Antarctica
 | |
| Area | 14,200,000 km2 5,500,000 sq mi[1] |
|---|---|
| Population | 1,000 to 5,000 (seasonal) |
| Population density | <0.01/km2 <0.03/sq mi |
| Demonym | Antarctic |
| Internet TLD | .aq |
| Largest settlements | |
| UN M49 code | 010 |
Antarctica (/ænˈtɑːrktɪkə/ (
listen))[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).
Antarctica is, on average, the coldest, driest, and windiest of the continents, and it has the highest average
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
Etymology
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').[4] The Greek philosopher Aristotle wrote in Meteorology about an "Antarctic region" in c. 350 BCE.[5] 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,[6] 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.[4]
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 of such a land lasted until the discovery of Australia.[7]
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.[8][9] 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.[10] Antarctica was adopted in the 1890s, with the first use of the name being attributed to the Scottish cartographer John George Bartholomew.[11]
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.[note 2] Rivers exist in Antarctica, the longest being the Onyx. Antarctica covers more than 14.2 million km2 (5,500,000 sq mi), making it the fifth-largest continent, slightly less than 1.5 times the area of the United States. 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.[13]
The
Antarctica is divided into West Antarctica and East Antarctica by the Transantarctic Mountains, which stretch from Victoria Land to the Ross Sea.[16][17] The vast majority of Antarctica is covered by the Antarctic ice sheet, which averages 1.9 km (1.2 mi) in thickness.[18] The ice sheet extends to all but a few oases, which, with the exception of the McMurdo Dry Valleys, are located in coastal areas.[19] Several Antarctic ice streams flow to one of the many Antarctic ice shelves, a process described by ice-sheet dynamics.[20]
from the northwest, the highest peak in AntarcticaEast 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.[21] There are numerous islands surrounding Antarctica, most of which are volcanic and very young by geological standards.[22] The most prominent exceptions to this are the islands of the Kerguelen Plateau, the earliest of which formed around 40 Ma.[22][23]
Geologic history
From the end of the Neoproterozoic era to the Cretaceous, Antarctica was part of the supercontinent Gondwana.[28] Modern Antarctica was formed as Gondwana gradually broke apart beginning around 183 Ma.[29] For a large proportion of the Phanerozoic, Antarctica had a tropical or temperate climate, and it was covered in forests.[30]
Palaeozoic era (540–250 Ma)
sp. leaf from the Permian of AntarcticaDuring the
Antarctica became glaciated during the
Mesozoic era (250–66 Ma)
The continued warming dried out much of Gondwana. During the Triassic, Antarctica was dominated by
The
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).[47] 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 possibly meridiolestidans.[48][49] Marsupials are thought to have dispersed into Australia via Antarctica by the early Eocene.[50]
Around 53 Ma, Australia-
Present day
The geology of Antarctica, largely obscured by the continental ice sheet,[55] is being revealed by techniques such as remote sensing, ground-penetrating radar, and satellite imagery.[56] Geologically, West Antarctica closely resembles the South American Andes.[57] The Antarctic Peninsula was formed by geologic uplift and the transformation of sea bed sediments into metamorphic rocks.[58]
West Antarctica was formed by the merging of several
East Antarctica is geologically varied. Its formation began during the Archean Eon (4,000 Ma–2,500 Ma), and stopped during the Cambrian Period.[60] It is built on a craton of rock, which is the basis of the Precambrian Shield.[61] 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.[62] In coastal areas such as the Shackleton Range and Victoria Land, some faulting has occurred.[63][64]
Coal was first recorded in Antarctica near the
Climate
Antarctica is the coldest, windiest, and driest of Earth's continents.[1] 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.[68] 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.[69] Average temperatures can reach a minimum of between −80 °C (−112 °F) in the interior of the continent during winter and a maximum of over 10 °C (50 °F) near the coast in summer.[70]
Antarctica is a
Regional differences
East Antarctica is colder than its western counterpart because of its higher elevation.
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.[75] 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.[76] In February 2020, the continent recorded its highest temperature of 18.3 °C (64.9 °F), which was 0.8 °C (1.4 °F) higher than the previous record attained in March 2015.[77]
There is some evidence that surface
Glaciers and floating ice
, photographed in November 2011Precipitation in Antarctica occurs in the form of snow, which accumulates and forms the giant ice sheet that covers the continent.
Sea ice and ice shelves
Sea ice extent expands annually during the Antarctic winter, but most of it melts in the summer.[83] The ice is formed from the ocean, and does not contribute to changes in sea level.[84] 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.[85]
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.[86] 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.[87]
In 2002 the Antarctic Peninsula's Larsen-B ice shelf collapsed.[88] In early 2008, about 570 km2 (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,[89][90] prior to its collapse in 2009.[91] As of 2022[update], 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.[92]
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 58 m (190 ft).[93] In addition, Antarctica stores around 70% of global freshwater as ice.[94] The continent is losing mass due to the increased flow of its glaciers toward the ocean.[95] The loss of mass from Antarctica's ice sheets is partially offset by additional snow falling back onto it.[96] 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.[97] Antarctica's total contribution to sea level rise has been estimated to be 8 to 14 mm (0.31 to 0.55 in).[96][95]
Most of the ice loss has taken place on the Antarctic Peninsula and West Antarctica.[98] Estimates of the mass balance of the East Antarctic Ice Sheet as a whole range from slightly positive to slightly negative.[95][99] Increased ice outflow has been observed in some regions of East Antarctica, particularly at Wilkes Land.[95]
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.[100] A tipping point for the West Antarctic ice sheet is estimated to be between 1.5 and 2.0 °C (2.7 and 3.6 °F) of global warming. A full collapse would likely not take place unless warming reaches between 2 and 3 °C (3.6 and 5.4 °F), and may occur within centuries under pessimistic assumptions. This full collapse would lead to 2 to 5 meters (6.6 to 16.4 feet) of sea level rise. At 3 °C, parts of the East Antarctic ice sheet are also projected to be fully lost, and total ice loss would lead to around 6 to 12 meters (20 to 39 feet) or more of sea level rise.[101]
Ozone depletion
Scientists have studied the
The ozone depletion can cause a cooling of around 6 °C (11 °F) 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.[103] 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.[109][110]
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
Animals
with juvenilesInvertebrate life of Antarctica includes species of microscopic
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.[114] 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.[115] The Antarctic fur seal was very heavily hunted in the 18th and 19th centuries for its pelt by seal hunters from the United States and the United Kingdom.[116] Leopard seals are apex predators in the Antarctic ecosystem and migrate across the Southern Ocean in search of food.[117]
There are approximately 40 bird species that breed on or close to Antarctica, including species of
A
Fungi
About 1,150 species of fungi have been recorded in the Antarctic region, of which about 750 are non-lichen-forming.[120][121] Some of the species, having evolved under extreme conditions, have colonized structural cavities within porous rocks and have contributed to shaping the rock formations of the McMurdo Dry Valleys and surrounding mountain ridges.[122]
The simplified
The same features can be observed in algae and cyanobacteria, suggesting that they are adaptations to the conditions prevailing in Antarctica. This has led to speculation that life on Mars might have been similar to Antarctic fungi, such as Cryomyces antarcticus and Cryomyces minteri.[122] Some of the species of fungi, which are apparently endemic to Antarctica, live in bird dung, and have evolved so they can grow inside extremely cold dung, but can also pass through the intestines of warm-blooded animals.[123][124]
Plants
Throughout its history, Antarctica has seen a wide variety of plant life. In the Cretaceous, it was dominated by a fern-conifer ecosystem, which changed into a temperate rainforest by the end of that period. During the colder Neogene (17–2.5 Ma), a tundra ecosystem replaced the rainforests. The climate of present-day Antarctica does not allow extensive vegetation to form.[125] A combination of freezing temperatures, poor soil quality, and a lack of moisture and sunlight inhibit plant growth, causing low species diversity and limited distribution. The flora largely consists of bryophytes (25 species of liverworts and 100 species of mosses). There are three species of flowering plants, all of which are found in the Antarctic Peninsula: Deschampsia antarctica (Antarctic hair grass), Colobanthus quitensis (Antarctic pearlwort) and the non-native Poa annua (annual bluegrass).[126]
Other organisms
Of the 700 species of algae in Antarctica, around half are marine phytoplankton. Multicoloured snow algae are especially abundant in the coastal regions during the summer.[127] Bacteria have been found as deep as 800 m (0.50 mi) under the ice.[128] It is thought to be likely that there exists a native bacterial community within the subterranean water body of Lake Vostok.[129] The existence of life there is thought to strengthen the argument for the possibility of life on Jupiter's moon Europa, which may have water beneath its water-ice crust.[130] There exists a community of extremophile bacteria in the highly alkaline waters of Lake Untersee.[131][132] The prevalence of highly resilient creatures in such inhospitable areas could further bolster the argument for extraterrestrial life in cold, methane-rich environments.[133]
Conservation and environmental protection
Island, photographed in 1992
The first international agreement to protect Antarctica's biodiversity was adopted in 1964.[134] The overfishing of krill (an animal that 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, an international treaty that came into force in 1980, regulates fisheries, aiming to preserve ecological relationships.[1] Despite these regulations, illegal fishing—particularly of the highly prized Patagonian toothfish which is marketed as Chilean sea bass in the U.S.—remains a problem.[135]
In analogy to the 1980 treaty on
The pressure group
Despite these protections, the biodiversity in Antarctica is still at risk from human activities.
History of exploration
19th century
in his Voyage au Pôle Sud (1846)Sealers were among the earliest to go closer to the Antarctic landmass, perhaps in the earlier part of the 19th century. The oldest known human remains in the Antarctic region was a skull, dated from 1819 to 1825, that belonged to a young woman on Yamana Beach at the South Shetland Islands. The woman, who was likely to have been part of a sealing expedition, was found in 1985.[145]
The first person to see Antarctica or its ice shelf was long thought to have been the British sailor Edward Bransfield, a captain in the Royal Navy, who discovered the tip of the Antarctic peninsula on 30 January 1820. However, a captain in the Imperial Russian Navy, Fabian Gottlieb von Bellingshausen, recorded seeing an ice shelf on 27 January.[146] The American sealer Nathaniel Palmer, whose sealing ship was in the region at this time, may also have been the first to sight the Antarctic Peninsula.[147]
The
On 22 January 1840, two days after the discovery of the coast west of the Balleny Islands, some members of the crew of the 1837–1840 expedition of the French explorer Jules Dumont d'Urville disembarked on the Dumoulin Islands, off the coast of Adélie Land, where they took some mineral, algae, and animal samples erected the French flag and claimed French sovereignty over the territory.[152] The American captain Charles Wilkes led an expedition in 1838–1839 and was the first to claim he had discovered the continent.[153] The British naval officer James Clark Ross failed to realise that what he referred to as "the various patches of land recently discovered by the American, French and English navigators on the verge of the Antarctic Circle" were connected to form a single continent.[154][155][156][note 5] The American explorer Mercator Cooper landed on East Antarctica on 26 January 1853.[159]
The first confirmed landing on the continental mass of Antarctica occurred in 1895 when the Norwegian-Swedish whaling ship Antarctic reached Cape Adare.[160]
20th century
During the Nimrod Expedition led by the British explorer
The American explorer Richard E. Byrd led four expeditions to Antarctica during the 1920s, 1930s, and 1940s, using the first mechanised tractors. His expeditions conducted extensive geographical and scientific research, and he is credited with surveying a larger region of the continent than any other explorer.[164] In 1937, Ingrid Christensen became the first woman to step onto the Antarctic mainland.[165] Caroline Mikkelsen had landed on an island of Antarctica, earlier in 1935.[166]
The South Pole was next reached on 31 October 1956, when a U.S. Navy group led by Rear Admiral George J. Dufek successfully landed an aircraft there.[167] Six women were flown to the South Pole as a publicity stunt in 1969.[168][note 6] In the summer of 1996–1997, Norwegian explorer Børge Ousland became the first person to cross Antarctica alone from coast to coast, helped by a kite on parts of the journey.[169] Ousland holds the record for the fastest unsupported journey to the South Pole, taking 34 days.[170]
Population
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 the 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 from Britain.[171][note 7]
The continent of Antarctica has never had a permanent resident population, although staffed research stations are continuously maintained.[172] 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. Some of the research stations are staffed year-round, the winter-over personnel typically arriving from their home countries for a one-year assignment. The Russian Orthodox Holy Trinity Church at the Bellingshausen Station on King George Island opened in 2004; it is manned year-round by one or two priests, who are similarly rotated every year.[173][174]
The first child born in the southern polar region was a Norwegian girl,
The
Politics
Antarctica's status is regulated by the 1959
.jpg){kind=link}
_(Permian;_Antarctica)_1_(49063572172)_(cropped).jpg){kind=link}
.jpg){kind=link}
.jpg){kind=link}
.jpg){kind=link}
.jpg){kind=link}