An image of Antarctica differentiating its landmass (dark grey) from its ice shelves (light grey) and sea ice (white)

The Antarctic ice sheet is one of two ice sheets on Earth and covers about 98% of the Antarctic continent. It is the largest single mass of ice on Earth, with an average thickness of over 2 kilometres (1.2 mi).[1] It is distinct from the Antarctic sea ice. The Antarctic ice sheet covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice.[2] The other ice sheet on Earth is the Greenland ice sheet.

The continent-wide average surface temperature trend of Antarctica is positive and significant at >0.05 °C (0.09 °F)/decade since 1957.[3] A 2018 systematic review of all previous studies and data by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) found that Antarctica lost 2720 ± 1390 gigatons of ice during the period from 1992 to 2017 with an average rate of 109 ± 56 Gt per year, enough to contribute 7.6 millimeters to sea level rise once all detached icebergs melt.[4]

Geography

The Antarctic ice sheet covers an area of almost 14 million square kilometres (5.4 million square miles) and contains 26.5 million cubic kilometres (6,400,000 cubic miles) of ice.[2] A cubic kilometer of ice weighs approximately 0.92 metric gigatonnes, meaning that the ice sheet weighs about 24,380,000 gigatonnes.

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.

The Antarctic ice sheet is divided by the Transantarctic Mountains into two unequal sections called the East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS). Other sources divide the Antarctic ice sheet into three sections: the East and West Antarctic Ice Sheets and thirdly the Antarctic Peninsula Ice Sheet.[5]: 2234 

The EAIS rests on a major land mass, but the bed of the WAIS is, in places, more than 2,500 meters (8,200 feet) below sea level. It would be seabed if the ice sheet were not there. The WAIS is classified as a marine-based ice sheet, meaning that its bed lies below sea level and its edges flow into floating ice shelves. The WAIS is bounded by the Ross Ice Shelf, the Filchner-Ronne Ice Shelf, and outlet glaciers that drain into the Amundsen Sea.

Changes due to climate change

Temperature

Antarctic Skin Temperature Trends between 1981 and 2007, based on thermal infrared observations made by a series of NOAA satellite sensors. Skin temperature trends do not necessarily reflect air temperature trends.[6]

According to a 2009 study, Antarctica's average surface temperature trend is positive and significant at >0.05 °C/decade since 1957.[7][8][9][10] West Antarctica has warmed by more than 0.1 °C/decade since 1960. This warming is strongest in winter and spring. Although this is partly offset by fall cooling in East Antarctica, this occurred only during the 1980s and 1990s.[7][8][9]

Changes in ice mass

This section is an excerpt from Climate change in Antarctica § Observed changes in ice mass.[edit]
Contrasting temperature trends across parts of Antarctica, as well as its remoteness, mean that some locations lose mass, particularly at the coasts, while others that are more inland continue to gain it, and estimating an average trend can be difficult.[11] In 2018, a systematic review of all previous studies and data by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) estimated an increase in West Antarctic ice sheet annual mass loss from 53 ± 29 Gt in 1992 to 159 ± 26 Gt in the final five years of the study. On the Antarctic Peninsula, the study estimated to −20 ± 15 Gt per year with an increase in loss of roughly 15 Gt per year after year 2000, with a significant role played by the loss of ice shelves.[12] The review's overall estimate was that of Antarctica losing 2720 ± 1390 gigatons of ice during the period from 1992 to 2017 with an average rate of 109 ± 56 Gt per year. This would amount to 7.6 millimeters to sea level rise.[12] Then, though, a 2021 analysis of data from four different research satellite systems (Envisat, European Remote-Sensing Satellite, GRACE and GRACE-FO and ICESat) indicated annual mass loss of only about 12 Gt from 2012-2016, due to much greater ice gain in East Antarctica than estimated earlier, which had offset most of the losses from West Antarctica.[13] East Antarctic ice sheet can still gain mass in spite of warming because effects of climate change on the water cycle increase precipitation over its surface, which then freezes and helps to build up more ice.[14]: 1262 

Satellite measurements by NASA indicate a still increasing sheet thickness above the continent, outweighing the losses at the edge.[15] The reasons for this are not fully understood, but suggestions include the climatic effects on ocean and atmospheric circulation of the ozone hole,[16] and/or cooler ocean surface temperatures as the warming deep waters melt the ice shelves.[17]

A study published in 2019, covering four decades of information in Antarctica, revealed the total mass loss which increased gradually per decade.[18] The majority of mass loss was in the Amundsen Sea sector, which experienced loss as high as 159 ±8 Gt/y. Other areas have not experienced significant losses, such as the East Ross ice shelf. This study revealed an acceleration of near 280% over the four decades. The study questions previous hypotheses, such as the belief that the heavy melt began in the 1940s to 1970s, suggesting that more recent anthropogenic actions have caused accelerated melt.[18]

Ice loss of Antarctic ice sheet (Gigatons)[18]
Period Mean Range
1979-1990 40 ±9
1989-2000 50 ±14
1999-2009 166 ±18
2009-2017 252 ±26

Floating ice and land ice

Visualization of NASA's mission Operation IceBridge dataset BEDMAP2, obtained with laser and ice-penetrating radar, collecting surface height, bedrock topography and ice thickness.
The bedrock topography of Antarctica, critical to understand dynamic motion of the continental ice sheets.

Ice enters the sheet through precipitation as snow. This snow is then compacted to form glacial ice that moves under gravity towards the coast. Most of it is carried by fast-moving ice streams. The ice then passes into the ocean, forming floating ice shelves. These shelves then melt or calve to give icebergs that eventually melt.

If the movement of ice to the sea is balanced by snow falling on the land then global sea levels remain unaffected. A warming climate in the southern hemisphere transports more moisture to Antarctica, growing the interior ice sheets, while calving events along the coast increase, allowing interior ice quicker access to the sea.

A 2006 paper derived from satellite data, measuring changes in the gravity of the ice mass, suggested that the total amount of ice in Antarctica had begun decreasing.[19] 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. It reported that the East Antarctic Ice Sheet was in balance, but the West Antarctic Ice Sheet was losing mass. This was largely due to acceleration of ice streams such as Pine Island Glacier. These results agree closely with the 2006 report.[20][21] An estimate published in November 2012, based on Gravity Recovery and Climate Experiment data as well as on an improved glacial isostatic adjustment model discussed systematic uncertainty in the estimates, and by studying 26 separate regions, estimated an average yearly mass loss of 69 ± 18 Gt/y from 2002 to 2010 (a sea-level rise of 0.16 ± 0.043 mm/y). The mass loss was geographically uneven, mainly occurring along the Amundsen Sea coast, while the West Antarctic Ice Sheet mass was roughly constant and the East Antarctic Ice Sheet gained in mass.[22]

Antarctic sea ice anomalies have roughly 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, although the increase was not statistically significant. The atmospheric warming is linked to the mass loss in West Antarctica of the 2000s. This mass loss is more likely to be due to increased melting of the ice shelves because of changes in ocean circulation patterns. The patterns may be linked to atmospheric circulation changes that may explain the warming trends in West Antarctica. Melting of the ice shelves in turn allows the ice streams to speed up.[23] The melting and disappearance of the floating ice shelves has only a minor effect on sea level, which is due to salinity differences.[24][25][26] The most important consequence of the increased melting is to increase the speed of the ice streams on land.

Impacts on sea level rise

Around 90% of the Earth's ice mass is in Antarctica,[27] which, if melted, would cause sea levels to rise by 58 meters (190 feet).[28]

The Antarctic ice sheet holds approximately 61% of all fresh water on Earth, equivalent to about 58 meters of sea level rise[29] if all the ice were above sea level.

A 2018 systematic review of all previous studies and data by the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) found that Antarctica lost 2720 ± 1390 gigatons of ice during the period from 1992 to 2017 with an average rate of 109 ± 56 Gt per year, enough to contribute 7.6 millimeters to sea level rise once all detached icebergs melt.[30]

This section is an excerpt from Sea level rise § Causes.[edit]
A graph showing ice loss sea ice, ice shelves and land ice. Land ice loss contributetes to SLR
Earth lost 28 trillion tonnes of ice between 1994 and 2017: ice sheets and glaciers raised the global sea level by 34.6 ± 3.1 mm. The rate of ice loss has risen by 57% since the 1990s−from 0.8 to 1.2 trillion tonnes per year.[31]
The three main reasons warming causes global sea level to rise are the expansion of oceans due to heating, water inflow from melting ice sheets and water inflow from glaciers. Glacier retreat and ocean expansion have dominated sea level rise since the start of the 20th century.[32] Some of the losses from glaciers are offset when precipitation falls as snow, accumulates and over time forms glacial ice. If precipitation, surface processes and ice loss at the edge balance each other, sea level remains the same. Because of this precipitation began as water vapor evaporated from the ocean surface, effects of climate change on the water cycle can even increase ice build-up. However, this effect is not enough to fully offset ice losses, and sea level rise continues to accelerate.[33][34][35][36]

Situation during geologic time scales

Polar climatic temperature changes throughout the Cenozoic, showing glaciation of Antarctica toward the end of the Eocene, thawing near the end of the Oligocene and subsequent Miocene re-glaciation.

The icing of Antarctica began in the Late Palaeocene or middle Eocene between 60[37] and 45.5 million years ago[38] and escalated during the Eocene–Oligocene extinction event about 34 million years ago. CO2 levels were then about 760 ppm[39] 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.[40] 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.[41] The opening of the Drake Passage may have played a role as well[42] though models of the changes suggest declining CO2 levels to have been more important.[43]

The Western Antarctic ice sheet declined somewhat during the warm early Pliocene epoch, approximately five to three million years ago; during this time the Ross Sea opened up.[44] But there was no significant decline in the land-based Eastern Antarctic ice sheet.[45]

See also

References

  1. ↑ "Ice Sheets". National Science Foundation.
  2. 1 2 Amos, Jonathan (2013-03-08). "Antarctic ice volume measured". BBC News. Retrieved 2014-01-28.
  3. ↑ Steig, E. J.; Schneider, D. P.; Rutherford, S. D.; Mann, M. E.; Comiso, J. C.; Shindell, D. T. (2009). "Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year". Nature. 457 (7228): 459–462. Bibcode:2009Natur.457..459S. doi:10.1038/nature07669. PMID 19158794. S2CID 4410477.
  4. ↑ Shepherd, Andrew; Ivins, Erik; Rignot, Eric; Smith, Ben; van den Broeke, Michiel; Velicogna, Isabella; Whitehouse, Pippa; Briggs, Kate; Joughin, Ian; Krinner, Gerhard; Nowicki, Sophie (June 2018). "Mass balance of the Antarctic Ice Sheet from 1992 to 2017". Nature. 558 (7709): 219–222. Bibcode:2018Natur.558..219I. doi:10.1038/s41586-018-0179-y. hdl:2268/225208. ISSN 1476-4687. PMID 29899482. S2CID 186244208.
  5. ↑ IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C.  Méndez, S. Semenov, A. Reisinger (eds.)]. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.
  6. ↑ NASA (2007). "Two Decades of Temperature Change in Antarctica". Earth Observatory Newsroom. Archived from the original on 20 September 2008. Retrieved 2008-08-14. NASA image by Robert Simmon, based on data from Joey Comiso, GSFC.
  7. 1 2 Steig, Eric (2009-01-21). "Temperature in West Antarctica over the last 50 and 200 years" (PDF). Retrieved 2009-01-22.
  8. 1 2 Steig, Eric. "Biography". Archived from the original on 29 December 2008. Retrieved 2009-01-22.
  9. 1 2 Steig, E. J.; Schneider, D. P.; Rutherford, S. D.; Mann, M. E.; Comiso, J. C.; Shindell, D. T. (2009). "Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year". Nature. 457 (7228): 459–462. Bibcode:2009Natur.457..459S. doi:10.1038/nature07669. PMID 19158794. S2CID 4410477.
  10. ↑ Ingham, Richard (2009-01-22). "Global warming hitting all of Antarctica". The Sydney Morning Herald. Retrieved 2009-01-22.
  11. ↑ King, M. A.; Bingham, R. J.; Moore, P.; Whitehouse, P. L.; Bentley, M. J.; Milne, G. A. (2012). "Lower satellite-gravimetry estimates of Antarctic sea-level contribution". Nature. 491 (7425): 586–589. Bibcode:2012Natur.491..586K. doi:10.1038/nature11621. PMID 23086145. S2CID 4414976.
  12. 1 2 IMBIE team (13 June 2018). "Mass balance of the Antarctic Ice Sheet from 1992 to 2017". Nature. 558 (7709): 219–222. Bibcode:2018Natur.558..219I. doi:10.1038/s41586-018-0179-y. hdl:2268/225208. PMID 29899482. S2CID 49188002.
  13. ↑ Zwally, H. Jay; Robbins, John W.; Luthcke, Scott B.; Loomis, Bryant D.; Rémy, Frédérique (29 March 2021). "Mass balance of the Antarctic ice sheet 1992–2016: reconciling results from GRACE gravimetry with ICESat, ERS1/2 and Envisat altimetry". Journal of Glaciology. 67 (263): 533–559. doi:10.1017/jog.2021.8. Although their methods of interpolation or extrapolation for areas with unobserved output velocities have an insufficient description for the evaluation of associated errors, such errors in previous results (Rignot and others, 2008) caused large overestimates of the mass losses as detailed in Zwally and Giovinetto (Zwally and Giovinetto, 2011).
  14. ↑ Fox-Kemper, B.; Hewitt, H.T.; Xiao, C.; Aðalgeirsdóttir, G.; Drijfhout, S.S.; Edwards, T.L.; Golledge, N.R.; Hemer, M.; Kopp, R.E.; Krinner, G.; Mix, A. (2021). Masson-Delmotte, V.; Zhai, P.; Pirani, A.; Connors, S.L.; Péan, C.; Berger, S.; Caud, N.; Chen, Y.; Goldfarb, L. (eds.). "Chapter 9: Ocean, Cryosphere and Sea Level Change" (PDF). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA: 1270–1272.
  15. ↑ "NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses". NASA. October 30, 2015. Retrieved 24 December 2022.
  16. ↑ Turner, John; Overland, Jim (2009). "Contrasting climate change in the two polar regions" (PDF). Polar Research. 28 (2). doi:10.3402/polar.v28i2.6120.
  17. ↑ Bintanja, R.; van Oldenborgh, G. J.; Drijfhout, S. S.; Wouters, B.; Katsman, C. A. (31 March 2013). "Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion". Nature Geoscience. 6 (5): 376–379. Bibcode:2013NatGe...6..376B. doi:10.1038/ngeo1767.
  18. 1 2 3 Rignot, Eric; Mouginot, Jérémie; Scheuchl, Bernd; van den Broeke, Michiel; van Wessem, Melchior J.; Morlighem, Mathieu (2019-01-22). "Four decades of Antarctic Ice Sheet mass balance from 1979–2017". Proceedings of the National Academy of Sciences. 116 (4): 1095–1103. Bibcode:2019PNAS..116.1095R. doi:10.1073/pnas.1812883116. ISSN 0027-8424. PMC 6347714. PMID 30642972.
  19. ↑ Velicogna, Isabella; Wahr, John; Scott, Jim (2006-03-02). "Antarctic ice sheet losing mass, says University of Colorado study". Science. University of Colorado at Boulder. Archived from the original on 9 April 2007. Retrieved 2007-04-21.
  20. ↑ Rignot, E.; Bamber, J. L.; Van Den Broeke, M. R.; Davis, C.; Li, Y.; Van De Berg, W. J.; Van Meijgaard, E. (2008). "Recent Antarctic ice mass loss from radar interferometry and regional climate modelling". Nature Geoscience. 1 (2): 106. Bibcode:2008NatGe...1..106R. doi:10.1038/ngeo102. S2CID 784105.
  21. ↑ Rignot, E. (2008). "Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR data". Geophysical Research Letters. 35 (12): L12505. Bibcode:2008GeoRL..3512505R. doi:10.1029/2008GL033365.
  22. ↑ King, M. A.; Bingham, R. J.; Moore, P.; Whitehouse, P. L.; Bentley, M. J.; Milne, G. A. (2012). "Lower satellite-gravimetry estimates of Antarctic sea-level contribution". Nature. 491 (7425): 586–589. Bibcode:2012Natur.491..586K. doi:10.1038/nature11621. PMID 23086145. S2CID 4414976.
  23. ↑ Payne, A. J.; Vieli, A.; Shepherd, A. P.; Wingham, D. J.; Rignot, E. (2004). "Recent dramatic thinning of largest West Antarctic ice stream triggered by oceans". Geophysical Research Letters. 31 (23): L23401. Bibcode:2004GeoRL..3123401P. CiteSeerX 10.1.1.1001.6901. doi:10.1029/2004GL021284. S2CID 4891690.
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  30. ↑ Shepherd, Andrew; Ivins, Erik; Rignot, Eric; Smith, Ben; van den Broeke, Michiel; Velicogna, Isabella; Whitehouse, Pippa; Briggs, Kate; Joughin, Ian; Krinner, Gerhard; Nowicki, Sophie (June 2018). "Mass balance of the Antarctic Ice Sheet from 1992 to 2017". Nature. 558 (7709): 219–222. Bibcode:2018Natur.558..219I. doi:10.1038/s41586-018-0179-y. hdl:2268/225208. ISSN 1476-4687. PMID 29899482. S2CID 186244208.
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  32. ↑ Mengel, Matthias; Levermann, Anders; Frieler, Katja; Robinson, Alexander; Marzeion, Ben; Winkelmann, Ricarda (8 March 2016). "Future sea level rise constrained by observations and long-term commitment". Proceedings of the National Academy of Sciences. 113 (10): 2597–2602. Bibcode:2016PNAS..113.2597M. doi:10.1073/pnas.1500515113. PMC 4791025. PMID 26903648.
  33. ↑ Trisos, C. H., I. O. Adelekan, E. Totin, A. Ayanlade, J. Efitre, A. Gemeda, K. Kalaba, C. Lennard, C. Masao, Y. Mgaya, G. Ngaruiya, D. Olago, N. P. Simpson, and S. Zakieldeen 2022: Chapter 9: Africa. In Climate Change 2022: Impacts, Adaptation and Vulnerability [H.-O. Pörtner, D.C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 2043–2121 |doi=10.1017/9781009325844.011.
  34. ↑ IMBIE team (13 June 2018). "Mass balance of the Antarctic Ice Sheet from 1992 to 2017". Nature. 558 (7709): 219–222. Bibcode:2018Natur.558..219I. doi:10.1038/s41586-018-0179-y. hdl:2268/225208. PMID 29899482. S2CID 49188002.
  35. ↑ Rignot, Eric; Mouginot, Jérémie; Scheuchl, Bernd; van den Broeke, Michiel; van Wessem, Melchior J.; Morlighem, Mathieu (22 January 2019). "Four decades of Antarctic Ice Sheet mass balance from 1979–2017". Proceedings of the National Academy of Sciences. 116 (4): 1095–1103. Bibcode:2019PNAS..116.1095R. doi:10.1073/pnas.1812883116. PMC 6347714. PMID 30642972.
  36. ↑ Zwally, H. Jay; Robbins, John W.; Luthcke, Scott B.; Loomis, Bryant D.; Rémy, Frédérique (29 March 2021). "Mass balance of the Antarctic ice sheet 1992–2016: reconciling results from GRACE gravimetry with ICESat, ERS1/2 and Envisat altimetry". Journal of Glaciology. 67 (263): 533–559. doi:10.1017/jog.2021.8. Although their methods of interpolation or extrapolation for areas with unobserved output velocities have an insufficient description for the evaluation of associated errors, such errors in previous results (Rignot and others, 2008) caused large overestimates of the mass losses as detailed in Zwally and Giovinetto (Zwally and Giovinetto, 2011).
  37. ↑ Barr, Iestyn D.; Spagnolo, Matteo; Rea, Brice R.; Bingham, Robert G.; Oien, Rachel P.; Adamson, Kathryn; Ely, Jeremy C.; Mullan, Donal J.; Pellitero, Ramón; Tomkins, Matt D. (21 September 2022). "60 million years of glaciation in the Transantarctic Mountains". Nature Communications. 13 (1): 5526. doi:10.1038/s41467-022-33310-z. hdl:2164/19437. ISSN 2041-1723.
  38. ↑ Sedimentological evidence for the formation of an East Antarctic ice sheet in Eocene/Oligocene time Archived 2012-06-16 at the Wayback Machine Palaeogeography, palaeoclimatology, & palaeoecology ISSN 0031-0182, 1992, vol. 93, no1-2, pp. 85–112 (3 p.)
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