Antarctica , the fifth largest continent, c.5,500,000 sq mi (14,245,000 sq km), asymmetrically centered on the South Pole and almost entirely within the Antarctic Circle.

Geology and Geography

Antarctica consists of two major regions: W Antarctica (c.2,500,000 sq mi/6,475,000 sq km), a mountainous archipelago that includes the Antarctic Peninsula , and E Antarctica (c.3,000,000 sq mi/7,770,000 sq km), geologically a continental shield. They are joined into a single continental mass by an ice sheet thousands of feet thick. At the seaward margins of the ice sheet masses of ice break off and float away as icebergs, leaving ice cliffs. Where the outward creep of the ice is channeled into ice streams (zones of more rapid flow), great floating ice tongues project into the sea; where mountains retard outward movement, the flow is channeled into great valley glaciers.

Less than 5% of Antarctica is free of ice; these areas include mountain peaks, arid "dry valleys," small coastal areas, and islands. Except for mountain ranges (some buried beneath the ice), much of E Antarctica's rock surface is near sea level; however, the continent's domed, snow-covered glacial surface rises to about 13,000 ft (4,000 m). In W Antarctica there is great variation in the subglacial relief, suggesting mountainous islands or submerged ranges separated by deep sounds beneath the ice cover. Since the 1970s more than 100 lakes of liquid water have been identified underneath the continental ice; the largest known of these is Lake Vostok , which lies 2.5 mi (4 km) beneath the Russian Vostok research station in E Antarctica. Many of the lakes are connected by subglacial rivers.

The two major coastal indentations are the Ross Sea, facing the Pacific Ocean, and the Weddell Sea, facing the Atlantic Ocean. At the head of each sea are great ice shelves, the Ross ice shelves in the Ross Sea and the Ronne and the Filchner ice shelves in the Weddell Sea. Partly aground but mostly afloat, these nearly level ice shelves are from 600 to 4,000 ft (180-1,220 m) thick. They move steadily toward the sea and are fed by valley glaciers, ice streams, and surface snow accumulations. Smaller ice shelves are found all along the coast.

The Transantarctic Mts (c.3,500-14,300 ft/1,100-4,400 m high), which extend from the east side of the Filchner Ice Shelf to the western portal of the Ross Sea, form the inner margin of E Antarctica. Primarily formed by block faulting (see mountains ), the lower slopes have a complex structure of late Precambrian and early Paleozoic metamorphic rocks. These are overlaid by essentially horizontal sedimentary rock, mainly of continental or near-shore origin and ranging in age from the Devonian period to the early Jurassic, which are similar to rocks found in Australia, S Africa, and E South America; coal-bearing Permian strata are also found there. Distinctive plant, insect, fish, and animal fossils in the Triassic and Jurassic strata strongly indicate that the continents of the Southern Hemisphere are parts of an ancient supercontinent, Gondwanaland, which broke up in the late Mesozoic era. The continents have since drifted to their present positions.

The ice-drowned, mountainous archipelago of W Antarctica is related to the Andes Mts. of South America and is structurally connected to them by way of the Antarctic Peninsula and the Scotia Arc (South Georgia and the South Orkney and South Sandwich islands). The complex structure consists of highly folded metasedimentary strata from Paleozoic to Pliocene epochs. There has been much volcanism down to the present. Mountains of the Antarctic Peninsula rise to c.11,000 ft (3,350 m); the mountains of Marie Byrd Land have comparable heights. The Ellsworth Mts., at the head of Ronne Ice Shelf, are the highest in Antarctica; Vinson Massif (16,860 ft/5,140 m) is the continent's highest peak. A variety of mineral deposits have been discovered in Antarctica, but the extent of the deposits is largely unknown and their relative inaccessibility makes their utility doubtful.

Antarctica is surrounded by the world's stormiest seas. A belt of pack ice surrounds the continent; only a few areas are ice-free at the end of most summers. The physical boundary most widely accepted today for the antarctic region is the Antarctic Convergence, a zone c.25 mi (40 km) wide encircling the earth along a fluctuating, zigzagging line between 48°S and 61°S,. Within this zone the colder and denser north-flowing antarctic surface waters sink beneath warmer and saltier subantarctic waters; the difference in temperature and chemical content of the water on the two sides of the zone is reflected in noticeable differences in air temperature and in marine life. These differences and other characteristics have led oceanographers to regard the waters around Antarctica as a fifth ocean, the Southern Ocean (also known as the Antarctic Ocean).

Climate

Antarctic climate is characterized by low temperature, high wind velocities, and frequent blizzards. Rapidly changing weather is typical of coastal locations, where temperatures for the warmest month average around freezing. Winter minimums drop as low as -40°F (-40°C). High altitude and continuous darkness in winter combine to make the interior of Antarctica the coldest place on earth. Summer temperatures are unlikely to be warmer than 0°F (-18°C); winter mean temperatures are -70°F (-57°C) and lower. The lowest temperature ever recorded on earth was -126.9°F (-88.3°C) at Vostok, a Russian station. Precipitation is in the form of snow; the annual water equivalent in the interior is c.2 in. (5 cm) and c.10 in. (25 cm) in coastal areas. In the dry, dust-free air one can see for tens of miles in clear weather; distances are deceptive, and mirages are common. Scattering of light by blowing snow or low clouds causes "whiteouts" in which the sky blends with the snow-covered surface, eliminating the horizon; no condition is more feared by aviators.

Antarctic Life

There is no native human population in Antarctica, nor are there any large land animals. Few species are adapted to the antarctic environment, but individuals of these few species are numberless. Life that depends completely on the land is limited to microscopic life in summer meltwater ponds, tiny wingless insects living in patches of moss and lichens, and two types of flowering plants (both in the Antarctic Peninsula). Birds and seals that spend part of their time on land (e.g., emperor and Adélie penguins and the brown skua—the most southerly bird and a notorious predator—and Weddell, crabeater, and Ross seals) are dependent on the surrounding sea for food. Antarctic waters are rich in plankton, which serves as food for krill, small shrimplike crustaceans that are the principal food of baleen whales, crabeater seals, Adélie penguins, and several kinds of fish.

Fur and elephant seals, which spend the summers on islands north of lat. 65°S were the basis for 19th-century commercial activity in Antarctica. In the 20th cent., commercial interest shifted to baleen whales. Fur seals are recovering from the slaughter of the 19th cent., as are the elephant seals. Whaling has been declining since the peak year of 1930-31. In 1986 the International Whaling Commission imposed a moratorium on commercial whaling; the moratorium, however, has not been adhered to by all nations.

History of Exploration

Early Expeditions

Although there was for centuries a tradition that another land lay south of the known world, attempts to find it were defeated by the ice. Antarctica's frigid nature was revealed by the second voyage (1772-75) of the English explorer Capt. James Cook . He did not see the continent as he circumnavigated the world, but he was the first to cross the Antarctic Circle. British and U.S. seal hunters followed him to South Georgia, an island in the S Atlantic.

In 1819 the British mariner William Smith discovered the South Shetland Islands. Returning in 1820, he and James Bransfield of the British navy explored and roughly mapped the Shetlands and part of the shore of the Antarctic Peninsula. Searching for rookeries, sealers explored the coastal and offshore regions of the Antarctic Peninsula. Most notable were the British captains James Weddell, George Powell, and Robert Fildes and the Americans Nathaniel B. Palmer, Benjamin Pendleton, Robert Johnson, and John Davis. Davis made the first landing on the antarctic continent (Feb. 7, 1821) at Hughes Bay on the Antarctic Peninsula. First to spend the winter in Antarctica, on King George Island in 1821, were 11 men from the wrecked British vessel Lord Mellville.

After 1822 fur sealing declined, but in 1829-30 Palmer and Pendleton led a sealing and exploring expedition that included Dr. James Eights, the first U.S. scientist to visit Antarctica. John Biscoe, a British navigator, circumnavigated Antarctica from 1830 to 1832, sighting Enderby Land in 1831 and exploring the western side of the Antarctic Peninsula in 1832. John Balleny and Peter Kemp were other British sealers who made discoveries in E Antarctica in the 1830s.

Four naval exploring expeditions visited Antarctica in the first half of the 19th cent. Capt. T. T. Bellingshausen was the leader of a Russian expedition that circumnavigated Antarctica (1819-21). He apparently was the first to see (1820) the part of the continent that is now called Queen Maud Land. In W Antarctica he discovered (1821) Peter I Island and Alexander Island. Admiral J. S. C. Dumont d'Urville led a French expedition to the Pacific Ocean that made two visits to Antarctica. He explored in the area of the Antarctic Peninsula in 1838 and in 1840 discovered Clarie Coast and Adélie Coast in E Antarctica. In 1840 Lt. Charles Wilkes, leader of the U.S. Exploring Expedition to the Pacific (1838-42), sailed along the coast of E Antarctica for 1,500 mi (2,400 km), sighting land at nine points. British Capt. James C. Ross commanded two vessels on an expedition (1841-43) that discovered Victoria Land in E Antarctica, the Ross Sea, and the Ross Ice Shelf and explored and mapped the western approaches of the Weddell Sea.

Inland and to the Pole

In the 1890s, after a half-century of neglect, interest in Antarctica was revived. Norwegian and Scottish whaling firms sent ships (1892-93) to investigate the possibilities of whaling around the Antarctic Peninsula, and a Norwegian vessel examined the Ross Sea area, where a landing was made (1895) on Cape Adare. C. A. Larsen began whaling at South Georgia island in 1904-5, and the seas of the Scotia Arc became the center of Antarctic whaling until after 1926.

The 1890s also marked the beginning of a period of extensive Antarctic exploration, during which 16 exploring expeditions from nine countries visited the continent. For the first time, many of them were financed by private individuals and sponsored by scientific societies. It was a period of innovation and hardship in an extremely harsh, little-known environment. The Belgian expedition under Lt. Adrien de Gerlache was beset in the pack ice in Mar., 1898, and the ship drifted west across the Bellingshausen Sea for a year before it was released. A British expedition led by C. E. Borchgrevink was the first to establish a base for wintering on the continent (Cape Adare, 1899) and the first to make sledge journeys. Different parts of the Antarctic Peninsula and the islands of the Scotia Arc were explored by de Gerlache (1897-98), a Swedish expedition under Dr. Otto Nordenskjold (1901-4), the Scottish National Antarctic Expedition led by W. S. Bruce (1902-4), and two French expeditions led by Dr. Jean B. Charcot (1903-5 and 1908-10). Nordenskjold spent two winters in Antarctica before being rescued after his ship was crushed by ice.

Exploration in the Ross Sea area during this period was characterized by long inland journeys. Four British expeditions had bases on Ross Island at McMurdo Sound. British Capt. R. F. Scott headed two expeditions (1901-4 and 1910-13), E. H. Shackleton led another expedition (1907-9), and A. E. Mackintosh headed the Ross Sea Party of Shackleton's unsuccessful Trans-Antarctic Expedition (1914-17). Roald Amundsen , a Norwegian, set up his base at the Bay of Whales, an indentation in the front of the Ross Ice Shelf, and a Japanese expedition (1911-12) was ship-based. The British expeditions carried out extensive exploration and scientific investigation of Victoria Land. Shackleton sledged to within 97 mi (156 km) of the South Pole (Jan., 1909), but it was Amundsen who reached the Pole first, on Dec. 14, 1911. Scott reached it on Jan. 17, 1912, but he and four companions perished on the return trip.

The Weddell Sea border of E Antarctica was seen first by Bruce (1904), and it was later explored by the German expedition of Dr. Wilhelm Filchner, discoverer of the Filchner Ice Shelf, whose ship was beset and drifted in the Weddell Sea through the winter of 1912 before being released. Shackleton reached the Weddell Sea in Jan., 1915. He had planned to sledge to McMurdo Sound, via the South Pole, but his ship was beset and crushed in the ice, and his party lived on ice floes until they finally reached Elephant Island in boats. From there Shackleton made his epic voyage of c.800 mi (1,290 km) to South Georgia in an open boat.

Two other expeditions explored E Antarctica during the early 20th cent.—Dr. Erich von Drygalski 's well-equipped German expedition (1901-3) was cut short on the Wilhelm II Coast when the ship was beset; and Douglas Mawson , leader of the Australasian Expedition (1911-14) established bases at Commonwealth Bay on the George V Coast and on the Queen Mary Coast. Five major sledge journeys were made from Commonwealth Bay; two men perished and Mawson barely survived.

Technological Advances in Exploration

In the period following World War I, scientific and technological advances were applied to further antarctic exploration. The first airplane flight in Antarctica (Nov. 26, 1928) was by Sir George Hubert Wilkins , an Australian who later flew down the eastern side of the Antarctic Peninsula. However, it was U.S. explorer Richard E. Byrd who most successfully coordinated radios, tractors, airplanes, and aerial cameras for the purposes of exploration.

On his first expedition Byrd established his base, Little America, near the site of Amundsen's old base at the Bay of Whales. From Little America he made the first flight over the South Pole on Nov. 29, 1929. On this expedition Marie Byrd Land was discovered and explored from the air. On his second expedition (1933-35) Byrd successfully integrated flights with long sledge and tractor journeys in a more complete exploration of Marie Byrd Land.

In 1929-30 three other expeditions were also using aircraft for short flights over the coast. Wilkins in 1929-30 operated in the Bellingshausen Sea. A Norwegian captain, Hjalmar Riiser-Larsen, explored (1929-30) the coast of E Antarctica from Enderby Land to Coats Land; the area was later claimed by Norway as Queen Maud Land. In Nov., 1935, U.S. explorer Lincoln Ellsworth made the first transantarctic flight, from Dundee Island at the tip of the Antarctic Peninsula to the Bay of Whales, landing four times en route. The British Graham Land Expedition explored the Antarctic Peninsula by sea, air, and dog team from 1935 to 1937, using a different base each winter. Germany made a calculatedly spectacular effort at aerial surveying when two aircraft flying from a catapult ship photographed approximately 135,000 sq mi (350,000 sq km) of Queen Maud Land.

The Norwegians had done considerable exploration and mapping during the first two decades of antarctic whaling in the Scotia Arc. In 1925-26 they introduced pelagic whaling with factory ships that could operate in the open sea. Between 1927 and 1937 Lars Christensen led an extensive program of aerial exploration and mapping of the coast of E Antarctica from the Weddell Sea to the Shackleton Ice Shelf. Also allied to whaling were the investigations in physical oceanography, marine biology, and coastal mapping carried out by the Discovery Committee of the British Colonial Office from 1925 to 1939. Their major achievement was the discovery of the Antarctic Convergence.

International Rivalry

The 1930s were a period of international rivalry in Antarctica, and the map was cut into wedgelike territorial claims that in some places overlapped. Although the U.S. government did not make a claim or recognize those of other nations, it supported antarctic exploration. The U.S. Antarctic Service Expedition (1939-41), directed by Byrd, introduced the notion of permanent bases, one of which was set up at the Bay of Whales and another on Stonington Island W of the Antarctic Peninsula. The onset of World War II forced the evacuation of the bases, but before the war ended Great Britain, in order to offset claims by Chile and Argentina, had established permanent bases on the Antarctic Peninsula and off-lying islands.

Interest in Antarctica intensified after the war, and several governments established permanent agencies to direct antarctic affairs. Great Britain, Argentina, and Chile continued the system of scientific bases in the Antarctic Peninsula and Scotia Arc. Australia established bases on Heard and Macquarie islands, and France founded one on the Adélie Coast. From 1945 to 1957 the U.S. navy conducted Operation Highjump, an expedition involving c.5,000 men. About 60% of the coastline was photographed, as well as much of the interior bordering the Ross Ice Shelf.

The Ronne Antarctic Research Expedition (1947-48), led by Finn Ronne, was the last privately sponsored U.S. expedition. Using Byrd's old base on Stonington Island, Ronne closed the unexplored gap at the head of the Weddell Sea. A portent of the international cooperation soon to follow, the Norwegian-British-Swedish Antarctic Expedition was organized by the respective governments and scientific societies for exploration and scientific investigation in Queen Maud Land.

The International Geophysical Year

The International Geophysical Year (IGY), from July, 1957, through Dec., 1958, was planned to correspond with a period of maximum sunspot activity. As part of the IGY, 12 nations maintained 65 stations and operational facilities in Antarctica. The more difficult logistical problems of establishing inland bases were undertaken by the United States and the USSR. The American effort, termed "Operation Deep Freeze," concentrated on the building of McMurdo Station, a major base of operations, on Ross Island; five other U.S. stations were established, including one at the South Pole. The Russians concentrated on E Antarctica, building Mirnyy, a station on the Queen Mary Coast, and three bases inland: Komsomolskaya, Vostok (at the South Magnetic Pole), and Sovetskaya. Britain maintained 14 stations, and Argentina, Chile, France, Australia, Belgium, Japan, Norway, South Africa, and New Zealand also participated.

From 1951 to 1958, Dr. Vivian Fuchs led the British Commonwealth Trans-Antarctic Expedition's traverse with tractors from the Weddell Sea to McMurdo Sound via the South Pole, conducting a seismic and magnetic profile en route. Long-distance flights by U.S. planes covered c.2,000,000 sq mi (5,180,000 sq km) in 1955-56. These and later support flights, the tractor journeys to build bases, and geophysical traverses by tracked vehicles during the IGY left little of the continent that had not been seen.

The Antarctic Treaty and Current Research

The success of the IGY effort led to the signing (1959) of the Antarctic Treaty by representatives of the 12 nations that had been involved in the IGY. The treaty prohibits military operations, nuclear explosions, and the disposal of radioactive wastes in Antarctica and provides for cooperation in scientific investigation and the exchange of scientific data. In 1991, 24 nations signed a protocol to the 1959 treaty barring for 50 years the exploration of Antarctica for oil or minerals. The accord also contained provisions covering wildlife protection, waste disposal, and marine pollution. The treaty, which now has 46 member nations, did not end national claims to Antarctica, and in the 21st cent. claimant nations extended their claims over the continental shelf offshore to the maximum (350 nautical mi) allowed by international law.

Of the 12 nations involved in the IGY, some dropped their programs, others suspended and then renewed operations; those that have been continually involved have reduced the size of their programs. Some stations have been closed, new ones have been opened, and old ones have had to be replaced. Twenty-eight nations now operate more than 35 year-round research stations on the continent; additional stations are operated in the summer. At McMurdo the United States has built a scientific village where people may be housed in summer and winter. From McMurdo other U.S. bases are supported by air. The National Science Foundation (NSF) finances the U.S. programs. Mapping is done by the U.S. Geological Survey. Russian research has suffered from financial difficulties after the collapse of the Soviet Union and was cut back in the 1990s.

In the early 1970s fossil finds and geological studies gave further support to the theory of continental drift. Sediment samples obtained by the Ocean Drilling Project (1985) off the coast of Queen Maud Land indicate ice sheets covered E Antarctica over 37 million years ago. Since the late 1980s scientists have researched seasonal ozone depletion, or "holes," in the stratosphere above Antarctica, which allows harmful levels of ultraviolet radiation from the sun to reach the earth (see ozone layer ); they have also queried whether the rising incidence of iceberg calving in E Antarctica and increased snowfall in W Antarctica are related to global warming and climate change. In 1997, through a joint effort of NASA and the Canadian Space Agency, the first radar satellite images of the entire continent were made. These revealed new information on Antarctica's network of ice streams as well as features lying far below the surface of the ice. Since the 1990s cruise ships have plied the waters off the continent during the antarctic summer in increasing numbers.

Bibliography

See T. Hatherton, ed., Antarctica (1965); L. B. Quartermain, South to the Pole (1967); H. G. R. King, The Antarctic (1969); L. O. Quam, ed., Research in the Antarctic (1971); K. J. Bertrand, Americans in Antarctica, 1775-1948 (1971); R. S. Lewis and P. M. Smith, ed., Frozen Future (1973); A. Parsons, ed., Antarctica: The Next Decade (1987); R. K. Headland, Chronological List of Antarctic Expeditions and Related Historical Events (1989); A. Gurney, Below the Convergence: Voyages toward Antarctica, 1699-1839 (1997) and The Race to the White Continent (2000).

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 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 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 1839–43 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 world—with 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

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 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 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 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 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 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.

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.

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 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 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

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 The Antarctic continent was first charted by James Cook in 1773–4, though it was not fully explored until the twentieth century. In a race to reach the South Pole, the Norwegian Roald Amundsen was the first to arrive on 15 December 1911. The ill-fated British expedition led by Captain Robert Falcon Scott (b. 1868, d. 1912) did not arrive there until 18 January 1912. (The myth of Scott's amateurism against Amundsen's professionalism has been largely refuted, since temperatures on Scott's route were 40°F below the expected average.) Most of Antarctica's territory was claimed by Britain (British Antarctic Territory) in 1908, New Zealand (Ross Dependency) in 1923, Australia (Australian Antarctic Territory) in 1933, France (Adélie Land) in 1938, Norway (Queen Maud Land) in 1939, Chile (Antarctic Peninsula) in 1940, and Argentina (Antarctic Peninsula) in 1942. However, these claims have not been recognized by either the USA or the Soviet Union (Russia). The Antarctic Treaty signed in 1959 by twelve nations, including Britain, the USA, the Soviet Union, France, and Japan, guaranteed the continuation of peaceful research, the banning of military or nuclear activity, and the establishment of a system of mutual inspection. The treaty was valid for 30 years. In 1991, the Antactic Treaty was extended by the Antarctic Environmental Protocol, which was signed in Madrid and became effective in 1998. Ratified by 26 countries, it banned the exploitation of the continent's mineral resources for another 50 years, and kept it free from direct environmental pollution. Its ice masses have been particularly vulnerable to the advance of global warming. In May 2002, an area the size of Luxemburg broke off the ice shelf of the Antarctic. Such events would give gradual rise to the sea level, ultimately putting at risk entire states close to the sea level.

Antarctica A continent centred on the South Pole, situated mainly within the Antarctic Circle and almost entirely covered by an ice sheet. Exploration at first concentrated on establishing the existence of a continent. Bransfield, Biscoe, Foster, Wilkes, Ross, and Dumont D'Urville all explored the coastline of Antarctica between 1820 and 1840. Later explorers concentrated on reaching the South Pole. SCOTT pioneered the way in 1902, followed by SHACKELTON in 1908; in 1911 AMUNDSEN was the first to reach the Pole, and Scott reached it a month later. The American aviator Richard Byrd flew over the South Pole in 1929. Although there is no permanent human habitation, Norway, Australia, France, New Zealand, and the UK claim sectors of the continent (Argentina and Chile claim parts of the British sector); its exploration and exploitation are governed by an international treaty (Antarctic Treaty) of 1959 renewed in 1991.

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

Antarctica A continent around the South Pole whose name means ‘Opposite the Arctic’ from the Greek anti ‘opposite’ and arktikos ‘Arctic’.

Antarctica •bicker, clicker, dicker, flicker, kicker, liquor, nicker, picker, pricker, shicker, slicker, snicker, sticker, ticker, tricker, vicar, whicker, Wicca, wicker •bilker, milker, Rilke •blinker, clinker, drinker, finca, freethinker, Glinka, Inca, inker, jinker, shrinker, sinker, Soyinka, stinker, stotinka, thinker, tinker, Treblinka, winker •frisker, whisker •kibitka, Sitka •Cyrenaica • Bandaranaike •perestroika • Baedeker • melodica •Boudicca • trafficker • angelica •replica •basilica, silica •frolicker, maiolica, majolica •bootlicker • res publica • mimicker •Anneka • arnica • Seneca • Lineker •picnicker •electronica, harmonica, Honecker, japonica, Monica, moniker, Salonica, santonica, veronica •Guernica • Africa • paprika •America, erica •headshrinker • Armorica • brassica •Jessica • lip-syncer • fossicker •Corsica •Attica, hepatica, sciatica, viatica •Antarctica • billsticker •erotica, exotica •swastika