Antarctic ice sheet
The Antarctic ice sheet is one of the two polar ice caps of the Earth. It is the largest single mass of ice on Earth, it covers an area of 14 million square kilometres and contains 26.5 million cubic kilometres of ice. A cubic kilometer of ice weighs one metric gigaton, meaning that the ice sheet weighs 26,500,000 gigatons. 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to about 58 m of sea-level rise. In East Antarctica, the ice sheet rests on a major land mass, while in West Antarctica the bed can extend to more than 2,500 m below sea level. In contrast to the melting of the Arctic sea ice, sea ice around Antarctica was expanding as of 2013. Satallite measurements by NASA indicate a still increasing sheet thickness above the continent, outweighing the losses at the edge; the reasons for this are not understood, but suggestions include the climatic effects on ocean and atmospheric circulation of the ozone hole, and/or cooler ocean surface temperatures as the warming deep waters melt the ice shelves.
The icing of Antarctica began in the middle Eocene about 45.5 million years ago and escalated during the Eocene–Oligocene extinction event about 34 million years ago. CO2 levels were about 760 ppm and had been decreasing from earlier levels in the thousands of ppm. Carbon dioxide decrease, with a tipping point of 600 ppm, was the primary agent forcing Antarctic glaciation; the glaciation was favored by an interval when the Earth's orbit favored cool summers but oxygen isotope ratio cycle marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an ice age of some size. The opening of the Drake Passage may have played a role as well though models of the changes suggest declining CO2 levels to have been more important; the Western Antarctic ice sheet declined somewhat during the warm early Pliocene epoch 5 to 3 million years ago. But there was no significant decline in the land-based Eastern Antarctic ice sheet. According to a 2009 study, the continent-wide average surface temperature trend of Antarctica is positive and significant at >0.05 °C/decade since 1957.
West Antarctica has warmed by more than 0.1 °C/decade in the last 50 years, this warming is strongest in winter and spring. Although this is offset by fall cooling in East Antarctica, this effect is restricted to the 1980s and 1990s. Ice enters the sheet through precipitation as snow; this snow is compacted to form glacier ice which moves under gravity towards the coast. Most of it is carried to the coast by fast moving ice streams; the ice passes into the ocean forming vast floating ice shelves. These shelves melt or calve off to give icebergs that melt. If the transfer of the ice from the land to the sea is balanced by snow falling back on the land there will be no net contribution to global sea levels; the general trend shows that a warming climate in the southern hemisphere would transport more moisture to Antarctica, causing the interior ice sheets to grow, while calving events along the coast will increase, causing these areas to shrink. A 2006 paper derived from satellite data, measuring changes in the gravity of the ice mass, suggests that the total amount of ice in Antarctica has begun decreasing in the past few years.
A 2008 study compared the ice leaving the ice sheet, by measuring the ice velocity and thickness along the coast, to the amount of snow accumulation over the continent. This found that the East Antarctic Ice Sheet was in balance but the West Antarctic Ice Sheet was losing mass; this was due to acceleration of ice streams such as Pine Island Glacier. These results agree with the gravity changes. An estimate published in November 2012 and based on the GRACE data as well as on an improved glacial isostatic adjustment model discussed systematic uncertainty in the estimates, by studying 26 separate regions, estimated an average yearly mass loss of 69 ± 18 Gt/y from 2002 to 2010; the mass loss was geographically uneven occurring along the Amundsen Sea coast, while the West Antarctic Ice Sheet mass was constant and the East Antarctic Ice Sheet gained in mass. Antarctic sea ice anomalies have followed the pattern of warming, with the greatest declines occurring off the coast of West Antarctica. East Antarctica sea ice has been increasing since 1978, though not at a statistically significant rate.
The atmospheric warming has been directly linked to the mass losses in West Antarctica of the first decade of the twenty-first century. This mass loss is more to be due to increased melting of the ice shelves because of changes in ocean circulation patterns. Melting of the ice shelves in turn causes; the melting and disappearance of the floating ice shelves will only have a small effect on sea level, due to salinity differences. The most important consequence of their increased melting is the speed up of the ice streams on land which are buttressed by these ice shelves. A group of scientists with the University of California updated previous results ranging from 1979 to 2017, which improved time series for more accurate results, their article, published January 2019, covered four decades of information in Antarctica, revealing the total mass loss which increased per decade. 40 ± 9 Gt/y from 1979 to 1990, 50 ± 14 Gt/y from 1989 to 2000, 166 ±18 Gt/y from 1999 to 2009 and 252 ±26 Gt/y from 2009 to 2017.
The majority of mass loss
The Antarctic is a polar region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other island territories located on the Antarctic Plate or south of the Antarctic Convergence; the Antarctic region includes the ice shelves and all the island territories in the Southern Ocean situated south of the Antarctic Convergence, a zone 32 to 48 km wide varying in latitude seasonally. The region covers some 20 percent of the Southern Hemisphere, of which 5.5 percent is the surface area of the Antarctic continent itself. All of the land and ice shelves south of 60°S latitude are administered under the Antarctic Treaty System. Biogeographically, the Antarctic ecozone is one of eight ecozones of the Earth's land surface; the maritime part of the region constitutes the area of application of the international Convention for the Conservation of Antarctic Marine Living Resources, where for technical reasons the Convention uses an approximation of the Convergence line by means of a line joining specified points along parallels of latitude and meridians of longitude.
The implementation of the Convention is managed through an international Commission headquartered in Hobart, Australia, by an efficient system of annual fishing quotas and international inspectors on the fishing vessels, as well as satellite surveillance. Most of the Antarctic region is situated south of 60°S latitude parallel, is governed in accordance with the international legal regime of the Antarctic Treaty System; the Treaty area covers the continent itself and its adjacent islands, as well as the archipelagos of the South Orkney Islands, South Shetland Islands, Peter I Island, Scott Island and Balleny Islands. The islands situated between 60°S latitude parallel to the south and the Antarctic Convergence to the north, their respective 200-nautical-mile exclusive economic zones fall under the national jurisdiction of the countries that possess them: South Georgia and the South Sandwich Islands, Bouvet Island, Heard and McDonald Islands. Kerguelen Islands are situated in the Antarctic Convergence area, while the Falkland Islands, Isla de los Estados, Hornos Island with Cape Horn, Diego Ramírez Islands, Campbell Island, Macquarie Island and Saint Paul Islands, Crozet Islands, Prince Edward Islands, Gough Island and Tristan da Cunha group remain north of the Convergence and thus outside the Antarctic region.
A variety of animals live in Antarctica for at least some of the year, including: Seals Penguins South Georgia pipits Albatrosses Antarctic petrels Whales Fish, such as Antarctic icefish, Antarctic toothfish Squid, including the colossal squid Antarctic krillMost of the Antarctic continent is permanently covered by ice and snow, leaving less than 1 percent of the land exposed. There are only two species of flowering plant, Antarctic hair grass and Antarctic pearlwort, but a range of mosses, liverworts and macrofungi; the first Antarctic land discovered was the island of South Georgia, visited by the English merchant Anthony de la Roché in 1675. Although myths and speculation about a Terra Australis date back to antiquity, the first confirmed sighting of the continent of Antarctica is accepted to have occurred in 1820 by the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on Vostok and Mirny; the first human born in the Antarctic was Solveig Gunbjørg Jacobsen born on 8 October 1913 in Grytviken, South Georgia.
The Antarctic region had no indigenous population when first discovered, its present inhabitants comprise a few thousand transient scientific and other personnel working on tours of duty at the several dozen research stations maintained by various countries. However, the region is visited by more than 40,000 tourists annually, the most popular destinations being the Antarctic Peninsula area and South Georgia Island. In December 2009, the growth of tourism, with consequences for both the ecology and the safety of the travellers in its great and remote wilderness, was noted at a conference in New Zealand by experts from signatories to the Antarctic Treaty; the definitive results of the conference was presented at the Antarctic Treaty states' meeting in Uruguay in May 2010. The Antarctic hosts the world's largest protected area comprising 1.07 million km2, the South Georgia and the South Sandwich Islands Marine Protection Area created in 2012. The latter exceeds the surface area of another vast protected territory, the Greenland National Park’s 972,000 km2.
Because Antarctica surrounds the South Pole, it is theoretically located in all time zones. For practical purposes, time zones are based on territorial claims or the time zone of a station's owner country or supply base. Antarctic Circle History of Antarctica Krupnik, Michael A. Lang, Scott E. Miller, eds. Smithsonian at the Poles: Contributions to International Polar Year Science. Washington, D. C.: Smithsonian Institution Scholarly Press, 2009. British Services Antarctic Expedition 2012 Committee for Environmental Protection of Antarctica Secretariat of the Antarctic Treaty CCAMLR Commission Antarctic Heritage Trusts International Association of Antarctica Tour Operators Map of the Antarctic Convergence The South Atlantic and Subantarctic Islands
Lambert Glacier is a major glacier in East Antarctica. At about 60 miles wide, over 250 miles long, about 2,500 m deep, it holds the Guinness world record for the world's largest glacier, it drains 8% of the Antarctic ice sheet to the east and south of the Prince Charles Mountains and flows northward to the Amery Ice Shelf. It flows in part of exits the continent at Prydz Bay; this glacier was delineated and named in 1952 by American geographer John H. Roscoe who made a detailed study of this area from aerial photographs taken by Operation Highjump, 1946–47, he gave the name "Baker Three Glacier", using the code name of the Navy photographic aircraft and crew that made three flights in this coastal area in March 1947 resulting in geographic discoveries. The glacier was described in Gazetteer No. 14, Geographic Names of Antarctica, but the feature did not appear on published maps. As a result the name Lambert Glacier, as applied by the Antarctic Names Committee of Australia in 1957 following mapping of the area by Australian National Antarctic Research Expeditions in 1956, has become established for this feature.
It was named for Bruce P. Lambert, Director of National Mapping in the Australian Department of National Development; the glacier is important in the study of climate change because small changes in the climate can have significant consequences for the flow of ice down the glacier. Most studies of the Lambert Glacier are done with remote sensing due to the harsh conditions in the area; the photo reproduced here shows a small tributary right-flank glacier flowing down from the ice-covered East Antarctic Plateau, flanked by slower-moving ice flowing down over a steep escarpment. The ice-fall which so impressively illustrates the flow characteristics of glacier ice is only about 6 km wide, Lambert Glacier proper is off the bottom right corner of the photo; the ice here is flowing at about 500 m per year, but velocities of over 1200 m per year are known at the edge of the Amery Ice Shelf, fed by this gigantic stream of ice. On the lower photo north is at the bottom, the ice velocities are as follow: Brown areas—up to 50 m per year.
Green areas—up to 250 m per year. Blue areas—up to 500 m per year. Purple areas—around 1000 m per year. Red area—up to 1200 m per year. Ice stream List of glaciers in the Antarctic List of Antarctic ice streams This article incorporates public domain material from the United States Geological Survey document "Lambert Glacier"
Kangerlussuaq Glacier is the largest glacier on the east coast of the Greenland ice sheet. It flows into the head of the second largest fjord in East Greenland. In 2016 the glacier had retreated further inland than at any time in the previous 33 years. Continued rapid retreat is likely. List of glaciers in Greenland Glaciers Not On Simple, Upward Trend Of Melting sciencedaily.com, Feb. 21, 2007 "Two of Greenland's largest glaciers shrank dramatically... between 2004 and 2005. And less than two years they returned to near their previous rates of discharge
In geology, bedrock is the lithified rock that lies under a loose softer material called regolith within the surface of the crust of the Earth or other terrestrial planets. Bedrock refers to the substructure composed of hard rock exposed or buried at the earths surface, an exposed portion of bedrock is called an outcrop. Bedrock may have various chemical and mineralogical compositions and can be igneous, metamorphic or sedimentary in origin; the bedrock may be overlain by weathered regolith which includes soil and the subsoil. The surface of the bedrock beneath the soil cover is known as rockhead in engineering geology, its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be thick, such that the bedrock lies hundreds of meters below the surface. Bedrock when exposed or within the subsurface may experience weathering and erosion by external factors. Weathering may be physical or chemical and alters the structure of the rock and may cause it to erode and or alter over time based on the interactions between the mineralogy and its interactions.
Bedrock may experience subsurface weathering at its upper boundary, forming saprolite. A geologic map of an area will show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed. Geology – The study of the composition, physical properties, history of Earth's components, the processes by which they are shaped. Outcrop Regolith – A layer of loose, heterogeneous superficial deposits covering solid rock Soil – mixture of organic matter, gases and organisms that together support life Weathering – Breaking down of rocks and minerals as well as artificial materials through contact with the Earth's atmosphere and waters Rafferty, John P. "Bedrock GEOLOGY". Encyclopedia Britannica. Encyclopedia Britannica. Retrieved 1 April 2019. Harris, The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Vol. 1. 5th ed. Farmington Hills, MI: Gale, 2014. P515-516. Media related to Bedrock at Wikimedia Commons
Greenlandic: Sermeq Kujalleq known as Ilulissat Glacier or Jakobshavn Glacier, the Danish: Jakobshavn Isbræ, is a large outlet glacier in West Greenland. It ends at the sea in the Ilulissat Icefjord. Jakobshavn Glacier drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs pass out of the fjord every year. Icebergs breaking from the glacier are so large that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord. Studied for over 250 years, the Jakobshavn Glacier has helped develop modern understanding of climate change and icecap glaciology. Ilulissat Icefjord was declared a UNESCO World Heritage Site in 2004. Jakobshavn has been a name used for this glacier in scientific literature since 1853 when Danish geologist Hinrich Johannes Rink referred to it as Jakobshavn Isstrøm, it is sometimes referred to in the international scientific literature as Jakobshavn Isbræ glacier.
Isbræ is Danish for glacier. It is commonly known by the anglicised version, Jakobshavn Glacier; the local name for this glacier is Sermeq Kujalleq, where "sermeq" is Greenlandic for'glacier' and "kujalleq" means'southern'. It lies south of the town Ilulissat. UNESCO's World Heritage Site website uses this name, in connection with mention of the Ilulissat Icefjord world heritage site, which includes the downstream end of the glacier. There is evidence; the abandoned settlement of Sermermiut lies just to the north of the glacier, much nearer than Ilulissat. The glacier is sometimes referred to as Ilulissat Glacier; this form replaces Jakobshavn with Ilulissat because of the change in the name of the town. Jakobshavn is one of the fastest moving glaciers, flowing at its terminus at speeds that used to be around 20 metres per day but are over 45 metres per day when averaged annually, with summer speeds higher; the speed of Jakobshavn Glacier varied between 5,700 and 12,600 metres per year between 1992 and 2003.
The ice stream's speed-up and near-doubling of ice flow from land into the ocean has increased the rate of sea level rise by about 0.06 millimetres per year, or 4 percent of the 20th century rate of sea level rise. Jakobshavn Isbrae, retreated 30 km from 1850–1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining the Greenland Ice Sheet; the glacier terminus region had a consistent velocity of 20 metres per day, from season to season and year to year, the glacier seemed to be in balance from 1955-1985. After 1997 the glacier began to accelerate and thin reaching an average velocity of 34 metres per day in the terminus region, it thinned at a rate of up to 15 metres per year and retreated 5 km in six years. Jakobshavn has afterwards slowed to near its pre-1997 speed, with the terminus retreat still occurring. On Jakobshavn the acceleration began at the calving front and spread up-glacier 20 km in 1997 and up to 55 km inland by 2003; the position of this calving front, or terminus, fluctuated by 2.5 km around its annual mean position between 1950 and 1996.
The first mechanism for explaining the change in velocity is the "Zwally effect" and is not the main mechanism, this relies on meltwater reaching the glacier base and reducing the friction through a higher basal water pressure. A moulin is the conduit for the additional meltwater to reach the glacier base; this idea, proposed by Jay Zwally, was observed to be the cause of a brief seasonal acceleration of up to 20% on the Jakobshavns Glacier in 1998 and 1999 at Swiss Camp. The acceleration was less than 10 % in 1996 and 1997 for example, they offered a conclusion that the "coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming". The acceleration of the three glaciers had not occurred at the time of this study and they were not concluding or implying that the meltwater increase was the cause of the aforementioned acceleration. Examination of rapid supra-glacial lake drainage documented short term velocity changes due to such events, but they had little significance to the annual flow of the large outlet glaciers.
The second mechanism is a "Jakobshavn effect", coined by Terry Hughes, where a small imbalance of forces caused by some perturbation can cause a substantial non-linear response. In this case an imbalance of forces at the calving front propagates up-glacier. Thinning causes the glacier to be more buoyant becoming afloat at the calving front, is responsive to tidal changes; the reduced friction due to greater buoyancy allows for an increase in velocity. The reduced resistive force at the calving front is propagated up glacier via longitudinal extension in what R. Thomas calls a backforce reduction; this mechanism is supported by the data indicating no significant seasonal velocity changes at the calving front and the acceleration propagating upglacier from the calving front. The cause of the thinning could be a combination of increased surface ablation and basal ablation as one report presents data that show a sudden increase in subs
Thwaites Glacier is an unusually broad and fast Antarctic glacier flowing into Pine Island Bay, part of the Amundsen Sea, east of Mount Murphy, on the Walgreen Coast of Marie Byrd Land. Its surface speeds exceed 2 km/yr near its grounding line, its fastest flowing grounded ice is centred between 50 and 100 km east of Mount Murphy, it was named by ACAN after Fredrik T. Thwaites, a glacial geologist and professor emeritus at the University of Wisconsin–Madison. Thwaites Glacier drains into West Antarctica’s Amundsen Sea and is watched for its potential to raise sea levels. Along with Pine Island Glacier, Thwaites Glacier has been described as part of the "weak underbelly" of the West Antarctic Ice Sheet, due to its apparent vulnerability to significant retreat; this hypothesis is based on both theoretical studies of the stability of marine ice sheets and recent observations of large changes on both of these glaciers. In recent years, the flow of both of these glaciers has accelerated, their surfaces lowered, the grounding lines retreated.
In 2011, using geophysical data collected from flights over Thwaites Glacier, a study by scientists at Columbia University’s Lamont-Doherty Earth Observatory showed a rock feature, a ridge 700 meters tall that helps anchor the glacier and helped slow the glacier's slide into the sea. The study confirmed the importance of seafloor topography in predicting how the glacier will behave in the near future. However, the glacier has been considered to be the biggest threat on relevant time scales, for rising seas, current studies aim to better quantify retreat and possible impacts. Since the 1980s, the glacier has had a net loss of over 600 billion tons of ice. Swamp-like canal areas and streams underlie the glacier; the upstream swamp canals feed streams with dry areas between the streams which retard flow of the glacier. Due to this friction the glacier is considered stable in the short term. A University of Washington study, using satellite measurements and computer models, determined that the Thwaites Glacier will melt, leading to an irreversible collapse over the next 200 to 1000 years.
The Thwaites Glacier Tongue, or Thwaites Ice Tongue, is about 50 km wide and has progressively shortened due to ice calving, based on the observational record. It was delineated from aerial photographs collected during Operation Highjump in January 1947. On 15 March 2002, the National Ice Center reported that an iceberg named B-22 broke off from the ice tongue; this iceberg was about 85 km long by 65 km wide, with a total area of some 5,490 km². As of 2003, B-22 had broken into five pieces, with B-22A still in the vicinity of the tongue, while the other smaller pieces had drifted farther west; the Thwaites Iceberg Tongue was a large iceberg tongue, aground in the Amundsen Sea, about 32 km northeast of Bear Peninsula. The feature was about 112 km long and 32 km wide, in January 1966 its southern extent was only 5 km north of Thwaites Glacier Tongue, it consisted of icebergs which had broken off from the Thwaites Ice Tongue and ran aground, should not be confused with the latter, still attached to the grounded ice.
It was delineated by the USGS from aerial photographs collected during Operation Highjump and Operation Deepfreeze. It was first noted in the 1930s, but detached from the ice tongue and broke up in the late 1980s. An underwater cavity with an area two-thirds the size of Manhattan was discovered underneath the glacier, according to a NASA study released in January 2019; the cavity formed in the previous three years and is nearly a thousand feet tall speeding up the glacier's decay. Pine Island Glacier Retreat of glaciers since 1850 List of volcanoes in Antarctica List of seamounts in the Southern Ocean This article incorporates public domain material from the United States Geological Survey document "Thwaites Glacier"