Greenland Ice Sheet

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Greenland Ice Sheet
82% of the area of ​​Greenland is covered by the Greenland Ice Sheet

82% of the area of ​​Greenland is covered by the Greenland Ice Sheet

location Greenland
Type Ice sheet
length 2530 km
surface 1,801,000 km² (2012)
Altitude range 3275  m  -  0  m
width Max. 1094 km
Ice thickness ⌀ 1673 m; Max. 3,366.5 m
Ice volume 2,911,000 km³
Coordinates 77 °  N , 41 °  W Coordinates: 77 °  N , 41 °  W
Greenland Ice Sheet (Greenland)
Greenland Ice Sheet
Template: Infobox Glacier / Maintenance / Image description missing
Ice thickness map
Topography without an ice sheet

The Greenland ice sheet (also Greenland ice cap ) is an ice sheet , which with an area of approximately 1.8 million square kilometers about 82% of the area of Greenland covered. It is the second largest permanently iced area in the world after the Antarctic Ice Sheet .

Spatial expansion

Retreat of the Jakobshavn Isbræ
Glacier tongue on Greenland

In north-south direction, the length of the ice sheet is approximately 2,500 kilometers. The widest point with about 1,100 kilometers is approximately 77 ° N to 78 ° N. On average, the ice is more than 1.5 km thick; in places the thickness is more than three kilometers. The volume is estimated to be approximately 2.9 million cubic kilometers. Assuming an average ice density of 917 kg / m³, this results in a mass of around 2.67 million gigatons (2.67 × 10 18  kg). If this ice were to melt completely, this would result in a global rise in sea level of around seven meters.

In most places the ice sheet does not reach the sea, so that, unlike in Antarctica, no extensive ice shelves have formed. However, the ice flows through some large valleys over mighty outlet glaciers and reaches the sea, where they calve and in this way release most of the icebergs into the North Atlantic. A well-known outlet glacier on the west side of Greenland is the Jakobshavn Isbræ , which at its end has an exceptionally high flow rate of 20 to 22 meters per day and is responsible for around 10% of all icebergs of Greenlandic origin.

In addition to the ice sheet, there are also some isolated glaciers and ice caps with a total area of ​​less than 100,000 square kilometers on the outer edge of Greenland . Due to the weight of the ice masses, the earth's crust below sinks into the earth's mantle (see →  isostasy ). Most of Greenland is therefore roughly at sea level or even below.

Development of the ice sheet in the Cenozoic

Eocene to Miocene

For a long time, scientists have been of the opinion that larger glacier and sea ​​ice formations in the Arctic took place for the first time near the Pliocene - Pleistocene transition (2.7 to 2.4 mya). In the meantime, more recent studies, based on a large number of proxy data, provide clear indications of sporadic, relatively large-scale glaciation processes since the Eocene (beginning at approx. 48/47 mya). In addition, analyzes of deep-sea drill cores from the Fram Strait and off South Greenland support the assumption that Greenland was almost continuously covered by ice for the past 18 million years (and thus also during the Miocene optimum climate).

In this context, parallel climate developments from the Antarctic are regularly used for comparison. For example, a cooling postulated for the Arctic 41 million years ago could also be demonstrated for the southern polar regions, which signals a global temperature decline. The same applies to the climate change associated with a significant reduction in CO 2 at the Eocene- Oligocene border (33.9 mya). The evaluation of marine carbonates from the tropical Pacific using the stable oxygen isotopes 18 O / 16 O supports several cooling scenarios for both poles from the Eocene to the early Oligocene. With regard to Greenland, however, the volume and extent of the ice caps of that time are still largely unexplained, although the existence of icebergs (and thus also those of outlet glaciers ) is considered certain.

Pliocene and Pleistocene

The primary cause of the rapidly increasing arctic glaciation at the beginning of the Pleistocene was often cited in older specialist literature as the merger of the South American and Caribbean plates and the resultant formation of the Panama Isthmus , probably 2.76 million years ago. The interrupted water exchange between the Pacific and Atlantic changed the oceanic circulation and caused the creation of the Gulf Stream , which diverted warm surface water into the North Atlantic. The resulting increased evaporation and cloud formation rate led, according to this explanatory model, to snowier winters and ultimately to increased glacier growth including the expansion of the Greenland Ice Sheet.

According to the current state of knowledge, evaporation processes and winter snowfall as icing factors only played a subordinate role. It is predominantly assumed that the increasing Arctic glaciation is associated with a significant decrease in the global CO 2 concentration, which means that the summer months in particular were cooler. Some studies state a first cooling phase in the late Pliocene (3.2 mya) and a second after the beginning of the Pleistocene (2.4 mya), during which the CO 2 content fell from originally 375 to 425 ppm to 275 to 300 ppm, with a further decrease during the subsequent cold-time cycles. This development was apparently reinforced by a periodically occurring constellation of the orbital parameters ( Milanković cycles ) with the tendency towards reduced solar radiation ( insolation ) in the northern hemisphere.

The Greenland Ice Sheet recorded frequent losses of mass in the various warm phases ( interglacials ) of the Quaternary Ice Age, the extent of which, however, is unclear. Even for the well-researched interglacial of the Eem warm period (about 126,000 to 115,000 years ago), only relatively rough estimates exist with regard to the decrease in ice volume. Most studies assume that during the Eem warm period, sea levels were 6 to 9 meters above current levels. According to calculations, the Greenland Ice Sheet has a proportion of meltwater with an approximate mean value in the range of 1.5 to 2.5 meters, the remainder is distributed between the thermal expansion of the seawater and the melting of mountain glaciers (∼1 m) as well as larger Extent to the significant reduction in West Antarctic ice cover. According to this, the Greenland Ice Sheet lost 20 to 30 percent of its mass during this period at partially higher temperatures than in the previous 21st century, with individual studies generally applying higher values ​​and estimating a decrease of up to 60 percent.

climate

Temperatures on the ice sheet are lower than in the rest of Greenland. Annual lows of below −30 ° C are reached. In summer the top layer of ice thaws, which causes the formation of air bubbles in the ice to make it appear completely white. In winter, on the other hand, the ice takes on a clear, blue-green hue. One of the largest onshore strong wind fields on earth is located on the ice sheet (see strong wind field ).

The ice sheet as documentation of climate development

The ice sheet consists of compressed snow that has accumulated over a period of more than 100,000 years. Samples were taken from boreholes up to three kilometers deep, from which conclusions can be drawn about temperatures in the past, the extent of the oceans, precipitation, chemical composition of the atmosphere, volcanic activity and many other processes and situations in recent geological history.

Influence of global warming

In the course of global warming , the ice sheet has been melting at record speed in recent years. Between 1979 and 2002 the area affected by the meltdown in the summer months increased by 16%. The runoff of the melt water through crevices and cracks in the ice in turn accelerates the thawing process. In a study conducted by the Jet Propulsion Laboratory of NASA is believed that this is also reason, the glaciers of Greenland that move sea with increasing speed toward. According to satellite measurements, the annual ice loss increased from 96 km 3 to 220 km 3 between 1996 and 2005 and to an average of 273 km 3 per year between 2006 and 2008 . Other measurements, which add up the individual losses of all glaciers, show a net loss of 145 km 3 for 2008 . Between 2011 and 2014, the ice sheet on Greenland lost an average of around 269 billion tons of ice per year. The mass loss has increased sixfold since the 1980s. Greenland has raised sea levels by 13.7 mm since 1972, half of that in the past 8 years.

A study by the Technical University of Denmark shows that the northeast of the Greenland ice sheet is also beginning to melt. So far, this region has been considered stable. This finding emerged after evaluating the data from ice thickness measurements by aircraft and from satellites for the years 2003 to 2012. According to the researchers, the region has lost ten billion tons of ice annually since 2003, meaning that north-east Greenland may have contributed approximately 0.03 millimeters to the rise in sea levels. The cause of the melt may be a chain reaction to the warm summer of 2003.

Over the past few decades, blocking high pressure areas have occurred over Greenland more frequently , so that warmer, more humid air flows in and, by Greenland standards, high temperatures occur more frequently. Observations and simulations suggest that the melting of the Arctic sea ice will significantly change the weather patterns over Greenland.

The 3rd report of the Intergovernmental Panel on Climate Change , published in 2001, predicts a rise in sea level of 0.2 to 0.6 meters between 1990 and 2090 if global warming of three degrees Celsius is reached . About two-thirds of this increase is due to the thermal expansion of sea water, while one-third is due to the melting of land ice. A partial melting of the ice sheets in Greenland and Antarctica has not yet been taken into account due to insufficient evidence. An average loss of 100 km 3 of the Greenland ice sheet would lead to a sea level rise of 0.03 meters over 100 years.

A study by Michael Bevis and colleagues published in December 2018 assumes that the Greenland ice sheet is melting faster and thus contributing to a more rapid rise in sea levels than earlier calculations had estimated. The authors attributed this development to the combination of sustained global warming with positive temperature fluctuations of the North Atlantic Oscillation during the Arctic summer, which makes the surface mass of Greenland increasingly unstable towards the southwest - an effect that has hardly been taken into account in previous scenarios.

Global warming of more than 3 degrees Celsius could lead to a complete melting of the Greenland ice sheet, combined with a sea level rise of 7.2 m. Since large areas of the surface of the continental shelf on which the ice sheet rests are now close to or below sea level, it is to be expected that Greenland would initially be partially covered by the sea after the ice has melted rapidly and completely. However, in the course of many millennia, the island would rise again completely above sea level , similar to Scandinavia since the end of the Pleistocene (see →  postglacial uplift ).

One hypothesis states that if the ice sheet melts more quickly, the flow of warm water into the North Atlantic would be considerably reduced, because the increased fresh water input could disrupt the thermohaline circulation in the area of ​​the North Atlantic drift , and thus the Gulf Stream system. As a result, the temperature rise in the North Atlantic, including Western Europe, could slow down, which would reduce the rate of melting of the Greenland inland ice again. A change in the flow conditions in the oceans is discussed as one of the reasons for the emergence of a cold period .

Web links

Commons : Greenland Ice Sheet  - Collection of images, videos and audio files

literature

  • Climate Change, the Scientific Basis . IPCC, 2001 [1] , [2] , and [3] (English)
  • National Report to IUGG, Rev. Geophys. Vol. 33 Suppl . American Geophysical Union, 1995 [4]
  • ACIA, Impacts of a Warming Arctic: Arctic Climate Impact Assessment . Cambridge University Press, 2004 [5]
  • Möller, Dietrich (1994) The West-East Profile of the International Glaciological Greenland Expedition (EGIG). Earth sciences; 12, 3; 80-82; doi : 10.2312 / geosciences.1994.12.80 .

Individual evidence

  1. ^ A b britannica.com Greenland Ice Sheet
  2. ↑ a b c d e Byrd Polar Research Center - Research Wiki: Greenland Factsheet ( Memento January 2, 2015 in the Internet Archive ), accessed on February 20, 2013
  3. ↑ Jørn Thiede, Catherine Jessen, Paul Knutz, Antoon Kuijpers, Naja Mikkelsen, Niels Nørgaard-Pedersen, Robert F. Spielhagen: Millions of Years of Greenland Ice Sheet History Recorded in Ocean Sediments . (PDF) In: Polar Research (GEOMAR Helmholtz Center for Ocean Research Kiel) . 80, No. 3, 2011, pp. 141–159.
  4. ↑ Linda C. Ivany, Kyger C. Lohmann, Franciszek Hasiuk, Daniel B. Blake, Alexander Glass, Richard B. Aronson, Ryan M. Moody: Eocene climate record of a high southern latitude continental shelf: Seymour Island, Antarctica . (PDF) In: The Geological Society of America (GSA) Bulletin . 120, No. 5/6, pp. 659-678. doi : 10.1130 / B26269.1 .
  5. ↑ James S. Eldrett, Ian C. Harding, Paul A. Wilson, Emily Butler, Andrew P. Roberts: Continental ice in Greenland during the Eocene and Oligocene . (PDF) In: Nature . 446, March 2007, pp. 176-179. doi : 10.1038 / nature05591 .
  6. ↑ Aradhna Tripati, Dennis Darby: Evidence for ephemeral middle Eocene to early Oligocene Greenland glacial ice and pan-Arctic sea ice . (PDF) In: Nature Communications . March 9, 2018. doi : 10.1038 / s41467-018-03180-5 .
  7. ↑ Aaron O'Dea, Harilaos A. Lessios, Anthony G. Coates, Ron I. Eytan, Sergio A. Restrepo-Moreno, Alberto L. Cione, Laurel S. Collins, Alan de Queiroz, David W. Farris, Richard D. Norris, Robert F. Stallard, Michael O. Woodburne, Orangel Aguilera, Marie-Pierre Aubry, William A. Berggren, Ann F. Budd, Mario A. Cozzuol, Simon E. Coppard, Herman Duque-Caro, Seth Finnegan, Germán M . Gasparini, Ethan L. Grossman, Kenneth G. Johnson, Lloyd D. Keigwin, Nancy Knowlton, Egbert G. Leigh, Jill S. Leonard-Pingel, Peter B. Marko, Nicholas D. Pyenson, Paola G. Rachello-Dolmen, Esteban Soibelzon, Leopoldo Soibelzon, Jonathan A. Todd, Geerat J. Vermeij, Jeremy BC Jackson: Formation of the Isthmus of Panama . In: Science Advances . 2, No. 8, August 2016. doi : 10.1126 / sciadv.1600883 .
  8. ↑ KT Lawrence, S. Sosdian, HE White, Y. Rosenthal: North Atlantic climate evolution through the Pliocene-Pleistocene climate transitions . (PDF) In: Earth and Planetary Science Letters . 300, No. 3-4, December 2010, pp. 329-342. doi : 10.1016 / j.epsl.2010.10.013 .
  9. ^ Matteo Willeit, Andrey Ganopolski, Reinhard Calov, Alexander Robinson, Mark Maslin: The role of CO 2 decline for the onset of Northern Hemisphere glaciation . (PDF) In: Quaternary Science Reviews . 119, July 2015, pp. 22–34. doi : 10.1016 / j.quascirev.2015.04.015 .
  10. ^ RE Kopp, A. Dutton, AE Carlson: Centennial to millennial-scale sea-level change during the Holocene and Last Interglacial periods . (PDF) In: Past Global Changes Magazine . 25, No. 3, 2017, pp. 148–149. doi : 10.22498 / pages.25.3.148 .
  11. ↑ Chris SM Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran , Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, Alan Cooper: Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica . In: PNAS . February 2020. doi : 10.1073 / pnas.1902469117 .
  12. ^ A. Dutton, K. Lambeck: Ice Volume and Sea Level During the Last Interglacial . (PDF) In: Science . 337, No. 6091, July 2012, pp. 216-219. doi : 10.1126 / science.1205749 .
  13. ↑ Michael J. O'Leary, Paul J. Hearty, William G. Thompson, Maureen E. Raymo, Jerry X. Mitrovica, Jody M. Webster: Ice sheet collapse following a prolonged period of stable sea level during the last interglacial . (PDF) In: Nature Geoscience . 6, July 2013, pp. 796-800. doi : 10.1038 / ngeo1890 .
  14. ^ EJ Stone, PD. J. Lunt, JD Annan, JC Hargreaves: Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise . (PDF) In: Climate of the Past . 9, March 2013, pp. 621-639. doi : 10.5194 / cp-9-621-2013 .
  15. ^ A. Robinson, R. Calov, A. Ganopolski: Greenland ice sheet model parameters constrained using simulations of the Eemian Interglacial . (PDF) In: Climate of the Past . 7, No. 2, April 2011, pp. 381-396. doi : 10.5194 / cp-7-381-2011 .
  16. ↑ Global Wind Atlas. Retrieved September 8, 2019 .
  17. ↑ NY Times : In Greenland, Ice and Instability Andrew C. Revkin, Jan. 8, 2008 (in English)
  18. ↑ Changes in the Velocity Structure of the Greenland Ice Sheet ( Memento from February 22, 2014 in the Internet Archive ), Eric Rignot & Pannir Kanagaratnam , 2006, Science 311, pages 986–990 (PDF article; 395 kB)
  19. ↑ Michiel van den Broeke et al .: "Partitioning Recent Greenland Mass Loss". Science , November 13, 2009, accessed November 13, 2009 .
  20. ^ Arctic Report Card Greenland ( Memento October 15, 2011 in the Internet Archive ), Jason E. Box et al. 2009, NOAA (in English)
  21. ↑ Malcolm McMillan et al .: A high-resolution record of Greenland mass balance . In: Geophysical Research Letters . 2016, doi : 10.1002 / 2016GL069666 .
  22. ↑ Jérémie Mouginot, Eric Rignot et al. a .: Forty-six years of Greenland Ice Sheet mass balance from 1972 to 2018. In: Proceedings of the National Academy of Sciences. , S. 201904242, doi : 10.1073 / pnas.1904242116 .
  23. ↑ enveya.com: Northeast of Greenland is beginning to melt ( Memento from March 23, 2014 in the Internet Archive ) Article from March 22, 2014 on enveya.com, accessed on March 23, 2014
  24. ↑ Jiping Liu et al. a .: Has Arctic Sea Ice Loss Contributed to Increased Surface Melting of the Greenland Ice Sheet? In: Journal of Climate . May 2016, doi : 10.1175 / JCLI-D-15-0391.1 .
  25. ↑ IPCC Third Assessment Report Climate Change 2001, Chapter 11.5 ( Memento of March 5, 2016 in the Internet Archive ), Future Sea Level Changes (in English)
  26. ↑ Bevis, M. et al. (2019). Accelerating changes in ice mass within Greenland, and the ice sheet's sensitivity to atmospheric forcing. Proceedings of the National Academy of Sciences . https://doi.org/10.1073/pnas.1806562116
  27. ↑ IPCC Third Assessment Report Climate Change 2001, Table 11.3 ( Memento from January 2, 2017 in the Internet Archive ), Some physical characteristics of ice on Earth (in English)
  28. ↑ IPCC Third Assessment Report Climate Change 2001, Chapter 9.3.4.3 ( Memento of March 4, 2016 in the Internet Archive ), Thermohaline circulation changes (in English)