of sharks and rays are found only in the Pacific. The Port Jackson shark eats primarily clams and other mollusks, using its powerful jaws to crack the shells. This particular shark has a long history; its form has remained unchanged for the past 150 million years. More than twenty species of whales, porpoises, and dolphins live only in the Pacific. In the southern regions, leopard and fur seals can be found.
More than 40 percent of commercial catches of fish with fins, such as anchovies and tuna, come from the Pacific. Other Pacific resources with commercial importance include offshore deposits of iron ore near Japan, and tin near Southeast Asia.
The Atlantic Ocean
The Atlantic Ocean contains about 25 percent of all the water in the World Ocean. Its volume is 73,902,416 cubic miles (307,902,776 cubic kilometers).
The Atlantic Ocean
Location: East of North and South America, west of Europe and Africa
Area: 33,000,000 square miles (86,000,000 square kilometers) Average Depth: 12,100 feet (3,688 meters)
Although its waters are typically less salty than those of the Pacific, its northern portion is the warmest and saltiest area in the World Ocean. This is due, in part, to water flowing into it from the Mediterranean. Its circulation is limited because the northern portion is hemmed in by continents, and because its waters do not readily mix with those of the Arctic Ocean to the north. Currents are stronger than in the southern Atlantic.
The mid-ocean ridge forms an S-shape in the Atlantic basin and divides it into two parallel sections. Some peaks along the ridge form islands, such as the Azores. Its deepest trench is the Puerto Rico with a depth of 28,232 feet (8,605 meters).
The most familiar Atlantic current is the Gulf Stream, which flows along the eastern coast of North America. A number of currents in the North Atlantic form a clockwise gyre. In the South Atlantic, currents form a counterclockwise gyre.
The Atlantic is geologically young, and its bottom-dwelling animals are descendants of animals that migrated there from other oceans. As a result, the numbers of bottom-dwelling species are few. In its equatorial and temperate regions, nektonic and planktonic animals are abundant. Many ocean travelers, such as sharks, whales, and sea turtles, cross the southern regions when they migrate.
Atlantic resources include diamonds found off the southwest coast of Africa, sand and gravel off the coast of northwest Europe, and oil and gas in the Caribbean and North Sea regions. Fish taken commercially from the Atlantic include salmon, lobster, shrimp, crabs, sardines, and anchovies.
The science of oceanography began in the northern Atlantic, and many theories about oceans are based on studies made there. The northern portion of the Atlantic differs from its southern portion and from the Indian and Pacific Oceans, so these generalizations cannot be automatically accepted.
The Antarctic Ocean
The Antarctic Ocean is sometimes called the Southern Ocean. It encircles the continent of Antarctica, and in winter ice forms over more than 50 percent of the ocean’s surface. Glaciers break free of the continent periodically and drift seaward to join floating ice shelves.
The Antarctic Ocean
Location: Surrounding the continent of Antarctica
Area: 12,451,000 square miles (32,249,000 square kilometers) Average Depth: 12,238 feet (3,730 meters)
In the north, the mid-ocean ridge borders the Antarctic basin. The basin itself reaches a depth of about 18,400 feet (5,600 meters).
Currents in the Antarctic Ocean flow from west to east and the water is turbulent (rough). The area is windy and usually cloud covered.
The amount of daylight varies dramatically at the south pole. In winter, it is dark almost all of the time, and light almost all of the time in summer. Growth of phytoplankton is limited to spring and summer seasons.
The most important zooplankton is krill, which is food for baleen whales, seals, sea birds, fish, and squid. Among invertebrates, squid are common and play an important part in the food web. They are eaten by sperm whales and albatrosses.
Most fish in the Antarctic are bottom-dwellers, where they tend to live on or near the continental margins. Many, such as the Antarctic cod, contain a kind of antifreeze in their body fluids that allows them to live at temperatures below freezing.
Sea birds, such as penguins, breed on the continent. The Adelie penguin is the most numerous. Breeding colonies are usually densely packed because ice-free land is limited.
Among mammals, baleen whales, toothed whales, and seals thrive there. Overhunting in the area has threatened many species, especially the blue whale, and it is not known if some of these species will survive. In 1982, the Convention for the Conservation of Antarctic Marine Living Resources was agreed to by concerned nations in order to better regulate fishing in the Antarctic Ocean.
The Red Sea
The Red Sea lies in the heart of the Middle East and is surrounded by desert. In the south it is connected to the Gulf of Aden and the Indian Ocean by means of the Straits of Bab el Mandeb. In the north, it is linked to the Mediterranean Sea by means of the Gulf of Aqaba and the Gulf of Suez.
The Red Sea
Location: East of Egypt, Sudan, and Ethiopia; west of Saudi Arabia and Yemen
Area: 169,000 square miles (437,700 square kilometers) Average Depth: 1,730 feet (524 meters)
The Red Sea started to form 40 million years ago when the area that is now Saudi Arabia broke away from the continent of Africa. The sea floor here is still spreading at a rate of 0.5 inch (1 centimeter) per year, and scientists consider the Red Sea a “baby” ocean that will, after about 200 million years, be as large as the current Atlantic Ocean.
The presence of surrounding desert lands causes a high degree of evaporation in the Red Sea making its water very salty. No fresh water is added because no rivers drain into it. Another source of its saltiness is the presence of hot salty pools approximately 1.3 miles (2.1 kilometers) below its surface. It is believed that the salt in these pools comes from sediments found in some parts of the Red Sea. These sediments are rich in iron, manganese, zinc, and copper, and may prove very valuable when methods for mining them become practical.
In summer, winds come from the northwest and currents flow toward the Gulf of Aden. In winter, a southeasterly wind causes the surface currents to flow in the opposite direction.
Normally, the Red Sea is a bluish-green color. However, it is heavily populated by orange colored algae that turn reddish-brown when they die. This may be why it was named the Red Sea.
Over 400 species of corals are found here. As the corals form reefs, they attract the types of fish that thrive in those areas. The largest fish that live in the Red Sea are whale sharks. Manta rays are also common. Other fish include snappers, grouper, parrotfish, and sardines.
Animals found in the Red Sea are important to human life. Sea cucumbers, a sausage-shaped invertebrate, are common. They are a Far Eastern delicacy making them commercially important, as are prawns, a type of tropical shrimp. Pearls from oysters in the Red Sea are famous for their high quality. Mother-of-pearl, taken from the shell of another sea animal, the mollusk, is used to make shirt buttons and other decorations.
The process of desalting ocean water to produce fresh water is becoming more common in countries bordering the Red Sea. There are eighteen desalination factories along the Saudia Arabian border. These factories remove salt from water to make it drinkable.
The Red Sea has been important for transportation since at least 2000 BC. Until 1869, the only access to the Red Sea was from the south; it was closed at its northern end until the Suez Canal was constructed by the British. The Suez Canal is a long channel that allows the waters of the Red Sea to mix with those of the Mediterranean. Ships going through the canal can reach the Indian Ocean without traveling all the way around the continent of Africa, a great savings of time and distance.
The Red Sea is made famous from the Bible because God gave Moses the power to part its waters. Moses was then able to lead the Israelites across the sea floor during their escape from bondage in Egypt.
The Mediterranean Sea
The Mediterranean Sea is the world’s largest inland sea. It lies between the continents of Europe and Africa. It is connected to the Atlantic in the west by the Straits of Gibraltar and to the Red Sea in the east by the Suez Canal. To the north, it joins the Aegean and Black Seas, which are also inland seas.
The Mediterranean Sea
Location: Between Europe and North Africa
Area: 1,145,000 square miles (2,965,500 square kilometers) Average Depth: 4,902 feet (1,494 meters)
The Mediterranean is bisected by a submarine ridge into eastern and western basins. Many of its islands were formed by volcanoes, some of which are still active. The region has many earthquakes. Its greatest depth, 16,814 feet (5,125 meters), is in the Matapan Trench.
The climate around the Mediterranean is warm and wet in the winter and hot and dry in the summer. Surface water temperatures range from about 41°F (5°C) in the north during the winter to 88°F (31°C) in the south during the summer. Many rivers flow into the Mediterranean, the largest of which is the Nile River of Egypt, but its water is very salty because of continual evaporation.
The warm water means less phytoplankton, and less phytoplankton means fewer animal species in general. The sea varies in temperature, salinity, and depth from place to place, and a variety of plant and animal life can be found. Invertebrates include crabs, lobsters, shrimp, oysters, mussels, clams, and squids. More than 400 species of fish are found there including bass, flounder, tuna, sharks, and mackerel.
Since ancient times, the Mediterranean has been a source of fish for people living in the surrounding countries. However, the catches are not large enough to be commercially important worldwide. Of greater economic importance is the discovery of oil and gas deposits beneath the sea floor.
The Mediterranean suffers from pollution as a result of industrial and municipal wastes dumped along the European coast. Oil tankers travel its waters and oil spills add to the problem. Efforts are being made to repair the damage.
The Mediterranean has been historically important since the Egyptian people began to explore it as early as 3000 BC. In later millennia, Crete, Greece, and Anatolia began to use it for trade and for ships of war. Between 300 BC and 100 AD, Rome ruled the sea. After the fall of Rome in 476 AD, the Arabs, Germans, Slavs, and Ottoman Turks each took a turn holding sway over the area. During the 1700s, the discovery of new sea routes to India around Africa made the Mediterranean less important for travel and commerce.
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Oceans and Estuaries
OCEANS AND ESTUARIES
A view of the Earth from a satellite shows an azure planet composed almost entirely of water. The oceans that cover two-thirds of the Earth's surface to an average depth of almost 2.5 miles contain 97% of the planet's water and have a profound influence on its environment. If the ocean basins were shallower, the seas would spread across the continents, and the only dry land areas would consist of a few major high mountain ranges projecting above a continuous layer of water.
During the twentieth century scientists came to appreciate the important role that the oceans play in maintaining the Earth's climate. The oceans determine weather and long-term climate changes. They can also cause widespread damage to human populations, destroying human lives and property. Scientists are also still discovering the incredible diversity of life forms within the ocean depths. The oceans are home to more than 80% of all the life forms found on earth. The many levels in the oceans' complex food chain interact by producing food and structures as habitat for other species, as well as consuming organic material and wastes. Primary producers, such as phytoplankton, seaweed, and algae, are eaten by small animals and fish, which in turn are eaten by larger fish. These in turn are eaten by birds, larger fish, and such mammals as seals and humans. Surface currents and deep currents mix the waters and move nutrients about, replenishing the food source for all marine life living at various depths, providing a bounteous food supply for all.
Origin of the Oceans
The terms "ocean" and "sea" are sometimes used interchangeably. Earth's oceans are the Pacific, Atlantic, Indian, Arctic, and Southern. Generally, seas are a portion of a larger ocean, although they may be partially or completely enclosed by land, such as the Mediterranean Sea, the Red Sea, and the Black Sea. There are about thirty-five seas in the world.
Oceanographers (scientists who study the oceans) believe that the oceans are some 500 million years old. They also think that both the atmosphere on Earth and the oceans were formed through a process called "degas-sing" of the Earth's deep interior. According to this theory, the ocean originated from the escape of water vapor from the melted rocks of the early Earth. The vapor rose to form clouds surrounding the cooling planet. After the Earth's temperature had cooled to a point below the boiling point of water, rain began to fall and continued falling for many centuries. As this water drained into the huge hollows of the planet's cracked surface, the ocean was formed. The force of gravity kept this water on Earth.
Oceans as Controller of Earth's Climate
Oceans play a major role in the Earth's weather and long-term climate change. The oceans have a huge capacity to store heat and can affect the concentration of atmospheric gases that control the planet's temperature. The top eight feet of the oceans holds as much heat as the entire atmosphere, making the oceans' ability to distribute heat a very important factor in climate changes. Changes such as unusually warm (El Niño) or cold currents (La Niña) in the eastern portion of the Pacific (the largest ocean) can disrupt global weather patterns.
The oceans play a crucial role in the cycle of carbon dioxide, a process affecting global warming. The world's oceans store some of the twenty-two billion tons of carbon dioxide added each year to the atmosphere by natural sources and the burning of fossil fuels. Some scientists believe that the oceans serve as a reservoir for about half of all the carbon dioxide emitted each year, while the other half accumulates in the atmosphere.
When Oceans Become Deadly
COASTAL POPULATIONS GROW.
Coastal areas are particularly vulnerable to natural hazards such as hurricanes, tidal waves, and their associated flooding. A December 2004 tsunami, triggered by a massive earthquake in the Indian Ocean, killed at least 200,000 people and caused massive damage in Indonesia, Sri Lanka, India, Thailand, and many small islands in the region. The true death toll from the tsunami may never be known, and the devastation was so overwhelming that it is difficult to attach a dollar figure to it.
This terrible catastrophe highlights the dangers inherent in living near the coast of a large body of water. In 2000 more than one-fifth of the world's population (more than one billion people) lived in coastal areas. This living preference places huge segments of the world population at risk from coastal hazards (episodic or chronic destructive natural system events that affect coastal areas), and has increased pollution of both oceans and estuaries.
Coastal areas are some of the fastest-growing parts of the United States. The National Oceanic and Atmospheric Administration (NOAA) reported that 54% of the U.S. population (occupying only 26% of the total land mass) lives in coastal counties. In the time period 1990–2000, seventeen of the fastest-growing counties in the United States were located along the coast and nineteen of the twenty most densely populated counties in the nation were coastal. The U.S. Census Bureau estimated that by 2010, 127 million people would live in coastal areas. According to Coastal Areas and Marine Resources (December 2001), a report from the National Coastal Assessment Group, by 2020 the coastal states of Florida, California, Texas, and Washington alone are expected to gain approximately eighteen million people.
According to "Thirty Years of Protecting Oceans and Coasts," a January 13, 2003, Environmental Protection Agency (EPA) press release, more than half of the United States population lives within fifty miles of the coasts. In addition, an estimated 180 million Americans visit United States coastal areas each year, spending more than $600 billion. One of every six jobs in the United States is marine-related, generating $54 billion in goods and services annually. Coastal waters provide diverse and biologically productive habitats, supporting 66% of all United States commercial and recreational fishing and 45% of all protected species.
The most common coastal hazard is the threat of the huge ocean storms that come ashore, generally during the warmer months of the year, and cause devastating damage to property and human life. These storms go by different names in different parts of the world. They are called hurricanes or tropical storms in the North Atlantic, eastern North Pacific, and western South Pacific. "Typhoon" is the common term used for storms in the China Sea and western North Pacific, while "cyclone" is the word used for a storm in the Arabian Sea, the Bay of Bengal, and the South Indian Ocean.
Because of the spinning of planet Earth, a serious tropical storm's spiral is counterclockwise north of the equator and clockwise in the Southern Hemisphere. These tropical storms are the most dangerous weather phenomenon known, causing destruction through their very strong winds, torrential rains, and storm surges. By far the greatest damage and the most deaths are caused by the storm surges, the elevated mounds of water pushed by the high winds. Surges can reach twenty feet or higher. In an ocean storm, a surge rolls over everything in its path, and combined with the violent waves and water currents the surges cause not only death and destruction, but also immense erosion of land.
Coastal hazards such as hurricanes, tropical storms, and northeasters bring high winds, storm surges, flooding, and shoreline erosion, all of which are particularly damaging to coastal areas. They are not usually considered disastrous unless they involve damage to people and their property. Recent impacts have been increasingly devastating. Estimated disaster losses in the United States range from $10 billion to $50 billion annually; the average cost of a major storm is $500 million. One of the primary factors contributing to the rise in disaster losses is the increasing population in high-risk coastal areas. Table 6.1 and Table 6.2 show the most deadly and the most costly tropical cyclones or hurricanes that made landfall on the U.S. mainland between 1900 and 2004.
The most costly tropical cyclone during this period was hurricane Andrew, which devastated southeast Florida and southern Louisiana in 1992. Although the death toll was relatively low, at thirty-five lives, the cost of damage done approached $35 billion and the storm left some 250,000 people homeless. In the fall of 2004 Florida was hit by four strong hurricanes (Charley, Frances, Ivan, and Jeanne) in just six weeks. Damages from these storms were estimated to cost $41 billion. The cost of large hurricanes has been rising, but because of advances in storm prediction and preparation, the cost in lives has declined. Table 6.2 lists the most costly hurricanes to strike the U.S. mainland between 1900 and 2004, but not one of the top ten on that list is also among the ten most deadly storms during the same period. In fact, only one of the twenty-five costliest storms is also among the ten deadliest, an unnamed storm that struck New England in 1938.
With populations growing in coastal areas, eliminating the destruction associated with tropical storms will be almost impossible. However, accurate forecasting and storm preparation are of increasing importance in continuing to keep death tolls from such storms to a minimum.
|1||Unnamed (TX, Galveston)||1900||4||8.000a|
|2||Unnamed (FL, Lake Okeechobee)||1928||4||1.836|
|3||Unnamed (FL, Keys)||1919||4||600b|
|4||Unnamed (New England)||1938||3c||600|
|5||Unnamed (FL, Keys)||1935||5||408|
|6||Audrey (Southwest LA, inland TX)||1957||4||390|
|8||Unnamed (LA, Grand Isle)||1909||4||350|
|9||Unnamed (LA, New Orleans)||1915||4||275|
|10||Unnamed (TX, Galveston)||1915||4||275|
|Note: Hurricanes, or tropical cyclones, were not named until the 1950s.|
|aThis figure could be as high as 10,000 to 12,000.|
|bOver 500 lost on ships at sea, 600–900 estimated deaths.|
|cMoving more than 30 miles per hour.|
|dOf the total lost 344 were lost on ships at sea.|
TRYING TO GUESS THE FUTURE.
Much research is targeted at understanding coastal storms so that their occurrences can be predicted and coastal residents warned. In addition to increasing the amount of property at risk, coastal population growth has created potentially life-threatening problems with storm warnings and evacuation. It has become increasingly difficult to ensure that the ever-rising numbers of residents and visitors can be evacuated and transported to adequate shelters during storm events. Sometimes hurricane evacuation decisions must be made well in advance of issuing hurricane warnings in order to mobilize the appropriate manpower and resources needed for the evacuation. Also, when a significant percentage of the coastal population has not experienced an event such as a hurricane, people are less likely to prepare and respond properly before, during, and after the event.
Why Is the Ocean So Salty?
The salinity (saltiness) of the ocean is the result of several ongoing natural processes. Salts are the end products of the naturally occurring reactions between acids and metals and metal-like substances in the environment. Early in the life of the planet, the oceans probably contained very little salt. However, since the first rains began descending on the young Earth many millions of years ago and ran over the land, breaking up rocks, absorbing and reacting with them to create dissolved solids (salts), and then transporting them to the oceans, the oceans have become progressively more salty. The activity of the hydrological cycle further concentrates the ocean salts.
|1||Andrew (Southeast FL and LA)||1992||5a||$34,954,825,000|
|2||Charley (FL, SC)||2004||4||14,000,000,000|
|5||Agnes (FL, Northeast U.S.)||1972||1||8,602,500,000|
|6||Betsy (Southeast FL and LA)||1965||3||8,516,866,023|
|8||Camille (MS, Southeast LA, VA)||1969||5||6,992,441,549|
|10||Diane (Northeast U.S.)||1955||1||5,540,676,187|
|11||Frederic (AL, MS)||1979||3||4,965,327,332|
|12||Floyd (Mid Atlantic & Northeast U.S.)||1999||2||4,666,817,360|
|13||Unnamed (New England)||1938||3b||4,748,580,000|
|15||Opal (Northwest FL, AL)||1995||3||3,520,596,085|
|16||Alicia (North TX)||1983||3||3,421,660,182|
|17||Carol (Northeast U.S.)||1954||3b||3,134,443,557|
|18||Carla (North & Central TX)||1961||4||2,550,580,095|
|19||Georges (FL Keys, MS, AL)||1998||2||2,494,800,000|
|21||Donna (FL, Eastern U.S.)||1960||4||2,407,888,443|
|22||Celia (South TX)||1970||3||2,015,663,203|
|23||Elena (MS, AL, Northwest FL)||1985||3||2,015,663,203|
|24||Bob (NC, Northeast U.S.)||1991||2||2,004,635,258|
|25||Hazel (SC, NC)||1954||4b||1,910,582,732|
|26||Unnamed (FL, MS, AL)||1926||4||1,738,042,353|
|27||Unnamed (North TX)||1915||4||1,544,253,659|
|28||Dora (Northeast FL)||1964||2||1,540,946,262|
|29||Eloise (Northwest FL)||1975||3||1,489,250,000|
|30||Gloria (Eastern US)||1985||3b||1,451,277,506|
|31||Unnamed (Northeast U.S.)||1944||3b||1,221,342,593|
|32||Beulah (South TX)||1967||3||1,113,122,363|
|aReclassified as category 5 in 2002.|
|bMoving more than 30 miles per hour.|
(See Figure 6.1.) The sun's heat vaporizes almost pure freshwater from the surface of the sea, leaving the salts behind. Table 6.3 shows the principal constituents of ocean water.
The salinity of the ocean is currently about thirty-five pounds per thousand pounds of seawater, or parts per thousand (ppt). This is similar to having a teaspoon of salt added to a glass of drinking water. In contrast, freshwater has less than 0.5 ppt. Salinity in estuaries varies from slightly brackish (0.5 to 5 ppt) at the freshwater end to moderately brackish (5 to 18 ppt), to highly saline (25 to 30 ppt) near the ocean.
Scientists estimate that the rivers and streams flowing from the United States into the ocean discharge 225 million tons of dissolved solids (salts) and 513 million tons of suspended sediment into the ocean each year. Throughout the world, rivers annually transport about four billion tons of dissolved salts to the ocean. Nearly
(parts per thousand)
|Total dissolved solids (salinity)||35.079|
an equal amount of salt is deposited by the ocean as sediment on its floor.
If the salt in the ocean were taken out and spread evenly over the Earth's entire land surface, it would form a layer more than 500 feet thick—about the height of a forty-story building. (See Figure 6.2.) Throughout the world the salinity of seawater is similar, although it is somewhat lower in the nearshore coastal waters, the polar seas, and near the mouths of large rivers.
USING SALINITY IN FORECASTING.
According to a January 29, 2003, National Aeronautics and Space Administration (NASA) news release ("Ocean Surface Salinity Influences El Niño Forecasts"), NASA-sponsored scientists at the University of Maryland may have discovered how to improve the ability to predict El Niño events by knowing the salt content of the ocean's surface. Scientists have found that salinity and temperature combine to affect the density of the ocean. Greater salinity results in an increase in ocean density with a corresponding depression of the sea surface height. In warmer, fresher waters, the density is lower, causing an elevation of the sea surface.
The surface salinity in two regions contributes to El Niño events: an area of warmer temperatures and lower salinity in the western Pacific, and the higher salinity and cooler temperatures in the eastern Pacific. Differences in surface salinity are related to changes in temperature and upper ocean heat content, which are parts of the El Niño phenomenon. They have the potential to influence the Earth's climate through air-sea interaction at the ocean's surface.
According to the article, the study is among the first to look at ocean salinity in El Niño; Southern Oscillation predictions and their relationship to tropical sea surface temperatures, sea level, winds, and fresh water from rain. Researchers studied data about sea surface temperatures, winds, rainfall, evaporation, sea surface height, and latent heat, for the period from 1980 through 1995. Using computer models, they performed a series of statistical predictions of the El Niño events for the period. They found that short-term predictions only require monitoring sea surface temperatures, while predictions over a season require the observation of sea level changes. They concluded that observations of salinity significantly improve predictions. When changes in salinity occur, they affect the El Niño event for the next six to twelve months. During this lag time, salinity changes have the potential to modify the layers of the ocean and affect the heat content of the western Pacific Ocean, the region where the unusual atmospheric and oceanic behavior associated with El Niño first develops.
Researchers believe that the study will be of great significance for the NASA Aquarius mission to monitor the surface salinity of the global ocean. According to data available on one of NASA's Aquarius mission Web sites (http://science.hq.nasa.gov/missions/satellite_59.htm, January 3, 2005), this mission is scheduled for launch in 2008 and will have an operational life of three years. Aquarius will provide the first global maps of salt concentration on the oceans' surfaces. Salt concentration has been a key area of scientific uncertainty in the oceans' capacity to store and transport heat, which in turn affects earth's climate and water cycle.
Coral Reefs—A Special Ocean Habitat
Coral reefs are among the richest marine ecosystems in terms of beauty, species, productivity, biomass (the amount of living matter), and structural complexity. They are dependent on intricate interactions between coral, which provides the structural framework, and the organisms that live among the coral. Corals thrive by acting at many levels in the food chain as producers of structures and food, and as consumers of organic material. Coral reefs thrive in nutrient-poor habitats by containing many species that have complex food chains to recycle the essential nutrients with great efficiency, making the reefs particularly vulnerable to any event or process that disrupts the recycling.
Almost every group of marine organisms has its greatest number of individual kinds of organisms in coral reefs. For example, more than 25% of all marine fish are found on the reefs. Estimates of fish productivity suggest that around 10% to 15% of the total worldwide catch comes from reefs. Since reefs occupy only about 600,000 square kilometers (less than 0.02%) of the ocean surface, their productivity and biodiversity are much greater than other marine ecosystems.
Most reefs form as long narrow ribbons along the edge between shallow and deep waters, and their assets are many. Fisheries for food, income from tourism and recreation, materials for new medicines, and shoreline protection from coastal storms are among the many economic benefits they provide.
CORAL REEF STRUCTURE.
Corals are simple, bottom-dwelling organisms related to the sea anemone and jellyfish. The basic building block of coral is a polyp, a tiny animal that has a common opening used to take in food and excrete wastes, surrounding a ring of tentacles. The weak stinging cells of the tentacles are used to capture small animal plankton from the water for food. Each polyp sits in its own tiny bowl in a limestone skeleton, which the coral is constantly building as it grows up from the ocean floor. Reef-building corals live in large colonies formed by the repeated divisions of genetically identical polyps. The colonies can take a wide variety of shapes including branched, leafy, or massive forms, which may grow continuously for thousands of years.
The cells of coral contain symbiotic algae that make organic matter through photosynthesis and release it into the water to feed their coral hosts. Symbiosis is the living together of two dissimilar organisms in intimate association or even close union for mutual benefit. The algae remove carbon dioxide and excreted nutrients while supplying food and nutrients to the coral and greatly enhance the rate at which the corals deposit their skeletons. The coral cells provide the algae with protective structure and access to light and nutrients. The vast majority of coral skeletons are white; their color comes from the pigmentation of the algae living among the polyps.
Because of their dependence on symbiotic algae, coral reefs can grow only under conditions favoring the algae. Coral reefs are confined to tropical waters because the algae require warm, shallow, well-lit waters that are free of turbidity and pollution. Corals act like plants, taking up dissolved and particulate material from the surrounding water and overgrowing one another in competition for light.
CORAL REEFS—ECOSYSTEMS AT RISK.
The proximity of coral reefs to land makes them particularly vulnerable to the effects of human actions. Because they depend on light, coral reefs can be severely damaged by silt smothering, nutrient enrichment leading to overgrowth by seaweed, and other factors that reduce water clarity and quality. Sport diving and overfishing for food and the aquarium trade can deplete species and damage coral, resulting in disruption to the intricate interactions among reef species, as well as coral decline. Introduction of exotic species through human activity can be devastating as the new predators consume the living reefs.
Coral "bleaching" is the unique response of corals to stress. The coral loses the microscopic algae that normally live within its cells and provide the coral with their color, their ability to rapidly grow skeleton, and much of their food. The bleached coral turns pale, transparent, or unusual colors, and then starves as it is unable to feed or reproduce. Increased bleaching is an early warning sign of deteriorating health and can be caused by extremes of light, temperature, or salinity. In the 1980s coral bleaching began to spread dramatically. In October 1998 NOAA announced that it had recorded record-breaking coral bleaching in the tropics. Warm sea surface temperatures due to El Niño are believed to be the primary cause.
Little is known about most coral reefs and their inhabitants, but scientists have begun the extensive and exhaustive studies necessary to determine if coral reefs are in decline and the causes of decline. Of prime concern is confirming the direct and indirect effects of human activities on coral reefs and their denizens.
CORAL REEFS IN THE UNITED STATES.
Coral reefs are found in only three places in the United States: Florida (primarily in the Florida Keys), throughout the Hawaiian archipelago, and in the offshore Flower Gardens of Texas. The Florida reef system is part of the Caribbean reef system, the third-largest barrier-reef ecosystem in the world. Five U.S. territories—American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands—also have lush reef areas. According to the 2000 Water Quality Inventory published by the EPA, the northwestern Hawaiian Islands make up 69% of the country's coral reef areas, by far the largest percentage in the United States and its territories. (See Figure 6.3.)
To protect the U.S. coral reefs, many have been placed in marine sanctuaries with varying degrees of protection. The full extent and condition of most U.S. coral reefs is only beginning to be studied as a special area of focus.
On September 26, 2002, NOAA released the first national assessment of the condition of coral reefs in the United States. The report, The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States, was prepared under the auspices of the U.S. Coral Reef Task Force, and establishes a baseline that now will be used for biennial reports on the health of coral reefs in the United States. NOAA also released A National Coral Reef Strategy, a report to Congress outlining specific action to address thirteen major goals, including the continuation of mapping and monitoring, to protect coral reefs.
According to The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States, there are an estimated 7,607 miles of United States reefs and a range of 4,479 to 31,470 miles of reefs off the Freely Associated States. An estimated 27% of the world's shallow water coral reefs may already be beyond recovery, and about 66% are severely degraded. The report also indicates that in all areas some coral reefs in the United States were in good-to-excellent health. However, every reef system was suffering from both human and natural disturbances. These reefs suffer from the same problems as do reefs all over the world, especially those resulting from rapidly growing coastal populations. The report states that 10.5 million people now live in U.S. coastal areas adjacent to shallow coral reefs, and every year about forty-five million people visit the areas.
Among the major causes of damage to coral reefs, according to the report, are human-induced pressures such as coastal pollution, coastal development and runoff, and destructive fishing practices. Ship groundings, diseases, changing climate, trade in coral and live reef species, alien species, marine debris, harmful tourist activity, and tropical storms also contribute to the damage.
Florida and the U.S. Caribbean were considered to be in the most unfavorable condition, mainly because of nearby dense populations and the effects of hurricanes, disease, overfishing, and a proliferation of algae. Live coral cover in the Florida Keys had declined 37% since 1997. Since 1982, white-band disease had killed nearly all the elkhorn and staghorn corals off the coasts of St. Croix (U.S. Virgin Islands), Puerto Rico, and southeast Florida.
Coral reefs are extremely important for a number of reasons. They are the Earth's largest biological structures. They are vital sources of food, jobs, chemicals, shoreline protection, and life-saving pharmaceuticals. Tourism in the United States and Freely Associated States coastal reef areas generated $17.6 billion in 2000. Commercial fishing generated an additional $246.9 million annually. In south Florida, reefs supported 44,500 jobs, providing a total annual income of $1.2 billion.
New and important discoveries about coral reefs continue to be made. According to Geoscience Australia, the Australian national agency for geoscience research and geospatial information, three previously uncharted coral reef patches were discovered in Queensland's Gulf of Carpentaria in mid-2003. The reefs cover about eighty square kilometers (30.8 square miles) at a mean depth of 28.6 meters (93.8 feet) beneath the water surface. The discovery of these reefs is significant in part because of commonly held scientific beliefs that no reefs could exist in the muddy waters of the southern Gulf of Carpentaria. In addition, according to a Geoscience Australia Web site describing the discovery (http://www.ga.gov.au/oceans/projects/smac_subreef4.jsp, August 3, 2004), "Sub-merged reefs may provide an important refuge for corals during the next few decades when near-surface reefs are threatened by widespread coral bleaching due to warmer global sea surface temperatures."
Nearshore waters occur in lakes, estuaries, and oceans, and reflect the conditions and activities within the watershed. A watershed is an area in which water, sediments, and dissolved materials drain to a common outlet, such as a lake, river, estuary, or ocean. The near-shore is an indefinite zone extending outward from the shoreline, well beyond the shallow water (in oceans and estuaries, beyond the zone where the waves break). It defines the area where the current is caused primarily by wave action as opposed to a current that is the result of water flow. Depending on the size of the water body, the nearshore waters may be minimal in size (a small lake) or very large (the coastal waters of the Atlantic Ocean).
Whether marine, estuarine, or fresh, nearshore waters serve a variety of functions. They are the prime recreational waters, providing opportunities for swimming, boating, diving, surfing, snorkeling, and fishing. Near-shore waters are intimately linked with wetlands and sea grasses and provide a unique habitat for a variety of plants and animals. These waters are the source of food and shelter for many species of fish and shellfish and provide habitat for 80% of the fish species in the United States. Nearshore waters also provide numerous opportunities for education and research for students, naturalists, and scientists.
Because of their proximity to the shoreline, nearshore waters are particularly vulnerable to pollution. As a result, water quality in most confined waters and some nearshore waters is deteriorating, which in turn affects the plant and animal life. In addition to pollution, near-shore waters are very vulnerable to the everyday (and to all appearances, harmless) activities of people. For example, swimming has been restricted in some shallow lagoons with coral reefs and beautiful beaches, because heavy use by swimmers resulted in chemical concentrations of suntan oil and lotion in the water that was high enough to kill or impair the coral reefs. Wakes from recreational powerboats in high-use areas have been shown to increase wave action, resulting in increased shoreline erosion. Increased pollutant levels from boat paints, spills during refueling, and leaks of gas and oil from recreational boat engines in areas of high recreational use affect both plants and animals. Private pier and boathouse construction result in shading of water, which contributes to sea grass decline. Balancing the need to accommodate the public's desire to enjoy water-related activities and ownership of waterfront property and the need to protect nearshore waters is a difficult management issue.
Estuaries are places of transition, where rivers meet the sea. An estuary is a partially enclosed body of water formed where freshwater from rivers flows into the ocean, mixing with the salty seawater. Salinity in estuaries varies from slightly brackish (0.5 to 5 ppt) at the freshwater end to moderately brackish (5 to 18 ppt) to highly saline (25 to 30 ppt) near the ocean. Although influenced by the tides, they are protected from the full force of ocean waves, winds, and storms by reefs, barrier islands, or fingers of land, mud, or sand that make up their seaward boundary. Estuaries come in all shapes and sizes. Examples include the Chesapeake Bay, Puget Sound, Boston Harbor, San Francisco Bay, and Tampa Bay. There are 130 estuaries in the United States.
The tidal sheltered waters of estuaries support unique communities of plants and animals, specially adapted for life under a wide range of conditions. Estuarine environments are incredibly productive, producing more organic matter annually than any equal-sized area of forest (including rain forests), grassland, or cropland. A wide range of habitats exists around and in estuaries, including shallow open water, tidal pools, sandy beaches, mud and sand flats, freshwater and salt marshes, rocky shores, oyster reefs, mangrove forests, river deltas, wooded swamps, and kelp and sea grass beds. Estuaries provide habitat for more than 75% of the U.S. commercial fish catch, and for 80% to 90% of the recreational fish catch.
Estuaries are very important to the economy of coastal communities and the United States. Nationwide, twenty-eight million jobs in fields as diverse as shipbuilding, tourism, commercial and recreational fishing, real estate, and other coastal industries are dependent on estuaries. Nearly 70% of the nation's population (about 180 million people) visit the coasts annually, generating $8 billion to $12 billion in revenue.
National Estuary Program
The Water Quality Act of 1987 created the National Estuary Program (NEP) as an alternative to the traditional command-and-control regulatory approaches to water quality programs. Congress recognized that in order to achieve long-term protection of living resources and water quality (the basic "fishable/swimmable" goal of the Clean Water Act), the participation of those most affected by the environmental decisions was critical. Based on the highly successful Chesapeake Bay Program (see below), with its collaborative approach to managing watersheds and estuaries, the NEP is a voluntary program.
To improve an estuary, the NEP brings together community members using a forum to establish working relationships and the trust necessary to find and implement solutions. Together, stakeholders define program goals and objectives, identify estuary problems, and design action plans to prevent or control pollution, while restoring habitats and living resources such as shellfish. This approach results in the adoption of a comprehensive conservation and management plan (CCMP) for implementation in each estuary. This integrated watershed-based, stakeholder-oriented, water resource management approach has led to some significant local environmental improvements since its founding. In 1987 the NEP consisted of six local estuary programs; as of 2005 it had grown to include twenty-eight estuaries in eighteen states and Puerto Rico.
Two examples of environmental improvement resulting from the NEP program can be found in the Leffis Key and Corpus Christi projects. The Leffis Key restoration project in Sarasota Bay, Florida, resulted in thirty acres of productive intertidal habitat being created and planted with more than 50,000 native plants and trees at a cost of $315,000. In Corpus Christi Bay, Texas, treated bio-solids were applied to a twenty-five-acre plot of aluminum mine tailings, resulting in plant growth promotion, wildlife habitat, and improved water quality. Biosolids are composed of sewage sludge that has been properly treated and processed to make a nutrient-rich material that can be safely recycled and applied as fertilizer.
Chesapeake Bay Program
The Chesapeake Bay ("the Bay") is the largest estuary in North America and one of the most productive estuaries in the world. It has a 64,000-square-mile watershed draining six states and the District of Columbia. Its watershed is home to 15.1 million people and 3,600 species of plants and animals. The Bay has 11,684 miles of shoreline and averages twenty-one feet deep, with hundreds of thousands of acres of very shallow water. It is 200 miles long and thirty-five miles wide at its widest point.
The Bay is an incredibly complex ecosystem that includes many important habitats and food webs. A food web is a complex food chain where many different species of plants and animals interact by producing food, consuming organic material, and recycling wastes. Primary producers like phytoplankton, algae, and sea grasses are eaten by small animals and fish, which then become meals for larger fish and animals. These, in turn, are eaten by birds, larger fish, and mammals.
Chesapeake Bay is a mixture of freshwater and salt-water from the Atlantic Ocean and is subject to seasonal weather. Plant and animal populations vary with changes in temperature, salinity, water clarity (light penetration), dissolved oxygen, and human impacts. Human impacts include activities such as overfishing, development, marina construction and operation, and farming. Excess nutrients, most of which comes from nonpoint sources (primarily agricultural activity and urban runoff) is the primary stressor in Chesapeake Bay. A nonpoint source is a source that is widely spread and has no fixed location.
The first estuary in the United States to be targeted for restoration and protection, the Bay is protected under its own federally mandated program, separate from the NEP. The Bay Program began in 1983 with a meeting of the governors of Maryland, Pennsylvania, and Virginia; the mayor of the District of Columbia; and the EPA administrator. These individuals signed the Chesapeake Bay Agreement committing their states and the District of Columbia to prepare plans for protecting and improving water quality and living resources in Chesapeake Bay. The Chesapeake Bay Program evolved as the institutional mechanism to restore the Bay and to meet the goals of the Chesapeake Bay Agreement. The program, which guides and coordinates multistate and multiagency activities, is the model for the NEP and has resulted in a Chesapeake Bay that is cleaner than it was in 1983.
Two important habitat alterations in Chesapeake Bay are the focus of intense restoration efforts. They are restoration of the once-extensive beds of submerged aquatic vegetation and oysters. Oyster reefs (oyster bars) play an important ecological role in the Bay. Oysters cluster together to grow upward and outward, creating a hard surface on the Bay's bottom and a three-dimensional structure used as habitat by many species. The hard oyster shell surfaces provide places of attachment for many sessile (not moving, permanently attached) species, including oyster larvae. They also provide habitat for worms, snails, and other invertebrates as well as food and protection for small fish and crabs. Many species of ducks find food on and around the oyster bars during the winter months.
Oysters have declined in Chesapeake Bay because of introduced oyster diseases, harvest pressure and use of harvesting techniques that have flattened the large three-dimensional reefs, silting, and other pollution. Oyster populations are at or below the level of being naturally sustaining. The loss of oyster populations and their reef habitats has had important consequences for the oysters, as well as many other Bay species.
Both Maryland and Virginia have large-scale federally and state funded programs underway to artificially create reefs with oyster shell and other materials such as fly ash, rock, concrete, and other recycled materials. Oyster sanctuaries (areas off-limits to harvest) are being established as brood-stock areas to enhance the oysters' ability to maintain self-sustaining populations through natural recruitment (the ability of a population to reproduce and replace animals lost). In addition, private organizations such as the Oyster Recovery Partnership, the Chesapeake Bay Foundation, and the Tidewater Oyster Gardening Association are using volunteers to grow and plant millions of small oysters in the sanctuaries and other restored areas.
Submerged Aquatic Vegetation
Sea grasses—or submerged aquatic vegetation (SAV)—are very important in the productivity and habitat of estuaries. These grasses are vascular plants that grow completely underwater and have special adaptations to help them survive in the aquatic environment. A vascular plant is one that takes nutrients in through its roots and transports them through its roots and stems to all parts of the plant. SAV plays an important ecological role by:
- Providing food and habitat for waterfowl, fish, shell-fish, crustaceans, and other invertebrates, as well as nursery habitat for the juveniles of many species, which hide from predators among the swaying fronds
- Producing oxygen in the water column through photosynthesis
- Filtering and trapping silt that can cloud the water and bury bottom-dwelling organisms such as oysters
- Protecting shorelines from erosion by retarding wave action
- Removing excess nutrients that could cause the growth of undesirable algae in the surrounding waters
The species of SAV in an estuary change in response to the salinity. Tidal fresh SAV species require a salinity of 0 to 0.5 ppt. Oligohaline (slightly brackish) species require 0.5 to 5 ppt. Mesohaline (moderately brackish) require 5 to 18 ppt, while polyhaline (high salinity) species require 18 to 30 ppt. Upstream activities, such as dam construction or water diversions, can radically alter freshwater flow into an estuary, changing the downstream salinity and thus the composition of SAV.
The health of SAV is a good indication of the health of an estuary. The single most important factor in SAV growth and survival is the amount of light that reaches the plants. When the amount of light is too low, the SAV can no longer photosynthesize and produce enough energy and food to grow. The amount of light reaching SAV is affected by turbidity, algae, epiphytes (microbes that attach to SAV leaf surface), and nutrients present in the water column. Significant reduction in SAV is a sign that an estuary is experiencing considerable stress. Reduction in SAV has been linked to decline in important fish, crab, shrimp, and waterfowl species.
Chesapeake Bay has experienced significant SAV decline. According to the Chesapeake Bay Program, up to 200,000 acres of SAV may have grown in the area historically, but by 1984 that number had shrunk to 38,000 acres. In some areas, the grasses are returning naturally. In other areas, large-scale SAV monitoring and planting activities are being undertaken to try to reverse the decline. According to an article in the April 2003 issue of the EPA's Coastlines newsletter ("Submerged Aquatic Vegetation Being Restored in Chesapeake Bay"), in 1992 the Chesapeake Bay Program helped to develop an initial Bay-wide goal of having 114,000 acres of SAV, reflecting the total SAV area that existed between 1971 and 1990. Since annual Bay-wide surveys began in 1985, SAV has substantially increased in many areas. According to the report 2001 Distribution of Submerged Aquatic Vegetation in Chesapeake Bay and Coastal Bays (Robert J. Orth and David J. Wilcox, Gloucester Point, VA: Virginia Institute of Marine Science, December 2002), in 2001 total SAV acreage in the Bay set a new record—77,855 acres.
Similarly, the Gulf of Mexico experienced a dramatic SAV decline during the second half of the twentieth century, documented in a number of studies conducted throughout the region. The National Wetlands Research Center reported in "Seagrasses in Northern Gulf of Mexico: An Ecosystem in Trouble" (June 2000) that sea grass acreage in bays and estuaries of the northern Gulf had declined between 12% and 66%. In addition, the sea grasses are changing in species composition, densities, and distribution. Many scientists believe that Gulf of Mexico SAV decline is directly related to nutrient enrichment and hypoxia (lack of oxygen).
OCEAN AND ESTUARINE FISHERIES—A
In many parts of the world, fish is the major source of protein in the diet. Humans on average worldwide obtain 16% of their animal protein from fish, and an estimated two billion people worldwide depend on fish for 40% of their protein supply. A staple in the diet of many cultures, fish are consumed in much greater quantities in countries other than the United States. The United States consumes only about 8% of the total world catch of fish and shell-fish. This supply comes from U.S. commercial fishermen, aquaculture producers, and imports.
In the 1990s the United Nations Food and Agriculture Organization (FAO) reported record world marine harvests of more than 100 million tons annually. Fisheries experts believed that the catch had peaked and that future harvests would begin to decline. The FAO supported this finding, claiming that most traditional marine fish stocks had reached full exploitation; therefore an intensified effort was unlikely to produce an increased catch, and any increase would produce a state of over-fishing.
Eighty-two percent of the fish caught in 1996 came from oceans and estuaries. Growing fish, shrimp, and other aquatic species on coastal and freshwater farms ("aquaculture") increased greatly during the 1990s, accounting for twenty-seven million tons in 1996, up from seven million tons in 1984. According to the FAO, aquaculture in 1996 accounted for 26% of food fish. Fifty-nine percent of aquaculture fish were freshwater farmed, while 41% were marine and estuarine farmed. Some scientists and fisheries experts predicted that aquaculture production would surpass the volume of harvest of wild fish in the first twenty-five years of the twenty-first century, but it is doubtful that aquaculture will ever be able to match the variety of species found in oceans and estuaries. According to Fisheries of the United States 2003, published in 2004 by the National Marine Fisheries Service, a part of NOAA, total aquaculture production in the United States in 2002 was 867 million pounds.
For centuries, freedom of the seas was the reigning doctrine, and the waters more than three nautical miles from shore were open to all. After the end of World War II in 1945, there was a boom in marine fishing, and fishermen began to engage in fierce competition over fishing grounds. In the 1970s, as conflict mounted, the world took a step toward curtailing fishing freedom on the high seas. As part of the Third United Nations Conference on the Law of the Sea, governments agreed to establish a zone no more than 200 nautical miles wide within which a coastal country has sole rights to natural resources. Known as an exclusive economic zone (EEZ), this area includes the most productive fishing grounds in the oceans. Outside the EEZ, however, freedom of the seas still largely stands.
Overfishing is the state created when fish catch exceeds the maximum sustainable yield (the amount of fish that can be harvested every year without depleting the natural breeding stock). When harvest exceeds recruitment (the ability of a fishery to reproduce and replace animals lost to the fishery), both the fish population and the fish catch decline, causing both ecological and economic harm. Although fishing directly affects the abundance of adult and juvenile fish, the growth and survival of fish in their early life stages depends on the presence of necessary ocean, coastal, estuarine, and river habitats. Lack of abundant, high-quality habitat can be as devastating to fisheries as overfishing.
According to the National Fisheries Institute (the U.S. trade association for commercial fishermen and seafood suppliers) Web site (http://www.nfi.org/), more than 170,000 people worked in the United States as commercial fishermen in 2005. These fishermen operate many different types of vessels, ranging in size from small one-person boats to large purse seiners and trawlers. The vast majority of these vessels are independently owned and family operated, and harvest more than 300 species of seafood from U.S. waters. Seventy percent of the harvest is caught with purse seine and trawl nets. A purse seine is a net that is deployed with floats and traps the fish in a purse-like bag when pulled from the sea. A trawl net is a large conical net that is weighted and dragged along the sea bottom to collect fish and other marine life.
Fisheries of the United States 2003 reported that per capita consumption of fishery products in 2003 was 16.3 pounds, an all-time high. U.S. commercial fish landings—the volume of fish brought to the dock by commercial fisheries—at ports in the fifty states amounted to 9.5 billion pounds and was valued at $3.3 billion in 2003.
NOAA described the general welfare of the U.S. living marine and estuarine resources as "guarded with vigilance needed." The decline in Northeast groundfish, the uncertain state of some West Coast salmon runs, and the reduced populations of sharks and other marine species are examples of areas that need special attention. Overfishing and habitat loss are causing many fisheries to fall below the levels required to produce long-term potential yield. The challenge is to maintain the long-term viability of the natural system, while at the same time addressing the social and economic needs of the fisheries.
In the United States, the EEZ is the responsibility of the federal government and regional fishery management councils. Nearshore fisheries, defined as those within zero to three miles of the coastline, are the responsibility of coastal states and interstate marine fishery commissions.
More than 33,000 square miles (an area about the size of Maine) of marine and estuarine water in the contiguous United States are classified as shellfish harvest waters under a program that is jointly administered by the coastal states and the National Shellfish Sanitation Program (NSSP). In this program shellfish are narrowly defined as "bivalves," that is, mollusks having two valves. Common bivalves are oysters, clams, and mussels. Once a common staple in the diet of people living near coastal waters, most bivalves are considered a delicacy today. The national commercial harvest of these mollusks is valued at more than $200 million when it is first put ashore.
Since the time of the Romans, bivalves have been identified as potential transmitters of infectious disease. The infectious and sometimes dangerous diseases that have been transmitted by bivalves range from typhoid and cholera to minor intestinal disorders. The disease agents may originate in the sewage of humans or other warm-blooded animals or may be naturally occurring in the environment. It is the unique biology of bivalves and the way in which people eat them that contribute to our vulnerability to disease.
Shellfish are filter feeders that tend to stay in one place and pump large amounts of water through their bodies. If pathogens (disease-causing bacteria and viruses) are present in the water, the bivalves may concentrate the pathogens in their tissues to levels that can cause disease in humans who eat the bivalves raw. The bivalves are not harmed by the microbes, and if exposed to clean water, will cleanse themselves. Crabs, shrimp, and other crustaceans do not concentrate the pathogens.
To protect the public that eats bivalves raw and to ensure a safe harvest, the coastal states carefully monitor the water and control commercial harvest under the NSSP guidelines. Special emphasis is given to identifying and eliminating the discharge of untreated or poorly treated human and animal sewage in harvest areas. Harvesting is restricted in waters that do not meet NSSP guidelines. States determine if an area is safe for harvesting by monitoring the concentrations of the indicator bacteria, total coliform, and fecal coliform. Indicator bacteria provide evidence of possible fecal contamination from human and domestic animal wastes. These wastes may contain pathogens that can be taken up and concentrated by the bivalves. Figure 6.4 shows the most common sources responsible for the presence of these indicator bacteria that led to shellfish harvest restrictions as reported by three states. The program has been very successful in preventing illness from contaminated bivalves, and outbreaks of illness rarely occur.
The filter feeding of bivalves also makes them vulnerable to the concentration of chemical contaminants that may be harmful to humans. Concentrations of chemicals in bivalves are directly related to the concentrations in the water column and the food that they consume. Because bivalves are low in body fat, they do not tend to bioaccumulate and retain chemicals to the extent that fish do.
NOAA has monitored chemical contaminants in mussels and oysters in its Mussel Watch Program since 1986. According to the latest report, issued in 2002, while the levels of most chemical contaminants were decreasing, others remained the same. The best news, however, was that none of the chemicals monitored were increasing in concentration.
THE 2000 NATIONAL WATER
In its 2000 National Water Quality Inventory (2002), the EPA reported that fourteen of the twenty-seven coastal states and territories had rated the water quality of some of their coastal waters. The states had assessed 14% of the 22,618 miles of national coastline excluding Alaska, or 5.5% (3,221 miles) of ocean shoreline (including Alaska's 36,000 miles of coastline). Of the 14% of ocean waters assessed, 79% fully supported their designated uses, 14% were impaired, and 7% were supporting uses but threatened. Designated uses are the beneficial water uses assigned to each water body by a state as part of its water quality standards. Examples of designated uses are fishing and drinking water supply.
In this 2000 EPA report, bacteria (pathogens) were identified by ten states as the leading contaminants of ocean shoreline waters, followed by oxygen-depleting substances and turbidity (cloudiness). (See Figure 6.5.) Bacteria provide evidence of possible fecal contamination that may cause illness. States use bacterial indicators to determine if oceans are safe for swimming or secondary contact recreation, such as water skiing. Figure 1.7 in Chapter 1 shows the pathways of bacteria to surface waters. The most common sources of bacteria are urban runoff, inadequately treated human sewage, and runoff from pastures and feedlots, all of which were identified by ten states as leading sources of ocean shoreline impairment (see Figure 6.6).
Turbidity is a measure of the relative clarity of water. Turbidity is caused by suspended matter or other impurities that make the water look cloudy. These impurities may include clay, silt, finely divided organic and inorganic matter, plankton, and other microscopic organisms. It interferes with the transmission of light to underwater grasses and other plant life in need of this light. If the transmission of light is reduced due to heavy silt in the water this can smother bottom-dwelling organisms such as oysters. Turbidity was responsible for more than 10% of the impaired ocean shoreline miles reported to the EPA in 2000. Three of the leading sources of ocean impairment are also contributors to turbidity. They are runoff from highly developed urban areas, agricultural activities, and construction projects (see Figure 6.6).
In general, most of the ocean waters assessed supported the five general-use categories shown for estuaries: aquatic life support, fish consumption, shellfishing, primary contact, and secondary contact. These categories represent summaries of the designated uses and their achievement provided by the states to the EPA. Waters that either support their designated uses only part of the time or do not support their uses at all are considered impaired. Good water quality supports primary contact (swimming without risk to public health) in 85% of the assessed ocean waters (the same percentage for use support in estuaries), and fish consumption (fish safe to eat) in 91% (compared to 52% of use support in estuaries).
In 94% of the waters assessed, the water was considered of good quality, capable of supporting aquatic life (suitable habitat for protection and propagation of desirable fish, shellfish, and other aquatic organisms). In the shellfish harvesting summary (water quality supports a population of bivalves free from toxicants and pathogens that could pose a health risk to people who eat them), 86% of the ocean waters assessed had good water quality that supported this use. In addition, good water quality in 91% of the ocean waters assessed supported secondary contact recreation (people can perform water-based activities such as water skiing and boating without risk of adverse human health effects).
Twenty-three of the twenty-seven coastal states provided data for use in the 2000 National Water Quality Inventory. These twenty-three states assessed 36% of the nation's estuaries. (See Figure 6.7.) Of the 31,072 square miles assessed, 49% supported their uses and 51% were impaired. Figure 6.8 shows the major pollutants in U.S. estuaries. Metals were the most common pollutants, followed by pesticides and oxygen-depleting substances. This pollution came primarily from municipal point sources, urban runoff and storm sewers, and industrial discharges.
As with the U.S. ocean shoreline, the five general use categories provide important details about the nature of water quality problems in estuaries. In general, most of the waters assessed supported the general use categories. The two use categories that showed the greatest impairment were aquatic life support (52% impairment) and fish consumption (48% impairment). Good water quality in 75% of the estuaries assessed supported use for shellfish harvesting, while 77% of the waters supported secondary contact recreation. Eighty-five percent of the estuarine waters assessed had good water quality for primary contact use.
Hundreds of times each year, beach closings take place to protect the public from possible exposure to pathogens (disease-causing organisms). The bacteria that cause the closings are generally harmless, but they are present in large numbers in the sewage of humans and warm-blooded animals. Their presence indicates the possible presence of disease-causing organisms.
The most common problem caused by swimming in contaminated water is gastroenteritis, contracted by swallowing water while swimming and characterized by diarrhea, nausea, vomiting, and cramps. While gastroenteritis is generally not harmful to healthy adults, it can cause serious illness in children and those with weakened immune systems such as the elderly, pregnant women, and people with chronic diseases.
The major pollution sources responsible for the closings and advisories include runoff of storm water following rainfall and sewage spills or overflows. Some beaches are closed "just in case," or issue advisories against swimming when rainfall exceeds certain levels. Almost every coastal state reported having at least one beach where storm water drains onto or near bathing beaches.
The EPA established the BEACH program in 1997 to significantly reduce the risk of waterborne illness at the nation's beaches and recreational waters through improvements in water protection programs and risk communication. Through the EPA's BEACH Watch Web site, the public can access detailed information on hundreds of individual coastal, Great Lakes, and freshwater beaches. Other information on local beach programs and health issues and links to other relevant sites are provided. Users can also learn more about how to avoid unnecessary exposure to contaminated water while at the beach.
In the EPA's survey of the beaches for the 2002 swimming season, thirty-one states and four territories (Guam, Puerto Rico, Northern Mariana Islands, and the U.S. Virgin Islands) representing all coastal and Great Lakes states reported data on 2,823 beaches. Of this total, 2,031 were coastal beaches and 729 were on inland waterways. About one-quarter of these beaches (25%) were affected by at least one advisory or closing event during 2002.
POLLUTANTS—SOURCES AND EFFECTS
Any number of man-made materials or excessive amounts of naturally occurring substances can adversely affect marine and estuarine waters and their inhabitants. Because water is such an effective solvent and dispersant, it is difficult to track and quantify many pollutants known to have been discharged into marine and estuarine waters, and in many cases the source of pollution may be unknown. Some pollutants, such as oil spills, are easily detected the moment they enter the water. Others, such as toxic chemicals, are less obvious, and their presence may remain undetected until they have caused extensive damage.
Oil is one of the world's most important fuels. Its uneven distribution on the planet, however, forces its transport over the high seas and through pipelines to distant lands. This inevitably results in accidents, some massive and some small, during drilling and transporting. In 1967 the 118,285-ton supertanker Torrey Canyon, carrying oil from Kuwait, caused the world's first massive marine oil spill off the coast of England.
Oil spills are a dramatic form of water pollution—visible, immediate, and sometimes severe. The sight of dead and dying otters and birds covered with black film arouses instant sympathy, and the bigger the spill, the more newsworthy it is. While it is true that oil can have a devastating effect on marine life, the size of the spill itself is often not the determining factor in the amount of damage it causes. Other factors include the amount and type of marine life in the area and weather conditions that would disperse the oil. Despite its drama, however, worldwide pollution from tanker spills is a relatively minor source of marine pollution. It represents a small fraction of the oil released to the environment worldwide when compared to industry sources, non-tanker shipping releases, and oil seepage from natural sources.
When the Exxon Valdez ran into a reef in Prince William Sound, Alaska, in March 1989, eleven million gallons of oil spilled into one of the richest and most ecologically sensitive areas in North America. A slick the size of Rhode Island threatened fish and wildlife. Otters died by the thousands, despite efforts by trained environmentalists and local volunteers to save them. Oil-soaked birds lined the shores, only to be eaten by larger predator birds, which then succumbed to dehydration and starvation because the ingested oil destroyed their metabolic systems.
OCEAN POLLUTION ACT OF 1990.
In response to the Exxon Valdez disaster, Congress passed the Oil Pollution Act of 1990 (OPA; PL 101–380). The majority of the OPA provisions were targeted at reducing the number of spills and reducing the quantity of oil spilled. Among its provisions were the creation of a $1 billion cleanup-damage fund (the money comes from a tax on the petroleum industry), advance planning for controlling spills, stricter crew standards, and the requirement that new tankers have double hulls. When equipped with two hulls, if the tanker's exterior hull is punctured, the interior hull holding the oil may still remain intact. (The Exxon Valdez was not double-hulled.) The law requires older tankers to be fitted with double hulls by 2010. The OPA also:
- Compels the use of escort tugboats in certain harbors to assist tankers.
- Requires standards for tank levels and pressure-monitoring devices to detect leaks in cargo tanks.
- Requires the Coast Guard to establish minimum standards for overfill devices to prevent overfill oil spills. (An overfill oil spill is the result of too much oil being pumped into a tanker during a transfer from a facility to a tanker or between two tankers. On occasion, overfill spills have involved large quantities of oil.)
The issue of continuing danger from older, single-hulled oil tankers on the seas was highlighted in testimony before the U.S. Senate Committee on Commerce, Science, and Transportation on January 3, 2003. Robert N. Cowen, senior vice president and chief operating officer of Overseas Shipholding Group, Inc., spoke of the need for the United States to prevent these vessels from trading to the United States. Cowen described the November 19, 2002, sinking of the oil tanker Prestige (which was carrying 77,000 tons of heavy fuel oil) off the coast of Spain. He pointed out that cargo from the Prestige continues to wash up on the coastline of Galicia, Spain, where it pollutes sensitive fishing grounds. In addition, the cargo is washing ashore in the Landes region near Bordeaux, France. Moreover, Cowen stated that the governments of Spain, France, and Portugal have moved to ban substandard tonnage from their waters. According to Cowen, the United States continues to allow these older tankers to come into United States waters to trade. Cowen asked the Senate to ensure that restrictions are enacted to prevent older, single-hulled vessels from trading to the United States.
DECLINES IN OIL SPILLS.
Declines in oil spills are being seen on a global scale. The International Tanker Owners Pollution Federation data show that between 1970 and 1979 the incident rate for large spills (more than 5,000 barrels) from the worldwide tanker industry was 24.2 spills per year. Between 1980 and 1989 that rate dropped to 8.9 spills per year. From 1990 to 1999 the global spill rate declined further, to 7.3 spills per year.
The decline in oil spills in the United States is even more dramatic. About ten million barrels (420 million gallons) of oil per day are delivered into the United States by ship. According to the U.S. Coast Guard, the incident rate of large spills in the United States since 1991 has been 0.5 spills per year. There were no large spills in U.S. waters in the period 1991 to 2000 (the latest data available).
The Coast Guard data also show that the amount of oil spilled by tankers has decreased dramatically. The total amount spilled in U.S. waters in 1990 was about 115,000 barrels; from 1991 to 2000 the total number was less than 8,000. In 1997 the number of barrels of oil spilled was the lowest ever since the Coast Guard began keeping its records in 1973. More than three-fourths of the 1997 spills were less than ten gallons—less than a car's fuel tank holds.
Although oil tanker spills are highly visible cases of pollution entering the oceans, the EPA estimated that only about 5% of the oil entering marine waters is the result of oil tanker spills. The Coast Guard estimates conclude that water and sewage treatment plants in the United States discharge twice as much oil each year as oil tankers spill. Other sources of oil entering marine waters include the oil from street runoff, industrial liquid wastes, recreational boats, commercial fishing vessels, and intentional discharge from ships flushing their oil tanks.
CLEANING UP OIL SPILLS.
Left alone, oil spills will eventually disappear as natural processes break down the oil. (See Figure 6.9.) If nothing is done, oil will "weather" naturally. Turbulent wave action and sunlight will break it down both chemically and physically. Within twenty-four to forty-eight hours, the most toxic portions of the oil will evaporate, posing less of a threat to wildlife. As the oil breaks up into smaller droplets, it is more easily attacked and digested by naturally occurring microbes, which will break it down into harmless substances. Human intervention to speed up this process can be more or less successful, depending on the spill size, its location, and the weather conditions. There are two basic approaches to cleaning up oil spills: use of dispersants and use of bioremediation agents. Two important differences exist in the way they work. One difference is the mechanism by which they clean up the oil. The other is where and how they are used. Recent research suggests that the best solution may be to use both techniques depending on the characteristics of the site.
Dispersants are products that are applied to the water surface to break up surface oil slicks and facilitate the movement of oil particles into the water column. Dispersants bind to oil on the water surface so that the oil can mix and disperse into the water, similar to the way grease and oil on dirty dishes bind to detergent so that the oil and grease can be washed away in rinse water. Scientific evidence suggests that dispersed oil is broken down more quickly than undispersed oil. This is believed to be caused by the increase in the total surface area of the oil in a slick due to dispersants breaking the slick up into small droplets and making it more vulnerable to breakdown by natural processes such as weathering and biodegradation (breakdown by microbes).
Bioremediation is the process by which microbes eat oil molecules by breaking down their long hydrocarbon chains. Bioremediation agents are almost always applied to residual oil on shorelines for long-term cleanup situations. Usually, heavy oil is first removed before bioremediation is attempted. Bioremediation agents act to speed up the biodegradation of the petroleum molecules, a process that would occur naturally anyway.
There are three types of bioremediation: nutrient enrichment, use of genetically engineered microorganisms designed to be especially effective at degrading oil, and techniques to make oxygen more available to native bacteria to speed up their breakdown of the oil. Nutrient enrichment generally takes the form of fertilizer addition to accelerate the reproduction of the naturally occurring oil-eating bacteria. Seeding is an attempt to introduce large numbers of the naturally occurring oil-eating bacteria to an oil spill site to jump-start the biodegradation process. This process has not been clearly shown to be effective.
Although genetically engineered microbes have been successfully used under controlled conditions in ground-water and other land-based hazardous waste sites, there has been no scientifically validated demonstration of their successful use in oil spill cleanup. The reported success of this approach in the aftermath of the explosion of the tanker Mega Borg off the Texas coast in 1990 has not been scientifically substantiated. Many scientists believe that the fire associated with this tanker explosion was the primary factor in the rapid breakdown and disappearance of the spill.
A new bioremediation technique that is gaining credibility is increasing the availability of oxygen to the naturally occurring oil-eating microbes. Oxygen availability is increased through the addition of special chemicals or tilling the oiled substrate. Tilling breaks the oiled surface into smaller units and increases the exposure of these surfaces to the air (oxygen), making the oil more vulnerable to microbe attack.
Marine debris is trash and garbage floating on the ocean or estuaries and washed up on beaches. Beaches and shorelines of U.S. estuaries and oceans are littered with debris carried to shore by the wind and tides. The effects of marine debris can be both costly to coastal communities and very dangerous to humans and aquatic life.
According to NOAA's online Ocean Report (http://www.publicaffairs.noaa.gov/oceanreport/index.html), marine debris is a major problem on beaches and in coastal waters, estuaries, and oceans. The report states that 80% of debris is washed, blown, or dumped from shore, while 20% is from recreational boats, ships, fishing vessels, and ocean platforms. The problem is exacerbated by the fact that most marine debris, such as cigarette butts, soda cans, plastic bags, and fishing gear, is man-made and slow to degrade. Some studies have shown that marine debris threatens more than 265 different species of marine and coastal wildlife through entanglement, smothering, and interference with digestive systems.
Certain types of marine debris, such as broken glass and medical waste wash-ups, can pose a serious threat to public health, causing beach closures and swimming advisories and robbing coastal communities of significant tourism dollars.
NOAA's Ocean Report cited these reasons for the persistence of marine debris:
- Implementation of effective marine debris control measures is currently hampered by a lack of consistent monitoring and identification of sources of debris.
- Implementation and enforcement of local anti-litter regulations and management of debris entering and exiting sewer systems are inadequate to effectively address the marine debris problem.
- Marine debris can be the result of small-scale pollution by individuals who consider their discharges or littering to be of negligible impact compared with large-scale polluters. However, the cumulative impact of continuous, small-scale pollution can be dramatic.
- Plastic makes up about 60% of the debris found on beaches. The increase in the use of various kinds of plastic as durable, lightweight packaging has heightened the need for proper management and disposal.
Trash that is washed up with the tide routinely litters beaches on both sides of the North American continent. In the summers of 1988 and 1989, medical refuse, such as syringes and blood vials, was found on ocean and estuarine beaches along many areas of the East Coast. Occurring about the same time as the growing public concern over AIDS and other needle-transmitted diseases, these occurrences provoked a public outcry for action. In response, Congress passed the 1988 Medical Waste Tracking Act (PL 92–532). The Act holds producers of medical waste accountable for safe disposal of the waste, or they risk penalties of up to $1 million in fines and five years in prison.
In 1990 the Agency for Toxic Substances and Disease Registry (ATSDR), a division of the U.S. Department of Health and Human Services, concluded that medical waste presents little danger to the general public. According to Dr. Maureen Lichveld, senior medical officer at the agency and coordinator for the research project, hospital medical wastes disposed of in the oceans represented no particular risk. The most pressing concern for future medical waste disposal comes from in-home health-care products used by people with chronic diseases, outpatient AIDS victims, and nursing homes. Subsequent studies by the Marine Conservancy, a private environmental group, indicated that medical waste accounts for only 0.01% of all waste washed up on the nation's beaches.
In July 1999 Royal Caribbean, one of the world's largest cruise lines, pleaded guilty in federal court to dumping oil and hazardous chemicals in U.S. waters and lying about it to the Coast Guard. They agreed to pay a record $18 million fine for polluting waters. This was in addition to the $9 million in criminal fines the company agreed to pay in a previous plea agreement. Six other cruise lines have pleaded guilty to illegal waste dumping since 1993 and have paid fines of up to $1 million. These cases have focused attention on the difficulties of regulating the fast-growing cruise-line industry, as most major ships sailing out of American ports are registered in foreign countries.
The luxury associated with cruise ships generates a lot of waste, much of which is reportedly disposed of through ocean dumping. In response to a petition from the Blue-water Network in 2000 on behalf of fifty-three organizations committed to protecting the oceans, the EPA is currently assessing cruise-ship discharges to U.S. waters. Among other things, the petition asks the EPA to:
- Quantify the volume of all waste streams such as sewage, garbage, fuel, and medical wastes from large passenger vessels and assess the adequacy of existing regulations to control the waste streams.
- Provide scientific assessment of the effects of the wastes on water quality, the marine environment, and human health.
- Identify options for a comprehensive monitoring, record keeping, and reporting regulation for all pollutants discharged into U.S. waters and wastes offloaded at U.S. ports from large passenger vessels.
- Evaluate the effect of repealing the National Pollutant Discharge Elimination System permit exemption for cruise ships and requiring them to have discharge permits.
In March 2001 the Central Council of Tlingit and Haida Indian Tribes of Alaska passed the resolution Object to Cruise Ship Dumping of Pollutants in Southeast Alaska Waters. The resolution cited a contamination threat to subsistence foods from cruise-ship wastes. The petition asked the federal and state governments to prohibit all discharges within twelve miles of the Alaska shore, require all cruise lines to have discharge monitoring devices, and to prohibit ships caught illegally discharging from entering southeast Alaskan waters.
Plastics such as bags, containers, bottle caps, and beverage carriers are dumped daily from oceangoing vessels, commercial and recreational fishing boats, offshore oil and gas platforms, and military ships. Other types of plastic debris—factory wastes, sewer overflows, illegal garbage dumping, and human littering—come from land sources. An estimated two million sea birds and 100,000 marine animals die each year as a result of ingesting or becoming entangled in plastic.
Another concern is commercial fishing nets. Once made of natural materials, these nets are now made mainly of durable, nondegradable plastic. When they are lost or discarded in the water, they pose a floating hazard to seals, dolphins, whales, and diving birds, which can become entangled in the nets. In 1988, thirty-one nations ratified an agreement making it illegal for their ships to dump plastic debris, including fishing nets, into the ocean. As part of that agreement, the United States enacted the Marine Plastics Pollution Research and Control Act (PL 100–220), effective in 1989. Among other regulations, the act imposed a $25,000 fine for each violation.
Plastic pellets are the raw materials that are melted and molded to create plastic products. About sixty billion pounds of resin pellets are manufactured in the United States annually. The two primary ways that these pellets enter water are direct spills during cargo handling operations at ports or spills at sea, and storm-water discharges that carry the pellets from industrial sites. Plastic pellets may persist in the water environment for years, depending on the resin type, the amount and types of pellet additives, and how the pellets react to sunlight, wave action, and weathering. Although pellets have been found in the stomachs of wildlife, primarily seabirds and sea turtles, their effects have not been clearly demonstrated to be harmful.
Since 1991 the Society of Plastics Industries, Inc. (SPI), the major national trade association for manufacturers who make about 75% of the plastic products in the United States, has been working with the EPA to identify and minimize the sources of plastic pellet entry into water. In July 1991 the SPI instituted Operation Clean Sweep, an industry-wide education campaign to encourage members to adopt the SPI 1991 Pellet Retention Environmental Code and the 1992 Processor's Pledge aimed at committing the U.S. plastics industry to total pellet containment. As of 2005 the Operation Clean Sweep mission remained "to help every plastic resin handling operation implement good housekeeping and pellet containment practices to work towards achieving zero pellet loss" (http://www.opcleansweep.org/overview/, 2005).
Another important problem has been termed "ghost fishing." This is the entrapment of fish and marine mammals by lost or abandoned nets, pots, fishing line, bottles, and other discarded objects. When marine creatures are entangled in old six-pack beverage binders, or caught in abandoned fishing nets, they suffer and may die.
In 1972 Congress enacted the Marine Protection, Research, and Sanctuaries Act (MPRSA; PL 92–532) to prohibit the dumping into the ocean of material that would unreasonably degrade or endanger human health or the marine environment. The MPRSA applies to waters within 200 miles of the U.S. coast and was amended in 1988 to prohibit dumping industrial waste and sewage sludge into the ocean. As a result, ocean dumping today is confined to material dredged from the bottom of water bodies in order to maintain navigation channels and berthing areas. According to information available on the EPA Web site in 2005, several hundred million cubic yards of sediment are dredged from waterways, ports, and harbors each year, and approximately 20% of this material is disposed of in the ocean. The remainder of the sediments are disposed of in inland waters, upland areas, or confined disposal areas adjacent to shorelines, or are used beneficially.
The MPRSA authorizes the EPA to assess civil penalties of up to $50,000 for each violation, as well as criminal penalties (seizure and forfeiture of vessels). For dumping of medical wastes, the Act authorizes civil penalties of up to $125,000 and criminal penalties of up to $250,000 and five years in prison, or both.
Every year, millions of tons of materials are dredged from freshwater river channels and harbors, as well as estuarine channels and coastal harbors, to clear or enlarge navigational channels, to maintain ship-berthing areas, to facilitate recreational boating, or for development purposes. Dredged material (spoil) may be clean sand and sediment, or it may contain concentrations of pesticides, metals, and other toxic chemicals, depending on where the dredged material originated. During the dredging process or when the dredged spoil is placed overboard, some pollutants that have settled into the sediment may be released into the water at the disposal site. Dredged spoil disposal is closely regulated by both the U.S. Army Corps of Engineers and the EPA, who require testing of spoil for contaminants prior to disposal.
Disposal of dredged spoil is a difficult problem. Although many environmental groups prefer land-based disposal to overboard disposal (placement of dredged materials in the ocean or other water body at a distance from the dredging location), land-based disposal is frequently not an option. Land adjacent to waterways is usually the most expensive land in the area because of its desirability for development, or it may be wetland and cannot be disturbed or filled.
Land-based disposal sites require large tracts of land where bermed or leveed containment areas can be built to hold the dredged spoil. Berms and levees are raised earthen structures used to form holding areas for dredged spoil. Depending on the composition of the spoil, the dredged material may take ten or more years to "dewater" (dry out) so that the berms can be dismantled and the land used for another purpose, or the containment pond converted to another use, such as fish ponds for aquaculture. Even if the land is available, many communities object to having the disposal area with its eight- to twenty-foot levees, claiming it is unsightly and lowers property values. Transporting dredged spoil (a slurry mud that is about 98% water) any distance to a land-based site, unless it can be pumped to the location, is prohibitively expensive and may require additional dredging to obtain access for the transport barges.
In many cases, ocean- and land-based disposal sites are not economically available to river and estuary sites that require dredging. Two techniques that are being used more often in these areas are artificial containment islands and wetland construction or rehabilitation. Island construction is frequently used where shipping channels need to be maintained through repeated dredging at five- to ten-year intervals, and the "island" site is used over a long time, or when the spoil is badly contaminated with toxic substances. In other cases, clean spoil is used to rebuild eroded islands. When filled and dewatered, island sites may become recreational areas or wildlife refuges, particularly nesting islands for birds. All island sites require extensive construction of costly bulkheads and other containment devices.
HARMFUL ALGAL BLOOMS
Harmful algal blooms (HABs) are having significant impacts on coastal and estuarine areas of the United States and the rest of the world, affecting the health of both humans and aquatic organisms and the vitality of local and regional economies. The number and diversity of reported HAB events have increased since the 1970s.
Understanding the causes of HABs and mitigating and preventing their consequences are national concerns. As a result, Congress passed the Harmful Algal Bloom and Hypoxia Research Act of 1998. The Act requires the formation of a federal multiagency task force to investigate the problem and report back to Congress with a plan and recommendations to address HAB and hypoxia. Amendments to the Act were introduced in both the House and the Senate in 2003. The House Science Committee, Subcommittee on Environment, Technology and Standards proposed that the amendment authorize the Coastal Ocean Science Program. The program is designed to focus on improving predictions of ecosystem trends, pollution, and coastal hazards. Congressman Brian Baird (Democrat of Washington) also introduced an amendment that requires the states and the president to develop and submit a plan "to protect the environment and public health from the impacts of harmful algal blooms" within one year of the date of enactment. As of April 2005 this legislation had made no headway in Congress.
What Are Harmful Algal Blooms?
Algae are microscopic, single-celled plants that live in the sea. The vast majorities of the thousands of algal species in U.S. coastal waters are not harmful and serve as the energy producers at the base of the food chain, without which higher life on earth would not exist. Occasionally the algae grow very fast or "bloom," creating dense, visible patches near the water surface. "Red tide" is a common name for events where certain algae containing reddish pigments "bloom" so that the water appears to be red. In most HAB events the rapidly developing algal bloom consumes all the oxygen in the water, resulting in hypoxia, which can have severe effects on local ecosystems. A small number of algal species produce potent neurotoxins that can be transferred through the food chain, where they affect and sometimes kill higher life forms such as shellfish, fish, birds, marine mammals, and humans that feed directly or indirectly on them.
Source of Harmful Algal Blooms
Most HABs are the result of the transport of offshore algal populations to inshore regions, that is, a naturally occurring physical relocation. For example, blooms of Gymnodinium breve, which causes neurotoxic shellfish poisoning, occur when algal cells from small offshore populations in the open Gulf of Mexico are blown into the west Florida shelf and into the coastal waters of other states bordering the Gulf of Mexico. This delivery of potentially harmful algal blooms from offshore to inshore regions in most areas of the world's coastal oceans occurs consistently but unpredictably. They occur even in areas that are unaffected by human activities. As a result, attempts to prevent HABs are somewhat impractical because people cannot control general oceanic circulation or even local coastal currents.
Increases in Harmful Algal Blooms
Harmful algal blooms are increasing in frequency and severity worldwide. Whether the increase is a direct result of cyclic or long-term variations in climate, other natural factors, or human activities is unclear. The frequency, duration, and intensity of algal blooms are related to a number of physical, biological, and chemical factors, the interaction of which is not clearly understood for many algal species.
Five possible reasons have been advanced for the increase in frequency and geographical extent of HAB events:
- Improved methods of detection and improved monitoring methods are detecting blooms that would previously have gone unreported.
- Introduction of new algal species into inshore areas through ship ballast water exchange or aquaculture.
- Reduction in populations of grazers (microscopic animals that eat the algae), resulting in their failure to control the algal population.
- Climate changes.
- Human activities that cause increases in nutrient levels or increased river discharge. (These are believed to be species-specific and not to apply to all HABs.)
All of these reasons are possible explanations and it is likely that it is a combination of one or more of these factors that causes HAB.
Effects on Human Health
The neurotoxins produced by some species of algae can be concentrated by bivalve mollusks (oysters, clams, and mussels) with no apparent ill effect to the bivalves. If bivalves with dangerous concentrations of neurotoxins are eaten by humans, severe illness or death can occur. In areas of the United States where HAB events occur, the densities of harmful algal species are heavily monitored in the water column by the coastal states as part of the NSSP. When the algal density exceeds certain levels, the areas are closed to bivalve harvesting until both the water column and the bivalve meat show the absence of neurotoxins.
Other human health effects from the neurotoxins include skin irritation from water contact and respiratory irritation from aerosols. Neurotoxin aerosols from sea spray have caused watery and stinging eyes, as well as breathing difficulties because the tiny acid droplets penetrate into and irritate the nasal passages and throat.
What Is Hypoxia?
Hypoxia (lack of oxygen) occurs when the dissolved oxygen level in the water column is less than two parts per million (ppm). It kills most of the bottom-dwelling life forms such as oysters and clams, and mobile marine organisms such as fish and shrimp either flee the area or die. For this reason, areas where hypoxic conditions exist are frequently referred to as "dead zones." Excess nutrient is the most frequent cause. Hypoxia is a worldwide problem that often occurs where rivers carrying large amounts of agricultural runoff empty into lakes, estuaries, oceans, and seas.
One location in the United States where hypoxia occurs is the Gulf of Mexico, off the Louisiana coast. The Gulf's hypoxic zone is comparable to the largest hypoxic areas in the world such as those in the Black and Baltic Seas. The Gulf of Mexico hypoxic zone, shown in Figure 6.10, is approximately 6,000–7,000 square miles of water where the oxygen level is below two ppm. Under normal conditions, dissolved oxygen levels would be five to six ppm.
The zone is caused by harmful algal blooms that are believed to be the result of the discharge of increased nutrients from the Mississippi River watershed into the Gulf of Mexico. The nutrients (nitrogen and phosphorus) come from fertilizers, animal wastes, and domestic sewage. The nitrate-nitrogen level in the main stem of the Mississippi River, which drains thirty-one states, has doubled since the 1950s. Figure 6.11 shows the Mississippi Basin watershed and the states whose rivers drain into it.
Correcting the problem requires a coordinated multi-state effort. The EPA, six other federal agencies, nine states, and two Native American tribes have developed an action plan to reduce nutrient loads reaching the Gulf. The Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (January 2000) was developed in response to the Congressional mandate in the Harmful Algal Bloom and Hypoxia Research Act of 1998. It has the goal of reducing the size of the hypoxic zone by 50% no later than 2015. The plan also called for implementation of nutrient management strategies to achieve a 30% reduction in the amount of nutrients reaching the Gulf of Mexico. Information generated through the research and monitoring portions of the plan will be used to modify future goals and actions as necessary.
The USGS has determined that about 25% of the nitrogen load in the Gulf comes from the Lower Mississippi River Valley, below the point where the Ohio River joins the Mississippi. In 2000 the USGS National Wetlands Center received funding to pursue the development of a strategy to use inland and coastal wetlands to reduce nutrients in this portion of the watershed.
Economic Consequences of Harmful Algal Blooms
Direct and indirect losses to local economies from HAB events are enormous. The amount of irretrievable revenue due to lost fish and shellfish production; impairment and loss of important ecosystems such as coral reefs; human illness and medical treatment; increased insurance rates for fisheries activities; unemployment and bankruptcy of seafood and recreational related businesses; loss of tourist dollars; and loss of sales for all seafood is staggering. For example, the 1991 outbreak of domoic acid in the state of Washington had a negative impact on the entire community, from the tourism industry to fisheries, with losses estimated between $15 million and $20 million.
During spring 2005 the New England region experienced the worst outbreak of the toxic alga Alexandrium fundyense in more than thirty years. The outbreak began in the Gulf of Maine in early May and spread into Massachusetts and Cape Cod Bays, resulting in the closing of coastal areas to shellfishing. In July 2005 the Woods Hole Oceanographic Institution estimated that the New England "red tide" was costing the local shellfish industry at least $3 million per week and had started a chain reaction of financial losses in the seafood processing and restaurant industries.
Even a nontoxic harmful algal bloom can have devastating consequences. In south Florida, blooms of macroalgae are overgrowing sections of coral reefs and seagrass beds. Coral reefs are a vital component of the Florida economy, attracting thousands of visitors each year. The seagrass beds are important to the survival of pink shrimp, spiney lobster, and finfish. Continued algae overgrowth could lead to severe economic losses for the local recreational, tourist, and seafood industries. In Washington state, Heterosigma akashiwo blooms have caused losses of $4 to $5 million per year to harvesters of wild and penned fish.
According to 2004 Economic Statistics for NOAA (April 2004), the economic impact of HABs in the United States averages $49 million per year. Individual outbreaks, however, can cause economic damage that exceeds the annual average. HAB outbreaks in Chesapeake Bay in 1997 cost the Maryland seafood and recreational fishing industries almost $50 million in just a few months. The report states that total public health effects resulting from shellfish poisoning by HABs averaged $22 million between 1987 and 1992. HAB events have also affected commercial fisheries. Losses of wild harvest and aquaculture average $18 million per year.
Preventing Harmful Algal Blooms
The U.S. Department of Commerce released a report, National Assessment of Harmful Algal Blooms in U.S. Waters (February 2001), which presents the findings of the federal multiagency task force created to investigate the problem of HABs. Because management options are limited, the focus for now remains on minimizing the impacts of HAB events.
Recommendations from the report include:
- Continue and enhance the state programs that regularly sample shellfish and shellfish harvest waters for presence of HABs and their toxins and have been effective for many years in reducing human illness and deaths.
- Develop communication programs that use educational and public health materials, electronic communication, and other techniques to educate and inform the public.
- Improve communication and information exchange among scientists; agencies; and federal, state, and local governments to increase cooperation and avoid duplicative effort.
- Improve sample collection techniques.
- Improve the laboratory and field detection methods for HABs, including rapid method development. Most of the standard laboratory tests take anywhere from four days to several weeks to provide a conclusive identification of the kind of algae causing the bloom. A rapid method would be one that could identify the organism and its concentration in the water within twenty-four to forty-eight hours. The level of toxicity is determined by injecting mice in the laboratory to see if they die. A rapid method would eliminate the mice and provide a chemical or other reaction that would give a definitive answer concerning toxicity levels within a few hours. Field methods that can be done easily at the site of the bloom do not exist.
- Establish long-term monitoring programs in areas currently affected by HABs and in areas that are likely to be affected in the future.
- Develop forecasting capabilities for the occurrence and impacts of HABs.
- Conduct basic research into the physiology, growth, and toxin production of HAB species; conditions that may stimulate blooms; and the toxin uptake, metabolism, and depuration in marine food webs, fisheries, and marine mammals.
These tools will allow states and local jurisdictions to prepare for the bloom events and communicate with the public in a timely manner, as well as provide data that can eventually be used in predictive models.
Some states that have the potential for HAB events have already established long-term monitoring programs, or are in the process of doing so, to gather information in advance of bloom situations. In addition, some research is being directed toward finding naturally occurring bacterial and viral populations that might be used in the biological control of HAB events.
Exotic species are plants, animals, and microbes that have been carried from one geographic region to another, either intentionally or unintentionally. Unintentional introduction includes transport in ballast water of ships, or as pests on imported fruits, vegetables, and animals or animal products. Prior to modern times, movement from one geographical region to another was infrequent and slow, allowing time for the ecology to absorb and counterbalance the newcomers.
Today, because of rapid transport, organisms can move across continents in a matter of hours or days. Once removed from their natural ecological system, where eons of evolution have established predator-prey relationships, competitive species, and other devices to maintain balance, exotic species may reproduce unchecked in their new locations because they have no natural competitors or predators.
Both estuarine and ocean habitats have suffered from exotic species introduction. In the Chesapeake Bay, MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus), two oyster diseases that have ravaged oyster populations, came to the Bay with oysters introduced from other regions. The coral reefs in the Northern Mariana Islands are being decimated by the introduction of the crown-of-thorns starfish. The green crab introduced from the Baltic Sea to the shores of New England occurs in such high numbers that the crab is believed to be eating young scallops and other valuable seafood.
Passage of the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 was a first step in attempting to prevent species migration. This legislation authorized the U.S. Fish and Wildlife Service and NOAA to adopt regulations to prevent the unintentional introduction of aquatic nuisance species. In 1999 the Invasive Species Council was created by presidential executive order to oversee efforts to control unwanted exotic species. The council is chaired jointly by the secretaries of Interior, Agriculture, and Commerce. Council members include the secretaries of State, Treasury, and Transportation, and the administrator of the EPA. To date, however, no method has been found to stop the potential flood of exotic species to the U.S. shores.
On April 13, 2005, Senators Carl Levin and Debbie Stabenow (both Democrats of Michigan) and Susan M. Collins (Republican of Maine) introduced into the U.S. Senate the National Aquatic Invasive Species Act of 2005 (NAISA). A similar bill was introduced into the House of Representatives at the same time. The proposed legislation would reauthorize and strengthen the National Invasive Species Act of 1996 so as to protect U.S. waters by preventing new introductions of aquatic invasive species.
If enacted, NAISA 2005 would accomplish its goals by:
- Regulating ballast discharge from commercial vessels
- Preventing invasive species introductions from other pathways
- Supporting state management plans
- Screening live aquatic organisms entering the United States for the first time in trade
- Authorizing rapid response funds
- Creating education and outreach programs
- Conducting research on invasion pathways, and prevention and control technologies
- Authorizing funds for state and regional grants
- Strengthening specific prevention efforts in the Great Lakes
As of July 2005 the Senate bill had been referred to the Committee on Environment and Public Works, and the companion bill in the House of Representatives had been referred to the Subcommittee on Fisheries and Oceans.
FUTURE OF OCEANS AND ESTUARIES
The environments of U.S. oceans and estuaries are flourishing at some locations, experiencing stress in others, and have been overwhelmed in a few localities. An increasing level of knowledge and awareness of environmental issues in the United States has led to more stringent regulatory protections for these ecosystems and a slow but steady reversal of a downward trend. Private organizations are taking on the formidable task of monitoring the nations' extensive coastlines. They are also organizing so that they may exert social and political pressure for continued action and progress in restoring damaged coastal ecosystems. Corporations, agencies, and citizens are forging alliances and other partnerships to protect and repair these systems. Volunteers of all ages and from all walks of life are giving time, talent, and money to participate in ecological restoration. Much has been done, but much more remains to be accomplished.
OCEANS . It is natural to begin a survey of the mythology of oceans with their eponymous deity, the Greek god Okeanos (etymology unknown). All evidence testifies that Okeanos was originally conceived as a river god, rather than a god of the salt sea. This illustrates a characteristic difficulty: To treat rivers, springs, and fountains, or the symbolic and religious associations of water in general, exceeds the compass of this article, but such distinctions are not always rigorous in the mythological traditions.
In the pantheon defined by Hesiod's Theogony, Okeanos is the offspring of Ouranos (Sky) and Gaia (Earth), and thus of the race of Titans that included Kronos, the father of Zeus. With his sister Tethys as consort, Okeanos produced the vast brood of Okeanids, spirits of rivers and streams. Parallel to Okeanos is Pontos (Sea): Born of Gaia alone, he unites with her to engender Nereus, whence the Nereids, a species of sea nymphs corresponding to the Okeanids. While Pontos remains a bare abstraction, Okeanos is imagined as dwelling with Tethys at the edge of the world, which he encircles. In descriptions of the shields of Achilles (Homer) and Herakles (attributed to Hesiod), Okeanos occupies the rim.
References in Homer (Iliad 14.200f., 244ff., 301f.), as well as in Plato, Vergil, Orphic texts, and elsewhere, identify Okeanos and Tethys as the source (genesis ) of gods or of the universe. Details of this cosmogony are obscure; according to one version, the primordial waters brought forth an egg that initiated the process of creation (Orphic fragments 54, 57). Okeanos was related to underworld rivers such as the Styx, which was his daughter, according to Hesiod (Theogony 361; cf. Plato, Phaedo 112e). The Isle of the Blessed, where souls of heroes dwelled, was in Okeanos's waters (Odyssey 4.562–568). The relationship between the cosmogonic role of Okeanos and water as the fundamental element in Thales's philosophy is moot.
Okeanos was occasionally represented in sculptures and sarcophagus reliefs, but does not appear to have had a specific cult. The sea was worshiped and appeased in the name of Poseidon, later identified with the Roman Neptune. The primitive evolution of Poseidon is obscure (he is conspicuously associated with the horse). In the Olympian scheme, Poseidon received the waters as his province from Zeus. He was responsible for maritime calm and turbulence, and for earthquakes. As consort of the Okeanid (or Nereid) Amphitrite, he was father of the gigantic Triton, whose torso terminated in a serpent's tail. Various pre-Olympian deities abided in the sea, notably Proteus, who shared with Nereus and with the Nereid Thetis (mother of Achilles) the power to metamorphose and to foretell the future.
The idea of encompassing waters survived into medieval geography, as in the map attached to Ibn Khaldūn's Muqaddimah (the name Ūqyānūs in one manuscript renders "Okeanos"). The earth is said by Islamic writers to float on the sea like a grape or an egg.
In the cultures of the ancient Near East, oceanic waters figured largely in cosmogonic myths. According to Sumerian tradition, in the beginning was Nammu (Sea), whence arose a mountain representing heaven and earth, later separated by the air god Enlil. In the Babylonian creation story, recited at the New Year, the primordial gods are two: the masculine Apsu, representing sweet waters, and the feminine Tiamat, the salt-water ocean, from whose union come the gods. Apsu is vanquished by younger gods, but Tiamat continues the battle with the help of Kingu and other monstrous offspring; she is defeated by the storm god Marduk and divided in two, one part of her being raised to contain the upper waters. From the Epic of Gilgamesh, it appears that the land of the dead was reached by crossing a body of water. The same narrative incorporates the Sumerian tradition of a great flood, perhaps representing a return to the primordial state.
In Canaanite myth, the senior deity El favors Yam (Sea) against his own son, Baal (associated with fertility and rain). Yam surrenders to Baal and is spared; also vanquished is the serpent Lotan, related to the Hebrew Leviathan (cf. also the defeats of Rahab and Tannin: Ps. 74:13, 89:11; Is. 51:9; etc.). The biblical sea waters seem to retain a threatening aspect, as though not entirely submissive to creation; certain passages indicate the sea as the site of God's throne (e.g., Ps. 104:3; Ez. 28:2).
In Egyptian sources, the waters of Nun, on which the earth rests, are sometimes identified as the origin of life. At the parting of the waters appears the primal hill. Nun was also conceived as surrounding the earth (like Okeanos), so that the sun emerged each day from his waters in the east. The route to the afterworld is the river Nile, host also to aquatic deities such as the crocodile, but because the Nile was believed to have its source in the netherworld (Pyramid Texts 1551a, 1557b), the distinction between river and primal waters is not absolute.
The Ṛgveda (10.121) alludes to a cosmic egg (Prajāpati) that emerged from water, an idea elaborated in later commentaries (Śatapatha Brāhmaṇa 11.1.6) that also record a flood. The identification of Varuṇa as god of the sea is post-Vedic. The ocean is the source of amṛta, the liquor of immortality (analogously, the Greek ambrosia is sometimes connected with the ocean). In Hindu mythology, the cobralike sea demons called nāga s (feminine dragons are called nāginis ) have their kingdom in the west or alternatively are imagined as dwelling in the underworld. In Cambodia, the first Khmer dynasty is said to have sprung from the union of the daughter of a nāga king with a Hindu prince.
In Chinese myth, where nature deities play a relatively unimportant part, the four seas that surround the earth are associated each with a dragon king. In one legend the king of all the dragons arose from the sea and prevented the first emperor of Qin from voyaging to the islands of the immortals. The antiquity of such stories is in doubt, as they appear to have been influenced by Hindu myth. Undeniably ancient (dating from the Zhou dynasty) is the story of the flood, which was dammed, channeled, and drained by the god Yu with the help of a dragon, Yu then became the founder of China's first dynasty.
The Ainu (the aborigines of Japan) tell of a small bird that dispersed the primal waters by the motion of its wings. In the Kojiki, the main compendium of ancient Japanese myth, the original chaos is compared to oily water, but the sea's major role appears in the tale of the sons of Ninigi, the divine ancestor of Japan's emperors. The younger son, Po-wori, a hunter, borrows and loses the fishhook of his brother Po-deri. A sea deity constructs a boat and advises Po-wori to sail to the palace of Watatsumi, god of the sea, and his daughter Tōyōtama. Po-wori marries Tōyōtama but later desires to return home. Watatsumi recovers the lost hook and gives his son-in-law two jewels to control the tides. Coming home on a crocodile, Po-wori subdues his elder brother. Tōyōtama, assuming the form of a crocodile, bears her husband a child and then returns to the sea, ashamed that he has observed her thus. Her younger sister tends and marries the son, and from this union is born the first Japanese emperor. Shrines are devoted to Watatsumi and other sea divinities.
Meander patterns on Paleolithic vessels of Europe, often in association with maternal figures, eggs, snakes, and waterfowl, suggest water as a fertility symbol. In the Finnish epic Kalevala (old version), which preserves Finno-Ugric traditions, the world is created out of eggs laid by an eagle on the knee that the hero Väinämöinen lifts from the sea (Väinä means "still water"). Väinämöinen subsequently sails to death's domain and escapes meshes laid to trap him by metamorphosing into various forms. The Saami (Lapp) god Cacce Olmai (Water Man), a deity of fishing, is said to assume various shapes; also reported is a mermaidlike creature called Akkruva, similar to the Inuit (Eskimo) Inue, a kind of merman.
In Celtic myths, there is a paradisiacal island called Brittia located in the ocean. This ancient account is transmitted by the Byzantine historian Procopius (cf. the Arthurian Avalon, the Irish Tir-na-nogue). Islands are the object of voyages by various heroes or demigods. Bran, a sea giant, encounters an isle of women, an isle of laughter and joy, and other fantastical places on his journey. Similarly, Brendan, in search of the Land of Promise, encounters enchanted islands and monsters; one island proves to be the back of a gigantic sea creature (cf. Sindbad's first voyage). The Roman general Sertorius is said by Plutarch to have attempted such a journey from Spain, which suggests a possible syncretism of Greek and Iberian traditions. The inspiration of Brendan's legend is evident in Dante's version of Odysseus's last voyage.
The province of the sea fell on the Celtic god or hero Ler, and more especially to his son, Manannán mac Lir, patron of sailors and merchants and the eponymous deity of the Isle of Man. Manannán rode the steed Enbarr, which could traverse water as easily as land (cf. the kelpie or sea horse in Scottish folklore).
In the Eddas, the god of the sea is Ægir (cognate with aqua ), a member of the race of giants who is friendly to the gods. His wife is Ran, and a kenning (metaphorical phrase) speaks of the waves of Ægir's daughters. Ægir is the gods' ale-brewer and a giver of banquets. Norse myth tells of various sea monsters such as the huge fishlike creature called the kraken, as well as mermen and mermaids (see the thirteenth-century King's Mirror ), the belief in which has persisted into modern times among fishermen of New England and elsewhere.
In the Americas, the creation myths of the Chorti, Maya Indians of Guatemala, mention four seas that are distinguished by color surrounding and beneath the world, with monstrous creatures (angels in Christianized versions) beyond the waters. Among the people of Santa Elena, there is a story of a race of giants who came from across the sea. There is a hint of a primal sea in the Popol Vuh, the sacred book of the Quiché Maya of Guatemala.
A widespread North American variant involves the creation of land upon the primordial ocean by means of a diver, whether divine, human, or animal, who brings mud or earth up from the sea bottom. In the Salinan version (California), a dove fetches the substance after a flood produced by the Old Woman of the Sea; a turtle is the agent in Maidu (California) and Blackfeet myth. In a Huron creation account, a toad is successful; in a Mandan (North Dakota) version, it is a duck, while other stories feature the muskrat (Assiniboine, Great Plains), the water beetle (Cherokee), and the crawfish (Yuchi). There are also versions in which the waters simply recede. The Navajo emergence myth, which like the Hopi myth describes four worlds associated with four directions and four colors, has four seas as well. The Winnebago Indians (Great Plains) distinguish two classes of water powers; streams are masculine, while the subterranean waters that uphold the earth are feminine.
Altaic myth (Siberia) also exhibits versions of the diver tale, with the diver as swallow, loon, goose, or other waterfowl. Elsewhere the diver is a man or devil, often in the guise of a bird; a Christian Romanian version casts Satan as the diver. In a Samoyed flood story, a bird discovers land in a manner reminiscent of the bird in the narrative of Noah's ark. The theme of the ark occurs also in Buriat myth. Mention may also be made of a Khanty (Yenisei River) creation story, according to which the earth rests on three great fish, the sinking of which generates floods.
In a Polynesian account, Māui or another deity brings land up from the sea bottom. A Maori tale tells of a conflict between Ta-whiri-ma-tea, the god of storms or winds, and his brother Tangaroa, here the father creator of the world. Ta-whiri-ma-tea attacks Tangaroa, who takes refuge in the ocean. One of Tangaroa's two children, representing fish, retreats to the water. The other child, representing reptiles, hides in the forest, whence the antagonism between the sea and humans, who are descended from the forest deity. The Polynesian practice of burying the dead in canoe-shaped dugouts may reflect a custom of setting bodies adrift to reach the ancestral home or land of the dead. It was believed that souls were carried to Bulotu, the Tongan land of the dead, in an invisible canoe presided over by Hikuleo, the Tongan god of the dead and half-brother of Tangaroa. Near his house, in one account, were the waters of life that could confer immortality. The land of the dead, usually located to the west, was the special destination of chiefs and other notables. Legends tell of parties sailing, usually by mistake, to Bulotu.
Marine myths are not widespread in Africa, but mention may be made of a Yao (Mozambique) story in which human beings are fished out of the sea by a chameleon.
From the foregoing survey, certain broad themes may be identified. The ocean is often conceived as the primordial element, from which land and sometimes living creatures emerge. It surrounds the earth and lies under it, and beyond its waters reside the departed or the blessed, who are sometimes visited by the intrepid voyager. Now and then flood waters challenge creation. The ocean is inhabited by various monsters, often serpentine and capable of metamorphosis. Marine deities are sometimes the ancestors of imperial dynasties. Finally, in some accounts the waters of the deep are life-giving, or the source of life-giving brews.
On the Greek Okeanos, the best study is Jean Rudhardt's Le thème de l'eau primordiale dans la mythologie grecque (Bern, 1971). For the Old Testament, there is a useful survey of oceanic themes in Phillipe Reymond's L'eau, sa vie, et sa signification dans l'ancien testament (Leiden, 1958). The ancient Near Eastern materials may be consulted in the collection edited by J. B. Pritchard, Ancient Near Eastern Texts relating to the Old Testament, 3d ed. (Princeton, N.J., 1969). A good sampling of creation myths, in which primordial waters play a prominent role, is Barbara C. Sproul's Primal Myths: Creating the World (San Francisco, 1979). The encyclopedic Mythology of All Races, 13 vols., edited by Louis H. Gray and George Foot Moore (Boston, 1916–1932), is uneven and often out of date in method and content, but it contains much firsthand material and is the most extensive compendium. Robert W. Williamson's Religious and Cosmic Beliefs of Central Polynesia, 2 vols. (1933; New York, 1977), presents the numerous variant versions. The volume Asiatic Mythology, edited by Joseph Hackin et al. (New York, 1932), is especially good on modern myths, as in the contribution on China by Henri Maspero.
The Japanese Kojiki is available in a new translation by Donald L. Philippi (Tokyo and Princeton, N.J., 1969). Sources of Celtic mythology are widely scattered, but there is a readable summary by Charles Squire, The Mythology of the British Islands: Celtic Myth and Legend, Poetry and Romance (1909; Fulcroft, Pa., 1975), though it is inconsistent in citing sources and not always reliable in interpretation; see also Marie-Louise Sjoestedt's Gods and Heroes of the Celts (London, 1949). There is some information relevant to oceans in Martin Ninck's Die Bedeutung des Wassers im Kult und Leben der Alten: Eine symbolgeschichtliche Untersuchung (Leipzig, 1921), along with rich if speculative interpretative suggestions. For works cited in the text, see The King's Mirror, translated by Laurence Marcellus Larson (New York, 1917); The Old Kalevala of Elias Lönnrot, translated by Francis Peabody Magoun, Jr. (Cambridge, Mass., 1969); and Pyramid Texts, edited by Samuel A. B. Mercer (New York, 1952), in which excursuses 14 and 15 are particularly relevant. For Ibn Khaldun, see Franz Rosenthal's translation of the Muquddimah, 3 vols., 2d ed. (Princeton, N.J., 1967); the map is the frontispiece to volume 1. A readable book on modern folklore is Horace Beck's Folklore and the Sea (Middletown, Conn., 1973). For Maya traditions, see John G. Foughts Chorti (Mayan) Texts (Philadelphia, 1972).
Cabartous, Alain. Le ciel dans la Mer: christianisme et civilisation maritime. Paris, 1990.
Costa, Giancarlo. Misteri e leggende del mare. Milan, 1994.
Fuson, Robert. Legendary Islands of the Ocean Seas. Sarasota, Fla., 1998.
Merrien, Jean. La légendaire de la mer. Rennes, France, 2003.
Oliver, J. G., ed. The Sea in Antiquity. Oxford, 2000.
David Konstan (1987)
ocean, interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
The World Ocean
Of the major units that comprise the world ocean, three—the Atlantic, Indian, and Pacific oceans—extend northward from Antarctica as huge "gulfs" separating the continents. The fourth, the Arctic Ocean, nearly landlocked by Eurasia and North America and nearly circular in outline, caps the north polar region. The Southern Ocean (also called the Antarctic Ocean) is now often considered a fifth, separate ocean, extending from the shores of Antarctica northward to about 60°S. The major oceans are further subdivided into smaller regions loosely called seas, gulfs, or bays. Some of these seas, such as the Sargasso Sea of the North Atlantic Ocean, are only vaguely defined, while others, such as the Mediterranean Sea or the Black Sea, are almost totally surrounded by land areas. Large and totally landlocked saltwater bodies such as the Caspian Sea are actually salt lakes.
The boundaries between oceans are usually designated by the continental land masses bordering them or by ridges in the ocean floor, which also serve as geographic boundaries. Where these features are absent (such as the ill-defined northern boundary of the Antarctic Ocean), the boundary is somewhat arbitrarily fixed by fluctuating zones of opposing currents that act as partial barriers to the mixing of waters between the two adjacent oceans.
The oceans are not uniformly distributed on the face of the earth. Continents and ocean basins tend to be antipodal, or diametrically opposed to one another, i.e., continents are found on the opposite side of the earth from ocean basins. For example, Antarctica is antipodal to the Arctic Ocean; Europe is opposed by the South Pacific Ocean. Furthermore, over two thirds of the earth's land area is found in the Northern Hemisphere, while the oceans comprise over 80% of the Southern Hemisphere.
The world ocean has an area of about 361 million sq km (139,400,000 sq mi), an average depth of about 3,730 m (12,230 ft), and a total volume of about 1,347,000,000 cu km (322,280,000 cu mi). Each cubic mile of seawater weighs approximately 4.7 billion tons and holds 166 million tons of dissolved solids. One of the most unique and intriguing aspects of ocean water is its salinity, or dissolved salt content. The measurement of salinity is essentially the determination of the amount of dissolved salts in 1 kg of ocean water and is expressed in parts per thousand (‰). Ocean salinities commonly range between 33 ‰ to 38 ‰, with an average of about 35 ‰. Thirty-five parts per thousand salinity is equivalent to 3.5% by weight. Six elements (chlorine, sodium, magnesium, sulfur, calcium, and potassium) constitute over 90% of the total salts dissolved in the oceans. Pressure in the ocean waters increases with increasing depth due to the weight of the overlying water. The pressure increases at the rate of 1 atmosphere for every 10 m (33 ft) of depth (1 atm=15 lb per sq in. or 1,016 dynes per sq cm). The average temperature of the oceans is 3.9°C (39°F).
It now appears that the waters making up the present oceans (and the gases that make up the present atmosphere) were not of cosmic origin, i.e., were not present in the primordial atmosphere. Instead, they were derived from the interior of the earth sometime in the first one or two billion years after the earth's formation. It is now also generally accepted that a new ocean crust has been forming more or less continuously for at least the past 200 million years through a process of volcanic activity along the midocean ridge system (see seafloor spreading), which consists of a series of underwater mountains. On the basis of present knowledge it seems highly probable that all ocean waters and atmospheric gases were gradually released by the separation of these volatile components from the silicate rocks of the crust and upper mantle through volcanic activity. (Molten lava is known to contain appreciable amounts of water and other volatiles that are released upon solidification.) With the passage of time, water released by volcanic activity gradually filled oceanic depressions.
Continental Shelves, Slopes, and Rises
Virtually all continents are surrounded by a gently sloping submerged plain called the continental shelf, which is an underwater extension of the coastal plain. The continental shelves are the regions of the oceans best known and the most exploited commercially. It is this region where virtually all of the petroleum, commercial sand and gravel deposits, and fishery resources are found. It is also the locus of waste dumping. Changes in sea level have alternatingly exposed and inundated portions of the continental shelf. Continental shelves vary in width from almost zero up to the 1,500-km-wide (930-mi) Siberian shelf in the Arctic Ocean. They average 78 km (48 mi) in width. The edge of the shelf occurs at a depth that ranges from 20 to 550 m (66 to 1,800 ft), averaging 130 m (430 ft). The shelves consist of vast deposits of sands, muds, and gravels, overlying crystalline rocks or vast thicknesses of consolidated sedimentary rocks. Although there is a great variation in shelf features, nonglaciated shelves are usually exceptionally flat, with seaward slopes averaging on the order of 205 m per km (10 ft per mi), or less than 1° of slope. The edge of the shelf, called the shelf break, is marked by an abrupt increase in slope to an average of about 4°.
The continental slopes begin at the shelf break and plunge downward to the great depths of the ocean basin proper. Deep submarine canyons, some comparable in size to the Grand Canyon of the Colorado River, are sometimes found cutting across the shelf and slope, often extending from the mouths of terrestrial rivers. The Congo, Amazon, Ganges, and Hudson rivers all have submarine canyon extensions. It is assumed that submarine canyons on the continental shelf were initially carved during periods of lower sea level in the course of the ice ages. Their continental slope extensions were carved and more recently modified by turbidity currents—subsea "landslides" of a dense slurry of water and sediment.
Many continental slopes end in gently sloping, smooth-surfaced features called continental rises. The continental rises usually have an inclination of less than 1/2°. They have been found to consist of thick deposits of sediment, presumably deposited as a result of slumping and turbidity currents carrying sediment off the shelf and slope. The continental shelf, slope, and rise together are called the continental margin.
Trenches, Plains, and Ridges
One of the most surprising findings of the early oceanographers was that the deepest parts of the oceans were not in the centers, as they had expected, but were in fact quite close to the margins of continents, particularly in the Pacific Ocean. Further exploration showed that these deeps were located in long V-shaped trenches bordering the seaward edge of volcanic island arcs. These trenches are one of the most striking features of the Pacific floor. Trenches virtually encircle the rim of the Pacific basin. The trenches have lengths of thousands of kilometers, are generally hundreds of kilometers wide, and extend 3 to 4 km (1.9–2.5 mi) deeper than the surrounding ocean floor. The greatest ocean depth has been sounded in the Challenger Deep of the Marianas Trench, a distance of 10,911.5 m (35,798.6 ft) below sea level.
The deep ocean floor begins at the seaward edge of the continental rise or marginal trench, if one is present, and extends seaward to the base of the underwater midocean mountains. Many relief features of great importance are present in this region. Vast abyssal plains cover significant portions of the deep ocean basin. Such plains are occasionally broken by low, oval-shaped abyssal hills. The abyssal plains cover about 30% of the Atlantic and nearly 75% of the Pacific ocean floors. They are among the flattest portions of the earth's crust and appear to be formed by the deposition of fine sediment carried by turbidity currents that have covered and smoothed out irregularities in the ocean floor.
One of the most significant features of the ocean basins is the midocean ridge. First discovered in the Atlantic Ocean on the Challenger expedition, its relief features were further investigated during the German Meteor expedition of 1925–26. By the early 1960s it had been confirmed that the Mid-Atlantic Ridge was only part of a continuous feature that extended 55,000 km (34,000 mi) through the Atlantic, Indian, South Pacific, and Arctic oceans. The ridge is a broad bulge in the ocean floor that rises 1 to 3 km (0.6–2 mi) above the adjacent abyssal plains. It has a variable width averaging more than 1,500 km (c.900 mi). It is crossed by a number of fracture zones (transform faults) and displays a deep rift 37 to 48 km (23–30 mi) wide and about 1.6 km (1 mi) deep at its very crest.
Relationship of the Ocean and the Atmosphere
The atmosphere affects the oceans and is in turn influenced by them. The action of winds blowing over the ocean surface creates waves and the great current systems of the oceans. When winds are strong enough to produce spray and whitecaps, tiny droplets of ocean water are thrown up into the atmosphere where some evaporate, leaving microscopic grains of salt buoyed by the turbulence of the air. These tiny particles may become nuclei for the condensation of water vapor to form fogs and clouds.
In turn, the oceans act upon the atmosphere—in ways not clearly understood—to influence and modify the world's climate and weather systems. When water evaporates, heat is removed from the oceans and stored in the atmosphere by the molecules of water vapor. When condensation occurs, this stored heat is released to the atmosphere to develop the mechanical energy of its motion. The atmosphere obtains nearly half of its energy for circulation from the condensation of evaporated ocean water.
Because the oceans have an extremely high thermal capacity when compared to the atmosphere, the ocean temperatures fluctuate seasonally much less than the atmospheric temperature. For the same reason, when air blows over the water, its temperature tends to come to the temperature of the water rather than vice versa. Thus maritime climates are generally less variable than regions in the interiors of the continents.
The relationships are not simple. The pattern of atmospheric circulation largely determines the pattern of oceanic surface circulation, which in turn determines the location and amount of heat that is released to the atmosphere. Also, the pattern of atmospheric circulation determines in part the location of clouds, which influences the locations of heating of the ocean surface.
Currents and Ocean Circulation
The surface circulation of the oceans is intimately tied to the prevailing wind circulation of the atmosphere (see wind). As the planetary winds flow across the water, frictional stresses are set up which push huge rivers of water in their path. The general pattern of these surface currents is a nearly closed system of currents, called gyres, which are approximately centered on the horse latitudes (about 30° latitude in both hemispheres). Major circulation of water in these gyres is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In the North Pacific and North Atlantic oceans, smaller counterclockwise gyres are developed partly due to the presence of the continents. These are centered on about 50°N lat. The most dominant current in the Southern Ocean is the West Wind Drift, which circles Antarctica in an easterly direction. The northern and southern hemispheric gyres are divided by an eastward flowing equatorial countercurrent, which essentially follows the belt of the doldrums. This countercurrent is caused by the return flow of water piled up along the eastward portion of the equatorial seas, and its return flow is uninhibited by the weak and erratic winds of the doldrums. Analysis of current records shows that a number of major currents, such as the Gulf Stream, have strong fast-moving currents beneath them trending in the opposite direction to the surface current. Such undercurrents, or countercurrents, appear to be as important and pervasive as the surface currents. In 1952 the Cromwell current was found flowing eastward beneath the south equatorial current of the Pacific. In 1961 a similar current was discovered in the Atlantic. See also tide.
Thermohaline circulation refers to the deepwater circulation of the oceans and is primarily caused by differences in density between the waters of different regions. It is mainly a convection process where cold, dense water formed in the polar regions sinks and flows slowly toward the equator. Most of the deep water acquires its characteristics in the Antarctic region and in the Norwegian Sea. Antarctic bottom water is the densest and coldest water in the ocean depths. It forms and sinks just off the continental slope of Antarctica and drifts slowly along the bottom as far as the middle North Atlantic Ocean, where it merges with other water. The circulation of ocean waters is vitally important in dispersing heat energy around the globe. In general, heat flows toward the poles in the surface currents, while the displaced cold water flows toward the equator in deeper ocean layers.
The Ocean as a Biological Environment
The oceans hold the answers to many important questions about the development of the earth and the history of life on earth. For instance, within the rocks and sediment of the ocean floors the geological history of the earth is recorded. Fossils in this sediment record a portion of the biological history of the earth at least back to the Jurassic period, which ended about 140,000,000 years ago. The first appearance of life on the earth is thought to have occurred in the oceans 2 or 3 billion years ago. The modern marine environment is divided into two major realms, the benthic and the pelagic, based upon the ecological characteristics and marine life associated with them. See also marine biology.
The Benthic Realm
The benthic realm refers to the floor of the oceans, extending from the high tide line to the greatest ocean depths. The organisms that live in or on the bottom are called benthos. The benthic realm is subdivided on the basis of depth into the littoral zone, which extends from high tide to a depth of about 200 m (660 ft), and the deep-sea realm. The benthic life forms are both sessile (attached) and motile (mobile). They are distributed from near-shore littoral regions to the ocean depths and play an important role in the food chain. Some benthonic life forms live by predation, others sift organic matter from the water, and others scavenge the bottom for organic debris that has settled there. Benthonic plants can live only in the euphotic zone, the uppermost 100–200 m (330–660 ft) of the ocean, where sunlight penetrates. Benthonic animals that live below the euphotic zone often must depend on the rain of organic debris from above to supply their food needs, and thus the deep regions of the benthic realm are not highly populated except in the areas around hydrothermal vents where chemosynthesis provides an alternative food source.
The Pelagic Realm
The pelagic realm consists of all of the ocean water covering the benthic realm. It is divided horizontally into the neritic, or fertile near-shore, province and the oceanic province. Vertically it is divided into the euphotic, or photic, zone and the aphotic (without sunlight) zone. Drifting, free-floating organisms, called plankton, and organisms with poor mobile ability populate the euphotic zone. Most plankton are microscopic or near-microscopic in size. Phytoplankton are photosynthetic bacteria (cyanbacteria) and floating algae, such as diatoms, dinoflagellates, and coccolithopores. Heterotrophic plankton (zooplankton) are floating animals and protozoans of the sea and rely on the phytoplankton as food sources. Foraminifera and radiolaria are the dominant protozoan zooplankton that secrete tests (shells), which become incorporated into the sediment of the ocean floor. Many juvenile forms of swimmers (such as shrimp) or bottom dwellers (such as barnacles) pass through a planktonic phase. Marine organisms capable of self-locomotion are called nektonic life forms. Fish, squid, and whales are examples of marine nekton.
Importance of the Ocean
Throughout history humans have been directly or indirectly influenced by the oceans. Ocean waters serve as a source of food and valuable minerals, as a vast highway for commerce, and provide a place for both recreation and waste disposal. Increasingly, people are turning to the oceans for their food supply either by direct consumption or indirectly by harvesting fish that is then processed for livestock feed. It has been estimated that as much as 10% of human protein intake comes from the oceans. Nevertheless, the food-producing potential of the oceans is only partly realized. Other biological products of the oceans are also commercially used. For example, pearls taken from oysters are used in jewelry, and shells and coral have been widely used as a source of building material.
Ocean water is processed to extract commercially valuable minerals such as salt, bromine, and magnesium. Although nearly 60 valuable chemical elements have been found dissolved in ocean water, most are in such dilute concentrations that commercial extraction is not profitable. In a few arid regions of the world, such as Ascension Island, Kuwait, and Israel, ocean water is desalinated to produce freshwater.
The shallow continental shelves have been exploited as a source of sands and gravels. In addition, extensive deposits of petroleum-bearing sands have been exploited in offshore areas, particularly along the Gulf and California coasts of the United States and in the Persian Gulf. On the deep ocean floor manganese nodules, formed by the precipitation of manganese oxides and other metallic salts around a nucleus of rock or shell, represent a potentially rich and extensive resource. Research is currently being conducted to explore nodule mining and metallic extraction techniques. Ocean water itself could prove to be a limitless source of energy in the event that nuclear fusion reactors are developed, since the oceans contain great quantities of deuterium.
The oceans also are important for recreational use, as each year more people are attracted to the sports of swimming, fishing, scuba diving, boating, and waterskiing. Ocean pollution, meantime, has escalated dramatically as those who use the oceans for recreational and commercial purposes, as well as those who live nearby, have disposed of more and more wastes there (see water pollution).
See also R. Carson, The Sea around Us (1961); J. Bardach, Harvest of the Sea (1968); J. R. Moore, ed., Oceanography (1971); R. Perry, The Unknown Ocean (1972); L. Paine, The Sea and Civilization (2013).
Oceans and Seas
Oceans and Seas
Earth is an oceanic planet. An ocean is defined as a very large body of saline water—water that contains approximately 35,000 parts per million (ppm) of sodium chloride (NaCl) and trace amounts of many other molecules. In contrast to salty ocean water, the freshwater that people are able to drink contains below 1,000 ppm of
NaCl. More than 70% of Earth's surface is covered by ocean, an area of about 224 million sq mi (580 million sq km). To put this into perspective, the continental United States occupies an area of 3.54 million sq mi (9.2 million sq km).
The continents segregate the global ocean into several large regions, which have been named individually; the Atlantic and Pacific Oceans are two examples. A sea is considered to be a large inlet of the ocean. An example of a sea is the Bay of Fundy, which lies northeast of the coast of Maine and is enclosed by the Canadian provinces of Nova Scotia and New Brunswick. Other examples include the Mediterranean Sea, Black Sea, and Caribbean Sea.
In 2007, it is still accurate to say that scientists know more about the solar system than the ocean. The formidable depth of the ocean (more than half of the ocean is about 10,000 ft/3,000 m deep) has, until the era of manned and unmanned undersea robotic exploration, prevented extensive exploration. Even in 2007, despite centuries of undersea exploration and use of twentieth-century innovations such as sonar, less than 10% of the ocean floor has been mapped in detail. However, more is known and is being learned about the chemistry of the ocean, ocean currents, ocean-influenced wind and weather patterns, and, particularly in the latter several decades of the twentieth century, how the ocean is part of Earth's changing climate.
Historical Background and Scientific Foundations
There are five large oceans—the Atlantic, Pacific, Indian, Arctic, and Southern (or Antarctic) Oceans. Despite their different names, these waters merge into one large global ocean, in which the continents sit as immense islands.
The ocean is a global highway that has been used as a transportation route for centuries. For example, the
dating of material from the ruins of settlements found at L'Anse aux Meadows, located in the far north of the Canadian province of Newfoundland, has shown that they were built by a Viking expedition under the command of Leif Eriksson around AD 1000.
Trans-Pacific travel may have taken place even earlier. In 1947, inspired by evidence indicating that travel may have occurred around AD 500 between South Pacific regions (including New Zealand) and the west coast of South America, Norwegian adventurer Thor Heyerdahl (1914–2002) sailed the Kon-Tiki—a raft constructed as it would have been at that time—from South America to the Tuamotu Islands, a distance of over 4,000 mi (6,400 km). The journey, completed in 101 days, was the first of many trans-Pacific voyages, demonstrating that even 15 centuries ago far-flung ocean journeys were possible.
The ocean currents and prevailing ocean winds that made these and other voyages possible are also powerful contributors to climate. The development of regions of high and low pressure in areas of the tropical ocean can generate winds that spawn extreme storms, such as cyclones.
Some winds that blow over ocean waters are present regularly. These so-called prevailing winds blow in different directions, depending on the hemisphere and distance from the equator. Trade winds immediately north of the equator blow from the northeast to the southwest, while those south of the equator blow from the southeast to the northwest. In the middle northern and southern latitudes, westerlies blow from the southwest to the northeast and from the northwest to the southeast, respectively.
The friction between the moving air and the water molecules tends to push the water along in the direction of the wind, and actually causes the water to pile up. Although gravity tends to pull the piled up water downward, another factor called the Coriolis force, which is generated by the rotation of Earth, causes the water to rotate to the right (clockwise) in the Northern Hemisphere and to the left (counterclockwise) in the Southern Hemisphere. The result is large mounds of water with a flow of water around them; these are known as gyres. Gyres produce currents in the Northern and Southern Hemispheres of the Atlantic and Pacific Oceans. The Gulf Stream is part of the North Atlantic Gyre.
Ocean currents, which make up about 10% of all ocean waters and are essentially rivers of water flowing within the surrounding ocean, influence climate depending upon whether the current is warmer or colder than the surrounding waters. The Gulf Stream is an example of a warm ocean current, which originates as a current in the Pacific Ocean. The United Kingdom enjoys a much more temperate climate than other regions at a similar northerly latitude because of the warm Gulf Stream waters that arc across the Atlantic and move southward past the country (along the European coast the current is known as the Carnary Current). Ultimately, this current flows back to the Pacific Ocean, and the cyclical global route of the current is repeated.
The flow of water in the ocean currents mixes colder waters nearer to the polar regions with the warmer waters in the mid-latitudes and equatorial regions. The warmer water from equatorial regions rises to the surface, while the colder polar waters sink to the bottom. The cold water moves to more tropical latitudes, where it warms and rises upward. This continuous cycling of water drives the formation of currents.
The air above currents will reflect the water temperature, so currents also help distribute warmer and colder air. In coastal areas, this movement of air influences weather. For example, in summer, coastal areas can be 10°F (5.5°C) or more cooler than inland areas that are not influenced by the ocean or the sea.
WORDS TO KNOW
CORIOLIS FORCE: The apparent tendency of a freely moving particle to swing to one side when its motion is referred to a set of axes that is itself rotating in space, such as Earth. The acceleration is perpendicular to the direction of the speed of the article relative to Earth's surface and is directed to the right in the Northern Hemisphere. Winds are affected by rotation of Earth so that instead of a wind blowing in the direction it starts, it turns to the right of that direction in the Northern Hemisphere; left in the Southern Hemisphere.
CYCLONE: An area of low pressure where winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
EL NIÑO: A warming of the surface waters of the eastern equatorial Pacific that occurs at irregular intervals of 2 to 7 years, usually lasting 1 to 2 years. Along the west coast of South America, southerly winds promote the upwelling of cold, nutrient-rich water that sustains large fish populations, that sustain abundant sea birds, whose droppings support the fertilizer industry. Near the end of each calendar year, a warm current of nutrient-poor tropical water replaces the cold, nutrient-rich surface water. Because this condition often occurs around Christmas, it was named El Ninño (Spanish for boy child, referring to the Christ child). In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Ninño conditions last for many months, more extensive ocean warming occurs and economic results can be disastrous. El Ninño has been linked to wetter, colder winters in the United States; drier, hotter summers in South America and Europe; and drought in Africa.
GULF STREAM: A warm, swift ocean current that flows along the coast of the Eastern United States and makes Ireland, Great Britain, and the Scandinavian countries warmer than they would be otherwise.
LA NIÑA: A period of stronger-than-normal trade winds and unusually low sea-surface temperatures in the central and eastern tropical Pacific Ocean; the opposite of El Ninño.
PHOTIC ZONE: Region of the ocean through which light penetrates and the place where photosynthetic marine organisms live.
PHOTOSYNTHESIS: The process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process, oxygen and water are released. Increased levels of carbon dioxide can increase net photosynthesis in some plants. Plants create a very important reservoir for carbon dioxide.
SALINITY: The degree of salt in water. The rise in sea level due to global warming would result in increased salinity of rivers, bays, and aquifers. This would affect drinking water, agriculture, and wildlife.
SONAR: Sound Navigation and Ranging (SONAR) is a remote sensing system with important military, scientific, and commercial applications. Active SONAR transmits acoustic (i.e., sound) waves. Passive SONAR is a listening mode to detect noise generated from targets. SONAR allows the determination of important properties and attributes of the target (i.e., shape, size, speed, distance, etc.).
TRADE WINDS: Surface air from the horse latitudes (subtropical regions) that moves back toward the equator and is deflected by the Coriolis Force, causing the winds to blow from the Northeast in the Northern Hemisphere and from the Southeast in the Southern Hemisphere. These steady winds are called trade winds because they provided trade ships with an ocean route to the New World.
Similar to the atmosphere above Earth's surface, the ocean depths have also been classified into several regions (zones). The distinction between one zone and another depends on the physical conditions of the water and on the nature of the life in the particular region. Sunlight can penetrate to a maximum depth of about 650 ft (198 m). This region is called the photic zone. Some of the organisms that live in the photic zone can convert the energy of sunlight into chemical energy that they can use to live and grow. This process is known as photosynthesis. Because of the huge numbers of photo-synthesizing organisms that inhabit the photic zone, it is the region of greatest concentration and diversity of life in the ocean.
Life in the deeper ocean relies on organic material that floats down from the surface (marine snow) or on other food sources, such as other creatures. With increasing depth, the temperature of the water decreases and the pressure increases. For example, at the resting place of the sunken luxury liner Titanic, 12,400 ft (3,780 m) below the ocean surface, the temperature hovers just above the freezing point and the pressure is about 2,500 lbs per sq in (a literally bone-crushing 2,500 times greater than the air pressure experienced at sea level).
Impacts and Issues
Computer models that simulate the ocean and climate have indicated that the addition of freshwater to the North Atlantic Ocean, precisely what could happen if the ice caps in the Arctic and Greenland melt, would disrupt the northward flow of warm Gulf Stream water. Indeed, a scientific paper published in a 2005 edition of the journal Nature reported on measurements of the Gulf Stream that found a 30% decrease in the northerly flow of the warm water as compared to surveys done in 1957, 1981, and 1992. Whether this finding was temporary or is the beginning of a more permanent change was unclear as of 2007.
Other studies indicate that the computer models may be playing out in real life. Measurements of the Arctic sea-ice have shown that the polar ice cap has decreased in thickness by about half since 2001. As the ice melts, the freshwater encased in the ice (which is transported to the Arctic by Siberian and northerly North American rivers) is being added to the Arctic Ocean. Disruption of the Arctic Ocean currents may be a consequence of this increased input of freshwater.
In addition, evidence suggests that global warming could alter the cyclical global current that flows between the Pacific and Atlantic Oceans. If so, the consequence could be global weather changes. Some scientists have suggested that El Niño—an oscillation of the ocean-atmosphere system characterized by unusually warm ocean temperatures in the tropical Pacific—may be related to global-warming-induced changes in global ocean currents. As of 2007, however, this view is not shared by the majority of scientists.
Most scientists do agree that the ocean is rising at a rate of several centimeters every decade. Moreover, many climatologists agree that La Niña—an oscillation of the ocean-atmosphere system characterized by colder than normal ocean temperatures in equatorial regions of the Pacific Ocean—may be one of the triggers that has spawned the increased frequency of Atlantic hurricanes, by increasing the temperature in the Atlantic equatorial region.
Primary Source Connection
For centuries, explorers searched for a passage connecting the Atlantic Ocean and the Pacific Ocean across present-day Canada. The Northwest Passage, a sea route in the Arctic Ocean that goes through the Canadian Arctic Archipelago, was finally navigated in the twentieth century. While permanent ice pack made commercial navigation of the Northwest Passage impracticable, warming temperatures have melted seasonal ice, making navigation of the Northwest Passage possible.
MELTING ICE CLEARS NORTHWEST PASSAGE
LONDON, Sept. 15 (UPI) —Extreme melting has made the fabled Northwest Passage from Europe to Asia fully navigable.
It is the first time since record-keeping began in 1978 that the passage linking the Atlantic and Pacific Oceans has been free of ice, the European Space Agency said.
The steadily shrinking ice, being monitored by satellite, has raised concerns about an acceleration in global warming, the BBC reported Saturday.
IN CONTEXT: DEEP IMPACTS
“Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise.”
Statement of the Intergovernmental Panel on Climate Change (IPCC) as formally approved at the 10th Session of Working Group I of the IPCC in Paris, France, during February 2007.
SOURCE: Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.
Ice also is melting in the Northeast Passage through the Russian Arctic, and that route now remains only partially blocked, the space agency said.
“melting ice clears northwest passage.” upi. september 15, 2007. <http://www.upi.com/newstrack/science/2007/09/15/melting_ice_clears_northwest_passage/5058/> (accessed december 4, 2007).
Desonie, Dana. Oceans: How We Use the Seas. New York: Chelsea House Publications, 2007.
Fujita, Rodney. Heal the Ocean: Solutions for Saving Our Seas. Gabriola Island, British Columbia, Canada: New Society Publishers, 1998.
Roberts, Callum. The Unnatural History of the Sea. Washington, DC: Island Press, 2007.
Bryden, H. L., H. R. Longworth, and S. A. Cunningham. “Slowing of the Atlantic Meridional Overturning Circulation at 25° N.” Nature 438 (December 1, 2005): 655–657.
“An Ocean Warmer Than a Hot Tub.” Woods Hole Oceanographic Institute, February 17, 2006. <http://www.whoi.edu/page.do?pid=12455&tid=282&cid=10366> (accessed November 1, 2007).
Brian D. Hoyle
Oceans are large bodies of salt water that surround Earth's continents and occupy the basins between them. The four major oceans of the world are the Atlantic, Arctic, Indian, and Pacific. These interconnected oceans are further divided into smaller regions of water called seas, gulfs, and bays.
The combined oceans cover almost 71 percent of Earth's surface, or about 139,400,000 square miles (361,000,000 square kilometers). The average temperature of the world's oceans is 39°F (3.9°C). The average depth is 12,230 feet (3,730 meters).
Origin of ocean water
One scientific theory about the origin of ocean water states that as Earth formed from a cloud of gas and dust more than 4.5 billion years ago, a huge amount of lighter elements (including hydrogen and oxygen) became trapped inside the molten interior of the young planet. During the first one to two billion years after Earth's formation, these elemental gases rose through thousands of miles of molten and melting rock to erupt on the surface through volcanoes and fissures (long narrow cracks).
Within the planet and above the surface, oxygen combined with hydrogen to form water. Enormous quantities of water shrouded the globe as an incredibly dense atmosphere of water vapor. Near the top of the atmosphere, where heat could be lost to outer space, water vapor condensed to liquid and fell back into the water vapor layer below, cooling the layer. This atmospheric cooling process continued until the first raindrops fell to the young Earth's surface and flashed into steam. This was the beginning of a fantastic rainstorm that, with the passage of time, gradually filled the ocean basins.
Words to Know
Continental margin: Underwater plains connected to continents, separating them from the deep ocean floor.
Fracture zone: Faults in the ocean floor that form at nearly right angles to the ocean's major ridges.
Guyot: An extinct, submarine volcano with a flat top.
Ridge: Very long underwater mountain ranges created as a by-product of seafloor spreading.
Rift: Crevice that runs down the middle of a ridge.
Seafloor spreading: Process whereby new oceanic crust is created at ridges.
Seamount: Active or inactive submarine volcano.
Cosmic rain. In mid-1997, however, scientists offered a new theory on the how the oceans possibly filled in. The National Aeronautics and Space Administration's Polar satellite, launched in early 1996, discovered that small comets about 40 feet (12 meters) in diameter are bombarding Earth's atmosphere at a rate of about 43,000 a day. These comets break up into icy fragments at heights 600 to 15,000 miles (960 to 24,000 kilometers) above ground. Sunlight then vaporizes these fragments into huge clouds, which condense into rain as they sink lower in the atmosphere.
Scientists calculate that this cosmic rain adds one inch of water to Earth's surface every 10,000 to 20,000 years. This amount of water could have been enough to fill the oceans if these comets have been entering Earth's atmosphere since the planet's beginning 4.5 billion years ago.
Ocean basins are that part of Earth's surface that extends seaward from the continental margins (underwater plains connected to continents, separating them from the deep ocean floor). Basins range from an average water depth of about 6,500 feet (2,000 meters) down into the deepest trenches. Ocean basins cover about 70 percent of the total ocean area.
The familiar landscapes of continents are mirrored, and generally magnified, by similar features in the ocean basin. The largest underwater mountains, for example, are higher than those on the continents. Underwater plains are flatter and more extensive than those on the continents. All basins contain certain common features that include oceanic ridges, trenches, fracture zones, abyssal plains, and volcanic cones.
Oceanic ridges. Enormous mountain ranges, or oceanic ridges, cover the ocean floor. The Mid-Atlantic Ridge, for example, begins at the tip of Greenland, runs down the center of the Atlantic Ocean between the Americas on the west and Africa on the east, and ends at the southern tip of the African continent. At that point, it stretches around the eastern edge of Africa, where it becomes the Mid-Indian Ridge. That ridge continues eastward, making connections with other ridges that eventually end along the western coastline of South and Central America. Some scientists say this is a single oceanic ridge that encircles Earth, one that stretches a total of more than 40,000 miles (65,000 kilometers).
In most locations, oceanic ridges are 6,500 feet (2,000 meters) or more below the surface of the oceans. In a few places, however, they actually extend above sea level and form islands. Iceland (in the North Atlantic), the Azores (about 900 miles [about 1,500 kilometers] off the coast of Portugal), and Tristan de Cunha (in the South Atlantic midway between southern Africa and South America) are examples of such islands.
Running along the middle of an oceanic ridge, there is often a deep crevice known as a rift, or median valley. This central rift can plunge as far as 6,500 feet (2,000 meters) below the top of the ridge that surrounds it. Scientists believe ocean ridges are formed when molten rock, or magma, escapes from Earth's interior to form the seafloor, a process known as seafloor spreading. Rifts may be the specific parts of the ridges where the magma escapes.
Trenches. Trenches are long, narrow, canyonlike structures, most often found next to a continental margin. They occur much more commonly in the Pacific than in any of the other oceans. The deepest trench on Earth is the Mariana Trench, which runs from the coast of Japan south and then west toward the Philippine Islands—a distance of about 1,580 miles (2,540 kilometers). Its deepest spot is 36,198 feet (11,033 meters) below sea level. The longest trench is located along the coast of Peru and Chile. Its total length is 3,700 miles (5,950 kilometers) and it has a maximum depth of 26,420 feet (8,050 meters). Earthquakes and volcanic activity are commonly associated with trenches.
Fracture zones. Fracture zones are regions where sections of the ocean floor slide past each other, relieving tension created by seafloor spreading at the ocean ridges. Ocean crust in a fracture zone looks like it has
been sliced up by a giant knife. The faults in a zone usually cut across ocean ridges, often nearly at right angles to the ridge. A map of the North Atlantic Ocean basin, for example, shows the Mid-Atlantic Ridge traveling from north to south across the middle of the basin, with dozens of fracture zones cutting across the ridge from east to west.
Abyssal plains. Abyssal plains are relatively flat areas of the ocean basin with slopes of less than one foot of elevation difference for each thousand feet of distance. They tend to be found at depths of 13,000 to 16,000 feet (4,000 to 5,000 meters). Oceanographers believe that abyssal plains are so flat because they are covered with sediments (clay, sand, and gravel) that have been washed off the surface of the continents for hundreds of thousands of years. On the abyssal plains, these layers of sediment have now covered up any irregularities that may exist in the rock of the ocean floor beneath them.
Abyssal plains found in the Atlantic and Indian Oceans tend to be more extensive than those in the Pacific Ocean. One reason for this phenomenon is that the majority of the world's largest rivers empty into either the Atlantic or the Indian Oceans, providing both ocean basins with an endless supply of the sediments from which abyssal plains are made.
Volcanic cones. Ocean basins are alive with volcanic activity. Magma flows upward from the mantle to the ocean bottom not only through rifts, but also through numerous volcanoes and other openings in the ocean floor. Seamounts are submarine volcanoes and can be either active or extinct. Guyots are extinct volcanoes that were once above sea level but have since receded below the surface. As they receded, wave or current action eroded the top of the volcano to a flat surface.
Seamounts and guyots typically rise about 0.6 mile (1 kilometer) above the ocean floor. One of the largest known seamounts is Great Meteor Seamount in the northeastern part of the Atlantic Ocean. It extends to a height of more than 1,300 feet (4,000 meters) above the ocean floor.
[See also Coast and beach; Continental margin; Currents, ocean; Oceanography; Ocean zones; Plate tectonics; Tides; Volcano ]
Oceans and Seas
Oceans and seas
Oceans are large bodies of saltwater connected together, unevenly covering 70% of the earth, and containing about 97% of Earth's water supply as salt water. The five major oceans, in descending order of size by area , are the Pacific Ocean (64 million square miles, about 165 million square kilometers), Atlantic Ocean (33 million square miles, about 85 million square kilometers), Indian Ocean (28 million square miles, about 70 million square kilometers), Southern Ocean (almost 8 million square miles, about 20 million square kilometers), and Arctic Ocean (5,000,000 square miles, almost 13 million square kilometers).
The Pacific Ocean is the largest ocean, covering about one third of the earth's surface, which is a bigger area than all of the continents combined. The Pacific Ocean is not only the home of the highest mountain on Earth (Mauna Kea, 33,476 ft, or 10,203 m), but also has the deepest trench (Mariana trench, 36,198 ft, or 11,033 m deep). The Atlantic Ocean is the second largest, covering 20% of Earth's surface. It is also the youngest among the five oceans, and it is the ocean where the most shipping occurs. The third largest ocean is the Indian Ocean, which provides an important trade route between Africa and Asia , and is home to the most expressed monsoon system. The next in size is the Southern Ocean, which surrounds Antarctica , and was officially named in the year 2000 by the International Hydrographic Organization. Finally, the Arctic Ocean is the smallest ocean of all five, but contains the widest continental shelf .
Seas are the smaller bodies of salt water connecting the oceans, which can be partially or entirely enclosed by land. Examples of seas adjacent to the oceans include the South China Sea (the largest sea), Caribbean Sea, Mediterranean Sea, Bering Sea, Gulf of Mexico , Hudson Bay, Gulf of California, Sea of Japan, and Persian Gulf. Examples of inland seas (or lakes ) are the Caspian Sea, Sea of Galilee, or Dead Sea.
Earth's oceans and seas are unique in that there is no other planet in our Solar System that has liquid water on its surface. Life on Earth began in the oceans, and today they still are the home to some of the most spectacular wildlife in the world. Most of the oceans' wildlife is located in the upper ocean layers, which contain about two percent of the oceans' volume. The oceans also play a significant role in the earth's water cycle. Oceans are a large source of water vapor for the atmosphere, which is important in heat transportation in the atmosphere in the form of latent heat. Additionally, the oceans gather water at the end of the water cycle not only from precipitation , but also from surface runoff and return flow from rivers and as groundwater flows from land. The oceans are major reservoirs in the carbon cycle. In order to double the current atmospheric carbon dioxide , it would be necessary to release only 2% of the carbon currently stored in the oceans.
Oceans produce important and widespread effects on Earth's atmosphere, weather , and climate . Oceans and land exhibit different heating and cooling properties; solar energy penetrates deeper into water than into land, and water can circulate that absorbed heat easily into deeper layers. Because the specific heat of water (the amount of heat required to raise the temperature of one gram of water by one degree Celsius) is higher than that of land, it takes about five times more energy to warm up water by one degree Celsius than to equally heat a rock . Consequently, oceans not only warm more slowly than land, but also cool more slowly. Oceans, therefore, act as a giant heat reservoir, which heats the land during winter and cools it during summer, moderating the climate of the land located next to it.
Oceans not only moderate the climate of adjacent areas by absorbing and storing solar energy, they also distribute heat between lower and higher latitudes by a global, interconnected system of ocean currents. An example of the climatic effects of oceans on lands is the Gulf Stream , which is not only part of the heat redistributing process by carrying warm waters towards higher latitudes, but also brings mild air to the British Isles and Northwest Europe , causing a significantly milder climate than it would normally have according to its latitudes.
Interesting examples of the interaction between the oceans and the atmosphere are the El Niño and La Niña phenomena patterns. Along with the Southern Oscillation, El Niño and La Niña influence not only nearby areas in the Pacific Ocean, but effect the entire global climate system, along with the ecologies and economies of many countries worldwide, from New Zealand to the United States.
As the oceans and seas are a significant part of the atmosphere and the climate system with many interactions and feedback mechanisms, there is a recent debate about their role in anthropogenic climate change, and also about the possible consequences of climate change for the oceans. Rising sea levels could occur due to both the thermal expansion of the oceans, and from the partial melting of the polar ice because of global warming . Although there is a debate between scientists about the possibility and the intensity of this prediction, if rising sea levels happen at any level, it could be potentially devastating for many coastal cities around the world.
See also El Niño and La Niña phenomena; Hydrologic cycle; Ocean circulation and currents
Oceans are large bodies of saltwater that surround Earth's continents and occupy the basins between them. Ocean basins are the part of the seafloor that lies beyond the margins of the continents, generally in water deeper than 600 ft (183 m). Therefore, an ocean is both larger in area and deeper than a sea.
Origin of ocean water
As Earth formed in a cloud of gas and dust more than 4.5 billion years ago, a huge amount of lighter elements, including hydrogen (H) and oxygen (O), became trapped inside the planet as the gases condensed and formed molten rock. Materials of different densities separated out; in the young planet's molten interior, heavy elements sank and light elements rose.
Gases rose through thousands of miles of molten and melting rock, to erupt on the surface through volcanoes and fissures.
Within the planet and above the surface, oxygen combined with hydrogen to form water (H20). Enormous quantities of water—enough to fill oceans if it were liquid—shrouded the globe as an incredibly dense atmosphere of water vapor. Near the top of the atmosphere, where heat could be lost to outer space , water vapor condensed to liquid and fell back into the water vapor layer below, cooling the layer. This atmospheric cooling process continued until the first raindrops fell to Earth's surface and flashed into steam.
Many geologists argue this process may have happened several times, because planetoids (rocks the size of moons or asteroids) were still colliding with the early earth until about 3.9 billion years ago. Monstrous planetoid impacts would have vaporized all the water on the planet's surface. Earth has been changed so much by plate tectonics that no vestige of its original appearance remains. Unlike Earth, the faces of the moon , Mars , and Mercury bear the marks of the turbulent earliest history of the solar system . Hellas Basin on Mars and Caloris Basin on Mercury are the scars of planet-shattering impacts. One of these giant craters can be seen from anywhere on Earth: the moon's large round dark "eye," called Mare Imbrium.
Lithospheric plates and the origin of the seafloor
The oceanic plates beneath the ocean waters and above the earth's mantle are made up of igneous rock, formed from the magma , or molten rock, at mid-oceanic ridges. If you think of the plates as the skin of the earth, then the mid-oceanic ridge system is a 38,000-mile-long (64,000 km) cut in that skin. This cut bleeds lava, and never heals, because as soon as a "scab" of solidified lava develops over it, the two sides are pulled apart—allowing more molten rock to ooze forth into the ocean water. In this way, plates of oceanic crust are formed; one long thin section at a time bonds to the most recently made edges.
It may be that most of the water on Earth today has been cycling between the oceans, the land, and Earth's atmosphere for more than four billion years. However, small amounts of "new" water escape the planet's interior, from volcanoes, even today.
Weather effects of ocean waters
Water possesses the unusual property of being able to absorb a large amount of heat energy before its temperature changes. It follows that water must lose a large amount of heat energy before it cools noticeably. The net result of this phenomenon is that water, more than air or earth, tends to remain at the temperature at which it is already. Water is not given to sudden, wild extremes of temperature. Therefore water has a strong moderating effect on climates. Where there is water, there are more moderate temperatures. A "maritime" (meaning "ocean-like") climate means a moist climate that rarely experiences temperature extremes.
Nearly all coasts experience this maritime effect, but it is especially apparent along coasts where there are large-scale oceanic currents . The moderating effects of the Gulf Stream are a good example. Caribbean sunshine warms the waters of the Gulf Stream in the tropics. This warm water then flows up the east coast of the United States and finally crosses the Atlantic to the coast of Western Europe . This warm current is why England's climate is so much warmer than areas at about the same latitude in North America . However, when the Gulf Stream is diverted southward, Western Europe experiences extreme cold-the last such event, during the fourteenth through nineteenth century, is known as the "Little Ice Age."
Opening and closing of ocean basins
Oceans, like most natural phenomena, exist across a span of time called a "life cycle." For a new ocean to be born, the earth's crust beneath an ocean or a continent must be torn, or rifted, apart.
An ocean basin ceases to exist because its lithosphere gets entirely subducted (that is what usually happens) or obducted (rare and localized). An ocean basin no longer grows when its mid-oceanic ridge gets pulled down into a subduction zone, or gets crammed into a mountain range on the side of a continent. If it is not growing any larger in area, then it can not replace the area it loses to subduction and obduction. Eventually the processes of subduction and obduction put all the oceanic crust of the dying ocean basin either under bordering continents (by subduction) or on top of the bordering continents (obduction). This life cycle of an ocean basin is the same no matter how long it takes or how large the ocean gets to be.
What happens to the water in the dying ocean? Remember, this process takes tens of millions of years. The water flows gradually into other oceans as the basin shrinks, and also departs through evaporation and precipitation .
Borgese, E., ed. Ocean Frontiers. New York; Harry N. Abrams Inc., 1992.
Brower, K. Realms of the Sea. Washington DC; National Geographic Society, 1991.
Earle, Sylvia A., and Eric Lindstrom. Atlas of the Ocean: TheDeep Frontier. Washington, DC: National Geographic Press, 2001.
Fischer, G., and G. Wefer. Use of Proxies in Paleoceanography. Berlin Heidelberg: Springer-Verlag, 1999.
Hamblin, W.K., and Christiansen, E.H. Earth's Dynamic Systems. 9th ed. Upper Saddle River: Prentice Hall, 2001.
Pinet, Paul R. Invitation to Oceanography. Boston: Jones & Bartlett, 2003.
Sverdrup, Keith A., et al. An Introduction to the World'sOceans. New York: McGraw-Hill, 2002.
Thurman, Harold V., and Alan P. Trujillo. Essentials ofOceanography. 7th ed. Englewood Cliffs, NJ: Prentice Hall, 2001.
Lee, Thomas. "Eleventh AMS Conference on Satellite Meteorology and Oceanography." Bulletin of the American Meteorological Society 83, no. 11 (2002): 1645-1648.
National Oceanic & Atmospheric Administration (NOAA). <http://www.noaa.gov>
KEY TERMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
- Continental shelf
—A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.
- Maritime climate
—A moist climate that is neither too hot nor too cold, caused by the moderating effect of water on temperatures.
- Pelagic sediment
—Sediment that exists in the open ocean, away from land.
- Pillow lava
—The form that basaltic lava takes when it is erupted deep under water.
—The deep, trough-like depressions in the ocean floor that oceanic crust descends into when it is destroyed.
- Turbidity currents
—Local, rapid-moving currents that result from water heavy with suspended sediment mixing with lighter, clearer water. Causes of turbidity currents are earthquakes or when too much sediment piles up on a steep underwater slope. They can move like avalanches.
Oceans are large bodies of saltwater that surround the continents and occupy the basins between them. Ocean basins are the part of the seafloor that lies beyond the margins of the continents, generally in water deeper than 600 feet (183 meters).
As Earth formed in a cloud of gas and dust more than 4.5 billion years ago, a huge amount of lighter elements, including hydrogen (H) and oxygen (O), became trapped inside the planet as the gases condensed and formed molten rock. Materials of different densities separated out; in the young planet’s molten interior, heavy elements sank and light elements rose.
Gases rose through thousands of miles of molten and melting rock, to erupt on the surface through volcanoes and fissures. Within the planet and above the surface, oxygen combined with hydrogen to form water (H20). Enormous quantities of water—enough to fill oceans if it were liquid—shrouded the globe as an incredibly dense atmosphere of water vapor. Near the top of the atmosphere, where heat could be lost to outer space, water vapor condensed to liquid and fell back into the water vapor layer below, cooling the layer. This atmospheric cooling process continued until the first raindrops fell to Earth’s surface. Over thousands of years, and perhaps at different times during the life of Earth, the surface depressions filled to create the oceans.
It may be that most of the water on Earth today has been cycling between the oceans, the land, and Earth’s atmosphere for more than four billion years. However, small amounts of “new” water escape the planet’s interior, from volcanoes, even today.
Water absorbs a large amount of heat energy before its temperature changes. Put the other way round, water must lose a large amount of heat energy before it cools noticeably. The net result of this phenomenon is that water, more than air or earth, tends to remain at the temperature at which it is already. Water is not given to sudden, wild extremes of temperature. Therefore water has a strong moderating effect on climates. Where there is water, there are more moderate temperatures. A maritime (oceanlike) climate tends to be moister and subject to less fluctuation in temperature than regions far from the ocean such as the interior of the United States.
Nearly all coasts experience this maritime effect, but it is especially apparent along coasts where there are large ocean currents. The moderating effects of the Gulf Stream are a good example. Caribbean sunshine warms the waters of the Gulf Stream in the tropics. This warm water then flows up the east coast of the United States and Canada until crossing the Atlantic to the coast of Western Europe. This warm current is why England’s climate is so much warmer than areas at about the same latitude in North America. However, when the Gulf Stream is diverted southward, Western Europe experiences extreme cold—the last such event, during the fourteenth through nineteenth century, is known as the “Little Ice Age.”
The moderating influence of the Gulf Stream may be changing. Evidence published in 2005 suggests that the flow of the Gulf Stream may be diminishing. If this proves to be the case, the climate of regions like England could be profoundly affected.
Continental shelf —A relatively shallow, gently sloping, submarine area at the edges of continents and large islands, extending from the shoreline to the continental slope.
Maritime climate —A moist climate that is neither too hot nor too cold, caused by the moderating effect of water on temperatures.
Pelagic sediment —Sediment in the open ocean.
Pillow lava —The shape adopted by lava when it erupts deep under water.
Trenches —Deep, trough-like depressions in the ocean floor.
Dinwiddie, Robert, Louise Thomas, and Fabien Cousteau. Ocean. New York: DK Adult, 2006.
Hutchinson, Stephen and Lawrence E. Hawkins. Oceans: A Visual Guide. Tonawanda: Firefly Books, 2005.