Antarctica is 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.

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, 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 lakes of liquid water have been found underneath the continental ice; the largest known of these is Lake Vostok (174 mi by 36 mi/280 km by 60 km; 1600 ft/500 m deep), which lies 2.5 mi (4 km) beneath the Russian Vostok research station in E Antarctica.

��� 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 roughly between the 50th and 60th parallels of latitude. 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.

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 (40). 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 (18); winter mean temperatures are 70 (57) and lower. The lowest temperature ever recorded on earth was 126.9 (88.3) 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.

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 Ad�lie penguins and the brown skuathe most southerly bird and a notorious predatorand 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, Ad�lie 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.

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 Ad�lie 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 Ad�lie 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.

��� Of the 12 nations involved in the IGY, some have dropped their programs, others have 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. 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. Ecological research is carried out at the Lake Hoare Camp in Taylor Valley, across McMurdo Sound. The National Science Foundation (NSF) finances the U.S. programs. Logistical support was in the hands of the U.S. navy until 1998, when air support was taken over by the New York Air National Guard; other functions (kitchen, stores, security, transportation) were contracted to a commercial organization. Mapping is done by the U.S. Geological Survey. Russian research has suffered from financial difficulties in recent years 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 ozone depletion, or �holes,� in the stratosphere above Antarctica, which allows harmful levels of ultraviolet radiation from the sun to reach the earth; they have also queried whether the rising incidence of iceberg calving is related to global warming. 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.

Mount Erebus