Kullanıcı:Sralp2/deneme2

Antarctica is divided in two by the Transantarctic Mountains close to the neck between the Ross Sea and the Weddell Sea. The portion west of the Weddell Sea and east of the Ross Sea is called West Antarctica and the remainder East Antarctica, because they roughly correspond to the Western and Eastern Hemispheres relative to the Greenwich meridian.

Elevation colored by relief height

About 98% of Antarctica is covered by the Antarctic ice sheet, a sheet of ice averaging at least 16 km (9,9 mi) thick. The continent has about 90% of the world's ice (and thereby about 70% of the world's fresh water). If all of this ice were melted, sea levels would rise about 60 m (200 ft). In most of the interior of the continent, precipitation is very low, down to 20 mm (0,8 in) per year; in a few "blue ice" areas precipitation is lower than mass loss by sublimation and so the local mass balance is negative. In the dry valleys, the same effect occurs over a rock base, leading to a desiccated landscape.

West Antarctica is covered by the West Antarctic Ice Sheet. The sheet has been of recent concern because of the real, if small, possibility of its collapse. If the sheet were to break down, ocean levels would rise by several metres in a relatively geologically short period of time, perhaps a matter of centuries. Several Antarctic ice streams, which account for about 10% of the ice sheet, flow to one of the many Antarctic ice shelves: see ice-sheet dynamics.

East Antarctica lies on the Indian Ocean side of the Transantarctic Mountains and comprises Coats Land, Queen Maud Land, Enderby Land, Mac. Robertson Land, Wilkes Land, and Victoria Land. All but a small portion of this region lies within the Eastern Hemisphere. East Antarctica is largely covered by the East Antarctic Ice Sheet.

Mount Erebus, an active volcano on Ross Island

Vinson Massif, the highest peak in Antarctica at 4.892 m (16.050 ft), is located in the Ellsworth Mountains. Antarctica contains many other mountains, on both the main continent and the surrounding islands. Mount Erebus on Ross Island is the world's southernmost active volcano. Another well-known volcano is found on Deception Island, which is famous for a giant eruption in 1970. Minor eruptions are frequent and lava flow has been observed in recent years. Other dormant volcanoes may potentially be active. In 2004, an underwater volcano was found in the Antarctic Peninsula by American and Canadian researchers. This unnamed volcano may be active.

Antarctica is home to more than 70 lakes that lie at the base of the continental ice sheet. Lake Vostok, discovered beneath Russia's Vostok Station in 1996, is the largest of these subglacial lakes. It was once believed that the lake had been sealed off for 500,000 to one million years but a recent survey suggests that, every so often, there are large flows of water from one lake to another.

There is some evidence, in the form of ice cores drilled to about 400 m (1.300 ft) above the water line, that Lake Vostok's waters may contain microbial life. The frozen surface of the lake shares similarities with Jupiter's moon, Europa. If life was discovered in Lake Vostok, it would strengthen the argument for the possibility of life on Europa. On 7 February 2008, a NASA team embarked on a mission to Lake Untersee, searching for extremophiles in its highly alkaline waters. If found, these resilient creatures could further bolster the argument for extraterrestrial life in extremely cold, methane-rich environments.

Geology

The bedrock topography of Antarctica, critical to understand dynamic motion of the continental ice sheets.

Ana madde: Geology of Antarctica

Subglacial topography ve bathymetry of bedrock underlying Antarctica ice sheet

The above map shows the subglacial topography of Antarctica. As indicated by the scale on left-hand side, blue represents portion of Antarctica lying below sea level. The other colors indicate Antarctic bedrock lying above sea level. Each color represents an interval of 2.500 ft (760 m) in elevation. Map is not corrected for sea level rise or isostatic rebound, which would occur if the Antarctic ice sheet completely melted to expose the bedrock surface.

Topographic map of Antarctica after removing the ice sheet and accounting for both isostatic rebound and sea level rise. Hence, this map suggests what Antarctica may have looked like 35 million years ago, when the Earth was warm enough to prevent the formation of large-scale ice sheets in Antarctica.

Geological history and paleontology

More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time, Gondwana gradually broke apart and Antarctica as we know it today was formed around 25 million years ago. Antarctica was not always cold, dry, and covered in ice sheets. At a number of points in its long history, it was farther north, experienced a tropical or temperate climate, was covered in forests, and inhabited by various ancient life forms.

Paleozoic era (540–250 Ma)

During the Cambrian period, Gondwana had a mild climate. West Antarctica was partially in the Northern Hemisphere, and during this period large amounts of sandstones, limestones and shales were deposited. East Antarctica was at the equator, where sea floor invertebrates and trilobites flourished in the tropical seas. By the start of the Devonian period (416 Ma), Gondwana was in more southern latitudes and the climate was cooler, though fossils of land plants are known from this time. Sand ve silts were laid down in what is now the Ellsworth, Horlick ve Pensacola Mountains. Glaciation began at the end of the Devonian period (360 Ma), as Gondwana became centered around the South Pole and the climate cooled, though flora remained. During the Permian period, the plant life became dominated by fern-like plants such as Glossopteris, which grew in swamps. Over time these swamps became deposits of coal in the Transantarctic Mountains. Towards the end of the Permian period, continued warming led to a dry, hot climate over much of Gondwana.

Mesozoic era (250–66 Ma)

As a result of continued warming, the polar ice caps melted and much of Gondwana became a desert. In Eastern Antarctica, seed ferns became established, and large amounts of sandstone and shale were laid down at this time. Synapsids, commonly known as "mammal-like reptiles", were common in Antarctica during the Late Permian ve Early Triassic and included forms such as Lystrosaurus. The Antarctic Peninsula began to form during the Jurassic period (206–146 Ma), and islands gradually rose out of the ocean. Ginkgo trees and cycads were plentiful during this period. In West Antarctica, coniferous forests dominated through the entire Cretaceous period (146–66 Ma), though Southern beech became more prominent towards the end of this period. Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only three Antarctic dinosaur genera (Cryolophosaurus and Glacialisaurus, from the Hanson Formation, and Antarctopelta) have been described to date. It was during this period that Gondwana began to break up.

Gondwana breakup (160–23 Ma)

The cooling of Antarctica occurred stepwise, as the continental spread changed the oceanic currents from longitudinal equator-to-pole temperature-equalizing currents to latitudinal currents that preserved and accentuated latitude temperature differences.

Africa separated from Antarctica around 160 Ma, followed by the Indian subcontinent, in the early Cretaceous (about 125 Ma). By the end of the Cretaceous, about 66 Ma, Antarctica (then connected to Australia) still had a tropical to subtropical climate, complete with a marsupial fauna. About 40 Ma Australia-New Guinea separated from Antarctica, so that latitudinal currents could isolate Antarctica from Australia, and the first ice began to appear. During the Eocene–Oligocene extinction event about 34 million years ago, CO₂ levels have been found to be about 760 ppm and had been decreasing from earlier levels in the thousands of ppm.

Around 23 Ma, the Drake Passage opened between Antarctica and South America, resulting in the Antarctic Circumpolar Current that completely isolated the continent. Models of the changes suggest that declining CO₂ levels became more important. The ice began to spread, replacing the forests that then covered the continent.

Neogene Period (23–0.05 mya)

Since about 15 Ma, the continent has been mostly covered with ice.

Intermittent warm periods allowed Nothofagus shrubs to cling to the Sirius group in the Dominion Range as late as 3–4 Ma. After that the Pleistocene ice-age covered the whole continent and destroyed all major plant life on it.

Geology of present-day Antarctica

Glaciers and rock outcrops in Marie Byrd Land seen from NASA's DC-8 aircraft

The geological study of Antarctica has been greatly hindered by the fact that nearly all of the continent is permanently covered with a thick layer of ice. However, new techniques such as remote sensing, ground-penetrating radar ve satellite imagery have begun to reveal the structures beneath the ice.

Geologically, West Antarctica closely resembles the Andes mountain range of South America. The Antarctic Peninsula was formed by uplift and metamorphism of sea bed sediments during the late Paleozoic and the early Mesozoic eras. This sediment uplift was accompanied by igneous intrusions and volcanism. The most common rocks in West Antarctica are andesite ve rhyolite volcanics formed during the Jurassic period. There is also evidence of volcanic activity, even after the ice sheet had formed, in Marie Byrd Land ve Alexander Island. The only anomalous area of West Antarctica is the Ellsworth Mountains region, where the stratigraphy is more similar to the eastern part of the continent.

East Antarctica is geologically varied, dating from the Precambrian era, with some rocks formed more than 3 billion years ago. It is composed of a metamorphic ve igneous platform which is the basis of the continental shield. On top of this base are various modern rocks, such as sandstones, limestones, coal and shales laid down during the Devonian and Jurassic periods to form the Transantarctic Mountains. In coastal areas such as Shackleton Range ve Victoria Land some faulting has occurred.

The main mineral resource known on the continent is coal. It was first recorded near the Beardmore Glacier by Frank Wild on the Nimrod Expedition, and now low-grade coal is known across many parts of the Transantarctic Mountains. The Prince Charles Mountains contain significant deposits of iron ore. The most valuable resources of Antarctica lie offshore, namely the oil ve natural gas fields found in the Ross Sea in 1973. Exploitation of all mineral resources is banned until 2048 by the Protocol on Environmental Protection to the Antarctic Treaty.

Climate

Ana madde: Climate of Antarctica

The blue ice covering Lake Fryxell, in the Transantarctic Mountains, comes from glacial meltwater from the Canada Glacier and other smaller glaciers.

Near the coast, December looks fairly temperate.

Antarctica is the coldest of Earth's continents. The coldest natural temperature ever recorded on Earth was at the Soviet (now Rusyan) Vostok Station in Antarctica on 21 July 1983. For comparison, this is 11 °C (20 °F) colder than subliming dry ice at one atmosphere of partial pressure, but since CO₂ only makes up 0.039% of air, temperatures of less than -150 °C would be needed to produce dry ice snow in Antarctica. Antarctica is a frozen desert with little precipitation; the South Pole itself receives less than 10 cm (4 in) per year, on average. Temperatures reach a minimum of between and in the interior in winter and reach a maximum of between 5 °C (41 °F) and 15 °C (59 °F) near the coast in summer. Sunburn is often a health issue as the snow surface reflects almost all of the ultraviolet light falling on it. Given the latitude, long periods of constant darkness or constant sunlight create climates unfamiliar to human beings in much of the rest of the world.

The snow surface at Dome C Station is typical of most of the continent's surface.

East Antarctica is colder than its western counterpart because of its higher elevation. Weather fronts rarely penetrate far into the continent, leaving the center cold and dry. Despite the lack of precipitation over the central portion of the continent, ice there lasts for extended periods. Heavy snowfalls are common on the coastal portion of the continent, where snowfalls of up to 122 metre (4.803 in) in 48 hours have been recorded.

At the edge of the continent, strong katabatic winds off the polar plateau often blow at storm force. In the interior, wind speeds are typically moderate. During clear days in summer, more solar radiation reaches the surface at the South Pole than at the equator because of the 24 hours of sunlight each day at the Pole.

Antarctica is colder than the Arctic for three reasons. First, much of the continent is more than 3.000 m (9.800 ft) above sea level, and temperature decreases with elevation in the troposphere. Second, the Arctic Ocean covers the north polar zone: the ocean's relative warmth is transferred through the icepack and prevents temperatures in the Arctic regions from reaching the extremes typical of the land surface of Antarctica. Third, the Earth is at aphelion in July (i.e., the Earth is furthest from the Sun in the Antarctic winter), and the Earth is at perihelion in January (i.e., the Earth is closest to the Sun in the Antarctic summer). The orbital distance contributes to a colder Antarctic winter (and a warmer Antarctic summer) but the first two effects have more impact.

The aurora australis, commonly known as the southern lights, is a glow observed in the night sky near the South Pole created by the plasma-full solar winds that pass by the Earth. Another unique spectacle is diamond dust, a ground-level cloud composed of tiny ice crystals. It generally forms under otherwise clear or nearly clear skies, so people sometimes also refer to it as clear-sky precipitation. A sun dog, a frequent atmospheric optical phenomenon, is a bright "spot" beside the true sun.

Population

Ayrıca bakınız: Demographics of Antarctica ve Research stations in Antarctica

The "ceremonial" South Pole, at Amundsen–Scott Station

Several governments maintain permanent manned research stations on the continent. The number of people conducting and supporting scientific research and other work on the continent and its nearby islands varies from about 1,000 in winter to about 5,000 in the summer, giving it a population density between 000.007 kişi/kilometrekare (18,12992/sq mi) and 000.035 kişi/kilometrekare (90,64958/sq mi) at these times. Many of the stations are staffed year-round, the winter-over personnel typically arriving from their home countries for a one-year assignment. An Orthodox church, Trinity Church, opened in 2004 at the Russian Bellingshausen Station is also manned year-round by one or two priests, who are similarly rotated every year.

Port Lockroy Museum

The first semi-permanent inhabitants of regions near Antarctica (areas situated south of the Antarctic Convergence) were British and American sealers who used to spend a year or more on South Georgia, from 1786 onward. During the whaling era, which lasted until 1966, the population of that island varied from over 1,000 in the summer (over 2,000 in some years) to some 200 in the winter. Most of the whalers were Norwegian, with an increasing proportion of Britons. The settlements included Grytviken, Leith Harbour, King Edward Point, Stromness, Husvik, Prince Olav Harbour, Ocean Harbour ve Godthul. Managers and other senior officers of the whaling stations often lived together with their families. Among them was the founder of Grytviken, Captain Carl Anton Larsen, a prominent Norwegian whaler and explorer who, along with his family, adopted British citizenship in 1910.

The first child born in the southern polar region was Norwegian girl Solveig Gunbjørg Jacobsen, born in Grytviken on 8 October 1913, and her birth was registered by the resident British Magistrate of South Georgia. She was a daughter of Fridthjof Jacobsen, the assistant manager of the whaling station, and Klara Olette Jacobsen. Jacobsen arrived on the island in 1904 and became the manager of Grytviken, serving from 1914 to 1921; two of his children were born on the island.

Emilio Marcos Palma was the first person born south of the 60th parallel south (the continental limit according to the Antarctic Treaty), as well as the first one born on the Antarctic mainland, in 1978 at Base Esperanza, on the tip of the Antarctic Peninsula; his parents were sent there along with seven other families by the Argentine government to determine if family life was suitable on the continent. In 1984, Juan Pablo Camacho was born at the Frei Montalva Station, becoming the first Chilean born in Antarctica. Several bases are now home to families with children attending schools at the station. As of 2009, eleven children were born in Antarctica (south of the 60th parallel south): eight at the Argentinean Esperanza Base and three at the Chilean Frei Montalva Station.

Biodiversity

Ayrıca bakınız: Antarctic ecozone, Antarctic microorganism ve Wildlife of Antarctica

Emperor penguins in Ross Sea, Antarctica

Animals

Few terrestrial vertebrates live in Antarctica. Invertebrate life includes microscopic mites like the Alaskozetes antarcticus, lice, nematodes, tardigrades, rotifers, krill ve springtails. The flightless midge Belgica antarctica, up to 6 milimetre (0,2 in) in size, is the largest purely terrestrial animal in Antarctica. The snow petrel is one of only three birds that breed exclusively in Antarctica.

Varieties of marine animals exist and rely, directly or indirectly, on the phytoplankton. Antarctic sea life includes penguins, blue whales, orcas, colossal squids and fur seals. The emperor penguin is the only penguin that breeds during the winter in Antarctica, while the Adélie penguin breeds farther south than any other penguin. The rockhopper penguin has distinctive feathers around the eyes, giving the appearance of elaborate eyelashes. King penguins, chinstrap penguins, and gentoo penguins also breed in the Antarctic.

The Antarctic fur seal was very heavily hunted in the 18th and 19th centuries for its pelt by sealers from the United States and the United Kingdom. The Weddell seal, a "true seal", is named after Sir James Weddell, commander of British sealing expeditions in the Weddell Sea. Antarctic krill, which congregates in large schools, is the keystone species of the ecosystem of the Southern Ocean, and is an important food organism for whales, seals, leopard seals, fur seals, squid, icefish, penguins, albatrosses and many other birds.

A census of sea life carried out during the International Polar Year and which involved some 500 researchers was released in 2010. The research is part of the global Census of Marine Life (CoML) and has disclosed some remarkable findings. More than 235 marine organisms live in both polar regions, having bridged the gap of 12.000 km (7.456 mi). Large animals such as some cetaceans and birds make the round trip annually. More surprising are small forms of life such as mudworms, sea cucumbers and free-swimming snails found in both polar oceans. Various factors may aid in their distribution – fairly uniform temperatures of the deep ocean at the poles and the equator which differ by no more than 5 °C, and the major current systems or marine conveyor belt which transport egg and larva stages.

Fungi

About 400 species of lichen-forming fungi are known to exist in Antarctica.

About 1150 species of fungi have been recorded from Antarctica, of which about 750 are non-lichen-forming and 400 are lichen-forming. Some of these species are cryptoendoliths as a result of evolution under extreme conditions, and have significantly contributed to shaping the impressive rock formations of the McMurdo Dry Valleys and surrounding mountain ridges. The apparently simple morphology, scarcely differentiated structures, metabolic systems and enzymes still active at very low temperatures, and reduced life cycles shown by such fungi make them particularly suited to harsh environments such as the McMurdo Dry Valleys. In particular, their thick-walled and strongly melanized cells make them resistant to UV-light. Those features are observed in different Antarctic fungi which can be shown by molecular studies to belong in different taxonomic orders. They can also be observed in algae and cyanobacteria, suggesting that these are adaptations to the conditions prevailing in Antarctica. This has led to speculation that, if life ever occurred on Mars, it might have looked similar to Antarctic fungi such as Cryomyces minteri. Some of these fungi are also apparently endemic to Antarctica. Endemic Antarctic fungi also include certain dung-inhabiting species which have had to evolve in response to the double challenge of extreme cold while growing on dung, and the need to survive passage through the gut of warm-blooded animals.

Plants

The climate of Antarctica does not allow extensive vegetation to form. A combination of freezing temperatures, poor soil quality, lack of moisture, and lack of sunlight inhibit plant growth. As a result, the diversity of plant life is very low and limited in distribution. The flora of the continent largely consists of bryophytes. There are about 100 species of mosses and 25 species of liverworts, but only two species of flowering plants, both of which are found in the Antarctic Peninsula: Deschampsia antarctica (Antarctic hair grass) and Colobanthus quitensis (Antarctic pearlwort). Growth is restricted to a few weeks in the summer.

Other organisms

Red fluid pours out of Blood Falls at Taylor Glacier

Seven hundred species of algae exist, most of which are phytoplankton. Multicolored snow algae ve diatoms are especially abundant in the coastal regions during the summer. Bacteria have been found living in the cold and dark as deep as a half-mile deep under the ice.

Conservation

The dumping of waste (even old vehicles), such as here at the Russian Bellingshausen Station in 1992, is prohibited since the entry into force of the Protocol on Environmental Protection in 1998.

The Protocol on Environmental Protection to the Antarctic Treaty (also known as the Environmental Protocol or Madrid Protocol) came into force in 1998, and is the main instrument concerned with conservation and management of biodiversity in Antarctica. The Antarctic Treaty Consultative Meeting is advised on environmental and conservation issues in Antarctica by the Committee for Environmental Protection. A major concern within this committee is the risk to Antarctica from unintentional introduction of non-native species from outside the region.

The passing of the Antarctic Conservation Act (1978) in the U.S. brought several restrictions to U.S. activity on Antarctica. The introduction of alien plants or animals can bring a criminal penalty, as can the extraction of any indigenous species. The overfishing of krill, which plays a large role in the Antarctic ecosystem, led officials to enact regulations on fishing. The Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), a treaty that came into force in 1980, requires that regulations managing all Southern Ocean fisheries consider potential effects on the entire Antarctic ecosystem. Despite these new acts, unregulated and illegal fishing, particularly of Patagonian toothfish (marketed as Chilean Sea Bass in the U.S.), remains a serious problem. The illegal fishing of toothfish has been increasing, with estimates of 32,000 tonnes (35,300 short tons) in 2000.

Politics

Emblem of the Antarctic Treaty since 2002.

29 National Antarctic Programs together supporting science in Antarctica (2009)

Antarctica has no government, although various countries claim sovereignty in certain regions. Although a few of these countries have mutually recognized each other's claims, the validity of these claims is not recognized universally.

New claims on Antarctica have been suspended since 1959 and Antarctica is considered politically neutral. Its status is regulated by the 1959 Antarctic Treaty and other related agreements, collectively called the Antarctic Treaty System. Antarctica is defined as all land and ice shelves south of 60° S for the purposes of the Treaty System. The treaty was signed by twelve countries including the Sovyetler Birliği (and later Russia), the United Kingdom, Arjantin, Şili, Australia, and the United States. It set aside Antarctica as a scientific preserve, established freedom of scientific investigation and environmental protection, and banned military activity on Antarctica. This was the first arms control agreement established during the Cold War.

In 1983, the Antarctic Treaty Parties began negotiations on a convention to regulate mining in Antarctica. A coalition of international organizations launched a public pressure campaign to prevent any minerals development in the region, led largely by Greenpeace International, which established its own scientific station–World Park Base–in the Ross Sea region and conducted annual expeditions to document environmental effects of humans on Antarctica. In 1988, the Convention on the Regulation of Antarctic Mineral Resources (CRAMRA) was adopted. The following year, however, Australia and France announced that they would not ratify the convention, rendering it dead for all intents and purposes. They proposed instead that a comprehensive regime to protect the Antarctic environment be negotiated in its place. The Protocol on Environmental Protection to the Antarctic Treaty (the 'Madrid Protocol') was negotiated as other countries followed suit and on 14 January 1998 it entered into force. The Madrid Protocol bans all mining in Antarctica, designating Antarctica a 'natural reserve devoted to peace and science'.

HMS Endurance: the Royal Navy's Antarctic patrol ship

The Antarctic Treaty prohibits any military activity in Antarctica, including the establishment of military bases and fortifications, military manoeuvers, and weapons testing. Military personnel or equipment are permitted only for scientific research or other peaceful purposes. The only documented military land manoeuvre was Operation NINETY by the Argentine military.

The United States military issues the Antarctica Service Medal to military members or civilians who perform research duty in Antarctica. The medal includes a "wintered over" bar issued to those who remain on Antarctica for two six-month seasons.

Antarctic territories

Ana madde: Territorial claims in Antarctica

Date	Country	Territory	Claim limits	Map
1908		Şablon:Ülke veri British Antarctic Territory	20°W to 80°W
1923		Ross Dependency	150°W to 160°E
1924		Şablon:Ülke veri French Southern and Antarctic Lands Adélie Land	142°2'E to 136°11'E
1929		Peter I Island	68°50′G 90°35′B
1933		Australian Antarctic Territory	160°E to 142°2'E and 136°11'E to 44°38'E
1939		Queen Maud Land	44°38'E to 20°W
1940		Şablon:Ülke veri Antártica Chilena Province Antártica	53°W to 90°W
1943		Şablon:Ülke veri Argentine Antarctica	25°W to 74°W
–	None	Unclaimed territory (Marie Byrd Land)	90°W to 150°W (except Peter I Island)

The Argentine, British, and Chilean claims all overlap, and have caused friction. On 18 December 2012, the British Foreign and Commonwealth Office named a previously unnamed area Queen Elizabeth Land in tribute to Queen Elizabeth II's Diamond Jubilee. On 22 December 2012, the UK ambassador to Argentina, John Freeman, was summoned to the Argentine government as protest against the claim. Argentine–UK relations had previously been damaged throughout 2012 due to disputes over the sovereignty of the nearby Falkland Islands, and the 30th anniversary of the Falklands War.

The areas shown as Australia's ve New Zealand's claims were British territory until they were handed over following the countries' independence. Australia currently claims the largest area. The claims of Britain, Australia, New Zealand, France and Norway are all recognized by each other.

Other countries participating as members of Antarctic Treaty have a territorial interest in Antarctica, but the provisions of the Treaty do not allow them to make their claims while it is in force.

• has a designated 'zone of interest' that is not an actual claim.
• has formally reserved its right to make a claim.
• has inherited the Soviet Union's right to claim territory under the original Antarctic Treaty.
• has formally reserved its right to make a claim.
• reserved its right to make a claim in the original Antarctic Treaty.

Economy

There is no economic activity in Antarctica at present, except for fishing off the coast and small-scale tourism, both based outside Antarctica.

Although coal, hydrocarbons, iron ore, platinum, copper, chromium, nickel, gold and other minerals have been found, they have not been in large enough quantities to exploit. The 1991 Protocol on Environmental Protection to the Antarctic Treaty also restricts a struggle for resources. In 1998, a compromise agreement was reached to place an indefinite ban on mining, to be reviewed in 2048, further limiting economic development and exploitation. The primary economic activity is the capture and offshore trading of fish. Antarctic fisheries in 2000–01 reported landing 112,934 tonnes.

Small-scale "expedition tourism" has existed since 1957 and is currently subject to Antarctic Treaty and Environmental Protocol provisions, but in effect self-regulated by the International Association of Antarctica Tour Operators (IAATO). Not all vessels associated with Antarctic tourism are members of IAATO, but IAATO members account for 95% of the tourist activity. Travel is largely by small or medium ship, focusing on specific scenic locations with accessible concentrations of iconic wildlife. A total of 37,506 tourists visited during the 2006–07 Austral summer with nearly all of them coming from commercial ships. The number was predicted to increase to over 80,000 by 2010.

There has been some concern over the potential adverse environmental and ecosystem effects caused by the influx of visitors. A call for stricter regulations for ships and a tourism quota has been made by some environmentalists and scientists. The primary response by Antarctic Treaty Parties has been to develop, through their Committee for Environmental Protection and in partnership with IAATO, "site use guidelines" setting landing limits and closed or restricted zones on the more frequently visited sites. Antarctic sight seeing flights (which did not land) operated out of Australia and New Zealand until the fatal crash of Air New Zealand Flight 901 in 1979 on Mount Erebus, which killed all 257 aboard. Qantas resumed commercial overflights to Antarctica from Australia in the mid-1990s.

Antarctic fisheries in 1998–1999 (1 July – 30 June) reported landing 119,898 tonnes. Unregulated fishing landed five to six times more than the regulated fishery, and allegedly illegal fishing in Antarctic waters in 1998 resulted in the seizure (by France and Australia) of at least eight fishing ships. See Ocean fisheries#Southern Ocean.

About 30 countries maintain about seventy research stations (40 year-round or permanent, and 30 summer-only) in Antarctica, with an approximate population of 4000 in summer and 1000 in winter.

The ISO 3166-1 alpha-2 "AQ" is assigned to the entire continent regardless of jurisdiction. Different country calling codes and currencies are used for different settlements, depending on the administrating country. The Antarctican dollar, a souvenir item sold in the United States and Canada, is not legal tender.

Research

Ayrıca bakınız: Research stations in Antarctica

A full moon and 25-second exposure allowed sufficient light for this photo to be taken at Amundsen–Scott South Pole Station during the long Antarctic night. The station can be seen at far left, the power plant in the center and the mechanic's garage in the lower right. The green light in the background is the Aurora Australis.

Each year, scientists from 28 different nations conduct experiments not reproducible in any other place in the world. In the summer more than 4,000 scientists operate research stations; this number decreases to just over 1,000 in the winter. McMurdo Station, which is the largest research station in Antarctica, is capable of housing more than 1,000 scientists, visitors, and tourists.

Researchers include biologists, geologists, oceanographers, physicists, astronomers, glaciologists, and meteorologists. Geologists tend to study plate tectonics, meteorites from outer space, and resources from the breakup of the supercontinent Gondwana. Glaciologists in Antarctica are concerned with the study of the history and dynamics of floating ice, seasonal snow, glaciers, and ice sheets. Biologists, in addition to examining the wildlife, are interested in how harsh temperatures and the presence of people affect adaptation and survival strategies in a wide variety of organisms. Medical physicians have made discoveries concerning the spreading of viruses and the body's response to extreme seasonal temperatures. Astrophysicists at Amundsen–Scott South Pole Station study the celestial dome and cosmic microwave background radiation. Many astronomical observations are better made from the interior of Antarctica than from most surface locations because of the high elevation, which results in a thin atmosphere, low temperature, which minimizes the amount of water vapour in the atmosphere, and absence of light pollution, thus allowing for a view of space clearer than anywhere else on Earth. Antarctic ice serves as both the shield and the detection medium for the largest neutrino telescope in the world, built 2 km (1,2 mi) below Amundsen-Scott station.

Since the 1970s, an important focus of study has been the ozone layer in the atmosphere above Antarctica. In 1985, three British scientists working on data they had gathered at Halley Station on the Brunt Ice Shelf discovered the existence of a hole in this layer. It was eventually determined that the destruction of the ozone was caused by chlorofluorocarbons emitted by human products. With the ban of CFCs in the Montreal Protocol of 1989, climate projections indicate that the ozone layer will return to 1980 levels between 2050 and 2070.

In September 2006, NASA satellite data revealed that the Antarctic ozone hole was larger than at any other time on record, 27.5 million km² (10.6 million sq mi). The impacts of the depleted ozone layer on climate changes occurring in Antarctica are not well understood.

In 2007, The Polar Geospatial Center was founded. The Polar Geospatial Center uses geospatial ve remote sensing technology to provide mapping services to American federally funded research teams. Currently, the Polar Geospatial Center can image all of Antarctica at 50 cm resolution every 45 days.

On 6 September 2007, Belgian-based International Polar Foundation unveiled the Princess Elisabeth station, the world's first zero-emissions polar science station in Antarctica to research climate change. Costing $16.3 million, the prefabricated station, which is part of International Polar Year, was shipped to the South Pole from Belçika by the end of 2008 to monitor the health of the polar regions. Belgian polar explorer Alain Hubert stated: "This base will be the first of its kind to produce zero emissions, making it a unique model of how energy should be used in the Antarctic." Johan Berte is the leader of the station design team and manager of the project which conducts research in climatology, glaciology ve microbiology.

In January 2008, the British Antarctic Survey (BAS) scientists, led by Hugh Corr and David Vaughan, reported (in the journal Nature Geoscience) that 2,200 years ago, a volcano erupted under Antarctica's ice sheet (based on airborne survey with radar images). The biggest eruption in Antarctica in the last 10,000 years, the volcanic ash was found deposited on the ice surface under the Hudson Mountains, close to Pine Island Glacier.

Meteorites

Antarctic meteorite, named ALH84001, from Mars

Meteorites from Antarctica are an important area of study of material formed early in the solar system; most are thought to come from asteroids, but some may have originated on larger planets. The first meteorite was found in 1912, and named the Adelie Land meteorite. In 1969, a Japanese expedition discovered nine meteorites. Most of these meteorites have fallen onto the ice sheet in the last million years. Motion of the ice sheet tends to concentrate the meteorites at blocking locations such as mountain ranges, with wind erosion bringing them to the surface after centuries beneath accumulated snowfall. Compared with meteorites collected in more temperate regions on Earth, the Antarctic meteorites are well-preserved.

This large collection of meteorites allows a better understanding of the abundance of meteorite types in the solar system and how meteorites relate to asteroids and comets. New types of meteorites and rare meteorites have been found. Among these are pieces blasted off the Moon, and probably Mars, by impacts. These specimens, particularly ALH84001 discovered by ANSMET, are at the center of the controversy about possible evidence of microbial life on Mars. Because meteorites in space absorb and record cosmic radiation, the time elapsed since the meteorite hit the Earth can be determined from laboratory studies. The elapsed time since fall, or terrestrial residence age, of a meteorite represents more information that might be useful in environmental studies of Antarctic ice sheets.

In 2006, a team of researchers from Ohio State University used gravity measurements by NASA's GRACE satellites to discover the 300-mil (480 km)-wide Wilkes Land crater, which probably formed about 250 million years ago.

In January 2013, an 18 kg (40 lb) meteorite was discovered frozen in ice on the Nansen ice field by a Search for Antarctic Meteorites, Belgian Approach (SAMBA) mission.

Ice mass and global sea level

Ayrıca bakınız: Current sea level rise

The motion of ice in Antarctica

Due to its location at the South Pole, Antarctica receives relatively little solar radiation. This means that it is a very cold continent where water is mostly in the form of ice. Precipitation is low (most of Antarctica is a desert) and almost always in the form of snow, which accumulates and forms a giant ice sheet which covers the land. Parts of this ice sheet form moving glaciers known as ice streams, which flow towards the edges of the continent. Next to the continental shore are many ice shelves. These are floating extensions of outflowing glaciers from the continental ice mass. Offshore, temperatures are also low enough that ice is formed from seawater through most of the year. It is important to understand the various types of Antarctic ice to understand possible effects on sea levels and the implications of global cooling.

Sea ice extent expands annually in the Antarctic winter and most of this ice melts in the summer. This ice is formed from the ocean water and floats in the same water and thus does not contribute to rise in sea level. The extent of sea ice around Antarctica has remained roughly constant in recent decades, although the thickness changes are unclear.

Melting of floating ice shelves (ice that originated on the land) does not in itself contribute much to sea-level rise (since the ice displaces only its own mass of water). However it is the outflow of the ice from the land to form the ice shelf which causes a rise in global sea level. This effect is offset by snow falling back onto the continent. Recent decades have witnessed several dramatic collapses of large ice shelves around the coast of Antarctica, especially along the Antarctic Peninsula. Concerns have been raised that disruption of ice shelves may result in increased glacial outflow from the continental ice mass.

On the continent itself, the large volume of ice present stores around 70% of the world's fresh water. This ice sheet is constantly gaining ice from snowfall and losing ice through outflow to the sea. Overall, the net change is slightly positive at approximately 33Gt/year with significant regional variation. West Antarctica is currently experiencing a net outflow of glacial ice, which will increase global sea level over time. A review of the scientific studies looking at data from 1992 to 2006 suggested that a net loss of around 50 gigatonnes of ice per year was a reasonable estimate (around 0.14 mm of sea level rise). Significant acceleration of outflow glaciers in the Amundsen Sea Embayment may have more than doubled this figure for 2006.

East Antarctica is a cold region with a ground base above sea level and occupies most of the continent. This area is dominated by small accumulations of snowfall which becomes ice and thus eventually seaward glacial flows. The mass balance of the East Antarctic Ice Sheet as a whole is thought to be slightly positive (lowering sea level) or near to balance. However, increased ice outflow has been suggested in some regions.

Effects of global warming

Warming trend from 1957–2006

Ayrıca bakınız: Antarctic sea ice

Some of Antarctica has been warming up; particularly strong warming has been noted on the Antarctic Peninsula. A study by Eric Steig published in 2009 noted for the first time that the continent-wide average surface temperature trend of Antarctica is slightly positive at >0.05 °C (0.09 °F) per decade from 1957 to 2006. This study also noted that West Antarctica has warmed by more than 0.1 °C (0.2 °F) per decade in the last 50 years, and this warming is strongest in winter and spring. This is partly offset by fall cooling in East Antarctica. There is evidence from one study that Antarctica is warming as a result of human carbon dioxide emissions., but this remains ambiguous. The amount of surface warming in West Antarctica, while large, has not led to appreciable melting at the surface, and is not directly affecting the West Antarctic Ice Sheet's contribution to sea level. Instead the recent increases in glacier outflow are believed to be due to an inflow of warm water from the deep ocean, just off the continental shelf. The net contribution to sea level from the Antarctic Peninsula is more likely to be a direct result of the much greater atmospheric warming there.

In 2002 the Antarctic Peninsula's Larsen-B ice shelf collapsed. Between 28 February and 8 March 2008, about 570 kilometrekare (220 sq mi) of ice from the Wilkins Ice Shelf on the southwest part of the peninsula collapsed, putting the remaining 15.000 km² (5.800 sq mi) of the ice shelf at risk. The ice was being held back by a "thread" of ice about 6 km (4 mi) wide, prior to its collapse on 5 April 2009. According to NASA, the most widespread Antarctic surface melting of the past 30 years occurred in 2005, when an area of ice comparable in size to California briefly melted and refroze; this may have resulted from temperatures rising to as high as 5 °C (41 °F).

A study published in Nature Geoscience in 2013 (online in December 2012) identified central West Antarctica as one of the fastest-warming regions on Earth. The researchers present a complete temperature record from Antarctica's Byrd Station and assert that it "reveals a linear increase in annual temperature between 1958 and 2010 by 2.4±1.2 °C".

Ozone depletion

Image of the largest Antarctic ozone hole ever recorded due to CFCs accumulation (September 2006)

Ana madde: Ozone depletion

Each year a large area of low ozone concentration or "ozone hole" grows over Antarctica. This hole covers almost the whole continent and was at its largest in September 2008, when the longest lasting hole on record remained until the end of December. The hole was detected by scientists in 1985 and has tended to increase over the years of observation. The ozone hole is attributed to the emission of chlorofluorocarbons or CFCs into the atmosphere, which decompose the ozone into other gases.

Some scientific studies suggest that ozone depletion may have a dominant role in governing climatic change in Antarctica (and a wider area of the Southern Hemisphere). Ozone absorbs large amounts of ultraviolet radiation in the stratosphere. Ozone depletion over Antarctica can cause a cooling of around 6 °C in the local stratosphere. This cooling has the effect of intensifying the westerly winds which flow around the continent (the polar vortex) and thus prevents outflow of the cold air near the South Pole. As a result, the continental mass of the East Antarctic ice sheet is held at lower temperatures, and the peripheral areas of Antarctica, especially the Antarctic Peninsula, are subject to higher temperatures, which promote accelerated melting. Models also suggest that the ozone depletion/enhanced polar vortex effect also accounts for the recent increase in sea-ice just offshore of the continent.

See also

• Antarctic Circle
• Antarctic Plate
• Arctic
• List of mountain ranges in Antarctica
• North Pole
• South Pole

External links

• Antarctica. – In Our Time, BBC. (şimdi dinle)
• Curlie'de Antarctic region (DMOZ tabanlı)
• "Antarctica". The World Factbook (2024 bas.). CIA. Arşivlenmesi gereken bağlantıya sahip kaynak şablonu içeren maddeler (link)
• British Services Antarctic Expedition 2012
• Antarctic Treaty Secretariat, de facto government
• British Antarctic Survey (BAS)
• U.S. Antarctic Program Portal
• Australian Antarctic Division
• South African National Antarctic Programme – Official Website
• Portals on the World – Antarctica from the Library of Congress
• NASA's LIMA (Landsat Image Mosaic of Antarctica) (USGS mirror)
• The Antarctic Sun (Online newspaper of the U.S. Antarctic Program)
• Antarctica and New Zealand (NZHistory.net.nz)
• Journey to Antarctica in 1959 – slideshow by The New York Times
• Listen to Ernest Shackleton describing his 1908 South Pole Expedition
• The recording describing Shackleton's 1908 South Pole Expedition was added to the National Film and Sound Archive's Sounds of Australia registry in 2007

Şablon:Featured article