Antarctic ice sheet

Antarctic ice sheet
NASA Goddard's Scientific Visualization Studio · Public domain · source
Name	Antarctic ice sheet
Caption	Satellite composite image of the continent
Type	Continental ice sheet
Location	Antarctica
Area	~14 million km²
Thickness	Average 2.16 km, max ~4.9 km
Volume	~26.5 million km³
Status	Retreating

Antarctic ice sheet. It is the largest single mass of ice on Earth, containing about 61% of the planet's fresh water. Covering nearly all of the continent of Antarctica, it holds a volume of ice that, if melted, would raise global sea level by approximately 58 meters. Its dynamics are a critical component of the global climate system and a primary focus of modern glaciology and climate science.

Formation and History

The initial formation of continental-scale ice began during the Eocene-Oligocene transition around 34 million years ago, driven by the tectonic isolation of Antarctica following the opening of the Drake Passage and the Tasmanian Gateway. This led to the development of the Antarctic Circumpolar Current, which thermally isolated the continent. Major expansion occurred during the Miocene epoch, with the sheet reaching its approximate modern extent by the Pliocene. Evidence from sediment cores, such as those retrieved by the ANDRILL project, and isotopic data from the EPICA ice core at Dome C, show it has undergone significant fluctuations in response to changes in Earth's orbital parameters, known as Milankovitch cycles, and atmospheric carbon dioxide concentrations.

Structure and Composition

The ice sheet is broadly divided into two major, geologically distinct components: the larger, thicker East Antarctic Ice Sheet, which rests on continental bedrock largely above sea level, and the smaller, more dynamic West Antarctic Ice Sheet, which is grounded on bedrock far below sea level. Key structural features include major ice streams like the Pine Island Glacier and Thwaites Glacier, which drain the interior. The composition is primarily meteoric ice, formed from accumulated snow compressed over millennia, containing a detailed record of past climate within trapped air bubbles and chemical impurities. The underlying bedrock is mapped by surveys such as BedMachine and radar missions like Operation IceBridge.

Climate Impact and Changes

The ice sheet exerts a dominant influence on the Southern Hemisphere's climate, helping drive atmospheric circulation patterns like the polar vortex and the Southern Annular Mode. Its bright surface, or high albedo, reflects a significant amount of solar radiation. Recent changes, documented by satellites like NASA's GRACE and GRACE-FO and the European Space Agency's CryoSat-2, include sustained mass loss, particularly from the Amundsen Sea Embayment. This loss is linked to warming of the Southern Ocean and associated increased basal melt of floating ice shelves by circumpolar deep water, processes studied by institutions like the British Antarctic Survey and the Alfred Wegener Institute.

Contribution to Sea Levels

Since the early 1990s, the ice sheet's contribution to global sea level rise has accelerated. The Intergovernmental Panel on Climate Change reports that between 1992 and 2020, Antarctica contributed roughly 14 mm to global mean sea level. The West Antarctic Ice Sheet is considered potentially unstable due to marine ice sheet instability, wherein retreating grounding lines on reverse-sloped bedrock can lead to self-sustaining collapse. The East Antarctic Ice Sheet, long considered stable, has shown signs of vulnerability in basins like Totten Glacier, which holds ice equivalent to several meters of sea level rise.

Melting and Breakup Dynamics

Primary melting occurs from below where warm ocean water intrudes onto continental shelves and melts floating ice shelves, as observed in the Amundsen Sea. This thinning reduces buttressing, allowing grounded ice to flow faster into the ocean. Major breakup events of ice shelves, such as the collapse of Larsen B Ice Shelf in 2002 and the disintegration of the Conger Ice Shelf in 2022, provide stark examples of rapid structural failure. The process of hydrofracturing, where meltwater on the surface fills and expands crevasses, is a key mechanism for such breakups, exacerbated by atmospheric warming events like those over the Antarctic Peninsula.

Scientific Research and Monitoring

International scientific efforts are coordinated through bodies like the Scientific Committee on Antarctic Research. Key research stations, including McMurdo Station, Amundsen–Scott South Pole Station, and Halley Research Station, serve as bases for field campaigns. Long-term monitoring relies on a fleet of satellites from agencies like NASA, ESA, and JAXA, measuring ice velocity, thickness, and gravity anomalies. Major collaborative projects, such as the International Thwaites Glacier Collaboration and the Ice Sheet Mass Balance Inter-comparison Exercise, aim to reduce uncertainties in predictions of future ice loss and its impact on coastal communities worldwide.

Category:Antarctica Category:Glaciers of Antarctica Category:Ice sheets