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Earth's southernmost continent From Wikipedia, the free encyclopedia
Antarctica (/ænˈtɑːrktɪkə/ )[note 1] is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. Antarctica is the fifth-largest continent, being about 40% larger than Europe, and has an area of 14,200,000 km2 (5,500,000 sq mi). Most of Antarctica is covered by the Antarctic ice sheet, with an average thickness of 1.9 km (1.2 mi).
.svg) | |
| Area | 14,200,000 km2 5,500,000 sq mi[1] |
|---|---|
| Population | 1,300 to 5,100 (seasonal) |
| Population density | 0.00009/km2 to 0.00036/km2 (seasonal) |
| Countries | 7 territorial claims |
| Time zones | All time zones |
| Internet TLD | .aq |
| Largest settlements | |
| UN M49 code | 010 |
Antarctica is, on average, the coldest, driest, and windiest of the continents, and it has the highest average elevation. It is mainly a polar desert, with annual precipitation of over 200 mm (8 in) along the coast and far less inland. About 70% of the world's freshwater reserves are frozen in Antarctica, which, if melted, would raise global sea levels by almost 60 metres (200 ft). Antarctica holds the record for the lowest measured temperature on Earth, −89.2 °C (−128.6 °F). The coastal regions can reach temperatures over 10 °C (50 °F) in the summer. Native species of animals include mites, nematodes, penguins, seals and tardigrades. Where vegetation occurs, it is mostly in the form of lichen or moss.
The ice shelves of Antarctica were probably first seen in 1820, during a Russian expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev. The decades that followed saw further exploration by French, American, and British expeditions. The first confirmed landing was by a Norwegian team in 1895. In the early 20th century, there were a few expeditions into the interior of the continent. British explorers Robert Falcon Scott and Ernest Shackleton were the first to reach the magnetic South Pole in 1909, and the geographic South Pole was first reached in 1911 by Norwegian explorer Roald Amundsen.[4]
Antarctica is governed by about 30 countries, all of which are parties of the 1959 Antarctic Treaty System. According to the terms of the treaty, military activity, mining, nuclear explosions, and nuclear waste disposal are all prohibited in Antarctica. Tourism, fishing and research are the main human activities in and around Antarctica. During the summer months, about 5,000 people reside at research stations, a figure that drops to around 1,000 in the winter. Despite the continent's remoteness, human activity has a significant effect on it via pollution, ozone depletion, and climate change. The melting of the potentially unstable West Antarctic ice sheet causes the most uncertainty in century-scale projections of sea level rise, and the same melting also affects the Southern Ocean overturning circulation, which can eventually lead to significant impacts on the Southern Hemisphere climate and Southern Ocean productivity.
The name given to the continent originates from the word antarctic, which comes from Middle French antartique or antarctique ('opposite to the Arctic') and, in turn, the Latin antarcticus ('opposite to the north'). Antarcticus is derived from the Greek ἀντι- ('anti-') and ἀρκτικός ('of the Bear', 'northern').[5] The Greek philosopher Aristotle wrote in Meteorology about an "Antarctic region" in c. 350 BCE.[6] The Greek geographer Marinus of Tyre reportedly used the name in his world map from the second century CE, now lost. The Roman authors Gaius Julius Hyginus and Apuleius used for the South Pole the romanised Greek name polus antarcticus,[7] from which derived the Old French pole antartike (modern pôle antarctique) attested in 1270, and from there the Middle English pol antartik, found first in a treatise written by the English author Geoffrey Chaucer.[5]
Belief by Europeans in the existence of a Terra Australis—a vast continent in the far south of the globe to balance the northern lands of Europe, Asia, and North Africa—had existed as an intellectual concept since classical antiquity. The belief in such a land lasted until the European discovery of Australia.[8]
During the early 19th century, explorer Matthew Flinders doubted the existence of a detached continent south of Australia (then called New Holland) and thus advocated for the "Terra Australis" name to be used for Australia instead.[9][10] In 1824, the colonial authorities in Sydney officially renamed the continent of New Holland to Australia, leaving the term "Terra Australis" unavailable as a reference to Antarctica. Over the following decades, geographers used phrases such as "the Antarctic Continent". They searched for a more poetic replacement, suggesting names such as Ultima and Antipodea.[11] Antarctica was adopted in the 1890s, with the first use of the name being attributed to the Scottish cartographer John George Bartholomew.[12]
Antarctica has also been known by the moniker Great White South, after which British photographer Herbert Ponting named one of his books on Antarctic photography, possibly as a counterpart to the epithet Great White North for Canada. [13]
Positioned asymmetrically around the South Pole and largely south of the Antarctic Circle (one of the five major circles of latitude that mark maps of the world), Antarctica is surrounded by the Southern Ocean.[note 2] Rivers exist in Antarctica; the longest is the Onyx. Antarctica covers more than 14.2 million km2 (5,500,000 sq mi), almost double the area of Australia, making it the fifth-largest continent, and comparable to the surface area of Pluto. Its coastline is almost 18,000 km (11,200 mi) long:[1] as of 1983[update], of the four coastal types, 44% of the coast is floating ice in the form of an ice shelf, 38% consists of ice walls that rest on rock, 13% is ice streams or the edge of glaciers, and the remaining 5% is exposed rock.[15]
The lakes that lie at the base of the continental ice sheet occur mainly in the McMurdo Dry Valleys or various oases.[16] Lake Vostok, discovered beneath Russia's Vostok Station, is the largest subglacial lake globally and one of the largest lakes in the world. It was once believed that the lake had been sealed off for millions of years, but scientists now estimate its water is replaced by the slow melting and freezing of ice caps every 13,000 years.[17] During the summer, the ice at the edges of the lakes can melt, and liquid moats temporarily form. Antarctica has both saline and freshwater lakes.[16]
Antarctica is divided into West Antarctica and East Antarctica by the Transantarctic Mountains, which stretch from Victoria Land to the Ross Sea.[18][19] The vast majority of Antarctica is covered by the Antarctic ice sheet, which averages 1.9 km (1.2 mi) in thickness.[20] The ice sheet extends to all but a few oases, which, with the exception of the McMurdo Dry Valleys, are located in coastal areas.[21] Several Antarctic ice streams flow to one of the many Antarctic ice shelves, a process described by ice-sheet dynamics.[22]
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East Antarctica comprises Coats Land, Queen Maud Land, Enderby Land, Mac. Robertson Land, Wilkes Land, and Victoria Land. All but a small portion of the region lies within the Eastern Hemisphere. East Antarctica is largely covered by the East Antarctic Ice Sheet.[23] There are numerous islands surrounding Antarctica, most of which are volcanic and very young by geological standards.[24] The most prominent exceptions to this are the islands of the Kerguelen Plateau, the earliest of which formed around 40 Ma.[24][25]
Vinson Massif, in the Ellsworth Mountains, is the highest peak in Antarctica at 4,892 m (16,050 ft).[26] Mount Erebus on Ross Island is the world's southernmost active volcano and erupts around 10 times each day. Ash from eruptions has been found 300 kilometres (190 mi) from the volcanic crater.[27] There is evidence of a large number of volcanoes under the ice, which could pose a risk to the ice sheet if activity levels were to rise.[28] The ice dome known as Dome Argus in East Antarctica is the highest Antarctic ice feature, at 4,091 metres (13,422 ft). It is one of the world's coldest and driest places—temperatures there may reach as low as −90 °C (−130 °F), and the annual precipitation is 1–3 cm (0.39–1.18 in).[29]
From the end of the Neoproterozoic era to the Cretaceous, Antarctica was part of the supercontinent Gondwana.[30] Modern Antarctica was formed as Gondwana gradually broke apart beginning around 183 Ma.[31] For a large proportion of the Phanerozoic, Antarctica had a tropical or temperate climate, and it was covered in forests.[32]
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During the Cambrian period, Gondwana had a mild climate.[33] West Antarctica was partially in the Northern Hemisphere, and during the time, large amounts of sandstones, limestones, and shales were deposited. East Antarctica was at the equator, where seafloor 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 then. Sand and silts were laid down in what is now the Ellsworth, Horlick, and Pensacola Mountains.
Antarctica became glaciated during the Late Paleozoic icehouse beginning at the end of the Devonian period (360 Ma), though glaciation would substantially increase during the late Carboniferous. It drifted closer to the South Pole, and the climate cooled, though flora remained.[34] After deglaciation during the latter half of the Early Permian, the land became dominated by glossopterids (an extinct group of seed plants with no close living relatives), most prominently Glossopteris, a tree interpreted as growing in waterlogged soils, which formed extensive coal deposits. Other plants found in Antarctica during the Permian include Cordaitales, sphenopsids, ferns, and lycophytes.[35] At the end of the Permian, the climate became drier and hotter over much of Gondwana, and the glossopterid forest ecosystems collapsed, as part of the End-Permian mass extinction.[35][36] There is no evidence of any tetrapods having lived in Antarctica during the Paleozoic.[37]
The continued warming dried out much of Gondwana. During the Triassic, Antarctica was dominated by seed ferns (pteridosperms) belonging to the genus Dicroidium, which grew as trees. Other associated Triassic flora included ginkgophytes, cycadophytes, conifers, and sphenopsids.[38] Tetrapods first appeared in Antarctica during the early Triassic, with the earliest known fossils found in the Fremouw Formation of the Transantarctic Mountains.[37] Synapsids (also known as "mammal-like reptiles") included species such as Lystrosaurus, and were common during the Early Triassic.[39]
The Antarctic Peninsula began to form during the Jurassic period (206 to 146 million years ago).[40] Africa separated from Antarctica in the Jurassic around 160 Ma, followed by the Indian subcontinent in the early Cretaceous (about 125 Ma).[41] Ginkgo trees, conifers, Bennettitales, horsetails, ferns and cycads were plentiful during the time.[42] In West Antarctica, coniferous forests dominated throughout the Cretaceous period (146–66 Ma), though southern beech trees (Nothofagus) became prominent towards the end of the Cretaceous.[43][44] Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only a few Antarctic dinosaur genera (Cryolophosaurus and Glacialisaurus, from the Early Jurassic Hanson Formation of the Transantarctic Mountains,[45] and Antarctopelta, Trinisaura, Morrosaurus and Imperobator from Late Cretaceous of the Antarctic Peninsula) have been described.[46][47][48][49]
During the early Paleogene, Antarctica remained connected to South America as well as to southeastern Australia. Fauna from the La Meseta Formation in the Antarctic Peninsula, dating to the Eocene, is very similar to equivalent South American faunas; with marsupials, xenarthrans, litoptern, and astrapotherian ungulates, as well as gondwanatheres and possibly meridiolestidans.[50][51] Marsupials are thought to have dispersed into Australia via Antarctica by the early Eocene.[52]
Around 53 Ma, Australia-New Guinea separated from Antarctica, opening the Tasmanian Passage.[53] The Drake Passage opened between Antarctica and South America around 30 Ma, resulting in the creation of the Antarctic Circumpolar Current that completely isolated the continent.[54] Models of Antarctic geography suggest that this current, as well as a feedback loop caused by lowering CO2 levels, caused the creation of small yet permanent polar ice caps. As CO2 levels declined further the ice began to spread rapidly, replacing the forests that until then had covered Antarctica.[55] Tundra ecosystems continued to exist on Antarctica until around 14-10 million years ago, when further cooling lead to their extermination.[56]
The geology of Antarctica, largely obscured by the continental ice sheet,[57] is being revealed by techniques such as remote sensing, ground-penetrating radar, and satellite imagery.[58] Geologically, West Antarctica closely resembles the South American Andes.[59] The Antarctic Peninsula was formed by geologic uplift and the transformation of sea bed sediments into metamorphic rocks.[60]
West Antarctica was formed by the merging of several continental plates, which created a number of mountain ranges in the region, the most prominent being the Ellsworth Mountains. The presence of the West Antarctic Rift System has resulted in volcanism along the border between West and East Antarctica, as well as the creation of the Transantarctic Mountains.[61]
East Antarctica is geologically varied. Its formation began during the Archean Eon (4,000 Ma–2,500 Ma), and stopped during the Cambrian Period.[62] It is built on a craton of rock, which is the basis of the Precambrian Shield.[63] On top of the base are coal and sandstones, limestones, and shales that were laid down during the Devonian and Jurassic periods to form the Transantarctic Mountains.[64] In coastal areas such as the Shackleton Range and Victoria Land, some faulting has occurred.[65][66]
Coal was first recorded in Antarctica near the Beardmore Glacier by Frank Wild on the Nimrod Expedition in 1907, and low-grade coal is known to exist across many parts of the Transantarctic Mountains.[67] The Prince Charles Mountains contain deposits of iron ore.[68] There are oil and natural gas fields in the Ross Sea.[69]
Antarctica is the coldest, windiest, and driest of Earth's continents.[1] Near the coast, the temperature can exceed 10 °C in summer and fall to below −40 °C in winter. Over the elevated inland, it can rise to about −30 °C in summer but fall below −80 °C in winter.
The lowest natural air temperature ever recorded on Earth was −89.2 °C (−128.6 °F) at the Russian Vostok Station in Antarctica on 21 July 1983.[70] A lower air temperature of −94.7 °C (−138.5 °F) was recorded in 2010 by satellite—however, it may have been influenced by ground temperatures and was not recorded at a height of 2 m (7 ft) above the surface as required for official air temperature records.[71][72]
Antarctica is a polar desert with little precipitation; the continent receives an average equivalent to about 150 mm (6 in) of water per year, mostly in the form of snow. The interior is dryer and receives less than 50 mm (2 in) per year, whereas the coastal regions typically receive more than 200 mm (8 in).[73] In a few blue-ice areas, the wind and sublimation remove more snow than is accumulated by precipitation.[74] In the dry valleys, the same effect occurs over a rock base, leading to a barren and desiccated landscape.[75] Antarctica is colder than the Arctic region, as much of Antarctica is over 3,000 m (9,800 ft) above sea level, where air temperatures are colder. The relative warmth of the Arctic Ocean is transferred through the Arctic sea ice and moderates temperatures in the Arctic region.[76]
East Antarctica is colder than its western counterpart because of its higher elevation. Weather fronts rarely penetrate far into the continent, leaving the centre cold and dry, with moderate wind speeds. Heavy snowfalls are common on the coastal portion of Antarctica, where snowfalls of up to 1.22 m (48 in) in 48 hours have been recorded. At the continent's edge, strong katabatic winds off of the polar plateau often blow at storm force. During the summer, more solar radiation reaches the surface at the South Pole than at the equator because of the 24 hours of sunlight received there each day.[1]
Climate change caused by greenhouse gas emissions from human activities occurs everywhere on Earth, and while Antarctica is less vulnerable to it than any other continent,[78] climate change in Antarctica has been observed. Since 1959, there has been an average temperature increase of >0.05 °C/decade since 1957 across the continent, although it had been uneven.[79] West Antarctica warmed by over 0.1 °C/decade from the 1950s to the 2000s, and the exposed Antarctic Peninsula has warmed by 3 °C (5.4 °F) since the mid-20th century.[80] The colder, stabler East Antarctica had been experiencing cooling until the 2000s.[81][82] Around Antarctica, the Southern Ocean has absorbed more oceanic heat than any other ocean,[83] and has seen strong warming at depths below 2,000 m (6,600 ft).[84]: 1230 Around the West Antarctic, the ocean has warmed by 1 °C (1.8 °F) since 1955.[80]
The warming of the Southern Ocean around Antarctica has caused the weakening or collapse of ice shelves, which float just offshore of glaciers and stabilize them. Many coastal glaciers have been losing mass and retreating, causing net-annual ice loss across Antarctica,[84]: 1264 although the East Antarctic ice sheet continues to gain ice inland. By 2100, net ice loss from Antarctica is expected to add about 11 cm (5 in) to global sea level rise. Marine ice sheet instability may cause West Antarctica to contribute tens of centimeters more if it is triggered before 2100.[84]: 1270 With higher warming, instability would be much more likely, and could double global, 21st-century sea-level rise.[85][86][87]
The fresh, 1100-1500 billion tons (GT) per year of meltwater from the ice dilutes the saline Antarctic bottom water,[88][89] weakening the lower cell of the Southern Ocean overturning circulation (SOOC).[84]: 1240 According to some research, a full collapse of the SOOC may occur a between 1.7 °C (3.1 °F) and 3 °C (5.4 °F) of global warming,[90] although the full effects are expected to occur over multiple centuries; these include less precipitation in the Southern Hemisphere but more in the Northern Hemisphere, an eventual decline of fisheries in the Southern Ocean and a potential collapse of certain marine ecosystems.[91] While many Antarctic species remain undiscovered, there are documented increases in Antarctic flora,[92] and large fauna such as penguins are already having difficulty retaining suitable habitat. On ice-free land, permafrost thaws release greenhouse gases and formerly frozen pollution.[93]
The West Antarctic ice sheet is likely to completely melt[94][95]
