Antarctica Surface

Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest continent, being about 40% larger than Europe, and has an area of . Most of Antarctica is covered by the Antarctic ice sheet, with an average thickness of .

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 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 . Antarctica holds the record for the lowest measured temperature on Earth, . The coastal regions can reach temperatures over in summer. Native species of animals include mites, nematodes, penguins, seals and tardigrades. Where vegetation occurs, it is mostly in the form of lichen.

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 in 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 were the first to reach the magnetic South Pole in 1909, and the geographic South Pole was first reached in 1911 by Norwegian explorers.

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 its remoteness, human activity has a significant impact on the continent via pollution, ozone depletion, and climate change.

Etymology

The name given to the continent originates from the word ''antarctic'', which comes from Middle French ' or ' ('opposite to the Arctic') and, in turn, the Latin ' ('opposite to the north'). ' is derived from the Greek ('anti-') and ('of the Bear', 'northern'). The Greek philosopher Aristotle wrote in ''Meteorology'' about an "Antarctic region" in . 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 , from which derived the Old French (modern ) attested in 1270, and from there the Middle English , found first in a treatise written by the English author Geoffrey Chaucer.

Until the discovery, belief by Europeans in the existence of a '—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 of such a land lasted until the discovery of Australia.

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. 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''. ''Antarctica'' was adopted in the 1890s, with the first use of the name being attributed to the Scottish cartographer John George Bartholomew.

Geography

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. Rivers exist in Antarctica, the longest being the Onyx. Antarctica covers more than , making it the fifth-largest continent, slightly less than 1.5 times the area of the United States. Its coastline is almost long: , 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.

The lakes that lie at the base of the continental ice sheet occur mainly in the McMurdo Dry Valleys or various oases. Lake Vostok, discovered beneath Russia's Vostok Station, is the largest sub-glacial 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. 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.

Antarctica is divided into West Antarctica and East Antarctica by the Transantarctic Mountains, which stretch from Victoria Land to the Ross Sea. The vast majority of Antarctica is covered by the Antarctic ice sheet, which averages in thickness. The ice sheet extends to all but a few oases, which, with the exception of the McMurdo Dry Valleys, are located in coastal areas. Several Antarctic ice streams flow to one of the many Antarctic ice shelves, a process described by ice-sheet dynamics.

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. There are numerous islands surrounding Antarctica, most of which are volcanic and very young by geological standards. The most prominent exceptions to this are the islands of the Kerguelen Plateau, the earliest of which formed around 40 Ma.

Vinson Massif, in the Ellsworth Mountains, is the highest peak in Antarctica at . 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 from the volcanic crater. 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. The ice dome known as Dome Argus in East Antarctica is the highest Antarctic ice feature, at . It is one of the world's coldest and driest places—temperatures there may reach as low as , and the annual precipitation is .

Geologic history

From the end of the Neoproterozoic era to the Cretaceous, Antarctica was part of the supercontinent Gondwana. Modern Antarctica was formed as Gondwana gradually broke apart beginning around 183 Ma. For a large proportion of the Phanerozoic, Antarctica had a tropical or temperate climate, and it was covered in forests.

Palaeozoic era (540–250 Ma)

During the Cambrian period, Gondwana had a mild climate. 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. 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. 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. There is no evidence of any tetrapods having lived in Antarctica during the Paleozoic.

Mesozoic era (250–66 Ma)

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. Tetrapods first appeared in Antarctica during the early Triassic, with the earliest known fossils found in the Fremouw Formation of the Transantarctic Mountains. Synapsids (also known as "mammal-like reptiles") included species such as ''Lystrosaurus'', and were common during the Early Triassic.

The Antarctic Peninsula began to form during the Jurassic period (206–146 Ma). ''Ginkgo'' trees, conifers, Bennettitales, horsetails, ferns and cycads were plentiful during the time. 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. 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, and ''Antarctopelta'', ''Trinisaura,'' ''Morrosaurus'' and ''Imperobator'' from Late Cretaceous of the Antarctic Peninsula) have been described.

Gondwana breakup (160–15 Ma)

Africa separated from Antarctica in the Jurassic around 160 Ma, followed by the Indian subcontinent in the early Cretaceous (about 125 Ma). During the early Paleogene, Antarctica remained connected to South America via the Isthmus of Scotia 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 meridiolestidans. Marsupials are thought to have dispersed into Australia via Antarctica by the early Eocene.

Around 53 Ma, Australia-New Guinea separated from Antarctica, opening the Tasmanian Passage. 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. 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. Since about 15 Ma, the continent has been mostly covered with ice.

Present day

The geology of Antarctica, largely obscured by the continental ice sheet, is being revealed by techniques such as remote sensing, ground-penetrating radar, and satellite imagery. Geologically, West Antarctica closely resembles the South American Andes. The Antarctic Peninsula was formed by geologic uplift and the transformation of sea bed sediments into metamorphic rocks.

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.

East Antarctica is geologically varied. Its formation began during the Archean Eon (4,000 Ma2,500 Ma), and stopped during the Cambrian Period. It is built on a craton of rock, which is the basis of the Precambrian Shield. 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. In coastal areas such as the Shackleton Range and Victoria Land, some faulting has occurred.

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. The Prince Charles Mountains contain deposits of iron ore. There are oil and natural gas fields in the Ross Sea.

Climate

Antarctica is the coldest, windiest, and driest of Earth's continents. The lowest natural air temperature ever recorded on Earth was at the Russian Vostok Station in Antarctica on 21 July 1983. A lower air temperature of was recorded in 2010 by satellite—however, it may have been influenced by ground temperatures and was not recorded at a height of above the surface as required for official air temperature records. Average temperatures can reach a minimum of between in the interior of the continent during winter and a maximum of over near the coast in summer.

Antarctica is a polar desert with little precipitation; the continent receives an average equivalent to about of water per year, mostly in the form of snow. The interior is dryer and receives less than per year, whereas the coastal regions typically receive more than . In a few blue-ice areas, the wind and sublimation remove more snow than is accumulated by precipitation. In the dry valleys, the same effect occurs over a rock base, leading to a barren and desiccated landscape. Antarctica is colder than the Arctic region, as much of Antarctica is over 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.

Regional differences

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 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.

Climate change

Over the second half of the 20th century, the Antarctic Peninsula was the fastest-warming place on Earth, closely followed by West Antarctica, but temperatures rose less rapidly during the early 21st century. Conversely, the South Pole, located in East Antarctica, barely warmed during much of the 20th century, but temperatures rose three times the global average between 1990 and 2020. In February 2020, the continent recorded its highest temperature of , which was higher than the previous record attained in March 2015.

There is some evidence that surface warming in Antarctica is due to human greenhouse gas emissions, but it is difficult to determine due to internal variability. A main component of climate variability in Antarctica is the Southern Annular Mode (a low-frequency mode of atmospheric variability of the Southern Hemisphere), which showed strengthened winds around Antarctica in the summer of the later decades of the 20th century, associated with cooler temperatures over the continent. The trend was at a scale unprecedented over the last 600 years; the most dominant driver of the mode of variability is likely the depletion of ozone above the continent.

Glaciers and floating ice

Precipitation in Antarctica occurs in the form of snow, which accumulates and forms the giant ice sheet that covers the continent. Under the force of gravity, the ice flows towards the coast. The ice then moves into the ocean, often forming vast floating ice shelves. These shelves can melt or form icebergs that eventually disintegrate when they reach warmer ocean waters.

Sea ice and ice shelves

Sea ice extent expands annually during the Antarctic winter, but most of it melts in the summer. The ice is formed from the ocean, and does not contribute to changes in sea level. The average extent of sea ice around Antarctica has changed little since satellites began to observe the Earth's surface in 1978; which is in contrast with the Arctic, where there has been rapid sea ice loss. A possible explanation is that thermohaline circulation transports warmed water to deeper layers in the Southern Ocean so that the surface remains relatively cool.

The melting of the ice shelves does not contribute much to sea level rise, as the floating ice displaces its own mass of water, but the ice shelves act to stabilize the land ice. They are vulnerable to warming water, which has caused large ice shelves to collapse into the ocean. The loss of ice shelf "buttressing" has been identified as the major cause of ice loss on the West Antarctic ice sheet, but has also been observed around the East Antarctic ice sheet.

In 2002 the Antarctic Peninsula's Larsen-B ice shelf collapsed. In early 2008, about of ice from the Wilkins Ice Shelf on the southwest part of the peninsula collapsed, putting the remaining of the ice shelf at risk. The ice was being held back by a "thread" of ice about wide, prior to its collapse in 2009. , the two most rapidly thinning ice shelves are those in front of the Pine Island and Thwaites glaciers. Both ice shelves act to stabilise the glaciers that feed into them.

Ice sheet loss and sea level rise

Antarctica contains about 90% of the world's ice. If all of this ice were melted, global sea levels would rise about . In addition, Antarctica stores around 70% of global freshwater as ice. The continent is losing mass due to the increased flow of its glaciers toward the ocean. The loss of mass from Antarctica's ice sheets is partially offset by additional snow falling back onto it. A 2018 systematic review study estimated that ice loss across the entire continent was 43 gigatonnes (Gt) per year on average during the period from 1992 to 2002, but accelerated to an average of 220 Gt per year during the five years from 2012 to 2017. Antarctica's total contribution to sea level rise has been estimated to be .

Most of the ice loss has taken place on the Antarctic Peninsula and West Antarctica. Estimates of the mass balance of the East Antarctic Ice Sheet as a whole range from slightly positive to slightly negative. Increased ice outflow has been observed in some regions of East Antarctica, particularly at Wilkes Land.

Future projections of ice loss depend on the speed of climate change mitigation and are uncertain. Tipping points have been identified in some regions; when a certain threshold warming is reached, these regions may start melting at a significantly faster rate. If average temperatures were to begin to fall, the ice would not immediately be restored. A tipping point for the West Antarctic ice sheet is estimated to be between of global warming. A full collapse would likely not take place unless warming reaches between , and may occur within centuries under pessimistic assumptions. This full collapse would lead to of sea level rise. At , parts of the East Antarctic ice sheet are also projected to be fully lost, and total ice loss would lead to around or more of sea level rise.

Ozone depletion

Scientists have studied the ozone layer in the atmosphere above Antarctica since the 1970s. In 1985, British scientists, working on data they had gathered at Halley Research Station on the Brunt Ice Shelf, discovered a large area of low ozone concentration over Antarctica. The 'ozone hole' covers almost the whole continent and was at its largest in September 2006; the longest-lasting event occurred in 2020. The depletion is caused by the emission of chlorofluorocarbons and halons into the atmosphere, which causes ozone to break down into other gases. The extreme cold conditions of Antarctica allow polar stratospheric clouds to form. The clouds act as catalysts for chemical reactions, which eventually lead to the destruction of ozone. The 1987 Montreal Protocol has restricted the emissions of ozone-depleting substances. The ozone hole above Antarctica is predicted to slowly disappear; by the 2060s, levels of ozone are expected to have returned to values last recorded in the 1980s.

The ozone depletion can cause a cooling of around in the stratosphere. The cooling strengthens the polar vortex and so prevents the outflow of the cold air near the South Pole, which in turn cools the continental mass of the East Antarctic ice sheet. The peripheral areas of Antarctica, especially the Antarctic Peninsula, are then subjected to higher temperatures, which accelerate the melting of the ice. Models suggest that ozone depletion and the enhanced polar vortex effect may also account for the period of increasing sea ice extent, lasting from when observation started in the late 1970s until 2014. Since then, the coverage of Antarctic sea ice has decreased rapidly.

Biodiversity

Most species in Antarctica seem to be the descendants of species that lived there millions of years ago. As such, they must have survived multiple glacial cycles. The species survived the periods of extremely cold climate in isolated warmer areas, such as those with geothermal heat or areas that remained ice-free throughout the colder climate.

Animals

Invertebrate life of Antarctica includes species of microscopic mites such as ''Alaskozetes antarcticus'', lice, nematodes, tardigrades, rotifers, krill and springtails. The few terrestrial vertebrates are limited to the sub-Antarctic islands. The flightless midge ''Belgica antarctica'', the largest purely terrestrial animal in Antarctica, reaches in size.

Antarctic krill, which congregates in large schools, is the keystone species of the ecosystem of the Southern Ocean, being an important food organism for whales, seals, leopard seals, fur seals, squid, icefish, and many bird species, such as penguins and albatrosses. Some species of marine animals exist and rely, directly or indirectly, on phytoplankton. Antarctic sea life includes penguins, blue whales, orcas, colossal squids and fur seals. The Antarctic fur seal was very heavily hunted in the 18th and 19th centuries for its Fur, pelt by Seal hunting, seal hunters from the United States and the United Kingdom. Leopard seals are apex predators in the Antarctic ecosystem and migrate across the Southern Ocean in search of food.

There are approximately 40 bird species that breed on or close to Antarctica, including species of petrels, penguins, cormorants, and gulls. Various other bird species visit the ocean around Antarctica, including some that normally reside in the Arctic. The emperor penguin is the only penguin that breeds during the winter in Antarctica; it and the Adélie penguin breed farther south than any other penguin.

A Census of Marine Life by some 500 researchers during the International Polar Year was released in 2010. The research found that more than 235 marine organisms live in both polar regions, having bridged the gap of . Large animals such as some cetaceans and birds make the round trip annually. Smaller forms of life, such as sea cucumbers and Pteropoda, free-swimming snails also found in both polar oceans. Factors that may aid in their distribution include temperature differences between the deep ocean at the poles and the equator of no more than and the major current systems or marine conveyor belts which are able to transport eggs and larva.

Fungi

About 1,150 species of Fungus, fungi have been recorded in the Antarctic region, of which about 750 are non-lichen

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