Antarctica

views updated Jun 11 2018

Antarctica

Antarcticaan overview

Geology

Climate

Plants and animals

Exploration of the continent

Scientific exploration

Current events

Resources

Of the Earths seven continentsNorth America, South America, Europe, Africa, Asia, Australia, and Antarcticathe last lies at the southern pole. It is the coldest, driest (in the sense of annual precipitation), and windiest continent. Ice covers 98% of the land, and its 5,100,000 sq mi (13,209,000 sq km) occupy nearly one-tenth of the Earths land surface, the same area as Europe and the United States combined. Despite the barrenness of the continent itself, the surrounding waters and islands teem with life all their own, and the continent plays a significant role in the climate and health of the entire planet.

Humans have never settled on Antarctica because of its brutal climate, but, since its discovery in the early 1800s, explorers and scientists have traveled across dangerous seas to study the continents winds, temperatures, rocks, wildlife, and ice; scientists treasure the unequaled chance at undisturbed research. As travel to the continent improves, tourists enjoy the opportunity to visit the last frontier on Earth; environmentalists focus on Antarctica as the only continent largely unspoiled by human hands; and, in an increasingly resource-hungry world, others look at the continent as a key source of oil and mineral resources. While some countries have tried to claim parts of the continent as their own, Antarctica is an independent continent protected by international treaty from ownership by any one country.

Antarcticaan overview

Antarctica does not have a town, a tree, or even a blade of grass on the entire continent. That does not mean that Antarctica is not vital to life on earth. Seventy percent of the worlds fresh water is frozen atop the continent. These icecaps reflect warmth from the Sun back into the atmosphere, preventing planet Earth from overheating. Huge icebergs break away from the stationary ice and flow north to mix with warm water from the equator, producing currents, clouds, and complex weather patterns. Creatures as small as microscopic phytoplankton and as large as whales live on and around the continent, including more than 40 species of birds. Thus, the continent provides habitats for vital links in the worlds food chain.

Based on findings of fossils, rocks, and other geological features similar to all of the other southern continents, geologists believe that millions of years ago Antarctica was part of a larger continent called Gondwanaland. About 200 million years ago, Gondwanaland broke apart into the separate continents of Antarctica, Africa, Australia, South America,

and India (which later collided with Asia to merge with that continent). Antarctica and these other continents drifted away from each other as a result of shifting of the plates of Earths crust, a process called continental drift, that continues today. The continent is currently centered roughly on the geographic South Pole, the point where all south latitudinal lines meet. It is the most isolated continent on earth, 600 mi (1,000 km) from the southernmost tip of South America and more than 1,550 mi (2,494 km) away from Australia.

Geology

Antarctica is considered both an islandbecause it is surrounded by waterand a continent. The land itself is divided into east and west parts by the Transantarctic Mountains. The larger side, to the east, is located mainly in the eastern longitudes. West Antarctica is actually a group of islands held together by permanent ice.

Almost all of Antarctica is under ice, in some areas by as much as 2 mi (3 km). The ice has an average thickness of about 6,600 ft (2,000 m), which is higher than many mountains in warmer countries. This grand accumulation of ice makes Antarctica the highest continent on Earth, with an average elevation of 7,500 ft (2,286 m).

While the ice is extremely high in elevation, the actual land mass of the continent is, in most places, well below sea level due to the weight of the ice. If all of this ice were to melt, global sea levels would rise by about 200 ft (65 m), flooding the worlds major coastal ports and vast areas of low-lying land. Even if only one-tenth of Antarcticas ice were to slide into the sea, sea levels would rise by 20 ft (6 m), severely damaging the worlds coastlines.

Under all that ice, the Antarctic continent is made up of mountains. The Transantarctic Mountains are the longest range on the continent, stretching 3,000 mi (4,828 km) from Ross Sea to Weddell Sea. Vinson Massif, at 16,859 ft (5,140 m), is the highest mountain peak. The few areas where mountains peek through the ice are called nunataks.

Among Antarcticas many mountain ranges lie three large, moon-like valleysthe Wright, Taylor, and Victoria Valleyswhich are the largest continuous areas of ice-free land on the continent. Known as the dry valleys, geologists estimate that it has not rained or snowed there for at least one million years. Any falling snow evaporates before it reaches the ground, because the air is so dry from the ceaseless winds and brutally cold temperatures. The dryness also means that nothing decomposes, including seal carcasses found to be more than 1,000 years old. Each valley is 25 mi (40 km) long and 3 mi (5 km) wide and provides rare glimpses of the rocks that form the continent and the Transantarctic Mountains.

Around several parts of the continent, ice forms vast floating shelves. The largest, known as the Ross Ice Shelf, is about the same size as Texas or Spain. The shelves are fed by glaciers on the continent, so the resulting shelves and icebergs are made up of frozen fresh water. Antarctica hosts the largest glacier on Earth; the Lambert Glacier on the eastern half of the continent is 25 mi (40 km) wide and more than 248 mi (400 km) long.

Gigantic icebergs are a unique feature of Antarctic waters. They are created when huge chunks of ice separate from an ice shelf, a cliff, or glacier in a process known as calving. Icebergs can be amazingly huge; an iceberg measured in 1956 was 208 mi (335 km) long by 60 mi (97 km) wide (larger than some small countries) and was estimated to contain enough fresh water to supply London, England, for 700 years. Only 10-15% of an iceberg normally appears above the waters surface, which can create great dangers to ships traveling in Antarctic waters. As these icebergs break away from the continent, new ice is added to the continent by snowfall.

Icebergs generally flow northward and, if they do not become trapped in a bay or inlet, will reach the Antarctic Convergence, the point in the ocean where cold Antarctic waters meet warmer waters. At this point, ocean currents usually sweep the icebergs from west to east until they melt. An average iceberg will last several years before melting.

Three oceans surround Antarcticathe Atlantic, Pacific, and Indian Oceans. Some oceanographers refer to the parts of these oceans around Antarctica as the Southern Ocean. While the saltwater that makes up these oceans does not usually freeze, the air is so cold adjacent to the continent that even the salt and currents cannot keep the water from freezing. In the winter months, in fact, the ice covering the ocean waters may extend over an area almost as large as the continent. This ice forms a solid ring close to the continent and loose chunks at the northern stretches. In October (early spring), as temperatures and strong winds rise, the ice over the oceans breaks up, creating huge icebergs.

Subantarctic islands are widely scattered across the ocean around Antarctica. Some, such as Tristan da Cunha and the Falkland Islands, have human populations that live there year-round. Others, including the Marion Islands, the Crozets and Kerguelen, St. Paul, Amsterdam, Macquarie, and Campbell Islands, have small scientific bases. Others are populated only by penguins, seals, and birds.

Strong winds blow constantly against the western shores of most of the northernmost islands, creating some of the stormiest seas in the world. Always wet in the summer, they are blanketed grasses in the summer and by snow in the winter. Further south, in the colder subantarctic, the islands are covered with snow for much of the year and may have patches of mosses, lichens, and grasses in the summer. Seals and enormous populations of sea birds, including penguins and petrels, come to the islands beaches and cliffs to breed in the summer.

The Falkland Islands, which are British Crown colonies, are the largest group of subantarctic islands, lying 300 mi (480 km) east of South America. Two main islands, East and West, have about 400 smaller islets surrounding them. The islands cover 6,200 sq mi (16,000 sq km). Much of the ground is covered with wet, springy turf, overlying thick beds of peat. Primary industries are farming and ranching of cattle and sheep.

Climate

Antarctica is the coldest and windiest place on Earth. The wind can gust up to 200 mph (322 km/h), or twice as hard as the average hurricane. Surprisingly, little snow actually falls in Antarctica; because the air is so cold, the snow that does fall turns immediately to ice.

Because of the way Earth tilts on its axis as it rotates around the Sun, both polar regions experience long winter nights and long summer days. At the South Pole itself, the sun shines around the clock during the six months of summer and virtually disappears during the cold winter months. The tilt also affects the angle at which the Suns radiation hits the Earth. When it is directly overhead at the equator, it strikes the polar regions at more indirect angles. As a result, the Suns radiation generates much less heat, even though the polar regions receive as much annual daylight as the rest of the world.

Even without the wind chill, the continents temperatures can be almost incomprehensible to anyone who has not visited there. In winter, temperatures may fall to 100°F (73°C). The worlds record for lowest temperature was recorded on Antarctica in 1960, when it fell to 126.9°F (88.3°C).

The coastal regions are generally warmer than the interior of the continent. The Antarctic Peninsula may get as warm as 50°F (10°C), although average coastal temperatures are generally around 32°F (0°C). During the dark winter months, temperatures drop drastically, however, and the warmest temperatures range from 4 to 22°F (20 to 30°C). In the colder interior, winter temperatures range from 40 to 94°F (40 to 70°C).

The strong winds that constantly travel over the continent as cold air races over the high ice caps and then flows down to the coastal regions are called katabatic winds. Winds associated with Antarctic blizzards commonly gust to more than 120 mi (193 km) per hour and are among the strongest winds on Earth. Even at its calmest, the continents winds can average 50-90 mi (80-145 km) per hour. Cyclones occur continually from west to east around the continent. Warm, moist ocean air strikes the cold, dry polar air and swirls its way toward the coast, usually losing its force well before it reaches land. These cyclones play a vital role in the exchange of heat and moisture between the tropical and the cold polar air.

While the Antarctic sky can be clear, a white-out blizzard may be occurring at ground level because the strong winds whip up the fallen snow. The wind redesigns the snow into irregularly shaped ridges, called sastrugi, which are difficult to traverse. Blizzards are common on the continent and have hindered several exploration teams from completing their missions.

Surprisingly, with all its ice and snow, Antarctica is the driest continent on Earth, based on annual precipitation amounts. The constantly cold temperatures have allowed each years annual snowfall to build up over the centuries without melting. Along the polar ice cap, annual snowfall is only 12 in (2.55 cm). More precipitation falls along the coast and in the coastal mountains, where it may snow 1020 in (25-51 cm) per year.

Plants and animals

While the Arctic region teems with life, the Antarctic continent itself is nearly barren due to the persistently cold and dry climate. Plants that grow in the region reflect this climate and geology. The pearl-wort (Colobanthus quitensis ) and grass (Deschampsia antarctica ) are the only two flowering plants on the continent. Both grow in a small area on or near the warmest part of the continent, the Antarctic Peninsula. Larger plants include mosses and lichens (a combination of algae and fungi) found along the coast and on the peninsula. Green, nonflowering liverworts live on the western side of the peninsula. Brightly colored snow algae often form on top of the snow and ice, coloring it red, yellow, or green.

A few hardy organisms live on rocks in the dry valleys; these are primarily lichens that hide inside the porous orange sandstone. These lichens, called cryptoendoliths or hidden in rock, use up more than 99.9% of their photosynthetic productivity simply to stay alive. In contrast, a typical plant uses 90% for survival. Ironically, the lichens found in these valleys are among the longest-living organisms on earth. The dry valleys also host pockets of algae, fungi, and bacteria between frozen rock crystals; these give scientists clues about how life might survive on a frozen planet like Mars.

Few creatures can survive Antarcticas brutal climate. Except for a few mites and midges, native animals do not exist on Antarcticas land. Life in the sea and along the coast of Antarctica and its islands, however, is often abundant. A wide variety of animals make the surrounding waters their home, from zoo-plankton to large birds and mammals. A few fish have developed their own form of antifreeze over the centuries to prevent ice crystals from forming in their bodies, while others have evolved into cold-blooded species to survive the cold.

The base of Antarcticas marine food chain is phytoplankton, which feed on the rich nutrients found in coastal waters. The zooplankton feed on the phytoplankton, which are in turn consumed by the native fish, birds, and mammals. Antarctic krill (tiny shrimp-like creatures about 1.5 in [4 cm] long) are the most abundant zooplankton and are essential to almost every other life form in the region. They swim in large pools and look like red patches on the ocean. At night, their crusts shimmer like billions of fireflies beneath the sea. Because of their abundance, krill have also been explored as a potential food source for humans.

Among the whales that make the southern oceans their home for at least part of the year are the blue, fin, sei, minke, humpback, and southern right whales. Known as baleen whales, this whale group has a bristly substance called baleen located in plates in their mouths that filter food such as krill from the water. In fact, the blue whale is the largest animal ever known to have lived on Earth. The blue whale eats 3 tons (6,000 pounds or 2.7 metric tons) of krill each day and has been measured to weigh up to 180 tons (163,000 kg) and span 124 ft (38 m) in length. After it was discovered in the 1800s, the blue whale was heavily hunted for its blubber, which was melted into oil for fuel. While scientists believe more than 200,000 existed before whaling, there are as few as 1,000 blue whales today. All baleen and toothed whales are now protected from hunting by international agreements.

Two toothed whales also swim in Antarctic waters, the sperm whale and the orca, or killer, whale. The sperm whale is the larger of the two, measuring as long as 60 ft (18 m) and weighing as much as 70 tons (63,500 kg). It can dive down to 3,300 ft (1,006 m).

More than half the seals in the world live in the Antarctictheir blubber and dense fur insulate them from the cold. Five species of true or earless seals live in the region: the Weddell, Ross, leopard, crabeater, and elephant. The Weddell seal is the only one that lives in the Antarctic year-round, on or under the ice attached to the continent in the winter. Using their saw-like teeth to cut holes in the ice for oxygen, they can dive down to 2,000 ft (610 m) to catch fish and squid. The seals use a complex system to control their bodies oxygen levels, which allows them to dive to such depths and stay underwater for as long as an hour.

The Ross seal, named for English explorer James Ross, is quick underwater and catches fish easily with its sharp teeth. It lives on the thickest patches of ice and is the smallest and least plentiful of the species. Leopard seals are long and sleek and are fierce predators, living on the northern edges of pack ice and in the sea or near penguin rookeries, where they eat small penguins and their eggs, as well as other seals. Crabeater seals are the most plentiful species of seal on Earth, with an estimated 40 million or more in the Antarctic region alone. Elephant seals are the largest species of seal; they live on the subantarctic islands and eat squid and fish. Unlike most seals, the males are much larger than the females. All five seal species are now protected under international law from hunting, which almost wiped out the Ross and elephant seals in the 1800s. One other type of seal, the southern fur seal, is also plentiful on Antarctica. It has visible ears and longer flippers than the true seals, which makes it much more agile on land as well as in the water.

Several seabirds make the Antarctic their home, including 24 species of petrels, small seabirds that dart over the water and nest in rocks along the shore. Examples include the albatross (a gliding bird with narrow, long wings that may live up to 40 years), the southern giant fulmar, dove prion, and snow petrel. Shore birds that feed in the shallow waters near the shoreline include the blue-eyed cormorant, the Dominican gull, and the brown skua, which eats the eggs and young of other birds. The Arctic tern is the worlds best at longdistance flying, because it raises its young in the Arctic but spends the rest of the year in the Antarctic, a distance of over 10,000 mi (16,090 km). Land birds include the wattled sheathbill, South Georgia pintail, and South Georgia pipit.

Of all the animals, penguins are the primary inhabitants of Antarctica. Believed to have evolved 4050 million years ago, they have oily feathers that provide a waterproof coat and a thick layer of fat for insulation. Penguins bones are solid, not like the bones of most birds, which are hollow and allow them to fly. While solid bones prevent penguins from flying, they add weight and make it easier for penguins to dive into the water for food. Because predators cannot live in the brutally cold climate, penguins do not need to fly; thus, their wings have evolved over the centuries to resemble flippers or paddles.

Seven of the 18 known species of penguins live on the Antarctic: the Adelie and emperor (both considered true Antarctic penguins because they live on the continent), the chinstrap, gentoo, macaroni, rockhopper, and king penguins. The Adelie is the most plentiful species of penguin and can be found over the widest area of the continent. These penguins spend their winters on the pack ice away from the continent then return to land in October to nest in large rookeries or colonies along the rocky coasts. The emperor penguin is the largest species of penguin; it is the only Antarctic bird never to set foot on land, and it breeds on sea ice attached to the mainland. Emperor penguins, the most popular type of penguin for zoos, are 4 ft (1.2 m) tall and can weigh up to 80 lb (30 kg). They are the hardiest of all the animals that inhabit the Antarctic, staying throughout the year while other birds head north to escape the brutal winter. They breed on the ice surface during the winter months because their immense size requires a longer incubation period. This schedule also ensures that the chicks will hatch in July or early spring in the Antarctic, providing the most days for the chicks to put on weight before the next winters cold arrives.

The female lays one egg on the ice, then walks up to 50 mi (80 km) to the open sea for food. When she returns, filled with food for the chick, the malewho has been incubating the egg atop the ice during the coldest winter monthsmakes the same trek out to sea to restore its body weight, which may drop by 50% during this period. The parents take turns traveling for food after the chick has hatched.

Because the emperor penguin is one of the few species that lives on Antarctica year-round, researchers believe it could serve as an indicator to measure the health of the Antarctic ecosystem. The penguins travel long distances and hunt at various levels in the ocean, covering wide portions of the continent. At the same time, they are easily tracked because the emperor penguins return to their chicks and mates in predictable ways. Such indicators of the continents health become more important as more humans travel to and explore Antarctica and as other global conditions are found to affect the southernmost part of the world.

Exploration of the continent

Greek philosopher Aristotle hypothesized more than 2,000 years ago that Earth was round and that the southern hemisphere must have a landmass large enough to balance the lands in the northern hemisphere. He called the probable but undiscovered land mass Antarktikos, meaning the opposite of the Arctic.

The Greek geographer and astronomer Ptolemy called Antarctica Terra Australis Incognita or unknown southern land in the second century AD. He claimed the land was fertile and populated but separated from the rest of the world by a region of torrid heat and fire around the equator. This concept was believed for several centuries, and the continent remained a mystery until James Cook crossed the Antarctic Circle and circumnavigated the continent in 1773. While he stated that the land was uninhabitable because of the ice fields surrounding the continent, he noted that the Antarctic Ocean was rich in whales and seals. For the next 50 years, hunters exploited this region for the fur and oil trade.

As hunting ships began traveling farther and farther south in the early 1800s to find fur seals, it was inevitable that the continent would be encountered and explored. Three countries claim first discovery rights to Antarctic land: Russia, due to explorer Fabian von Bellinghausen, on January 27, 1820; England as a result of English explorer Edward Bransfield, on January 30, 1820; and the United States by way of American sealer Nathaniel Palmer, on November 18, 1820. In actuality, American sealer John Davis was the first person to actually step onto the continent, on February 7, 1821.

James Weddell was a sealer who traveled to the continent on January 13, 1823. He found several previously unknown seal species, one of which later became known as the Weddell seal. He than took his two shipsthe Jane and the Beaufoy farther south than any explorer had previously traveled. He reached 74° south latitude on February 20, 1823, and the vast sea he had entered became known as the Weddell Sea.

In 1895, the first landing on the continent was accomplished by the Norwegian whaling ship Antarctic. The British were the first to spend a winter on Antarctica, in 1899. By 1911, a race had begun to see who would reach the South Pole first: the South Pole is an imaginary geographical center point at the bottom of Earth. Again, it was a Norwegian, Roald Amundsen, who was the first to succeed, reaching the South Pole on December 14, 1911. Robert Scott of England and his four men arrived a month later. While the first team made it home safely, the Scott team ran out of food and froze to death on their way home.

Airplanes first landed on Antarctica when Australian Hubert Wilkins flew 1,300 mi (2,092 km) over the Antarctic Peninsula in the 1920s, viewing terrain never before seen by another human. American Richard Byrd, the first person to fly over the North Pole in 1926, took his first Antarctic flight in 1929 and discovered a new mountain range he named Rockefeller. Thereafter, the continent was mapped and explored primarily from the air. Byrd continued his explorations to Antarctica over the next three decades and revolutionized the use of modern vehicles and communications equipment for polar exploration.

Scientific exploration

While various countries were busy claiming rights to Antarctica, scientists were cooperating effectively on research as early as 1875. Twelve nations participated in the first International Polar Year in 1882 and 1883. While most of the research was done in the Arctic, one German station was located in the Antarctic region. A second International Polar Year occurred in 1932-33, followed by the International Geophysical Year (IGY) from July 1, 1957 to December 31, 1958. This time, all twelve nations conducted research in Antarctica and set up base camps in various locations, some of which are still used today. Topics of research included the pull of gravity, glaciology, meteorites, cosmic rays, the southern lights, dynamics of the sun, the passage of comets near Earth, and changes in the atmosphere. Several organizations have been formed and agreements have been signed since these cooperative research projects to ensure that political conflicts do not arise concerning research and use of Antarctica.

KEY TERMS

Antarctic Circle The line of latitude at 66 degrees 32 minutes South, where there are 24 hours of daylight in midsummer and 24 hours of darkness in midwinter.

Antarctic convergence A 25-mi (40-km) region where cold Antarctic surface water meets warmer, subantarctic water and sinks below it.

Antarctic Ocean The seas surrounding the Antarctic continent, where the Atlantic, Pacific, and Indian Oceans converge.

Blubber Whale or seal fat used to create fuel.

Calving The process in which huge chunks of ice or icebergs break off from ice shelves and sheets or glaciers to form icebergs.

Dry valleys Areas on the continent where no rain is known to have fallen for more than two million years, and the extremely dry katabatic winds cause any snow blown into the valleys to evaporate before hitting the ground. The Taylor, Victoria, and Wright valleys are the largest continuous areas of ice-free land on the continent.

Glacier A river of ice that moves down a valley to the sea, where it breaks into icebergs.

Iceberg A large piece of floating ice that has broken off a glacier, ice sheet, or ice shelf.

Katabatic winds Fierce, dry winds that flow down along the steep slopes of the interior mountains of Antarctica, and along ice caps and glaciers on the subantarctic islands.

Krill Tiny sea animals or zooplankton that are the main food for most larger species in the Antarctic region.

Nunataks Mountain peaks that are visible above the ice and snow cover.

Pack ice Ice from seawater, which forms a belt approximately 3001,800 mi (4832,897 km) wide around the continent in winter.

South magnetic pole The point to which a compass is attracted and which is some distance from the geographic South Pole. It varies from year to year as Earths magnetic field changes.

South pole The geographically southernmost place on Earth.

Southern lights Also known as the aurora australis, they are streamers of different colors in the sky, especially at night, and are thought to be caused by electrical disturbances and cosmic particles in the upper atmosphere that are attracted by the South Magnetic Pole.

Subantarctica The region just north of Antarctica and the Antarctic Circle, but south of Australia, South America, and Africa.

Current events

A wide variety of research is continuing on Antarctica, primarily during the relatively warmer summer months from October to February, when temperatures may reach a balmy 3050°F (110°C). The cold temperatures and high altitude of Antarctica allow astronomers to put their telescopes above the lower atmosphere, which lessens blurring. During the summer months, they can study the Sun around the clock, because it shines 24 hours a day. Antarctica is also the best place to study interactions between solar wind and Earths magnetic field, temperature circulation in the oceans, unique animal life, ozone depletion, ice-zone ecosystems, and glacial history. Buried deep in Antarcticas ice lie clues to ancient climates, which may provide answers to whether Earth is due for global warming or the next ice age.

Scientists consider Antarctica to be a planetary bellwether, an early indicator of negative changes in the entire planets health. For example, researchers have determined that atmospheric ozone above Antarctica has mostly disappeared for part of the year annually since at least the late 1970s. The ozone layer over the continent serves as a protective layer of gas in the upper atmosphere that screens out the ultraviolet light from the Sun that is harmful to all life on Earth. This phenomenon is known as the Antarctic ozone hole.

Total atmospheric ozone has declined significantly over the last half century, but only the Antarctic has experienced a loss sufficiently great to constitute a hole in the ozone layer. The ozone hole was first observed in 1980 during the spring and summer months, from September through November. Each year, greater destruction of the layer has been observed during these months. The hole was measured to be about the size of the continental United States in 1994, and it lasts for longer intervals each year. The ozone holes of 2003-2005 were some of the widest and most depleted yet recorded. Scientists have identified various chemicals created and used by humans, such as chlorofluorocarbons (CFCs), as the cause of this destruction, and bans on uses of these chemicals are in effect in some countries. The ozone hole does not contribute to global climate change (discussed below), but ozone depletion does threaten life on Earth in a fundamental way.

Data from studies of the Antarctic ice cap have helped confirm that Earths climate is warming due to the burning of fossil fuels and other human activities. Global climate change is based on the atmospheric process known as the greenhouse effect, in which pollution prevents the heat energy of Earth from escaping into the outer atmosphere. Global warming is causing some of the Greenland and Antarctic ice caps to melt, an effect that will probably flood many coastal cities and coastal areas in the coming centuries. Data from Antarctic ice cores released in 2005 showed that the Earths greenhouse gas levels have risen since the beginning of the fossil-fuel era to levels higher than any in the last 650,000 years.

Most recently, a growing body of evidence is showing that the continents ice has fluctuated dramatically in the past few million years, vanishing completely from the continent once and from its western third at least several times. These collapses in the ice structure might be triggered by climatic change, such as global warming, or by far less predictable factors, such as volcanic eruptions under the ice. While the east Antarctic ice sheet has remained relatively stable because it lies on a single tectonic plate, the western ice sheet is a jumble of small plates whose erratic behavior has been charted through satellite data. The west Antarctic is also dominated by two seas, the Ross and Weddell, whose landward regions are covered by thick, floating shelves of ice. Some researchers speculate that if warmer, rising oceans were to melt this ice, the entire western sheet might disintegrate quickly, pushing global sea levels up by 1520 ft (56 m).

See also Gaia hypothesis; Greenhouse effect; Ozone layer depletion; Plate tectonics.

Resources

BOOKS

Fox, William. Terra Antarctica: Looking Into the Emptiest Continent. San Antonio, TX: Trinity University Press, 2005.

Hancock P. L., and B. J. Skinner, editors. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Hurley, Frank. South with Endurance: Shackletons Antarctic Expedition, 1914-1917. New York: Simon & Schuster, 2001.

McGonigal, David, and Lynn Woodworth. Antarctica: The Blue Continent. Richmond Hill, Ont.: Firefly Books, 2003.

PERIODICALS

Thomas, R., et al. Accelerated Sea-Level Rise from West Antarctica. Science. 306 (2004): 255-258.

Velicogna, Isabella, and John Wahr. Measurements of Time-Variable Gravity Show Mass Loss in Antarctica. Science. 311 (2006): 1754-1756.

Sally Cole-Misch

Antarctica

views updated Jun 27 2018

Antarctica

Of the seven continents on planet Earth—North America, South America , Europe , Africa , Asia , Australia , and Antarctica—the last lies at the southernmost tip of the world. It is the coldest, driest, and windiest continent . Ice covers 98% of the land, and its 5,100,000 sq mi (13,209,000 sq km) occupy nearly one-tenth of the Earth's land surface, or the same area as Europe and the United States combined. Despite its barren appearance, Antarctica and its surrounding waters and islands teem with life all their own, and the continent plays a significant role in the climate and health of the entire planet.

Humans have never settled on Antarctica because of its brutal climate, but, since its discovery in the early 1800s, explorers and scientists have traveled across dangerous seas to study the continent's winds, temperatures, rocks , wildlife , and ice. Scientists treasure the unequaled chance at undisturbed research; as travel to the continent improves, tourists enjoy the opportunity to visit the last "frontier" on the earth ; environmentalists focus on Antarctica as the only continent largely unspoiled by human hands; and, in an increasingly resource-hungry world, others look at the continent as a key source of oil and mineral resources. While some countries have tried to claim parts of the continent as their own, Antarctica is an independent continent protected by international treaty from ownership by any one country.


Antarctica—an overview

Antarctica does not have a town, a tree , or even a blade of grass on the entire continent. That does not mean that Antarctica is not vital to life on earth. Seventy percent of the world's fresh water is frozen atop the continent. These icecaps reflect warmth from the Sun back into the atmosphere, preventing planet Earth from overheating. Huge icebergs break away from the stationary ice and flow north to mix with warm water from the equator, producing currents , clouds , and complex weather patterns. Creatures as small as microscopic phytoplankton and as large as whales live on and around the continent, including more than 40 species of birds . Thus, the continent provides habitats for vital links in the world's food chain.

Geologists believe that, millions of years ago, Antarctica was part of a larger continent called Gondwanaland, based on findings of similar fossils, rocks, and other geological features on all of the other southern continents. About 200 million years ago, Gondwanaland broke apart into the separate continents of Antarctica, Africa, Australia, South America, and India (which later collided with Asia to merge with that continent). Antarctica and these other continents drifted away from each other as a result of shifting of the plates of the earth's crust, a process called continental drift that continues today. The continent is currently centered roughly on the geographic South Pole, the point where all south latitudinal lines meet. It is the most isolated continent on earth, 600 mi (1,000 km) from the southernmost tip of South America and more than 1,550 mi (2,494 km) away from Australia.


Geology

Antarctica is considered both an island—because it is surrounded by water—and a continent. The land itself is divided into east and west parts by the Transantarctic Mountains. The larger side, to the east, is located mainly in the eastern longitudes. West Antarctica is actually a group of islands held together by permanent ice.

Almost all of Antarctica is under ice, in some areas by as much as 2 mi (3 km). The ice has an average thickness of about 6,600 ft (2,000 m), which is higher than many mountains in warmer countries. This grand accumulation of ice makes Antarctica the highest continent on Earth, with an average elevation of 7,500 ft (2,286 m).

While the ice is extremely high in elevation, the actual land mass of the continent is, in most places, well below sea level due to the weight of the ice. If all of this ice were to melt, global sea levels would rise by about 200 ft (65 m), flooding the world's major coastal ports and vast areas of low-lying land. Even if only one-tenth of Antarctica's ice were to slide into the sea, sea levels would rise by 20 ft (6 m), severely damaging the world's coastlines.

Under all that ice, the Antarctic continent is made up of mountains. The Transantarctic Mountains are the longest range on the continent, stretching 3,000 mi (4,828 km) from Ross Sea to Weddell Sea. Vinson Massif, at 16,859 ft (5,140 m), is the highest mountain peak. The few areas where mountains peek through the ice are called nunataks.

Among Antarctica's many mountain ranges lie three large, moon-like valleys—the Wright, Taylor, and Victoria Valleys—which are the largest continuous areas of ice-free land on the continent. Known as the "dry valleys," geologists estimate that it has not rained or snowed there for at least one million years. Any falling snow evaporates before it reaches the ground, because the air is so dry from the ceaseless winds and brutally cold temperatures. The dryness also means that nothing decomposes, including seal carcasses found to be more than 1,000 years old. Each valley is 25 mi (40 km) long and 3 mi (5 km) wide and provides rare glimpses of the rocks that form the continent and the Transantarctic Mountains.




Around several parts of the continent, ice forms vast floating shelves. The largest, known as the Ross Ice Shelf, is about the same size as Texas or Spain. The shelves are fed by glaciers on the continent, so the resulting shelves and icebergs are made up of frozen fresh water. Antarctica hosts the largest glacier on Earth; the Lambert Glacier on the eastern half of the continent is 25 mi (40 km) wide and more than 248 mi (400 km) long.

Gigantic icebergs are a unique feature of Antarctic waters. They are created when huge chunks of ice separate from an ice shelf, a cliff, or glacier in a process known as calving. Icebergs can be amazingly huge; an iceberg measured in 1956 was 208 mi (335 km) long by 60 mi (97 km) wide (larger than some small countries) and was estimated to contain enough fresh water to supply London, England, for 700 years. Only 10-15% of an iceberg normally appears above the water's surface, which can create great dangers to ships traveling in Antarctic waters. As these icebergs break away from the continent, new ice is added to the continent by snowfall.

Icebergs generally flow northward and, if they do not become trapped in a bay or inlet, will reach the Antarctic Convergence, the point in the ocean where cold Antarctic waters meet warmer waters. At this point, ocean currents usually sweep the icebergs from west to east until they melt. An average iceberg will last several years before melting.

Three oceans surround Antarctica—the Atlantic, Pacific, and Indian Oceans. Some oceanographers refer to the parts of these oceans around Antartica as the Southern Ocean. While the saltwater that makes up these oceans does not usually freeze, the air is so cold adjacent to the continent that even the salt and currents cannot keep the water from freezing. In the winter months, in fact, the ice covering the ocean waters may extend over an area almost as large as the continent. This ice forms a solid ring close to the continent and loose chunks at the northern stretches. In October (early spring) as temperatures and strong winds rise, the ice over the oceans breaks up, creating huge icebergs.

Subantarctic islands are widely scattered across the ocean around Antarctica. Some, such as Tristan da Cunha and the Falkland Islands, have human populations that live there year-round. Others, including the Marion Islands, the Crozets and Kerguelen, St. Paul, Amsterdam, Macquarie and Campbell Islands, have small scientific bases. Others are populated only by penguins , seals , and birds.

Strong winds blow constantly against the western shores of most of the northernmost islands, creating some of the stormiest seas in the world. Always wet in the summer, they are blanketed by snow in the winter and grasses in the summer. Further south in the colder subantarctic, the islands are covered with snow for much of the year and may have patches of mosses, lichens , and grasses in the summer. Seals and enormous populations of sea birds, including penguins and petrels, come to the islands' beaches and cliffs to breed in the summer.

The Falkland Islands, which are British Crown colonies, are the largest group of subantarctic islands, lying 300 mi (480 km) east of South America. Two main islands, East and West, have about 400 smaller islets surrounding them. The islands cover 6,200 sq mi (16,000 sq km). Much of the ground is covered with wet, springy turf, overlying thick beds of peat. Primary industries are farming and ranching of cattle and sheep .


Climate

Antarctica is the coldest and windiest place on Earth. The wind can gust up to 200 MPH (322 km/h), or twice as hard as the average hurricane. Surprisingly, little snow actually falls in Antarctica; because the air is so cold, the snow that does fall turns immediately to ice.

Because of the way the Earth tilts on its axis as it rotates around the Sun, both polar regions experience long winter nights and long summer days. At the South Pole itself, the sun shines around the clock during the six months of summer and virtually disappears during the cold winter months. The tilt also affects the angle at which the Sun's radiation hits the earth. When it is directly overhead at the equator, it strikes the polar regions at more indirect angles. As a result, the Sun's radiation generates much less heat , even though the polar regions receive as much annual daylight as the rest of the world.

Even without the wind chill , the continent's temperatures can be almost incomprehensible to anyone who has not visited there. In winter, temperatures may fall to -100°F ( -73°C). The world's record for lowest temperature was recorded on Antarctica in 1960, when it fell to -126.9°F ( -88.3°C).

The coastal regions are generally warmer than the interior of the continent. The Antarctic Peninsula may get as warm as 50°F (10°C), although average coastal temperatures are generally around 32°F (0°C). During the dark winter months, temperatures drop drastically, however, and the warmest temperatures range from -4 to -22°F ( -20 to -30°C). In the colder interior, winter temperatures range from -40 to -94°F ( -40 to -70°C).

The strong winds that constantly travel over the continent as cold air races over the high ice caps and then flows down to the coastal regions, are called katabatic winds. Winds associated with Antarctica blizzards commonly gust to more than 120 mi (193 km) per hour and are among the strongest winds on Earth. Even at its calmest, the continent's winds can average 50-90 mi (80-145 km) per hour. Cyclones occur continually from west to east around the continent. Warm, moist ocean air strikes the cold, dry polar air and swirls its way toward the coast, usually losing its force well before it reaches land. These cyclones play a vital role in the exchange of heat and moisture between the tropical and the cold polar air.

While the Antarctic sky can be clear, a white-out blizzard may be occurring at ground level because the strong winds whip up the fallen snow. The wind redesigns the snow into irregularly shaped ridges, called sastrugi, which are difficult to traverse. Blizzards are common on the continent and have hindered several exploration teams from completing their missions.

Surprisingly, with all its ice and snow, Antarctica is the driest continent on Earth based on annual precipitation amounts. The constantly cold temperatures have allowed each year's annual snowfall to build up over the centuries without melting. Along the polar ice cap, annual snowfall is only 1-2 in (2.5-5 cm). More precipitation falls along the coast and in the coastal mountains, where it may snow 10-20 in (25-51 cm) per year.

Plants and animals

While the Arctic region teems with life, the Antarctic continent is nearly barren due to the persistently cold and dry climate. Plants that grow in the region reflect this climate and geology . The pearlwort (Colobanthus quitensis) and grass (Deschampsia antarctica) are the only two flowering plants on the continent. Both grow in a small area on or near the warmest part of the continent, the Antarctic Peninsula. Larger plants include mosses and lichens (a combination of algae and fungi ) found along the coast and on the peninsula. Green, nonflowering liverworts live on the western side of the peninsula. Brightly colored snow algae often form on top of the snow and ice, coloring it red, yellow, or green.

A few hardy organisms live on rocks in the dry valleys; these are primarily lichens that hide inside the porous orange sandstone. These lichens, called cryptoendoliths or "hidden in rock," use up more than 99.9% of their photosynthetic productivity simply to stay alive. In contrast, a typical plant uses 90% for survival. Ironically, the lichens found in these valleys are among the longest-living organisms on earth. The dry valleys also host pockets of algae, fungi, and bacteria between frozen rock crystals; these give scientists clues about how life might survive on a frozen planet like Mars .

Few creatures can survive Antarctica's brutal climate. Except for a few mites and midges, native animals do not exist on Antarctica's land. Life in the sea and along the coast of Antarctica and its islands, however, is often abundant. A wide variety of animals make the surrounding waters their home, from zooplankton to large birds and mammals . A few fish have developed their own form of antifreeze over the centuries to prevent ice crystals from forming in their bodies, while others have evolved into cold-blooded species to survive the cold.

The base of Antarctica's marine food chain is phytoplankton, which feed on the rich nutrients found in coastal waters. The zooplankton feed on the phytoplankton, which are in turn consumed by the native fish, birds, and mammals. Antarctic krill (tiny shrimplike creatures about 1.5 in [4 cm] long) are the most abundant zooplankton and are essential to almost every other life form in the region. They swim in large pools and look like red patches on the ocean. At night, their crusts shimmer like billions of fireflies beneath the sea. Because of their abundance, krill have also been explored as a potential food source for humans.

Among the whales that make the southern oceans their home for at least part of the year are the blue, fin, sei, minke, humpback, and southern right whales. Known as baleen whales, this whale group has a bristly substance called baleen located in plates in their mouths that filter food such as krill from the water. In fact, the blue whale is the largest animal ever known to have lived on Earth. The blue whale eats 3 tons (6,000 pounds or 2.7 metric tons) of krill each day and has been measured to weigh up to 180 tons (163,000 kg) and span 124 ft (38 m) in length. After it was discovered in the 1800s, the blue whale was heavily hunted for its blubber, which was melted into oil for fuel. While scientists believe more than 200,000 existed before whaling, there are as few as 1,000 blue whales today. All baleen and toothed whales are now protected from hunting by international agreements.

Two toothed whales also swim in Antarctic waters, the sperm and the orca or killer whale. The sperm whale is the larger of the two, measuring as long as 60 ft (18 m) and weighing as much as 70 tons (63,500 kg). It can dive down to 3,300 ft (1,006 m).

More than half the seals in the world live in the Antarctic—their blubber and dense fur insulate them from the cold. Five species of true or earless seals live in the region, the Weddell, Ross, leopard, crabeater, and elephant. The Weddell seal is the only one that lives in the Antarctic year-round, on or under the ice attached to the continent in the winter. Using their sawlike teeth to cut holes in the ice for oxygen , they can dive down to 2,000 ft (610 m) to catch fish and squid . The seals use a complex system to control their bodies' oxygen levels, which allows them to dive to such depths and stay underwater for as long as an hour.

The Ross seal, named for English explorer James Ross, is quick underwater and catches fish easily with its sharp teeth. It lives on the thickest patches of ice and is the smallest and least plentiful of the species. Leopard seals are long and sleek and are fierce predators, living on the northern edges of pack ice and in the sea or near penguin rookeries, where they eat small penguins and their eggs as well as other seals. Crabeater seals are the most plentiful species of seal on Earth, with an estimated 40 million or more in the Antarctic region alone. Elephant seals are the largest species of seal, live on the sub-antarctic islands, and eat squid and fish. Unlike most seals, the males are much larger than the females. All five seal species are now protected under international law from hunting, which almost wiped out the Ross and elephant seals in the 1800s. One other type of seal, the southern fur seal, is also plentiful on Antarctica. It has visible ears and longer flippers than the true seals, which makes it much more agile on land as well as in the water.

Several seabirds make the Antarctic their home, including 24 species of petrels, small seabirds that dart over the water and nest in rocks along the shore. Examples include the albatross (a gliding bird with narrow, long wings that may live up to 40 years), the southern giant fulmar, dove prion, and snow petrel. Shore birds that feed in the shallow waters near the shoreline include the blue-eyed cormorant, the Dominican gull, and the brown skua, which eats the eggs and young of other birds. The Arctic tern is the world's best at long-distance flying, because it raises its young in the Arctic but spends the rest of the year in the Antarctic, a distance of over 10,000 mi (16,090 km). Land birds include the wattled sheathbill, South Georgia pintail, and South Georgia pipit.

Of all the animals, penguins are the primary inhabitants of Antarctica. Believed to have evolved 40–50 million years ago, they have oily feathers that provide a waterproof coat and a thick layer of fat for insulation. Penguins' bones are solid, not hollow like those of most birds that allow them to fly. While solid bones prevent penguins from flying, they add weight and make it easier for penguins to dive into the water for food. Because predators cannot live in the brutally cold climate, penguins do not need to fly; thus, their wings have evolved over the centuries to resemble flippers or paddles.

Seven of the 18 known species of penguins live on the Antarctic: the Adelie and emperor (both considered true Antarctic penguins because they live on the continent), the chinstrap, gentoo, macaroni, rockhopper, and king penguins. The Adelie is the most plentiful species of penguin and can be found over the widest area of the continent. They spend their winters on the pack ice away from the continent, then return to land in October to nest in large rookeries or colonies along the rocky coasts. The emperor penguin is the largest species of penguin; it is the only Antarctic bird never to set foot on land, and it breeds on sea ice attached to the mainland. The most popular type of penguin for zoos, emperor penguins are 4 ft (1.2 m) tall and can weigh up to 80 lb (30 kg). They are the hardiest of all the animals that inhabit the Antarctic, staying throughout the year while other birds head north to escape the brutal winter. They breed on the ice surface during the winter months because their immense size requires a longer incubation period. This schedule also ensures that the chicks will hatch in July or early spring in the Antarctic, providing the most days for the chicks to put on weight before the next winter's cold arrives.

The female lays one egg on the ice, then walks up to 50 mi (80 km) to open sea for food. When she returns, filled with food for the chick, the male—who has been incubating the egg atop the ice during the coldest winter months—makes the same trek out to sea to restore its body weight, which may drop by 50% during this period. The parents take turns traveling for food after the chick has hatched.

Because the emperor penguin is one of the few species that lives on Antarctica year-round, researchers believe it could serve as an indicator to measure the health of the Antarctic ecosystem . The penguins travel long distances and hunt at various levels in the ocean, covering wide portions of the continent. At the same time, they are easily tracked because the emperor penguins return to their chicks and mates in predictable ways. Such indicators of the continent's health become more important as more humans travel to and explore Antarctica and as other global conditions are found to affect the southernmost part of the world.

Exploration of the continent

Greek philosopher Aristotle hypothesized more than 2,000 years ago that the earth was round and that the southern hemisphere must have a landmass large enough to balance the lands in the northern hemisphere. He called the probable but undiscovered land mass "Antarktikos," meaning the opposite of the Arctic.

The Greek geographer and astronomer Ptolemy called Antarctica "Terra Australis Incognita" or "unknown southern land" in the second century a.d. He claimed the land was fertile and populated but separated from the rest of the world by a region of torrid heat and fire around the equator. This concept was believed for several centuries, and the continent remained a mystery until James Cook crossed the Antarctic Circle and circumnavigated the continent in 1773. While he stated that the land was uninhabitable because of the ice fields surrounding the continent, he noted that the Antarctic Ocean was rich in whales and seals. For the next 50 years, hunters exploited this region for the fur and oil trade.

As hunting ships began traveling farther and farther south in the early 1800s to find fur seals, it was inevitable that the continent would be encountered and explored. Three countries claim first discovery rights to Antarctic land: Russia, due to explorer Fabian von Bellinghausen, on January 27, 1820; England as a result of English explorer Edward Bransfield, on January 30, 1820; and the United States by way of American sealer Nathaniel Palmer, on November 18, 1820. In actuality, American sealer John Davis was the first person to actually step onto the continent, on February 7, 1821.

James Weddell was a sealer who traveled to the continent on January 13, 1823. He found several previously unknown seal species, one of which later became known as the Weddell seal, then took his two ships—the Jane and the Beaufoy—farther south than any explorer had previously traveled. He reached 74° south latitude on February 20, 1823, and the vast sea he had entered became known as the Weddell Sea.

In 1895, the first landing on the continent was accomplished by the Norwegian whaling ship Antarctic. The British were the first to spend a winter on Antarctica, in 1899. By 1911, a race had begun to see who would reach the South Pole first: the South Pole is an imaginary geographical center point at the bottom of the earth. Again, it was a Norwegian, Roald Amundsen, who was the first to reach the South Pole on December 14, 1911. Robert Scott of England and his four men arrived a month later. While the first team made it home safely, the Scott team ran out of food and froze to death on their way home.

Airplanes first landed on Antarctica when Australian Hubert Wilkins flew 1,300 mi (2,092 km) over the Antarctic Peninsula in the 1920s, viewing terrain never before seen by another human. American Richard Byrd, the first person to fly over the North Pole in 1926, took his first Antarctic flight in 1929 and discovered a new mountain range he named Rockefeller. Thereafter, the continent was mapped and explored primarily from the air. Byrd continued his explorations to Antarctica over the next three decades and revolutionized the use of modern vehicles and communications equipment for polar exploration.


Scientific exploration

While various countries were busy claiming rights to Antarctica, scientists were cooperating effectively on research as early as 1875. Twelve nations participated in the first International Polar Year in 1882 and 1883. While most of the research was done in the Arctic, one German station was located in the Antarctic region. A second International Polar Year occurred in 1932-33, followed by the International Geophysical Year (IGY) from July 1, 1957 to December 31, 1958. This time, all twelve nations conducted research in Antarctica and set up base camps in various locations, some of which are still used today. Topics of research included the pull of gravity, glaciology, meteorites, cosmic rays, the southern lights, dynamics of the sun, the passage of comets near the earth, and changes in the atmosphere. Several organizations have been formed and agreements have been signed since these cooperative research projects to ensure that political conflicts do not arise concerning research and use of Antarctica.

Current events

A wide variety of research is continuing on Antarctica, primarily during the relatively warmer summer months from October to February when temperatures may reach a balmy 30–50°F ( -1–10°C). The cold temperatures and high altitude of Antarctica allow astronomers to put their telescopes above the lower atmosphere, which lessens blurring. During the summer months, they can study the Sun around the clock, because it shines 24 hours a day. Antarctica is also the best place to study interactions between solar wind and Earth's magnetic field , temperature circulation in the oceans, unique animal life, ozone depletion, ice-zone ecosystems, and glacial history. Buried deep in Antarcti ca's ice lie clues to ancient climates, which may provide answers to whether the earth is due for global warming or the next ice age.

Scientists consider Antarctica to be a planetary bellwether, an early indicator of negative changes in the entire planet's health. For example, they have discovered that a hole is developing in the ozone layer over the continent, a protective layer of gas in the upper atmosphere that screens out the ultraviolet light that is harmful to all life on Earth. The ozone hole was first observed in 1980 during the spring and summer months, from September through November. Each year, greater destruction of the layer has been observed during these months, and the first four years of the 1990s have produced the greatest rates of depletion thus far. The hole was measured to be about the size of the continental United States in 1994, and it lasts for longer intervals each year. Scientists have identified various chemicals created and used by humans, such as chlorofluorocarbons (CFCs) , as the cause of this destruction, and bans on uses of these chemicals have begun in some countries.

Researchers have also determined that a major climate change may have occurred in Antarctica in the 1980s and 1990s, based on recorded changes in ozone levels and an increase in cloudiness over the South Pole. This, coupled with a recorded weakening of the ozone shield over North America in 1991, has led scientists to conclude that the ozone layer is weakening around the entire planet.

Others are studying the ice cap on Antarctica to determine if, in fact, the earth's climate is warming due to the burning of fossil fuels . The global warming hypothesis is based on the atmospheric process known as the greenhouse effect , in which pollution prevents the heat energy of the earth from escaping into the outer atmosphere. Global warming could cause some of the ice cap to melt, flooding many cities and lowland areas. Because the polar regions are the engines that drive the world's weather system, this research is essential to identify the effect of human activity on these regions.

Most recently, a growing body of evidence is showing that the continent's ice has fluctuated dramatically in the past few million years, vanishing completely from the continent once and from its western third at least several times. These collapses in the ice structure might be triggered by climatic change, such as global warming, or by far less predictable factors, such as volcanic eruptions under the ice. While the east Antarctic ice sheet has remained relatively stable because it lies on a single tectonic plate, the western ice sheet is a jumble of small plates whose erratic behavior has been charted through satellite data. The west Antarctic is also dominated by two seas, the Ross and Weddell, whose landward regions are covered by thick, floating shelves of ice. Some researchers speculate that if warmer, rising oceans were to melt this ice, the entire western sheet might disintegrate quickly, pushing global sea levels up by 15-20 ft (5-6 m).

See also Gaia hypothesis; Greenhouse effect; Ozone layer depletion; Plate tectonics.


Resources

books

Anderson, J. B. Antarctic Marine Geology. Cambridge: Cambridge University Press, 1999.

Billings, Henry. Antarctica—Enchantment of the World. Chicago: Childrens Press, 1994.

Hancock P. L. and Skinner B. J., eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Hurley, Frank. South with Endurance: Shackleton's AntarcticExpedition, 1914-1917. New York: Simon & Schuster, 2001.

Joughin, I. "Antarctica: A Review of Recent Medical Research." Trends in Pharmacological Sciences. 23, no. 10 (2002): 487-490.

McGonigal, David. Lynn Woodworth, and Sir Edmund Hillary, eds. Antarctica and the Arctic: The Complete Encyclopedia. Westport, CT: Firefly Books, 2001.


periodicals

Grotta, Daniel and Sally. "Antarctica: Whose Continent is it Anyway?" Popular Science 240, no. 1 (1992): 62-7, 90-1.

Horgan, John. "Antarctic Meltdown." Scientific American 266, no. 3: 19-28.

Keeling, Ralph F. "Palaeoceanography: Antarctic Stratification and Glacial CO2." Nature 412, no. 6847 (2001): 605-606.

Kiernan, K. "Impacts of Geoscience Research on the Physical Environment of the Antarctic." Australian Journal of Earth Sciences 48, no. 5 (2001): 767.

Monastersky, Richard. "Antarctic Ozone Level Reaches New Low." Science News 144, no. 16: 247.

Monastersky, Richard. "Science on Ice." Science News 143, no. 15 (1993): 232-35.

Palca, Joseph. "Poles Apart, Science Thrives on Thin Ice." Science 255, no. 5042 (1992): 276-78.


Sally Cole-Misch

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Antarctic Circle

—The line of latitude at 66 degrees 32 minutes South, where there are 24 hours of daylight in midsummer and 24 hours of darkness in midwinter.

Antarctic convergence

—A 25-mi (40-km) region where cold Antarctic surface water meets warmer, subantarctic water and sinks below it.

Antarctic Ocean

—The seas surrounding the continent, where the Atlantic, Pacific, and Indian Oceans converge.

Blubber

—Whale or seal fat used to create fuel.

Calving

—The process in which huge chunks of ice or icebergs break off from ice shelves and sheets or glaciers to form icebergs.

Dry valleys

—Areas on the continent where no rain is known to have fallen for more than two million years, and the extremely dry katabatic winds cause any snow blown into the valleys to evaporate before hitting the ground. The Taylor, Victoria, and Wright valleys are the largest continuous areas of ice-free land on the continent.

Glacier

—A river of ice that moves down a valley to the sea, where it breaks into icebergs.

Iceberg

—A large piece of floating ice that has broken off a glacier, ice sheet, or ice shelf.

Katabatic winds

—Fierce, dry winds that flow down along the steep slopes of the interior mountains of Antarctica, and along ice caps and glaciers on the subantarctic islands.

Krill

—Tiny sea animals or zooplankton that are the main food for most larger species in the Antarctic region.

Nunataks

—Mountain peaks that are visible above the ice and snow cover.

Pack ice

—Ice from seawater, which forms a belt approximately 300–1,800 mi (483–2,897 km) wide around the continent in winter.

South magnetic pole

—The point to which a compass is attracted and which is some distance from the geographic South Pole. It varies from year to year as the earth's magnetic field changes.

South pole

—The geographically southernmost place on Earth.

Southern lights

—Also known as the aurora australis, they are streamers of different colors in the sky, especially at night, and are thought to be caused by electrical disturbances and cosmic particles in the upper atmosphere that are attracted by the South Magnetic Pole.

Subantarctica

—The region just north of Antarctica and the Antarctic Circle, but south of Australia, South America, and Africa.

Antarctica

views updated May 09 2018

Antarctica

Official name : Antarctica

Area: 14,000,000 square kilometers (5,405,430 square miles)

Highest point on mainland: Vinson Massif (5,140 meters/16,864 feet)

Lowest point on land: Bentley Subglacial Trench (2,540 meters/8,333 feet below sea level)

Hemispheres: Southern, Eastern, and Western

Time zone: Each research station chooses its own time zone (usually based on its home country)

Longest distances: Longest distance traversing the South Pole 5,339 kilometers (3,337 miles); shortest distance traversing the South Pole 1,234 kilometers (771 miles)

Land boundaries: None

Coastline: 17,968 kilometers (11,164 miles)

Territorial sea limits: None

1 LOCATION AND SIZE

The continent of Antarctica is almost entirely south of the Antarctic Circle (66.5°S), surrounded by the Southern Ocean. Both the geographic and magnetic South Poles are located on the continent. With a total area of about 14,000,000 square kilometers (5,405,430 square miles), Antarctica ranks fifth in size among the world's continents, larger than Australia or Europe. It is slightly less than one-and-one-half times the size of the United States.

2 TERRITORIES AND DEPENDENCIES

Antarctica is unique. It is a continent, but it has no native population or government. It does not belong to any one nation, but parts of Antarctica are claimed by seven different countries: Argentina, Australia, Chile, France, New Zealand, Norway, and the United Kingdom. The international community, however, does not recognize their claims, and they cannot enforce them under the terms of the Antarctic Treaty, which has been signed by forty-five nations of the world. First signed in 1961 by twelve nations, the treaty specifies that "Antarctica shall be used for peaceful purposes only." As of 2002, twenty-seven nations held consulting member status in the international treaty agreements protecting Antarctica.

3 CLIMATE

The average annual temperature in the interior is a frigid -57°C (-71°F), with a mean summer temperature of -40°C (-40°F) and an average winter temperature of -68°C (-90°F). In the coastal areas, the mean summer temperature is 0°C (32°F). McMurdo Station near the Ross Ice Shelf in East Antarctica has the most moderate climate, with a mean winter temperature of -9°C (16°F). The lowest temperature ever recorded on Earth was at Vostok, East Antarctica, where the mercury dipped to -89°C (-129°F) in 1983.

Since the 1950s, scientists have recorded an overall increase in temperature on Antarctica of about 2°C (4°F), which is much more than the increase in overall temperature elsewhere in the world. Five of the largest ice shelves have shrunk in size during this time period. Some scientists speculate that this is an early sign of global warming caused by human activity, but this theory has not been proven.

Antarctica has continuous daylight from mid-September to mid-March and six months of continuous darkness from mid-March to mid-September. During the daylight months, the continent receives more solar radiation than equatorial regions. Observation has shown that the layer of high-atmosphere ozone that helps reflect harmful solar radiation away from Earth's surface is thin to nonexistent over Antarctica. The ozone hole varies in size from season to season, but it appears to be expanding. Many blame human activity for this hole in the ozone, but the exact causes are unknown.

Most of the continent receives less than 5 centimeters (2 inches) of precipitation annually, in the form of snow.

4 TOPOGRAPHIC REGIONS

Antarctica is generally described as having two parts, West Antarctica and East Antarctica. West Antarctica lies directly south of the South American continent and includes the Antarctic Peninsula, which extends farther north than any other part of the continent. East Antarctica is the larger region; it lies south of the southern tips of Africa and Australia. East and West Antarctica are separated by the Transantarctic Mountains.

About 98 percent of the land area is permanently covered with ice. The remainder is exposed barren rock. Antarctica is generally mountainous, with elevations typically ranging from 2,000 to 4,000 meters (6,600 to 13,200 feet). Mountain peaks rise to heights in excess of 5,000 meters (16,500 feet).

There are no native vertebrate animals on Antarctica. The ocean waters surrounding Antarctica support several species of whale, seals (including the crabeater, elephant, and leopard seal), and about a dozen species of birds, the best-known of which are two varieties of penguin, the Adélie and Emperor. Penguins are birds, but they cannot fly.

5 OCEANS AND SEAS

Seacoast and Undersea Features

In 2000, the International Hydrographic Association drew boundaries for a new ocean, called the Southern Ocean, that encompasses all of the water south of 60° latitude. Since this decision, the ocean surrounding Antarctica has been called the Southern Ocean. Due to the great temperature differences between the ice and the open ocean, as well as the lack of any land to impede them, powerful winds blow across the Southern Ocean and the southernmost parts of the surrounding oceans.

The Southern Ocean is home to the Antarctic Circumpolar Current. This ocean current flows east completely around the earth in a great circle just to the north of Antarctica. The current is the most powerful on earth, and it is unique in that it is unimpeded by landforms as it travels around the globe. The current tends to keep cold water to the south, near Antarctica, and holds warmer water back to the north, with a relatively sharp boundary flowing down the middle of the current known as the Antarctic Convergence.

DID YOU KNOW?

Both the geographic and magnetic south poles are located on the continent of Antarctica. Earth's two geographic poles are designated as 90°N latitude/0° longitude (North Pole) and 90°S latitude/0° longitude (South Pole).

Earth's magnetic poles represent the two nearly opposite ends of the planet where the earth's magnetic intensity is the greatest. These locations are different than the geographic poles. The South Magnetic Pole is located at 66°S latitude and 139°E longitude on the Adélie Coast of Antarctica. The North Magnetic Pole is located at 78°N latitude and 104°W longitude in the Queen Elizabeth Islands of northern Canada.

Sea Inlets and Straits

All of the Antarctic seas are inlets of the Southern Ocean. The Bellingshausen Sea lies off the western coast of the Antarctic Peninsula. It is named for Russian explorer Fabian von Bellingshausen, the first person to sail completely around Antarctica in 181921. His expedition also gave names to Queen Maud Land and Peter I Island. Off of West Antarctica is the Amundsen Sea, named for the Norwegian explorer Roald Amundsen, who was the first explorer to reach the South Pole.

The Ross Sea lies off the coast of the Ross Ice Shelf directly south of New Zealand. Both are named for Sir James C. Ross, an explorer in the region in 183943 from the United Kingdom. The Weddell Sea is named for the British explorer James Weddell, who conducted an exploration in 1823. It is the body of water east of the Antarctic Peninsula.

The Drake Passage lies between Antarctica and South America, which is located hundreds of miles to the north of Antarctica.

Islands and Archipelagos

Antarctica's largest island, Alexander Island (43,200 square kilometers/16,700 square miles), is separated from the Antarctic Peninsula by the George VI Sound, although thick ice sheets connect the two land masses. There are dozens of smaller islands in the Bellingshausen Sea and Amundsen Seas, including Thurston, Siple, Carney, and Charcot Islands. Further north along the Antarctic Peninsula is Adelaide Island and the Palmer Archipelago. Most of these islands are connected to the mainland mass by ice.

Berkner Island (3,880 square kilometers/1,500 square miles), covered by the Ronne and Filchner Ice Shelves, lies in the McCarthy Inlet of the Weddell Sea. Roosevelt Island is the largest land mass found within the Ross Sea, but it is completely covered by the Ross Ice Shelf. Ross Island is smaller, but it has access to the ocean in the summer months.

The South Shetland Islands, situated between Antarctica and the southern tip of South America, include Deception Island and King George I Island, among others. Deception Island lies in an active volcanic field known as the Branfield Rift. It is a horseshoe-shaped island with a central caldera (a crater formed by the eruption of a volcano) that has a surface area of about 26 square kilometers (10 square miles) and is breached at one end to be accessible from the open sea. The water of the caldera is heated by underground volcanic activity and has at times reached the boiling point. Also lying in the ocean between Antarctica and South America are the South Orkney Islands, South Georgia, and the South Sandwich Islands. Zavadovski Island in the South Sandwich Islands is home to one of the largest penguin colonies in the worldwith a population estimated at two million penguins.

Coastal Features

Even during the summer, only a few coastal areas are ever free of ice, including parts of Wilkes Land in East Antarctica and parts of the Antarctic Peninsula. During the winter, the ocean around Antarctica freezes, surrounding the continent with ice that expands far out to sea. As winter proceeds, the ice surrounding the Antarctic land mass grows at the rate of about 103,600 square kilometers (40,000 square miles) per day. By the heart of winter, it is roughly six times larger than normal, expanding the effective size of the continent to 33,000,000 square kilometers (13,000,000 square miles).

Almost half of the coastal regions are covered by ice shelves, which are formed as thick fields of ice branch out into the ocean. The ice shelves meet the bottom of the ocean near the shores but narrow into surface ice sheets (with water beneath them) as they stretch away from the land. The shelves extend out into the water for hundreds of kilometers.

The Ross Sea and the Weddell Sea both contain enormous ice shelves. The Ross Ice Shelf in the sea of the same name is the larger of the two, with an area of roughly 336,770 square kilometers (130,100 square miles). The Ronne, Filchner, Larsen, and Riiser-Larsen Ice Shelves are all found in the Weddell Sea.

West Antarctica has a highly irregular coastline, with many small peninsulas and inlets, most of them ice-covered. The S-shaped Antarctic Peninsula extends far to the northeast. It comes closer to another continent (South America) than any other part of Antarctica. Away from the Weddell and Ross Seas, East Antarctica has a much more regular coastline than the western part of the continent. It arcs in a rough half circle from one sea to the other. Since this coast is much closer to the Antarctic Circle than that of West Antarctica, its ice shelves are smaller. The Amery Ice Shelf, along the East Antarctic coast, envelops most of Prydz Bay, that coastline's only significant indentation. East Antarctica extends north slightly beyond the Antarctic Circle at both Cape Ann and Cape Poinsett. The Shackleton Ice Shelf lies not far from the second of these capes. Cape Adare marks the point where the East Antarctic coast curves sharply inwards to form one side of the Ross Sea.

6 INLAND LAKES

While a large portion of the world's fresh water is located on Antarctica, it is present mostly in the form of ice. Non-frozen water does exist, however, in the lakes beneath the ice. These lakes are believed to be at least 30 meters (100 feet) deep. Scientists are studying these lakes to determine whether they support any marine life. To conduct their experiments, they must use exceptionally sterile methods to collect specimens in order to avoid contaminating the glacial environment.

DID YOU KNOW?

The discovery of the geographic South Pole is a story of one of the most famous exploration "races" in history. British adventurer Robert F. Scott set out to be the first person to reach the South Pole in 1909. At the same time, unbeknownst to Scott, Norwegian explorer Roald Amundsen was making secret plans to try the trip himself. When Amundsen set sail in 1910, he told his crew and government that he was on his way to the North Pole. Shortly after setting off, he switched directions and the race began. Amundsen reached the pole first, on December 14, 1911, and he set up a small tent and a flag to mark the occasion. This is what Scott saw when he arrived only a few weeks later on January 18, 1912. Unlike Amundsen, Scott and his crew did not survive the trip back from the South Pole. Today, the research station located at the South Pole is named in honor of these two explorers.

Antarctica's largest known lake, Lake Vostok (26,000 square kilometers/10,000 square miles), is approximately the same size as North America's Lake Erie, but it is buried under 3.5 kilometers (2.8 miles) of ice. Other lakes found in the McMurdo Dry Valleys include Lake Vanda, Lake Brownworth, Lake Fryxell, Lake Bonney, and Lake Hoare. These lakes are fed by runoff from the glaciers that lie in the deepest mountain valleys. During the summer, the air temperatures warm to about the freezing point (0°C/32°F), causing the glaciers to melt slightly and to send water flowing into small streams for a few weeks before the temperature again drops below freezing. The stream flow feeds the lakes, which lie beneath 3 meters (10 feet) of permanent ice cover.

7 RIVERS AND WATERFALLS

The only river of any significance in Antarctica is the Onyx River. With a length of about 25 kilometers (20 miles), it is the largest of the streams that flow during the summer months. The Onyx River flows into Lake Vanda.

8 DESERTS

Due to the lack of precipitation, the entire continent is technically considered a desert, despite the fact that it holds more than two-thirds of the world's fresh water. By definition, a desert is any barren land with very little rainfall, extreme temperatures (both hot and cold), and sparse vegetation. This definition can include a permanently cold region, such as Antarctica.

9 FLAT AND ROLLING TERRAIN

In Antarctica, glaciers (a large body of ice that moves over Earth's surface) completely cover the land beneath them, allowing only the most dramatic mountain peaks to poke through. Antarctica contains 90 percent of the world's natural ice total. Over land, it averages 2 kilometers (1.5 miles) thick, and is about 3.5 kilometers (3 miles) deep at its widest point. The East Antarctic glaciers are slightly larger than the West Antarctic glaciers. Some coastal areas support a few lichens during the summer months, but the ice sheets are otherwise barren.

Glaciers move over the land at a slow and steady pace. Dramatic formations and striations (stripes, believed to be remnants of volcanic ash) may be observed in the glaciers. The advancing edge of the glacier becomes a high sheer cliff as the top levels of ice push forward. The Antarctic polar ice cap moves an average of 10 meters (33 feet) each year.

In East Antarctica, the continent's largest valley glacier, the Lambert Glacier, lies over several mountain peaks that rise to 1,017 meters (3,355 feet). Massive sections of ice discharge from the Lambert Glacier to become part of the floating Amery Ice Shelf each year. Other noteworthy glaciers include the Skelton Glacier, Rennick Glacier, Recovery Glacier, and Beardmore Glacier.

Lying between the mountain peaks of the Transantarctic Mountains are Victoria Valley, Wright Valley, and Taylor Valley. These large, relatively ice-free territories are known collectively as the McMurdo Dry Valleys. They account for about 4,800 square kilometers (1,733 square miles) of dry land in an area measuring approximately 60 by 75 kilometers (48 by 60 miles). The valleys are ice-free because the mountains impede the flow of the sheet of ice that covers most of the rest of the continent. The valleys are filled with sandy, spongy gravel.

10 MOUNTAINS AND VOLCANOES

Dividing Antarctica into two regions, East Antarctica (Greater Antarctica) and West Antarctica (Lesser Antarctica), is the continent's major mountain range, the Transantarctic Mountains.

The Antarctic Peninsula, a finger of land jutting into the ocean from the mainland of West Antarctica, is also mountainous, with underlying volcanic activity. The Ellsworth Mountains of West Antarctica include the territory's highest point, the Vinson Massif (5,140 meters/16,864 feet). Other notable peaks in West Antarctica are Mount Sidley (4,181 meters/13,717 feet), Mount Jackson (4,189 meters/13,745 feet), and Mount Berlin (3,518 meters/11,543 feet).

East Antarctica features at least two active volcanoes, and scientists believe they will likely discover more that have peaks buried beneath the ice. Mount Erebus (3,794 meters/ 12,444 feet), one of the active volcanoes, is on Ross Island. Other notable peaks in East Antarctica are Mount Melbourne at 2,732 meters (9,016 feet) and the Gamgurtsev Subglacial Mountains at 4,030 meters (13,300 feet).

11 CANYONS AND CAVES

The Bentley Subglacial Trench, a canyon extending 2,540 meters (8,333 feet) below sea level, is covered by solid ice, making it the lowest point on Earth that is not underwater.

12 PLATEAUS AND MONOLITHS

Even where it is not mountainous, Antarctica's elevations are high. Its average elevation of roughly 2,440 meters (8,000 feet) is greater than that of any other continent. As a consequence, most of the land areas outside of the mountain ranges can be considered to be plateaus. Covered by thick ice, most of these plateaus have no names. A few exceptions are the Hollick-Kenyon and Rockefeller Plateaus in West Antarctica, and the Polar Plateau over the South Pole in East Antarctica. The elevation of the South Pole is 2,835 meters (9,355 feet).

13 MAN-MADE FEATURES

There are about seventy research stations on Antarctica that are operated by scientists from around the world. Only about half of these centers are used year-round; the others are occupied only during the summer months. Researchers come to Antarctica from many different fields of study, including astrophysics and astronomy, biology, meteorology, geology, oceanography, and biomedicine, among others. The largest research community is at McMurdo Station, governed by the United States and located on Hut Point Peninsula of Ross Island, which is the southernmost point of solid ground that is accessible by ship. There are more than one hundred structures in the complex, including a harbor, a landing strip, and the DASI (Degree Angular Scale Interferometer) telescope observation point for the study of cosmic microwave background radiation. Resident scientists number about twelve hundred people in the summer months and two hundred people in the winter.

14 FURTHER READING

Books

Campbell, David G. The Crystal Desert: Summers in Antarctica. Boston: Houghton Mifflin, 1992.

Mastro, Jim. Antarctica: A Year at the Bottom of the World. Boston: Little, Brown and Company, 2002.

Stewart, John. Antarctica: An Encyclopedia. Jefferson, NC: McFarland, 1990.

Wheeler, Sara. Terra Incognita: Travels in Antarctica. London: Vintage, 1997.

Web Sites

Antarctic Connection. http://www.antarcticconnection.com/antarctic/stations/index.shtml (accessed June 12, 2003).

Mount Erebus Volcano Observatory. http://www.ees.nmt.edu/Geop/mevo/mevo.html (accessed June 12, 2003).

"Warnings from the Ice," Nova. http://www.pbs.org/wgbh/nova/warnings/almanac.html (accessed June 12, 2003).

Antarctica

views updated May 18 2018

Antarctica

Among the seven continents on planet Earth, Antarctica lies at the southernmost tip of the world. It is the coldest, driest, and windiest continent. Ice covers 98% of the land, and its 5,100,000 sq mi (13,209,000 sq km) occupy nearly one-tenth of Earth's land surface, or the same area as Europe and the United States combined. Despite its barren appearance, Antarctica and its surrounding waters and islands teem with life all their own, and the continent plays a significant role in the climate and health of the entire planet.

Seventy percent of the world's fresh water is frozen atop continental Antarctica. These icecaps reflect warmth from the Sun back into the atmosphere, preventing planet Earth from overheating. Huge icebergs break away from the stationary ice and flow north to mix with warm water from the equator, producing currents, clouds , and complex weather patterns. Creatures as small as microscopic phytoplankton and as large as whales live on and around the continent, including more than 40 species of birds. Thus, the continent provides habitats for vital links in the world's food chain.

Geologists believe that, millions of years ago, Antarctica was part of a larger continent called Gondwanaland, based on findings of similar fossils , rocks, and other geological features on all of the other southern continents. About 200 million years ago, Gondwanaland broke apart into the separate continents of Antarctica, Africa , Australia , South America , and India (which later collided with Asia to merge with that continent). Antarctica and these other continents drifted away from each other as a result of shifting of the plates of the earth's crust , a process called continental drift that continues today. The continent is currently centered roughly on the geographic South Pole, the point where all south latitudinal lines meet. It is the most isolated continent on Earth, 600 mi (1,000 km) from the southernmost tip of South America and more than 1,550 mi (2,494 km) away from Australia.

Antarctica is considered both an island and a continent. The land itself is divided into east and west parts by the Transantarctic Mountains. The larger side, to the east, is located mainly in the eastern longitudes. West Antarctica is actually a group of islands held together by permanent ice.

Almost all of Antarctica is under ice, in some areas by as much as 2 mi (3 km). The ice has an average thickness of about 6,600 ft (2,000 m), which is higher than many mountains in warmer countries. This grand accumulation of ice makes Antarctica the highest continent on Earth, with an average elevation of 7,500 ft (2,286 m).

While the ice is extremely high in elevation, the actual landmass of the continent is, in most places, well below sea level due to the weight of the ice. If all of this ice were to melt, global sea levels would rise by about 200 ft (65 m), flooding the world's major coastal ports and vast areas of low-lying land. Even if only one-tenth of Antarctica's ice were to slide into the sea, sea levels would rise by 20 ft (6 m), severely damaging the world's coastlines.

Under all the ice, the Antarctic continent is made up of mountains. The Transantarctic Mountains are the longest range on the continent, stretching 3,000 mi (4,828 km) from Ross Sea to Weddell Sea. Vinson Massif, at 16,859 ft (5,140m), is the highest mountain peak. The few areas where mountains peek through the ice are called nunataks.

Among Antarctica's many mountain ranges lie three large, moon-like valleysthe Wright, Taylor, and Victoria Valleyswhich are the largest continuous areas of ice-free land on the continent. Known as the "dry valleys," geologists estimate that it has not rained or snowed there for at least one million years. Any falling snow evaporates before it reaches the ground, because the air is so dry from the ceaseless winds and brutally cold temperatures. The dryness also means that decomposition is slow, and seal carcasses there have been found to be more than 1,000 years old. Each valley is 25 mi (40 km) long and 3 mi (5 km) wide and provides rare glimpses of the rocks that form the continent and the Transantarctic Mountains.

Around several parts of the continent, ice forms vast floating shelves. The largest, known as the Ross Ice Shelf, is about the same size as Texas. The shelves are fed by glaciers on the continent, so the resulting shelves and icebergs are made up of fresh frozen water. Antarctica hosts the largest glacier on Earth; the Lambert Glacier on the eastern half of the continent is 25 mi (40 km) wide and more than 248 mi (400 km) long.

Gigantic icebergs are a unique feature of Antarctic waters. They are created when huge chunks of ice separate from an ice shelf, a cliff, or glacier in a process known as calving. Icebergs can be amazingly huge; an iceberg measured in 1956 was 208 mi (335 km) long by 60 mi (97 km) wide (larger than some small countries) and was estimated to contain enough fresh water to supply London, England, for 700 years. Only 1015% of an iceberg normally appears above the water's surface, which can create great dangers to ships traveling in Antarctic waters. As these icebergs break away from the continent, new ice is added to the continent by snowfall.

Icebergs generally flow northward and, if they do not become trapped in a bay or inlet, will reach the Antarctic Convergence, the point in the ocean where cold Antarctic waters meet warmer waters. At this point, ocean currents usually sweep the icebergs from west to east until they melt. An average iceberg will last several years before melting .

Three oceans surround Antarcticathe Atlantic, Pacific, and Indian Oceans. Some oceanographers refer to the parts of these oceans around Antarctica as the Southern Ocean. While the saltwater that makes up these oceans does not usually freeze, the air is so cold adjacent to the continent that even the salt and currents cannot keep the water from freezing . In the winter months, in fact, the ice covering the ocean waters may extend over an area almost as large as the continent. This ice forms a solid ring close to the continent and loose chunks at the northern stretches. In October (early spring) as temperatures and strong winds rise, the ice over the oceans breaks up, creating huge icebergs.

Because of the way the Earth tilts on its axis as it rotates around the Sun, both polar regions experience long winter nights and long summer days. At the South Pole itself, the sun shines around the clock during the six months of summer and virtually disappears during the cold winter months. The tilt also affects the angle at which the Sun's radiation hits the Earth. When it is directly overhead at the equator, it strikes the polar regions at more indirect angles. As a result, the Sun's radiation generates much less heat, even though the polar regions receive as much annual daylight as the rest of the world.

Even without the wind chill , the continent's temperatures can be almost incomprehensible to anyone who has not visited there. In winter, temperatures may fall to 100°F (73°C). The world's record for lowest temperature was recorded on Antarctica in 1960, when it fell to 126.9°F (88.3°C).

The coastal regions are generally warmer than the interior of the continent. The Antarctic Peninsula may get as warm as 50°F (10°C), although average coastal temperatures are generally around 32°F (0°C). During the dark winter months, temperatures drop drastically, however, and the warmest temperatures range from 4 to 22°F (20 to 30°C). In the colder interior, winter temperatures range from 40 to 94°F (40 to 70°C).

The strong winds that constantly travel over the continent as cold air races over the high ice caps and then flows down to the coastal regions, are called katabatic winds. Winds associated with Antarctica blizzards commonly gust to more than 120 mi (193 km) per hour and are among the strongest winds on Earth. Even at its calmest, the continent's winds can average 5090 mi (80145 km) per hour. Cyclones occur continually from west to east around the continent. Warm, moist ocean air strikes the cold, dry polar air and swirls its way toward the coast, usually losing its force well before it reaches land. These cyclones play a vital role in the exchange of heat and moisture between the tropical and the cold polar air.

Surprisingly, with all its ice and snow, Antarctica is the driest continent on Earth based on annual precipitation amounts. The constantly cold temperatures have allowed each year's annual snowfall to build up over the centuries without melting. Along the polar ice cap, annual snowfall is only 12 in (2.55 cm). More precipitation falls along the coast and in the coastal mountains, where it may snow 1020 in (2551 cm) per year.

Few creatures can survive Antarctica's brutal climate. Except for a few mites and midges, native animals do not exist on Antarctica's land. Life in the sea and along the coast of Antarctica and its islands, however, is often abundant. A wide variety of animals make the surrounding waters their home, from zooplankton to large birds and mammals. A few fish have developed their own form of antifreeze over the centuries to prevent ice crystals from forming in their bodies, while others have evolved into cold-blooded species to survive the cold.

Because the emperor penguin is one of the few species that lives on Antarctica year-round, researchers believe it could serve as an indicator to measure the health of the Antarctic ecosystem. The penguins travel long distances and hunt at various levels in the ocean, covering wide portions of the continent. At the same time, they are easily tracked because the emperor penguins return to their chicks and mates in predictable ways. Such indicators of the continent's health become more important as more humans travel to and explore Antarctica and as other global conditions are found to affect the southernmost part of the world.

A wide variety of research is continuing on Antarctica, primarily during the relatively warmer summer months from October to February when temperatures may reach a balmy 3050°F (110°C). The cold temperatures and high altitude of Antarctica allow astronomers to put their telescopes above the lower atmosphere, which lessens blurring. During the summer months, they can study the Sun around the clock, because it shines 24 hours a day. Antarctica is also the best place to study interactions between solar wind and Earth's magnetic field , temperature circulation in the oceans, unique animal life, ozone depletion, ice-zone ecosystems, and glacial history. Buried deep in Antarctica's ice lie clues to ancient climates, which may provide answers to whether the earth is due for global warming or the next ice age.

Scientists consider Antarctica to be a planetary bellwether, an early indicator of negative changes in the entire planet's health. For example, they have discovered that a hole is developing in the ozone layer over the continent, a protective layer of gas in the upper atmosphere that screens out the ultraviolet light that is harmful to all life on Earth. The ozone hole was first observed in 1980 during the spring and summer months, from September through November. Each year, greater destruction of the layer has been observed during these months, and the first four years of the 1990s have produced the greatest rates of depletion thus far. The hole was measured to be about the size of the continental United States in 1994, and it lasts for longer intervals each year. Scientists have identified various chemicals created and used by humans, such as chlorofluorocarbons (CFCs), as the cause of this destruction, and bans on uses of these chemicals have begun in some countries.

Researchers have also determined that a major climate change may have occurred in Antarctica in the 1980s and 1990s, based on recorded changes in ozone levels and an increase in cloudiness over the South Pole. This, coupled with a recorded weakening of the ozone shield over North America in 1991, has led scientists to conclude that the ozone layer is weakening around the entire planet.

Others are studying the ice cap on Antarctica to determine if, in fact, the earth's climate is warming due to the burning of fossil fuels . The global warming hypothesis is based on the atmospheric process known as the greenhouse effect , in which pollution prevents the heat energy of the earth from escaping into the outer atmosphere. Global warming could cause some of the ice cap to melt, flooding many cities and lowland areas. Because the polar regions are the engines that drive the world's weather system, this research is essential to identify the effect of human activity on these regions.

Most recently, a growing body of evidence is showing that the continent's ice has fluctuated dramatically in the past few million years, vanishing completely from the continent once and from its western third at least several times. These collapses in the ice structure might be triggered by climatic change, such as global warming, or by far less predictable factors, such as volcanic eruptions under the ice. While the east Antarctic ice sheet has remained relatively stable because it lies on a single tectonic plate, the western ice sheet is a jumble of small plates whose erratic behavior has been charted through satellite data.

See also Atmospheric pollution; Freshwater; Glacial land-forms; Glaciation; Greenhouse gases and greenhouse effect; Ice ages; Ice heaving and wedging; Ozone layer and hole dynamics; Polar axis and tilt

Antarctica

views updated May 29 2018

Antarctica

  • Area: 5,405,430 sq mi (14,000,000 sq km, approximation) / World Rank: 2
  • Location: Covers the South Pole in the Southern Hemisphere. Its territory forms the southernmost portions of the Eastern and Western Hemispheres.
  • Coordinates: 90°00′ S / 0°00′ E
  • Borders: None
  • Coastline: 11,164 mi (17,968 km)
  • Territorial Seas: None
  • Highest Point: Vinson Massif, 16,864 ft (5,140 m)
  • Lowest Point: Bentley Subglacial Trench, 8,333 ft (2,540 m) below sea level
  • Longest Distances: Longest distance traversing the South Pole 3,337 mi (5,339 km); shortest distance traversing the South Pole 771 mi (1,234 km)
  • Longest River: Onyx River, 20 mi (25 km)
  • Largest Lake: Lake Vostok, estimated size 10,000 sq mi (26,000 sq km), but buried under 2.8 mi (3.5 km) of ice.
  • Natural Hazards: Extreme cold; blizzards; cyclones; volcanoes; icebergs; high radiation due to ozone depletion
  • Population: No indigenous population; numbers of scientists and other research personnel from nearly 30 nations range seasonally from 1,000 to 4,000 or more. / World Rank: 207
  • Capital City: None
  • Largest City: McMurdo Station, in East Antarctica, summer population estimated at 1,200; winter, 250.

OVERVIEW

The continent of Antarctica is almost entirely south of the Antarctic Circle (66.5°S), with the South Pole located on it. Antarctica ranks fifth in size among the world's continents, being larger than Australia or Europe. It is surrounded by the Southern Ocean, and islands in this ocean (south of 60° latitude) are considered part of Antarctica.

Antarctica is generally described as having two parts, West Antarctica and East Antarctica. West Antarctica lies directly south of the South American continent, and includes the Antarctic Peninsula, which extends farther north than any other part of the continent. East Antarctica is the larger part of the continent, and lies south of the southern tips of Africa and Australia. East and West Antarctica are separated by the Transantarctic Mountains. Explorers and research scientists have given names to almost every stretch of the Antarctic coast, and to the notable geographic features they have discovered.

Located as it is in the far south, Antarctica is extremely cold, even during the summer. About 98 percent of the land area is permanently covered with ice sheet. The remainder is exposed barren rock. Antarctica is generally mountainous, with elevations typically ranging from 6,600 to 13,200 ft (2,000 to 4,000 m). Mountain peaks rise to heights in excess of 16,500 ft (5,000 m).

Antarctica is unique in that it does not belong to any nation. Parts of Antarctica are claimed by seven nations: Argentina, Australia, Chile, France, New Zealand, Norway, and the United Kingdom. However, their claims are not recognized by the international community, and are in abeyance under the terms of the Antarctic Treaty. This treaty went into effect in 1961, when it was first signed by 12 nations. The Treaty attempts to clarify issues related to territorial claims and to provide a framework for this unique and complex international cooperation. It specifies that "Antarctica shall be used for peaceful purposes only." Other nations that sponsor research in Antarctica have since become consulting members of the Treaty. As of 2002, there are 27 nations with consulting member status in the treaty agreements for Antarctica.

MOUNTAINS AND HILLS

Mountains

Dividing Antarctica into two regions, East Antarctica (Greater Antarctica) and West Antarctica (Lesser Antarctica), is the continent's major mountain range, the Transantarctic Mountains. Lying between the mountain peaks are Victoria Valley, Wright Valley, and Taylor Valley. These large, relatively ice-free areas, are known collectively as the McMurdo Dry Valleys. They account for about 1,733 sq mi (4,800 sq km) of territory free of ice in an area measuring approximately 48 by 60 mi (60 by 75 km). The areas are ice-free because the mountains impede the flow of the sheet of ice that covers most of the continent. The valleys are filled with sandy, spongy gravel. Glaciers flow into the deepest parts of the valleys from the surrounding mountains.

The Antarctic Peninsula, a finger of land jutting into the ocean from the mainland of West Antarctica, is also mountainous, with underlying volcanic activity. The Ellsworth Mountains of West Antarctica include the territory's highest point, the Vinson Massif (16,864 ft / 5,140 m). Other notable peaks in West Antarctica are Mount Sidley (13,717 ft / 4,181 m), Mount Jackson (13,745 ft / 4,189 m), and Mount Berlin 11,543 ft (3,518 m).

East Antarctica features at least two active volcanoes, and scientists believe they will likely discover more with peaks buried beneath the ice. Mount Erebus (12,444 ft/ 3,794 m), one of the active volcanoes, is on Ross Island. Other notable peaks in East Antarctica are Mount Melbourne at 9,016 ft (2,732 m), peaks lying beneath the Beardmore Glacier 14,942 ft (4,528 m), and the Gamgurtsev subglacial mountains 13,300 ft (4,030 m).

Plateaus

Even where it is not mountainous, Antarctica's elevations are high. It's average elevation of roughly 8,000 ft (2,440 m) is greater than that of any other continent. As a consequence, most of the land outside of the mountain ranges can be considered plateau. Covered by thick ice, most of these plateaus have no names. The Hollick-Kenyon and Rockefeller Plateaus can be found in West Antarctica. The Polar Plateau lies over the South Pole in East Antarctica. The elevation of the South Pole is 9,355 ft (2,835 m).

Glaciers

In Antarctica, glaciers (ice sheets) completely cover the land forms beneath them, allowing only the most dramatic mountain peaks to poke through. Antarctic ice represents 90 percent of the world's total. Over land it averages 1.5 mi (2 km) thick, and is about 3 mi (3.5 km) thick at its thickest point. The East Antarctic glacier (ice sheet) is slightly larger that the West Antarctic ice sheet. Some coastal areas support a few lichens during the summer months, but the ice sheets are otherwise barren.

Glaciers move over the land at a slow and steady pace. Dramatic formations and striations (stripes, believed to be remnants of volcanic ash) may be observed in the glaciers. The advancing edge of the glacier becomes a high sheer cliff as the top levels of ice push forward. The polar ice cap moves an average of 33 ft (10 m) each year.

In East Antarctica, the continent's largest valley glacier, the Lambert Glacier, lies over several mountain peaks that rise to 3,355 ft (1,017 m). Massive sections of ice discharge from the Lambert Glacier to become part of the floating Amery Ice Shelf each year. Other noteworthy glaciers include the Skelton Glacier, Rennick Glacier, Recovery Glacier, and Beardmore Glacier. The Bentley Subglacial Trench, a canyon extending 8,333 ft (2,540 m) below sea level, is covered by solid ice, making it the lowest point on earth not underwater.

INLAND WATERWAYS

Lakes

While a large portion of the world's fresh water is located on Antarctica, it is mostly in the form of ice. Antarctica's largest known lake, Lake Vostok, is approximately the size of North America's Lake Erie. Other lakes found in the McMurdo Dry Valleys, the valleys that lie between mountain peaks around the McMurdo Research Station in East Antarctica, include Lake Vanda, Lake Brownworth, Lake Fryxell, Lake Bonney, and Lake Hoare. These lakes are fed by glacial melt from the glaciers that lie in the deepest mountain valleys. During the summer, the air temperatures warm to about freezing (32°F / 0°C), causing the glaciers to melt slightly and to send water flowing into small streams for a few weeks, before the temperature again drops below freezing. The stream flow feeds the lakes, which lie beneath 10 ft (3 m) of permanent ice cover. Non-frozen water exists in the lakes beneath the ice. These lakes are believed to be 100 ft (30 m) deep or deeper. Scientists are studying these lakes to determine whether they support any marine life. To conduct their experiments, they must use exceptionally sterile methods to collect specimens, to avoid contaminating the glacial environment.

Rivers

The only river of any significance on Antarctica is the Onyx River. It is the largest of the streams that flow during the summer months. The Onyx River flows into Lake Vanda.

THE COAST, ISLANDS, AND THE OCEAN

The Southern Ocean

In 2000, the International Hydrographic Association delimited a new ocean, called the Southern Ocean, that encompasses all of the water south of 60° latitude. Since this decision Antarctica has been completely surrounded by the Southern Ocean. Before it was considered to border on the South Atlantic, South Pacific, and Indian Oceans. Due to the great temperature differences between the ice and the open ocean, as well as the lack of any land to impede them, powerful winds blow across the Southern Ocean and the southernmost parts of the surrounding oceans.

The Southern Ocean is home to the Antarctic Circumpolar Current. This ocean current flows east completely around the earth in a great circle to the north of Antarctica. The current is the most powerful on earth, and unique in that it is unimpeded by landforms in its passage around the globe. The current tends to keep cold water to the south, near Antarctica, and holds warmer water back to the north, with a relatively sharp boundary flowing down the middle of the current known as the Antarctic Convergence.

Sea Ice

Even during the summer only a few coastal areas are ever free of ice, including parts of Wilkes Land in East Antarctica and parts of the Antarctic Peninsula. During the winter the ocean around Antarctica freezes, surrounding the continent with ice that expands far out to sea. In winter the ice surrounding the Antarctic land mass grows at the rate of about 40,000 sq mi (103,600 sq km) per day. By the heart of winter it is roughly six times as extensive as normal, expanding the effective size of the continent to 13,000,000 sq mi (33,000,000 sq km).

Coastal Waters

The Bellingshausen Sea lies off the west coast of the Antarctic Peninsula; it is named for Russian explorer Fabian von Bellingshausen, the first to sail completely around Antarctica in 1819–21; his expedition also gave names to Queen Maud Land and Peter I island. Off of West Antarctica is the Amundsen Sea, named for the first man to reach the South Pole (on December 14, 1911), the Norwegian explorer Roald Amundsen.

The Ross Sea lies off the coast of the Ross Ice Shelf directly south of New Zealand; both are named for Sir James C. Ross, an explorer in the region in 1839–43 from the United Kingdom. Also named for a British explorer—James Weddell—is the Weddell Sea, the body of water east of the Antarctic Peninsula. Weddell conducted his expedition to Antactica in 1823.

The whales that inhabited the waters around Antarctica were hunted without controls in the late 1800s and the early decades of the 1900s, until the International Whaling Commission imposed protection for most species to prevent their extinction. A similar pattern developed for fur seals: they were hunted to the point of near-extinction, but since the 1978 promulgation of a treaty to protect them, populations have been thriving in Antarctica. Many species of penguin are also native to Antarctic waters.

Major Islands

Alexander Island (16,700 sq mi/43.200 sq km), Antarctica's largest island, is separated from the Antarctic Peninsula by the George VI sound, although thick ice sheets connect the two land masses. There are dozens of smaller islands in the Bellingshausen Sea and Amundsen Seas, including Thurston, Siple, Carney, and Charcot Islands. Further north along the Antarctic Peninsula is Adelaide Island and the Palmer Archipelago. Most of these islands are connected to the main land mass by ice.

Berkner Island (1,500 sq mi/3,880 sq km), covered by the Ronne and Filchner Ice Shelves, lies in the McCarthy Inlet of the Weddell Sea. Roosevelt Island is the largest found within the Ross Sea, but it is covered by the Ross Ice Shelf. Ross Island is smaller, but has access to the ocean in the summer months.

The South Shetland Islands, lying between Antarctica and the southern tip of South America, include Deception Island and King George I island, among others. Deception Island, which lies in an active volcanic field known as the Branfield Rift, is horseshoe shaped, with a caldera (surface area of about 10 sq mi/26 sq km) that is breached at one end and accessible from the open sea. The water of the caldera is heated by underground volcanic activity, and has at times reached the boiling point. Destructive volcanic eruptions occurred in 1967, 1969, 1970, and 1991; more eruptions are predicted for the future. Also lying in the ocean between Antarctica and South America are the South Orkney Islands, South Georgia, and the South Sandwich Islands. Zavadovski Island in the South Sandwich Islands is home to one of the largest penguin colonies in the world—estimated at two million penguins.

The Coast and Beaches

Ice shelves—thick fields of ice formed by glaciers that last year round—cover almost half the coastal regions. These glaciers move slowly toward the sea at speeds of less than one mile per hour (2,950 to 4,250 ft / 900 to 1300 m per year), and in some places extend out into the water for hundreds of miles.

The Ross Sea indents Antarctica on one side, the Weddell Sea on the other. Both have enormous ice shelves covering the parts of them closest to the shore and the South Pole. The Ross Ice Shelf, in the sea of the same name, is the largest with an area of roughly 130,100 sq mi (336,770 sq km). The Ronne, Filchner, Larsen, and Riiser-Larsen Ice Shelves are all found in the Weddell Sea.

West Antarctica has a highly irregular coastline, with many small peninsulas and inlets, most of them ice-covered. The S-shaped Antarctic Peninsula extends far to the northeast. It comes closer to another continent than any other part of Antarctica; South America is hundreds of miles to the north across the Drake Passage. Away from the Weddell and Ross Seas East Antarctica has a much more regular coastline than the western part of the continent. It arcs in a rough half circle from one sea to the other. For most of its length the coast is much closer to the Antarctic Circle than in West Antarctica, and as a consequence the ice shelves are smaller. Prydz Bay, the only significant indentation on the middle of the East Antarctic coast, is mostly covered by the Amery Ice Shelf. East Antarctica extends north slightly beyond the Antarctic Circle at Cape Ann and Cape Poinsett. The Shackleton Ice Shelf lies not far from the second of these capes. Cape Adare marks the point where the East Antarctic coast curves sharply inwards to form one side of the Ross Sea.

CLIMATE AND VEGETATION

Temperature

About 97 percent of the surface of Antarctica is permanently covered by ice, more than 15,000 ft (4500 m) thick at its thickest point. The mean annual temperature in the interior is a frigid -71°F (-57°C), with the mean summer temperature -40°F (-40°C) and mean winter temperature -90°F (-68°C). In the coastal areas the mean summer temperature is 32°F (0°C). McMurdo Station near the Ross Ice Shelf in East Antarctica has the most moderate climate, with a mean winter temperature of 16°F (–9C°). The lowest temperature ever recorded on Earth was at Vostok, East Antarctica, where a reading of - 129°F (-89°C) was taken in 1983.

Since the 1950s, scientists have recorded an overall increase in temperature on Antarctica of about 4°F (2°C), which is much more than the increase in overall temperature elsewhere in the world. Five of the largest ice shelves have shrunk in size during this time period. Some scientists speculate that this is an early sign of global warming caused by human activity, but this has not been proven.

Sunlight

Antarctica has continuous daylight from mid-September to mid-March, when the continent receives more solar radiation than equatorial regions; and six months of continuous darkness from mid-March to mid-September.

Observation has shown that the layer of high atmosphere ozone that helps reflect harmful solar radiation away from the Earth's surface is thin to nonexistent over Antarctica. The ozone hole varies in size from season to season but appears to be expanding. Many blame human activity for this hole in the ozone, but the exact causes are unknown.

Rainfall

Most of the continent receives less than 2 in (5 cm) of precipitation (in the form of snow) annually. Due to this lack of precipitation the entire continent is technically considered a desert, despite the fact that it holds more than two-thirds of the world's fresh water.

HUMAN POPULATION

There is no native human population. During the summer months, as many as several thousand scientists may be in residence at the scientific research stations in Antarctica; in addition, several thousand tourists travel to Antarctica by ship or airplane. Few scientists remain year round. McMurdo Station, a U.S. research station, is the largest settlement. Amundsen-Scott—another U.S. research station—is located at the South Pole.

NATURAL RESOURCES

Antarctica is believed to be rich in mineral resources, but the severe climate combined with the complexities of the international relationships has made exploration and exploitation impractical. Deposits of copper, lead, zinc, gold, and silver and extensive deposits of coal have been identified on the Antarctic Peninsula, and iron ore has been found in East Antarctica. A 1991 treaty restricts mineral exploration to scientific purposes only.

FURTHER READINGS

Campbell, David G. The Crystal Desert: Summers in Antarctica. Boston: Houghton Mifflin, 1992.

Mastro, Jim. Antarctica: A Year at the Bottom of the World. Boston: Little, Brown, 2002.

Mount Erebus Volcano Observatory. http://www.ees.nmt.edu/ Geop/mevo/mevo.html (accessed June 12, 2002).

Public Broadcasting Service. Antarctic Almanac. http://www.pbs.org/wgbh/nova/warnings/almanac.html (accessed June 12, 2002).

Stewart, John. Antarctica: An Encyclopedia. Jefferson, N.C.: McFarland, 1990.

Wheeler, Sara. Terra Incognita: Travels in Antarctica. London: Vintage, 1997.

GEO-FACT

I ce shelves are generally thought of as permanent, unlike the sea ice that forms around Antarctica in the winter only to melt again in the summer. However, it is common for parts of an ice shelf to break away, forming icebergs in a process called "calving." Most icebergs are small, but occasionally huge sections of the Antarctic ice shelves have been known to break away. An iceberg estimated to be the size of Belgium (208 mi / 260 km long and 60 mi / 75 km wide)—the largest recorded as of 2002—was sighted off Antarctica in November, 1956. In October, 1987, an iceberg measuring 1,750 sq mi (more than 4,500 sq km—nearly the size of Delaware) broke away from the Ross Ice Shelf.

In 1995 and then again in 2002, huge chunks of the Larsen Ice Shelf collapsed into the Weddell Sea, forming many icebergs. The area that collapsed in 2002 was roughly the size of Rhode Island, and contained approximately 500 million billion tons of sheet ice. The remaining ice shelf is only 40 percent of its pre-1995 size. These and other dramatic collapses have stimulated concerns about global warming.

Antarctica

views updated Jun 08 2018

Antarctica

Antarctica, lying at the southernmost tip of the world, is the coldest, driest, and windiest continent. Ice covers 98 percent of the land, and its 5,100,000 square miles (13,209,000 square kilometers) cover nearly one-tenth of Earth's land surface, about the same size as Europe and the United States combined. Despite its barren appearance, Antarctica and its surrounding waters and islands teem with life, and the continent plays a significant role in the climate and health of the entire planet.

Although humans have never settled on Antarctica because of its brutal climate, since its discovery in the early 1800s explorers and scientists have traveled across dangerous seas to study the continent's winds, temperatures, rocks, wildlife, and ice. While some countries have tried to claim parts of the continent as their own, Antarctica is an independent

continent protected by international treaty from ownership by any one country.

Overview

Archaeologists and geologists believe that millions of years ago Antarctica was part of a larger continent called Gondwanaland. About 200 million years ago, as a result of shifting in the plates of Earth's crust, Gondwanaland broke apart and created the separate continents of Antarctica, Africa, Australia, South America, and India. Antarctica is currently centered roughly on the geographic South Pole, the point where all south latitudinal lines meet. It is the most isolated continent on Earth, 600 miles (1,000 kilometers) from the southernmost tip of South America and more than 1,550 miles (2,500 kilometers) away from Australia.

Seventy percent of Earth's freshwater is frozen atop the continent. These icecaps reflect warmth from the Sun back into the atmosphere, preventing the planet from overheating. Huge icebergs break away from the stationary ice and flow north to mix with warm water from the equator, producing currents, clouds, and complex weather patterns. Creatures as small as microscopic phytoplankton and as large as whales live on and around the continent, including more than 40 species of birds.

Geology. Almost all of Antarctica is under ice, in some areas by as much as 2 miles (3 kilometers). The ice has an average thickness of about 6,600 feet (2,000 meters), which is higher than most mountains in warmer countries. This grand accumulation of ice makes Antarctica the highest continent on Earth, with an average elevation of 7,500 feet (2,286 meters). If all of this ice were to melt, global sea levels would rise by about 200 feet (65 meters), flooding the world's major coastal ports and vast areas of low-lying land.

Under the ice, the Antarctic continent is made up of mountains. The Transantarctic Mountains are the longest range on the continent, stretching 3,000 miles (4,828 kilometers) from the Ross to Weddell Seas. Vinson Massif, at 16,859 feet (5,140 meters), is the highest mountain peak. The few areas where mountains peak through the ice are called nunataks.

Around several parts of the continent, ice forms vast floating shelves. The largest, known as the Ross Ice Shelf, is about the same size as Texas or Spain. Since the shelves are fed by glaciers on the continent, the resulting shelves and icebergs are made up of frozen freshwater. The largest glacier on Earth, the Lambert Glacier on the eastern half of the continent, is 25 miles (40 kilometers) wide and more than 248 miles (400 kilometers) long.

Gigantic icebergs are a unique feature of Antarctic waters. They are created when huge chunks of ice separate from an ice shelf, a cliff, or a glacier, a process known as calving. Icebergs can be amazingly huge; an iceberg measured in 1956 was 208 miles (335 kilometers) long by 60 miles (97 kilometers) wide, and was estimated to contain enough freshwater to supply the water needs of London, England, for 700 years. Only 10 to 15 percent of an iceberg normally appears above the water's surface. As these icebergs break away from the continent, new ice is added to the continent by snowfall.

Icebergs generally flow northward and, if they don't become trapped in a bay or inlet, will reach the Antarctic convergence, the point in the ocean where cold Antarctic waters meet warmer waters. At this point, ocean currents usually sweep the icebergs from west to east until they melt. An average iceberg will last several years before melting.

Climate. Antarctica is the windiest and coldest place on Earth. The wind can gust up to 200 miles per hour, or twice as hard as the average hurricane. Little snow actually falls in Antarctica; because the air is so cold, what snow that does fall turns immediately to ice. In winter, temperatures may fall to 100°F (73°C). The world's record for lowest temperature was recorded on Antarctica in 1960, when it fell to 126.9°F (89.8°C).

Strong winds constantly travel over the continent as cold air races over the high ice caps and then flows down to the coastal regions. Winds associated with Antarctica blizzards commonly gust to more than 120 miles (193 kilometers) per hour, and are among the strongest winds on Earth. Even at its calmest, the continent's winds can average 50 to 90 miles (80 to 145 kilometers) per hour.

Even with all its ice and snow, Antarctica is the driest continent on Earth based on annual precipitation amounts. The constantly cold temperatures have allowed each year's annual snowfall to build up without melting over the centuries. Along the polar ice cap, annual snowfall is only 1 to 2 inches (2.5 to 5 centimeters). More precipitation falls along the coast and in the coastal mountains, where it may snow 10 to 20 inches (25 to 51 centimeters) per year.

Plants and animals. The Antarctic continent is nearly barren due to the persistently cold and dry climate. Hardy plants like pearlwort (a flowering plant), mosses, and lichen (a combination of algae and fungi) are found along the coast and on the Antarctic Peninsula, the warmest part of the continent.

Few creatures can survive Antarctica's brutal climate. Life in the sea and along the coast of Antarctica and its islands, however, is often abundant. Several seabirds make the Antarctic their home, including 24 species of petrels, small seabirds that dart over the water and nest in rocks along the shore. A wide variety of animals make the surrounding waters their home, from zooplankton (small floating organisms) to seals and whales.

Of all the animals, penguins are the primary inhabitants of Antarctica. Believed to have evolved 40 to 50 million years ago, they have oily feathers that provide a waterproof coat and a thick layer of fat for insulation. Penguins' bones are solid, not hollow as are those of most flying birds. Solid bones add weight, making it easier for penguins to dive into the water for food. These bones also prevent them from flying, but because they do not have predators that can live in the brutally cold climate, they do not need to fly. Thus their wings have evolved over the centuries to resemble flippers or paddles.

Words to Know

Antarctic Circle: The line of latitude at 66°32'S, where there are 24 hours of daylight in midsummer and 24 hours of darkness in midwinter.

Antarctic convergence: 25-mile (40-kilometer) region where cold Antarctic surface water meets warmer water and sinks below it.

Antarctic Ocean: The seas surrounding the continent, where the Atlantic, Pacific, and Indian Oceans converge.

Calving: When huge chunks of ice or icebergs break off from ice shelves and sheets.

Glacier: A river of ice that moves down a valley to the sea, where it breaks into icebergs.

Nunataks: Mountain peaks that thrust through the ice and snow cover.

South Pole: The geographically southernmost place on Earth.

Exploration of the continent

Greek philosopher Aristotle hypothesized more than 2,000 years ago that Earth was round and that the Southern Hemisphere must have a land-mass large enough to balance the lands in the Northern Hemisphere. He called the proposed land mass Antarktikos, meaning the opposite of the Arctic.

The continent remained a mystery until English navigator and explorer James Cook crossed the Antarctic Circle and sailed around the continent in 1773. While he stated that the land was uninhabitable because of the ice fields surrounding the continent, he noted that the Antarctic Ocean was rich in whales and seals. For the next 100 years, hunters exploited this region for the fur and oil trade, traveling ever farther and farther south.

In 1895, the first landing on the continent was accomplished by the Norwegian whaling ship Antarctic. The British were the first to spend a winter on Antarctica, in 1899. By 1911, a race had begun to see who would first reach the South Pole, an imaginary geographical center point at the bottom of Earth. Again, a Norwegian, Roald Amundsen, was the first to reach it, on December 14, 1911.

Scientific exploration

The International Geophysical Year (IGY), from July 1, 1957, to December 31, 1958, was a planned cooperative venture by scientists from 56 nations to study a variety of subjects. During this venture, 12 nations conducted research in Antarctica, setting up base camps in various locations, some of which are still used today. Topics of research included

the pull of gravity, cosmic rays, the southern lights, and changes in the atmosphere.

Since these cooperative research projects, several agreements have been signed to ensure that political conflicts do not arise concerning research and use of Antarctica. The Antarctic Treaty was signed on December 1, 1959, by the 12 nations involved in the IGY projects, and made official on June 23, 1961, after each country ratified it within their own governments. As of April 1994, 42 countries had committed themselves to the spirit of cooperation outlined in the treaty, making it one of the most successful international agreements ever created.

The treaty requires all countries to give up any territorial claims, to exchange scientific investigations and results, and to stop all military activity and weapons testing (including nuclear testing and the disposal of radioactive wastes) in the region. Any disputes that cannot be settled by negotiation or arbitration are sent to the International Court of Justice for settlement. The treaty thus sets aside 10 percent of Earth as a nuclear-free, demilitarized zone.

In 1991, the countries added the Protocol on Environmental Protection to the treaty. The Protocol grew out of concerns that poor habits by researchers and increasing numbers of tourists were increasing pollution problems on the continent. It requires countries to protect the continent's ecosystem (its community of plants and animals), paying particular attention to the production and disposal of wastes.

Current events

A wide variety of research is continuing on Antarctica. Astronomer's find the continent's cold temperatures and high altitude allow for a clearer view of the stars and planets. Antarctica is also the best place to study interactions between solar wind and Earth's magnetic field, temperature circulation in the oceans, unique animal life, ozone depletion, ice zone ecosystems, and glacial history. Buried deep in Antarctica ice lie clues to ancient climates, which may provide answers to whether Earth is due for global warming or the next ice age.

[See also Greenhouse effect; Ozone; Plate tectonics ]

Antarctica

views updated Jun 11 2018

Antarctica


The earth's fifth largest continent, centered asymmetrically around the South Pole. Ninety-eight percent of this land mass, which covers approximately 5.4 million mi2 (13.8 million km2), is covered by snow and ice sheets to an average depth of 1.25 mi (2 km). This continent receives very little precipitation, less than 5 in (12 cm) annually, and the world's coldest temperature was recorded here, at -128°F (-89°C). Exposed shorelines and inland mountain tops support life only in the form of lichens , two species of flowering plants, and several insect species. In sharp contrast, the ocean surrounding the Antarctic continent is one of the world's richest marine habitats. Cold water rich in oxygen and nutrients supports teeming populations of phytoplankton and shrimp-like Antarctica krill , the food source for the region's legendary numbers of whales , seals , penguins, and fish. During the nineteenth and early twentieth century, whalers and sealers severely depleted Antarctica's marine mammal populations. In recent decades the whale and seal populations have begun to recover, but interest has grown in new resources, especially oil, minerals, fish, and tourism.

The Antarctic's functional limit is a band of turbulent ocean currents and high winds that circle the continent at about 60 degrees south latitude. This ring is known as the Antarctic convergence zone. Ocean turbulence in this zone creates a barrier marked by sharp differences in salinity and water temperature. Antarctic marine habitats, including the limit of krill populations, are bounded by the convergence.

Since 1961 the Antarctic Treaty has formed a framework for international cooperation and compromise in the use of Antarctica and its resources. The treaty reserves the Antarctic continent for peaceful scientific research and bans all military activities. Nuclear explosions and radioactive waste are also banned, and the treaty neither recognizes nor establishes territorial claims in Antarctica. However, neither does the treaty deny pre-1961 claims, of which seven exist. Furthermore, some signatories to the treaty, including the United States, reserve the right to make claims at a later date. At present the United States has no territorial claims, but it does have several permanent stations, including one at the South Pole. Questions of territorial control could become significant if oil and mineral resources were to become economically recoverable. The primary resources currently exploited are fin fish and krill fisheries. Interest in oil and mineral resources has risen in recent decades, most notably during the 1973 "oil crisis." The expense and difficulty of extraction and transportation has so far made exploitation uneconomical, however.

Human activity has brought an array of environmental dangers to Antarctica. Oil and mineral extraction could seriously threaten marine habitat and onshore penguin and seal breeding grounds. A growing and largely uncontrolled fishing industry may be depleting both fish and krill populations in Antarctic waters. The parable of the Tragedy of the Commons seems ominously appropriate to Antarctica fisheries, which have already nearly eliminated many whale, seal, and penguin species. Solid waste and oil spills associated with research stations and with tourism pose an additional threat. Although Antarctica remains free of "permanent settlement," 40 year-round scientific research stations are maintained on the continent. The population of these bases numbers nearly 4,000. In 1989 the Antarctic had its first oil spill when an Argentine supply ship, carrying 81 tourists and 170,000 gal (643,500 l) of diesel fuel, ran aground. Spilled fuel destroyed a nearby breeding colony of Adele penguins (Pygoscelis adeliae ). With more than 3,000 cruise ships visiting annually, more spills seem inevitable. Tourists themselves present a further threat to penguins and seals. Visitors have been accused of disturbing breeding colonies, thus endangering the survival of young penguins and seals.

[Mary Ann Cunningham ]


RESOURCES

BOOKS

Child, J. Antarctica and South American Geopolitics. New York: Praeger, 1988.

Parsons, A. Antarctica: The Next Decade. Cambridge: Cambridge University Press, 1987.

Shapely, D. The Seventh Continent: Antarctica in a Resource Age. Baltimore: Johns Hopkins University Press for Resources for the Future, 1985.

Suter, K. D. World Law and the Last Wilderness. Sydney: Friends of the Earth, 1980.

Antarctica

views updated May 21 2018

Antarctica

In contrast to most North Americans who tend to think of Antarctica as a remote and isolated continent, many Latin Americans, especially those in the Southern Cone, view Antarctica as relatively close and linked to the South American mainland through geology, geopolitics, and history. The tip of the Antarctic Peninsula is only about 600 miles from Tierra del Fuego, and two South American nations, Argentina and Chile, have made formal claims of sovereignty to portions of Antarctica. Furthermore, the 1947 Rio Treaty (Inter-American Treaty of Reciprocal Assistance) defines the security zone of the Americas as extending to the South Pole and includes the sectors claimed by Argentina and Chile. Thus, there is reason to speak of a "South American quadrant" of Antarctica extending from the Greenwich Meridian (0 longitude) to 90 west longitude.

No human being had seen Antarctica until early in the nineteenth century, when, within a few short years, British, Russian, and U.S. sailors reported discovering it. There is also a suggestion (unfortunately without documentation) that sealers operating out of Buenos Aires might have seen Antarctica as early as 1817.

During the so-called heroic period of Antarctic exploration in the early twentieth century, the southern nations of Latin America supported expeditions from Europe and the United States by providing them with supplies and assisting in rescue efforts when necessary. Two noteworthy efforts were the Argentine rescue of a Swedish expedition in 1903 and that of Sir Ernest Shackleton's crew by the Chileans a decade later.

By the late 1940s seven nations had made sovereignty claims to Antarctica, three of which (Argentina, Chile, and Great Britain) overlapped in the South American Antarctic quadrant. The nationalistic regime of Juan Domingo Perón in Argentina stressed the linkage between the Argentine Antarctic claim and the effort to recover Las Malvinas (Falkland Islands). Tensions between Great Britain and Chile were exacerbated to the point that there were numerous diplomatic protests and at least one shooting incident.

To defuse Antarctic tensions, a group of twelve nations proposed a program of scientific cooperation (the International Geophysical Year, 1957–1958), and out of this effort grew the Antarctic Treaty (signed 1959; in force since 1961), which ensures that a demilitarized Antarctica is preserved for scientific study. The treaty does not permit new or expanded sovereignty claims, but does not require nations with preexisting claims to abandon them.

More than forty nations have signed the Antarctic Treaty, and almost half of these maintain permanent or temporary scientific stations on the ice. These include Argentina, Chile, Brazil, Uruguay, Peru, and Ecuador; Colombia and Cuba have also signed the treaty and have sent personnel to Antarctic bases of other countries.

Tensions over international competition for Antarctic resources, especially mineral deposits, were eased in October 1991 at a special meeting in Madrid, when the treaty members signed a "Protocol on Environmental Protection." The protocol confirms that Antarctica should be a special natural reserve dedicated to peace and science; a key provision bans mining activity in Antarctica for at least fifty years.

In September of 2004, the Buenos Aires-based Antarctic Treaty Secretariat was formally established by the Antarctic Treaty Consultative Meeting (ATCM) to oversee international involvement in Antarctica, and to support the annual ATCM and CEP (Committee for Environmental Protection) meetings.

See alsoRio Treaty (1947) .

BIBLIOGRAPHY

Peter J. Beck, The International Politics of Antarctica (1986).

Jack Child, Antarctica and South American Geopolitics: Frozen Lebensraum (1988); translated as Geopolítica del Cono Sur y la Antártida (1990).

Carlos J. Moneta, ed., La Antártida en el sistema interna-cional del futuro (1988).

M. J. Peterson, Managing the Frozen South: The Origin and Evolution of the Antarctic Treaty System (1988).

Philip J. Quigg, A Pole Apart (1983).

Deborah Shapley, The Seventh Continent: Antarctica in a Resource Age (1985).

Reader's Digest, Antarctica, 2d ed. (1990).

Additional Bibliography

Antarctic Treaty Secretariat, http://www.ats.aq/.

                                               Jack Child

Antarctica

views updated May 29 2018

Antarctica

Antarctica is the second-largest continent on Earth. The land mass covers 5,405,400 square miles (14 million sq. km), most of which is encased under a thick layer of ice. In some areas, the ice is as deep as 6,560 feet (2,000 meters). Only 2% of Antarctica's land is exposed, and those areas are nothing more than barren rock. Glaciers and ice shelves along the coast, as well as floating ice pieces, account for about 11% of Antarctica's total area. The country's highest point is Vinson Massif, at 16,863 feet (5,140 meters).

Antarctica is the coldest, windiest, highest, and driest continent. Temperatures vary according to season, altitude, and distance from the ocean. The eastern portion of Antarctica is cooler than the west. Temperatures average about -58° F (-50° C). During summer months, Antarctica is hit with more solar radiation than the equator in the same amount of time. Blizzards are common there, and storms often form over the ocean and travel along the continent's coast.

The continent has many natural resources, including iron ore, chromium, copper, gold, nickel, platinum, and other minerals. There are also small deposits of coal and hydrocarbons. Antarctica contains more than 80% of the world's freshwater. None of its natural resources have been mined or sold.

Antarctica is home to a variety of wildlife, including seals, whales, and penguins. These animals are well adapted for the icy climate they live in—the polar fish, for example, common in Antarctica's waters, is able to survive because it has anti-freezing agents in its blood. Several species are unique to Antarctica, including the King penguin.

There are no indigenous inhabitants of Antarctica. Several research stations are located there, and staff members are sometimes stationed temporarily. In the summer, the population sometimes rises to more than 4,000 people representing 25 different countries; during the winter, approximately 1,000 researchers are stationed there. There are radio broadcast stations available in Antarctica for communication. There are also 39 different landing facilities for airplanes. Planes must be fitted with skis to be able to land. There are no telephones or cars on Antarctica.

Antarctica is governed under the Antarctic Treat Summary, which was signed on December 1, 1959. Thirty nations signed the treaty, and another 14 countries are considered "observers." These nations have appointed members to a panel that consults and manages Antarctica. They meet each year to discuss environmental, scientific, and political issues. Today, rivalries remain between these countries, because many still wish to claim the continent as their own. Tourism has recently become more popular and is a growing industry.

Antarctica

views updated Jun 08 2018

Antarctica Fifth-largest continent (larger than Europe or Australasia), covering almost 10% of the world's total land area. Surrounding the South Pole, it is bordered by the Antarctic Ocean and the s sections of the Atlantic, Pacific, and Indian Oceans. Almost entirely within the Antarctic Circle, it is of great strategic and scientific interest. No people live here permanently, though scientists frequently stay for short periods to conduct research and exploration. Seven nations lay claim to sectors of it. Covered by an ice-sheet with an average thickness of c.1800m (5900ft), it contains c.90% of the world's ice and more than 70% of its freshwater.

http://www.antdiv.gov.au; http://www.antarctica.ac.uk

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