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Antarctica(ăntärk`tĭkə, –är`tĭkə), 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 PeninsulaAntarctic Peninsula,
glaciated mountain region of W Antarctica, extending c.1,200 mi (1,930 km) N toward South America; in the south, volcanic peaks rise to c.11,000 ft (3,350 m). Most of its NE coast is fringed by the Larsen ice shelf.
..... Click the link for more information. , 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 VostokVostok, Lake
, c.3,900 sq mi (10,000 sq km), c.155 mi (250 km) long and 30 mi (50 km) at its greatest width, in East Antartica beneath the remote Vostok research station. One of the largest subglacial lakes in Antarctica, the presumably freshwater lake is located beneath c.2.
..... Click the link for more information. , 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 MtsTransantarctic Mountains,
mountain chain stretching across Antarctica from Victoria Land to Coats Land; separating the E Antarctic and W Antarctic subcontinents. Mt. Markham (14,275 ft/4,351 m high), near the Ross Ice Shelf, is the highest peak.
..... Click the link for more information. (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 mountainsmountain,
high land mass projecting conspicuously above its surroundings and usually of limited width at its summit. Although isolated mountains are not unusual, mountains commonly form ranges, comprising either a single complex ridge or a series of related ridges.
..... Click the link for more information. ), 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 LandMarie Byrd Land,
area of W Antarctica, E of the Ross Shelf Ice and the Ross Sea and S of the Amundsen Sea; the Ford Ranges lie in the northwest part. The region was discovered and claimed for the United States by Richard E. Byrd in 1929.
..... Click the link for more information. 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 OceanSouthern Ocean
or Antarctic Ocean,
name sometimes given to those parts of the Pacific, Atlantic, and Indian oceans that surround Antarctica S of roughly 60°S.
..... Click the link for more information. (also known as the Antarctic Ocean).
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 −128.6°F; (−89.2°C;) at Vostok, a Russian station. (Satellite sensors have recorded an even lower but unofficial −135.8 [−93.2] in central East Antarctica.) 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 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
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 CookCook, James,
1728–79, English explorer and navigator. The son of a Yorkshire agricultural laborer, he had little formal education. After an apprenticeship to a firm of shipowners at Whitby, he joined (1755) the royal navy and surveyed the St.
..... Click the link for more information. . 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. RossRoss, Sir James Clark,
1800–1862, British polar explorer and rear admiral. In 1818 he accompanied his uncle, Sir John Ross, in search of the Northwest Passage and commanded the Erebus.
..... Click the link for more information. 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. BorchgrevinkBorchgrevink, Carsten Egeberg
, 1864–1934, Norwegian-Australian antarctic explorer. He emigrated to Australia in 1888, and in 1894 he went south in a whaling vessel and at Cape Adare took part in the first landing on the continent of Antarctica.
..... Click the link for more information. 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. BruceBruce, William Speirs
, 1867–1921, Scottish explorer and authority on the polar regions. He first went to the Antarctic as ship's surgeon in 1892 and later did survey work in Franz Josef Land and oceanographic work in the Arctic Ocean.
..... Click the link for more information. (1902–4), and two French expeditions led by Dr. Jean B. CharcotCharcot, Jean Baptiste
, 1867–1936, French neurologist and explorer in the antarctic region; son of Jean Martin Charcot. He became (1896) director of clinics at the Univ. of Paris but soon gave up medicine for exploration.
..... Click the link for more information. (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. ScottScott, Robert Falcon,
1868–1912, British naval officer and antarctic explorer. He commanded two noted expeditions to Antarctica. The first expedition (1901–4), in the Discovery,
..... Click the link for more information. headed two expeditions (1901–4 and 1910–13), E. H. ShackletonShackleton, Sir Ernest Henry,
1874–1922, British antarctic explorer, b. Ireland. The first of his voyages to Antarctica was made as a member of the expedition (1901–4) of Robert F. Scott.
..... Click the link for more information. led another expedition (1907–9), and A. E. Mackintosh headed the Ross Sea Party of Shackleton's unsuccessful Trans-Antarctic Expedition (1914–17). Roald AmundsenAmundsen, Roald
(Roald Engelbregt Grauning Amundsen) , 1872–1928, Norwegian polar explorer; the first person to reach the South Pole. He served (1897–99) as first mate on the Belgica
..... Click the link for more information. , 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 DrygalskiDrygalski, Erich von
, 1865–1949, German polar explorer. A professor of geography at the Univ. of Munich, he led an expedition that wintered (1892–93) in W Greenland.
..... Click the link for more information. 's well-equipped German expedition (1901–3) was cut short on the Wilhelm II Coast when the ship was beset; and Douglas MawsonMawson, Sir Douglas,
1882–1958, Australian antarctic explorer and geologist, b. England. His first geographical expedition was to the New Hebrides Islands as a geologist in 1903.
..... Click the link for more information. , 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 WilkinsWilkins, Sir George Hubert,
1888–1958, British explorer, b. Australia. He made a number of trips to Antarctica and to the Arctic. Valuable experience gained when he accompanied Vilhjalmur Stefansson's expedition (1913–18) to the Arctic and Sir Ernest Shackleton's
..... Click the link for more information. , an Australian who later flew down the eastern side of the Antarctic Peninsula. However, it was U.S. explorer Richard E. ByrdByrd, Richard Evelyn,
1888–1957, American aviator and polar explorer, b. Winchester, Va. He took up aviation in 1917, and after World War I he gained great fame in the air. He commanded the naval air unit with the arctic expedition of D. B. MacMillan in 1925.
..... Click the link for more information. 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 LandMarie Byrd Land,
area of W Antarctica, E of the Ross Shelf Ice and the Ross Sea and S of the Amundsen Sea; the Ford Ranges lie in the northwest part. The region was discovered and claimed for the United States by Richard E. Byrd in 1929.
..... Click the link for more information. 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 EllsworthEllsworth, Lincoln,
1880–1951, American explorer, b. Chicago, Ill. He was a surveyor and engineer in railroad building and later a prospector and mining engineer in NW Canada. He became the financial supporter and associate of Roald Amundsen in his arctic aviation ventures.
..... Click the link for more information. 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.
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 YearInternational Geophysical Year
(IGY), 18-month period from July, 1957, through Dec., 1958, during a period of maximum sunspot activity, designated for cooperative study of the solar-terrestrial environment by the scientists of 67 nations.
..... Click the link for more information. (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 48 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-nine nations now operate some 40 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 layerozone layer
region of the stratosphere containing relatively high concentrations of ozone, located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
..... Click the link for more information. ), They have also queried whether the rising incidence of iceberg calving in W Antarctica and increased snowfall in E Antarctica are related to global warmingglobal warming,
the gradual increase of the temperature of the earth's lower atmosphere as a result of the increase in greenhouse gases since the Industrial Revolution. Global warming and its effects, such as more intense summer and winter storms, are also referred to as climate
..... Click the link for more information. and climate change; satellite observations have indicated that glaciers in W Antarctica are thinning and their melting is accelerating. 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.
See T. Hatherton, ed., Antarctica (1965); L. B. Quartermain, South to the Pole (1967); H. G. R. King, The Antarctic (1969); K. J. Bertrand, Americans in Antarctica, 1775–1948 (1971); 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); J. McClintock, Lost Antarctica (2012).
the south polar continent, occupying the central part of the south polar region (the antarctic).
General information. The area of Antarctica is 13,975,000 sq km (including the shelf glaciers and the islands and ice caps connected by them to the mainland, which have an area of 1,582,000 sq km). The area of Antarctica including the continental shelf is 16,355,000 sq km. The long, narrow Antarctic Peninsula stretches in the direction of South America; its northern tip, Cape Sifre, extends to 63° 13’ S lat. (the northernmost point of Antarctica). The center of the continent, which is known as the pole of relative inaccessibility, is located 660 km from the south pole, at approximately 84° S lat., 64° E long. The coastline, which is more than 30,000 km long, has few indentations and along most of its length consists of ice shelves (barriers) as high as several dozens of meters.
Antarctica is the earth’s highest continent. The average altitude of the surface of the ice sheet is 2,040 m, which is 2.8 times the average altitude of the surface of the other continents (730 m). The average altitude of the native sub-glacial surface of Antarctica is 410 m.
Antarctica is divided into eastern and western regions on the basis of differences in geological structure and terrain. The surface of the ice sheet of Eastern Antarctica, which rises abruptly from the coast, becomes nearly horizontal in the interior. The central, highest part of the ice sheet—in the vicinity of the Sovetskoe Plateau—reaches an altitude of 4,000 m and constitutes the main ice shed or glacial center of Eastern Antarctica. Western Antarctica has three glacial centers, which are 2,000–2,500 m high. Numerous large, low plains of shelf ice stretch along the coast (usually 30–100 m above sea level). Two of these are enormous—the Ross Ice Shelf, with an area of 538,000 sq km, and the Filch-ner Ice Shelf, with an area of 483,000 sq km.
The terrain of the native (subglacial) surface of Eastern Antarctica consists of high mountain elevations alternating with deep depressions. Eastern Antarctica’s deepest depression lies south of the Knox Coast. The principal elevations are the Gamburtsev and Vernadskii subglacial mountains in the central part of Eastern Antarctica, which reach an altitude of 3,390 m. The Transantarctic Mountains are partially covered with ice (Mt. Kirkpatrick, 4,530 m). Rising above the surface of the ice are also ranges of Queen Maud Land, the Prince Charles Mountains, and others. The relief of Western Antarctica is more complex. The mountains break through the ice sheet more often, especially on the Antarctic Peninsula. The Sentinel Range of the Ellsworth Highland reaches an altitude of 5,140 m (Mt. Vinson massif), which is the highest point in Antarctica. In close proximity to these mountains is the deepest depression of Antarctica’s subglacial terrain—2,555 m. Antarctica’s continental shelf lies lower (at a depth of 400–500 m) than that of other continents.
E. S. KOROTKEVICH
Geological structure and minerals. The pre-Cambrian Antarctic platform (all of Eastern Antarctica, the central part of Western Antarctica, and part of Marie Byrd Land), which is flanked on the coast of the Pacific sector by Mesozoic plicate formations (the coastal region of the Bellingshausen and Amundsen seas and the Antarctic Peninsula), forms the larger part of the continent. The antarctic platform is heterogeneous in structure, and its age varies in different parts. The greater part of the eastern antarctic coastal region is an upper Archean (lower Proterozoic?) crystalline foundation, 15–20 km thick, consisting of diverse gneisses, crystalline schists, magmatites, dark granites, and other rocks. In various sectors of this foundation are layers of upper Proterozoic and lower Paleozoic sedimentary volcanic formations (the lower layers of the outer casing) or, more frequently, middle and upper Paleozoic terrigenous deposits with sills of trap rock (the upper layers of the outer casing). Precambrian and lower Paleozoic intrusions of gabbro-anorthosites and charnock-ites and early Mesozoic intrusions of nepheline syenites, connected with activization processes, occur widely in the crystalline foundation.
On the outskirts of the platform, within the limits of the Transantarctic Mountains and Marie Byrd Land, is the ancient Caledonian plate. Its foundation is formed by a two-tiered folded thickness, the lower part of which is a pre-Riphaeic gneiss-granite complex and the upper part of which consists of Riphaeic and Cambrian (possibly Ordovician) terrigenous and volcanic deposits up to 10 km thick. Intrusions of Lower Paleozoic granitoids are widespread throughout the plate.
The outer casing of the platform is composed here of a layer of deposits of various periods, from Devonian to Cretaceous (the Beacon series), consisting of diverse sandstones, aleurolites, and clay shales up to 3 km in thickness, with numerous strata of high-ash coals and Gondwanaland flora. In the lower half of the level, the series includes til-lites corresponding to the first glaciation of Antarctica (300 million years ago) and is topped by basalt covers with strata of tillites of the second glaciation of Antarctica (150 million years ago). Interspersing the Beacon sandstones are numerous flat masses of Triassic-Jurassic dolerite.
The fold belt of Antarctica is formed by three structural tiers. The bottom tier was raised toward the end of the Permian or during the Triassic period from a thick (10–12 km), geosynclinal Paleozoic carboniferous-terrigenous bed. The middle tier is semiplatformal (1–5 km), formed from the continental, sedimentary-volcanic Jurassic bed and Cretaceous marine terrigenous deposits. The upper tier, Cenozoic platformal (up to 2 km), is composed of andesite and basalt lavas mixed with strata of sandstone and conglomerates. Antarctica’s fold belt contains numerous gabbro-granite intrusions, mostly Cretaceous. Early Mesozoic folded structures composed of a very thick bed (over 10 km) of poorly metamorphosed carboniferousterrigenous deposits, which form the edge flexure of the antarctic platform, have been discovered in the area where the platform and the fold belt of Antarctica join (within the Ellsworth Highlands).
Deposits of anthracite and iron ore, traces of mica, graphite, rock crystal, and beryl—and also of gold, uranium, molybdenum, copper, nickel, lead, zinc, silver, and titanium—have been found in Antarctica. The paucity of mineral deposits is attributable to imperfect geological knowledge of the continent and its thick ice sheet. There is a great potential for mineral wealth in Antarctica; this conclusion is based on the similarity between the geological structure of the antarctic platform and the Gondwanaland platforms of the other continents in the southern hemisphere, as well as the similarity of the Antarctica fold belt to structures in the Andes.
M. G. RAVICH
The ice sheet and types of terrain. The terrain of Antarctica is divided into two sharply different types: glacial and native. Large, elevated glacial plateaus occupy the interior of the continent, passing into a gently sloping and then sloping-undulating declivity of the ice sheet toward the edges of the continent. The relief of the ice of the coastal region is more complex, with poorly dissected sectors of the edge of the ice sheet alternating with glacial tongues which are traversed by cracks and broad plains of shelf ice, above which rise sloping ice caps.
The basic morphological structures of the native terrain were apparently formed toward the end of the Neocene period, but their renewal took place in the Quaternary period as well. Large interior plains, above which rise block and folded-block formations, may be discerned within the limits of the continent. These mountainous formations were dissected by preglacial erosion and then were worn down by glaciers over almost their entire area. Some of the peaks were not covered by the ice sheet and were transformed by local—mostly cirque—glaciers and physical weathering agents—mainly frost.
The formation of volcanic cones (Erebus, 3,794 m; Terror, 3,262 m; and others) and leveled surfaces of native rock (peneplains) and their elevation to considerable altitudes are linked to the late Paleocene-Neocene and Quaternary periods of development of Antarctica. The mountainous areas often have relief of the alpine type. The terrain of the coastal antarctic oases consists of low hills. The presence of ancient coastal lines and terraces containing fossils of marine organisms indicates that the continent was raised in the Holocene period.
The antarctic ice sheet has apparently existed continuously since the Neocene period—sometimes shrinking, sometimes expanding. At present, most of the continent is covered by a thick ice sheet. No more than 0.2–0.3 percent of the continental area is ice-free. The average thickness of the ice is 1,720 m, and the volume is 24 million cu km, which constitutes approximately 90 percent of all the fresh water on the earth’s surface. All types of glaciers are found in Antarctica—from enormous ice sheets to small hanging and cirque glaciers. The antarctic ice sheet descends into the ocean (except in small sections of the coast composed of native rock), forming long stretches of shelf glaciers—flat ice slabs, as much as 700 m thick, which float on the water and rest at some points on elevations of the ocean bottom.
Depressions in the subglacial terrain, from the central regions of the continent toward the coast, are paths by which the ice moves out into the ocean. The ice moves faster in these than in other areas and is split into innumerable blocks by fissure systems. These are glacier tongues, which resemble mountain valley glaciers but usually flow within shores of ice. The largest of these is the Lambert, which is 700 km long and 30–40 km wide. The ice flow in glacier tongues reaches speeds of 1,000–1,500 m per year. Glaciers are fed by atmospheric precipitation, which amounts to about 2,200 cu km of accumulation per year over the entire ice sheet. Ablation of physical material (ice) occurs largely through the calving of icebergs; surface and subglacial melting and water drainage are minimal. The majority of researchers estimate the substance balance in the antarctic ice sheet as close to zero (until more exact data are obtained).
The areas of the surface that are not covered by ice are icebound by many years of permafrost, which penetrates some distance beneath the ice sheet and to the ocean bottom.
Climate. The climate of Antarctica is polar continental (with the exception of the coastal areas). Even though the winter polar night in central Antarctica lasts for several months, the annual total radiation is close to that of the equatorial zone—at Vostok Station, it is 5 gigajoules per sq m per yr [GJ/(m2 yr)] or 120 kilocalories per sq cm per year [kcal(cm2.yr)]; in the summer it is very high, up to 1.25 GJ/(m2.mo) or 30 kcal/(cm2-mo). Nevertheless, up to 90 percent of the incoming heat is reflected back into the atmosphere by the snow, and only 10 percent of it goes to warm the surface. The radiation balance of Antarctica is therefore negative, and the temperature of the air is very low.
The center of cold on our planet is located in central Antarctica. A temperature of -88.3°C was recorded at Vostok Station on Aug. 24, 1960. The average winter temperature ranges from -60° to -70°C, the average summer temperature from -30° to -50°C. Even in the summer the temperature never rises above -20°C. In the coastal regions, especially in the region of the Antarctic Peninsula, the temperature of the air rises to 10–12°C in the summer, but the average temperature of the warmest month (January) is 1°-2°C. The average monthly temperature in the winter (July) ranges from -8°C on the Antarctic Peninsula to -35°C on the edge of the Ross Ice Shelf. The cold air rolls down from the central regions of Antarctica, forming outward-blowing winds that attain great speeds at the coast (an average annual velocity of up to 12 m per sec) and turn into hurricane winds (up to 50–60 and sometimes 90 m/sec) upon coalescence with cyclonic air streams.
As a consequence of the predominance of descending currents, the relative humidity of the air is low (60–80 percent), and at the coast—especially in Antarctic oases—it falls to 20, and even 5, percent. There is also very little cloud cover. Precipitation is almost entirely in the form of snow. In the center of the continent the average annual snowfall is 30–50 mm; on the lower part of the continental slope it increases to 600–700 mm, diminishes slightly at the foot of the slope (400–500 mm), and then rises again on some of the ice shelves and on the northwest coast of the Antarctic Peninsula (700–800 and even 1,000 mm). Blizzards are very common because of the strong winds and abundant snowfall.
Large areas of exposed rock near the coast with distinctive natural conditions are known as antarctic oases. The largest of these are the Bunger, Westfall, Grierson, and Schiermacher oases and the Wright Valley (Dry Valley). They range in area from several dozen to several hundred sq km.
The nunataks—mountain ranges and peaks that break through the ice sheet—sometimes cover much larger areas.
The antarctic lakes, most of which are found in the coastal oases, are distinctive. Many have no outlets and are unusually high in salinity to the point of bitterness. Some remain frozen through the summer. Lagoons found among the coastal cliffs of the oasis and the encircling ice shelf, beneath which they are connected with the sea, are a characteristic feature of the terrain. The lagoons vary in salinity, depending on the influx of fresh melt water and the closeness of their link with the sea. Some of the lakes are situated in the mountains at altitudes as high as 1,000 m (the Taylor oases, the Wohlthat massif on Queen Maud Land, and the Victoria massif on Victoria Land).
Flora and fauna. The plant and animal world of Antarctica is very poor and distinctive, but not even the harshest areas of the continent are biologically sterile.
Natural regions. The whole of Antarctica and the coastal islands is situated in the antarctic desert zone and may be divided into three subzones, visible on extremely limited ice-free patches of dry land. These subzones are the northern, which comprises the northwest coast of the Antarctic Peninsula and the adjoining islands; the middle, comprising the coastal oases, the islands, cliffs, and mountain ranges along the entire coast of Antarctica; and the southern, comprising areas of dry land in the interior of the continent. Division into altitude belts is of much greater significance in Antarctica. The lower belt consists of the coast, including the ice shelves, up to an altitude of several hundred meters. This belt contains the most diverse scenery in Antarctica—ice shelves, the foot of the glacial slope, the lower parts of the glacial tongues, oases, and nunataks. Snow melts here not only near outcroppings of native rock but also on the ice sheet. Because of its proximity to the ocean and the relatively high atmospheric temperatures, practically all of the continent’s organic life is concentrated in the lower belt. The middle belt (up to an altitude of 3,000 m) includes the slope of the ice sheet, the inland glacial plateau of Western Antarctica, and the mountain ranges. The air temperature is below 0°C throughout the entire year. Thawing is observed only in the summer, near outcroppings of native rock. Because of the nearly constant strong outward-blowing winds, large sastrugi form on the snow-covered surface of the glacial slope. The surface of the inland plateau is covered with small sastrugi. Patches of lichens and algae, arthropods, and infrequently birds are found on the cliffs, which are warmed to above 0°C in the summer. The area above 3,000 m is one of perennial frost. The winds there are weak, the snow is grainy, and no large sastrugi form on the surface of the glacial plateau of central Antarctica. Even the surfaces of the native rocks of the mountain peaks in this belt never warm above the freezing point, and hardly any signs of plant or animal life are to be found.
On the basis of the zones, altitude belts, and the position and nature of the shelf ice, mountain ranges, and other orographical features of the territory, Antarctica may be divided into 15 regions (see Figure 1).
E. S. KOROTKEVICH