Oceanography

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Oceanography

Introduction

Oceanography, alternately known as oceanology or marine science, is a branch of science that studies the open oceans, coastal regions, and seas. The science of oceanography covers a wide variety of topics and scientific disciplines. Some examples are the movement of water as currents, influences of environmental factors on the direction and strength of currents, marine life including its diversity and threats to that diversity, the generation and dynamics of waves, and the interaction of the ocean and the atmosphere.

Given this diversity, oceanography is a varied science and includes physicists, microbiologists, biologists, ecologists, computer scientists, mathematicians, modelers, and chemists. Research often involves teams of scientists at facilities such as Woods Hole Oceanographic Institution, a large research and educational facility in the eastern United States.

Oceanography has taken on more importance since the 1970s, with the recognition that human activities are altering the ocean. Only a few decades ago, the notion that the chemistry and biology of the global ocean could be altered was dismissed, as the ocean was assumed to be so vast and its volume so great that any influence would be accommodated. However, changes in parameters, including water temperature and pH, have been verified. Some of these changes could be affecting the atmosphere.

Historical Background and Scientific Foundations

The roots of oceanography date back to the fourth century BC, when the Greek philosopher Aristotle made observations on tides. In the eighteenth century, James Cook included observations of the South Pacific Ocean in the chronicles of his voyages. By then, it had been recognized that knowledge of ocean patterns of wind and storms was essential to a safe voyage and exploitation of ocean currents as trade routes.

In addition to his observations that provided the underpinnings for his treatise on evolution, another aspect of Charles Darwin’s voyages on the HMS Beagle in the 1830s was his work on the formation of reefs. Such information proved valuable to seafarers, since collisions with reefs have claimed countless ships and many lives throughout recorded history.

Darwin and his contemporaries were true oceanographers, who were conducting research on the oceans. In Darwin’s time, more was being learned about ocean currents and the variation in ocean depth. The steep drop-off in depth beyond continental shelves was discovered in 1849; the upwelling of colder water from the deeper ocean at the edge of continental shelves brings nutrients closer to the surface, providing food for huge numbers of fish. Knowing where continentals shelves ended was key in increasing the productivity and reliability of the global fishery.

The first oceanography textbook was published in 1855, and oceanography emerged as a scientific discipline in 1871, with the first dedicated oceanography expedition funded by the British government.

By the beginning of the twentieth century, oceanographic research was flourishing around the world. In the United States, the Scripps Institution of Oceanography was established in San Diego in 1903, followed in 1930 by Woods Hole Oceanographic Institute in Woods Hole, Massachusetts.

A few examples of dedicated oceanographic facilities around the globe are the Bedford Institute of Oceanography (Canada), Ocean University of China, Institute of Oceanography and Fisheries (Croatia), National Institute of Oceanography (India), Institute of Marine Research (Norway), P. P. Shirov Institute of Oceanography (Russia), and the National Oceanography Centre (United Kingdom).

By the time Woods Hole was formed, explorations of the ocean were becoming more sophisticated. For example, the technique of echo sounding—in which pulses of sound energy are directed down into the water and the time and pattern of the returning reflected sound waves are used to measure depth and the presence of objects on the seabed—had been used to measure the Atlantic Ocean to depths of 70,000 ft (21,300 m).

By the 1970s, the use of unmanned robots to explore the ocean was accompanied by vehicles capable of carrying researchers. A famous example occurred in 1977, when the manned submersible Alvin was piloted by two Woods Hole researchers to the hydrothermal vents located at the Galápagos Rift, a volcanically active region in the Pacific. Subsequently, vents have been discovered at many locations around the globe, and the unique forms of life in the vicinity of the vents have been well-characterized.

Alvin and the other manned vehicles are termed “human-occupied vehicles” (HOVs) to distinguish them

WORDS TO KNOW

HYDROSPHERE: The total amount of liquid, solid, and gaseous water present on Earth.

IRON FERTILIZATION: A proposal to seed the ocean with iron to stimulate the growth of microorganisms, in order to trap carbon and so lessen the release of carbon dioxide to the atmosphere.

MARIANAS TRENCH: A canyon almost 36,000 ft (11,000 m) in depth located in the floor of the Pacific Ocean; it is the deepest point in the ocean.

SALINITY: Measurement of the amount of sodium chloride in a given volume of water.

from unmanned vehicles that are tethered to a ship, which are termed “autonomous undersea vehicles” (AUVs), and vehicles that can move independently, which are called “remotely operative vehicles” (ROVs).

Echo sounding is just one of many scientific techniques that contribute to oceanography. Classical techniques of physics, chemistry, and biology have been joined by modern computational methods including modeling. Some of the data are collected from instruments that are deployed from ships. There are many designs of unmanned probes that are tethered to a ship by a cable that can be thousands of feet long. The cable also joins the AUV to the command computer aboard ship, allowing the probe to be guided remotely.

The supporting cable once hindered the depth to which a probe could be sent. The weight of a cable tens of thousands of feet in length would be more than could be supported by a ship’s winch and by the ship itself without capsizing. However, in 2006, researchers at Woods Hole completed development of fiber-optic cables that housed the electrical connection to the remote shipboard computer. The fiber-optic cable is a fraction of the weight of the old version, making it feasible to manufacture a tethering cable capable of sending unmanned probes to the Marianas Trench, which at 7 mi (11 km) is the deepest part of the ocean.

ROVs operate independently, “flying” underwater while being remotely controlled onboard ship. Samples of water can be collected during flight of these vehicles for real-time analysis or can be stored for collection upon return of the probe to the ship.

Since 1964, Woods Hole has operated the National Deep Submergence Facility—a fleet of HOVs, AUVs, and ROVs for the benefit of the entire U.S. oceanographic research community.

Still other probes have been designed that are stationary. Whether deployed as buoys on the surface of the

IN CONTEXT: FUTURE CHALLENGES FOR OCEANOGRAPHERS

According to the Intergovernmental Panel on Climate Change (IPCC), climate change already impacts the oceans and seas. The research and monitoring of Earth’s marine systems provide important challenges for current and future oceanographers.

“At continental, regional and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones.”

SOURCE: Solomon, S., et al, eds. “IPCC, 2007: Summary for Policymakers.” In: 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.

ocean or on the seabed, these probes can carry an array of instruments that permit a great deal of data to be gathered simultaneously. As well, buoys can be deployed to drift with a current, collecting data over time to assess the current conditions at different locations.

In 2005, the University of Victoria in Canada deployed a series of seabed instruments in the Pacific Ocean off Canada’s west coast. The project, dubbed VENUS (Victoria Experimental Network Under the Sea) linked the probes via fiber-optic cable to create an undersea observatory that is connected to the Internet. Chemical data including temperature, salinity, turbidity, dissolved gas concentration, current speed and direction, sounds, and both video and still images are collected and sent in real time to labs, classrooms, science centers, and homes around the world. As of 2008, another array is being readied for deployment in the region.

Molecular biology techniques have also been harnessed for oceanographic research and can be used to detect target sequences of bacteria to allow one type of bacterium to be distinguished from another. This gives researchers the ability to analyze water samples to determine the diversity of microbial life in the ocean. In one example, a 2004 cruise to the Sargasso Sea by molecular biologist Craig Venter (1946–) revealed evidence of over one million new genes and thousands of previously unknown species of bacteria. In a second example, a team of Woods Hole researchers published a 2007 study documenting the discovery of a previously unknown bacterium that is able to use gases, such as butane (C₄H₁₀) and ethane (C₂H₆), as food in the absence of oxygen (O). Such research is establishing that a huge diversity of microbial life exists in the ocean.

Impacts and Issues

Oceanography has revealed the huge diversity of life that exists in the ocean, with much still left to discover. New studies are reinforcing the view that the ocean, which covers about 70% of Earth’s surface, is under threat from human activity.

Climate change that is being driven by human activity is altering the world’s oceans by increasing the temperature and the acidity of seawater, and altering the global circulation patterns of water. Studies conducted from virtually all regions of the globe, including both poles, are showing that marine life is being stressed by the changing oceans.

There are few areas of the ocean that have not been affected, according to a 2008 study published in the journal Science. Over 80% of the ocean has been affected by human activities, including overfishing, runoff of agricultural pesticides, pharmaceuticals, and sewage from coastal regions, with more than 40% of the ocean being in need of remediation. Regions of most concern include the North Sea, South and East China Seas, Caribbean Sea, Mediterranean Sea, Red Sea, Persian Gulf, Bering Sea, the western Pacific Ocean, and the east coast of North America.

As well, studies conducted since the 1990s have shown that the ability of the ocean to trap carbon (C) is diminishing, perhaps due to the increasing acidity of the water. As a result, more carbon has been escaping to the atmosphere, where it has contributed to atmospheric warming.

Among the proposals to deal with the diminishing carbon-trapping capacity of the ocean is the seeding of regions of the ocean with iron (Fe), which would stimulate the explosive growth of microorganisms such as algae. These algal blooms could sequester carbon. This approach, which has been termed “iron fertilization,” is controversial, with some critics arguing of the potential harm that could result from the deliberate manipulation of the ocean environment.

In February 2008, the private company Planktos indefinitely shelved its plans for iron fertilization. The initiative had been intended to generate carbon credits that would have been sold to countries and industries seeking to offset their greenhouse-gas emissions without as rigorous an emissions control program as would otherwise have been necessary.