Antarctica

Antarctica
Antarctica, fifth-largest of the Earth?s seven continents, located
almost entirely south of latitude 66?33? south (the Antarctic Circle),
and surrounding the South Pole. It is mostly circular in shape with a
long arm-the Antarctic Peninsula-reaching out towards South America,
and with two large indentations, the Ross and Weddell seas and their
ice shelves. Its total area is about 14.2 million sq km (5.5 million
sq mi) in summer. During the winter Antarctica doubles in size because
of the large amount of sea ice that forms at its periphery. The true
boundary of Antarctica is not the coastline of the continent itself
but the Antarctic Convergence, which is a sharply defined zone in the
southern extremities of the Atlantic, Indian, and Pacific oceans
between about latitude 48? south and latitude 60? south. At this
point, the colder waters flowing north from Antarctica mix with warmer
waters moving south. The Antarctic Convergence marks a definite
physical difference in the oceans. For these reasons, the water
surrounding the Antarctic continent is considered an ocean in itself,
often known as the Antarctic, or Southern Ocean.
Antarctica has no native population. Its residents are scientific and support staffs who usually stay no more than a year at a time. The first person born in Antarctica was Emilio Palma, the son of the commander of Argentina?s Esperanza Base, on January 7, 1978. Antarctica is more than 95 per cent ice covered and contains about 90 per cent of the world?s fresh water. Because of its thick ice cover, it is the highest of all continents, with an average elevation of about 2,300 m (7,500 ft). The highest point on the continent is Vinson Massif (5,140 m/16,864 ft); the lowest point appears to be the Bentley Subglacial Trench (2,499 m/8,200 ft below sea level) in West Antarctica. This trench is covered with more than 3,000 m (9,840 ft) of ice and snow. Lower points may exist under the ice, but they have not yet been discovered. Seven nations had announced territorial claims to parts of Antarctica, but since the Antarctic Treaty of 1961, these claims have been held aside in the interests of international cooperation in scientific research. (The claims had been made by Argentina, Australia, Chile, France, Great Britain, New Zealand, and Norway.) II the natural environment Antarctica exists today in an ice age. Future economic development of the ice-covered land mass is highly unlikely. Resource exploitation on the continental shelf is possible, but certainly not for many years to come. Marine life in the waters surrounding Antarctica is currently being developed economically. This marine life includes whales and a tiny, shrimp-like animal called krill. A Geological History Antarctica was a central part of the former supercontinent Gondwanaland. As Gondwanaland broke apart during the late Mesozoic and early Cenozoic eras (some 100 million years ago) to form the continents of the southern hemisphere, Antarctica drifted from the Tropical Zone to its present polar position. B Physiographic Regions Antarctica consists of two main geological areas. The larger of these, East Antarctica, is located mostly in the eastern hemisphere. It is probably a Precambrian shield, over 570 million years old, covered by thousands of metres of ice. West Antarctica, lying mostly within the western hemisphere, appears to be a continuation of the Andes of South America; glaciologists and geologists speculate that West Antarctica would become an island archipelago if the ice cover were removed. The two areas of Antarctica are separated by the Transantarctic Mountains, an uplift zone of mountains that extends across the entire continent, although portions are buried under the ice cover. Within these mountains are found many coal deposits and fossil remains related to the earlier tropical climate of Antarctica. In East Antarctica the geologically stable Precambrian shield is generally covered by sedimentary or igneous deposits. The geological structure of West Antarctica is less well known, but at least two active volcanoes are found in the area, the higher of which is Mount Erebus (3,794 m/12,448 ft). Antarctic soils are classified as dry polar desert soils, and their occurrence is limited to the several deglaciated (ice-free) valleys or oases and to parts of the northern Antarctic Peninsula. C Drainage and Water Resources The ice cover of Antarctica is continuously moving. Great ice rivers drain the interior of the continent and form the ice shelves. Coastal valleys drain parts of the mainland into the sea. Large tabular icebergs are formed as the edges of the ice shelves and glaciers calve off into the sea. Ice also extends over vast areas of the sea in the form of permanent floating ice shelves; the largest of these formations, the Ross Ice Shelf, is about the size of Spain and Portugal. The general isolation of Antarctica from the remainder of the world has allowed it to avoid the industrial pollution common to the other continents, so the snow and ice there are the purest in the world. Most scientific stations use snow melters to heat the ice and convert it to water for station use. D Climate Antarctica is the coldest continent. The lowest temperature ever recorded anywhere on Earth, -88.3? C (-126.9? F), was on August 24, 1960, at Vostok Station. The continent is also buffeted by heavy winds. In the interior, winds as high as 320 km/h (200 mph) have been recorded. These winds flow downslope from the interior towards the coast and, combined with the low temperatures, create dangerous wind-chill conditions. Three basic climatic regions can be distinguished in Antarctica. The interior is characterized by extreme cold and light snowfall; the coastal areas experience somewhat milder temperatures and much higher precipitation rates; and the Antarctic Peninsula has a warmer and wetter climate with above-freezing temperatures common. See alsoPolar Zone. Antarctica can be classified as a true desert; in the interior the average annual precipitation (in water) is only about 50 mm (2 in). Raging blizzards often occur, however, when winds pick up previously deposited snow and move it from place to place. Annual precipitation is much heavier along the coast, amounting to about 380 mm (15 in) in water. Here, heavy snowfalls occur when cyclonic storms pick up moisture from the surrounding seas; this moisture freezes and is deposited as snow over the coastal areas. Along the Antarctic Peninsula, especially the northern end, rain is as common as snow. The interior of Antarctica has almost continuous daylight during the southern hemisphere?s summer and darkness during the southern hemisphere?s winter. In coastal areas, which are further north, long periods of sunshine occur during the summer, but sunrises and sunsets occur during much of the rest of the year. E Vegetation The few plants that survive in Antarctica are restricted to the small ice-free areas. The continent has no trees, and vegetation is limited to about 350 species, mostly lichens, mosses, and algae. Lush beds of such vegetation exist in parts of the Antarctic Peninsula, and lichens have been discovered growing on isolated mountains within 475 km (295 mi) of the South Pole. Three species of flowering plants are also found on the Antarctic Peninsula. F Animal Life No land-based vertebrate animals inhabit Antarctica. Invertebrates, especially mites and ticks, which can tolerate the lower temperatures, exist in the Antarctic Peninsula but are still considered rare. The surrounding ocean, however, abounds in living creatures. Large numbers of whales feed on the rich marine life, especially krill. Six species of seals (including the crabeater, elephant, and leopard) and about 12 species of birds live and breed in the Antarctic. The most prominent inhabitant of the Antarctic is the penguin. A flightless bird, it lives on the pack ice and in the oceans around Antarctica, and breeds on the land or ice surfaces along the coast. Most typical are the Adélie and emperor penguins. G Mineral Resources Antarctica is thought to have large deposits of valuable mineral resources. Coal in commercially attractive deposits has been found, but no other minerals are known to exist in potentially useful amounts. Large deposits of oil and natural gas are believed to exist in Antarctica?s continental shelf. iii exploration Antarctica was not discovered until the early 1800s, largely because of its remoteness from the other continents. The ancient Greeks first theorized the existence of Antarctica when they assumed that the southern hemisphere must have large continents to balance those in the northern hemisphere. Captain James Cook of Great Britain was the first explorer to cross the Antarctic Circle in the 1770s, but even though he circumnavigated Antarctica, he never sighted the continent. From deposits of rock in icebergs at sea, Cook realized that a southern continent existed, but it was not the lush, populated place some had expected. A Early Exploration From 1819 to 1821, a Russian expedition under the naval officer and explorer Fabian von Bellingshausen circumnavigated Antarctica and discovered some offshore islands. Probably the first parties to sight the continent were those of the British naval officers Edward Bransfield and William Smith in January 1820, and of the American sealer Nathaniel Palmer in November of the same year. The first confirmed landing was made on February 7, 1821, by another American sealer, Captain John Davis. In 1823 the British whaler James Weddell discovered the sea that bears his name and penetrated to the southernmost point that any ship had then reached. Not until the 1840s, however, was Antarctica?s status as a continent established. Three separate national expeditions-a French expedition under Jules Dumont d?Urville, a British expedition under Sir James Clark Ross, and an American expedition under Captain Charles Wilkes-sailed along enough coastline to realize that the ice-covered land they saw was truly a continental land mass. From the late 19th until the early 20th century, numerous expeditions visited Antarctica. With the encouragement of the International Geographical Congress, expeditions were sent out by several different nations, including Belgium, commanded by Adrien de Gerlache; Britain, commanded by Robert Scott and Carsten Borchgrevink; and Germany, commanded by Erich von Drygalski. Gerlache took his expedition, the first truly scientific Antarctic expedition, to the Pacific Ocean side of the Antarctic Peninsula, became caught in the ice, and spent the winter of 1897-1898 there. The Borchgrevink expedition landed men at Cape Adare in 1899 and became the first group to spend the winter on land. The Scott expedition of 1901-1904 used Ross Island in McMurdo Sound as a base and explored the Ross Ice Shelf and Victoria Land. From 1901 to 1903, Drygalski, who was a geophysicist, led an expedition to the Indian Ocean coast of Antarctica. Both Scott and Drygalski carried captive balloons and used them for aerial observation of the surface of Antarctica. Also in the Antarctic at this time were privately sponsored expeditions from Sweden under Otto Nordenskjöld, from Scotland under William Bruce, and from France under Jean Charcot. B Attaining the South Pole The search for the South Pole was the dominant theme in the next series of Antarctic expeditions. From 1907 to 1909, Sir Ernest Shackleton led a British expedition to within about 156 km (97 mi) of the South Pole before turning back because of exhausted supplies. A second British expedition went into the field in 1910 under Robert Scott, as did a Norwegian expedition under Roald Amundsen. Using dogs to haul their sledges, Amundsen and a party of four reached the South Pole on December 14, 1911. Scott?s party of five reached the pole on January 18, 1912, after hauling their sledges by hand over the roughest part of their route. All of Scott?s party died on the return journey after the Norwegians successfully returned to their base. Shackleton returned to Antarctica in 1914 to attempt a crossing of the continent, but his ship, Endurance, became trapped in the ice and was crushed. Shackleton and his men made their way across ice floes to Elephant Island and were finally rescued in August 1916. C Aerial Exploration In the 1920s, aviation came to Antarctica. The Australian Sir George Wilkins and the American C. B. Eielson became the first to fly an aeroplane over the continent when they explored the Antarctic Peninsula from the air in 1928. The American explorer Richard E. Byrd established a large camp-Little America-on the Ross Ice Shelf in early 1929 and in November flew to the South Pole. Byrd returned to Antarctica in 1934 with another expedition. Both expeditions included a scientific research staff. Other aviation expeditions included those of Lincoln Ellsworth, an American, who flew across the continent in 1935; the Norwegians, who conducted extensive exploration along the coastlines; the Germans, who sent an aviation expedition in 1938 and 1939; and the American US Antarctic Service Expedition from 1939 to 1941. Following World War II, the United States sent the largest expedition ever to Antarctica. More than 4,000 men participated in Operation Highjump with some 13 ships and more than 20 aeroplanes. Much of the coast was photographed by air for the preparation of maps. D Recent Activities Long-term systematic exploration and scientific investigation of Antarctica began with the International Geophysical Year (igy)-July 1, 1957, to December 31, 1958. Twelve nations established more than 60 scientific stations in Antarctica during the igy and visited most parts of the continent. The highlight of the year in Antarctica was the Commonwealth Trans-Antarctic Expedition, led by Sir Vivian Fuchs and Sir Edmund Hillary, which made the first crossing of the continent in a three-month journey beginning in November 1957. When the igy came to a close, the 12 nations decided to continue their research during a year of International Geophysical Cooperation. Representatives of the 12 nations met in Washington, D.C., United States, in 1959 to draft and sign the Antarctic Treaty, which dedicated the entire continent to peaceful scientific investigation; it came into effect in 1961, suspending all territorial claims. In 1991, 24 nations approved a protocol to the treaty that would ban oil and other mineral exploration for at least 50 years. IV scientific research Significant scientific research has been accomplished in Antarctica, including studies of glaciology, meteorology, geomagnetism, international weather control, seismology, and ionospheric physics. The nutrient-rich oceans that surround Antarctica are an important focus of research. Biologists have discovered that fish in Antarctic waters have an antifreeze component to their blood that allows them to live in sub-zero temperatures. Studies conducted on the life histories of penguins, seals, and krill (a potential world food source) have provided much new information on the ecology of these species. Internationally conducted studies have resulted in an improved understanding of krill reproduction and allowed scientists to improve their predictions of safe limits for krill harvesting. Geologists have now visited most exposed rock areas of the continent, increasing knowledge of the basic geological structure and history of Antarctica. Glacial geologists studying the remains of past glaciers have discovered that Antarctica once contained much more ice than it now does. Fossil finds in Antarctica have included such achievements as the 1982 discovery of the first mammal remains found there and in 1986 of the first dinosaur fossil. Such fossils have by now provided a nearly complete sequential record of the breakup of the ancient supercontinent Gondwanaland. Vulcanologists have extensively studied Mount Siple and the active volcano Mount Erebus. Geologists have collected thousands of meteorites (including a few rare moon fragments), which are especially valued for having been preserved in ice with little weathering or other deterioration. The ice cover itself has long been the subject of intense study. Glaciologists from several countries have employed modern methods of investigation such as radio glaciology to obtain information on the landscape under the ice cover, and to discover large lakes between the earth and the bottom of the ice. Satellites have been used to plot the slow movement of the ice surface. Ice cores drilled from Antarctica, including a complete core to the bottom of the Ross Ice Shelf and one through the ice of West Antarctica at Byrd Station, enabled French, Russian, and American scientists to trace changes in the continent?s climate over a period of tens of thousands of years. French scientists have put radio transmitters on icebergs to plot their movement, and Australian and Saudi Arabian officials have considered the possibility of towing icebergs to arid regions for fresh water. Scientists have also been conducting studies of global warming on the continent. In 1995 an unusually large number of icebergs were created, radically altering the size of the ice shelf. Continuous weather records by meteorologists have been taken for some 25 years and are providing an understanding of Antarctica?s function in world climate. One such contribution has been the discovery, first noted by British scientists in 1985, that a so-called ozone hole develops each Antarctic spring in the stratosphere high above the continent and then more or less disappears by the end of the season. The meaning of this reduction in the ozone layer in the vicinity of the South Pole continues to be studied. It may be partly a natural phenomenon, but evidence indicates that the ozone loss is also related to the problem of the release of chlorofluorocarbons into the atmosphere. Doctors have made discoveries about the behaviour of viruses in a cold, isolated environment. Psychological and sleep studies are frequently conducted during the winter, when Antarctica is isolated from the outside world.

Antarctica 8.2 of 10 on the basis of 2032 Review.