Antarctic ice sheet

Antarctic ice sheet
Antarctic ice sheet (satellite photograph “ Blue Marble ”) data without ice shelf, according to
location	Antarctica
Type	Ice sheet
surface	12,300,000 km²
Ice thickness	⌀ 2126 m; Max. 4897 m (in the Astrolabe subglacial basin )
Ice volume	26,500,000 km³
Coordinates	90 °  S coordinates: 90 °  S

Antarctica without an ice sheet. 45% of the ice-bearing subsurface is below sea level.

The Antarctic ice sheet (also Antarctic ice sheet ) is one of two polar ice caps . It is the largest ice mass on earth and covers the Antarctic continent ( Antarctica ) almost completely. In the Antarctic ice sheet and the ice shelf it feeds , almost 90 percent of the ice and 70 percent of the earth's fresh water are bound. The area of ​​the ice sheet is 12.3 million square kilometers (plus 1.63 million km ^{2 of} ice shelves), the volume is 26.5 million cubic kilometers (plus 0.4 million km ^{3 of} ice shelf).

If it melted completely, this would theoretically result in a sea ​​level rise of around 58 meters. In the period 1979 to 2017, the mass loss of the Antarctic glaciers increased by about six times. While the ice loss was around 40 cubic kilometers per year from 1979 to 1990, it was already 252 cubic kilometers per year from 2009 to 2017. The West Antarctic Ice Sheet proved to be quite unstable during the last warm period 120,000 years ago.

The ice in West Antarctica is predominantly ice shelf ( Ross Ice Shelf , Filchner-Rønne Ice Shelf, etc.) or weighs down on rock that is below sea level (in the Bentley subglacial rift up to 2870 m deep); one therefore speaks of a marine ice sheet . This ice can melt relatively quickly due to a warmer ocean, but if it melted completely it would only contribute 3.4 m to the potential rise in sea level due to the low load. In East Antarctica , the proportion of ice lying below sea level is also considerable, according to more recent findings, corresponding to 19.2 m sea level rise.

Ice formation

In 2011 it was discovered that the ice sheet on the Dome A plateau does not only grow from above due to snowfall, but also from below. For example, water can accumulate on obstacles such as the Gamburzew Mountains and freeze over time or be pressed up against valley walls and, because it is then under less pressure, turn into ice. In this way, on average, up to a quarter of the ice mass was formed in the investigated area. In radar images of a polar expedition in summer 2008-2009, a 1100 meters powerful ice mushroom, which presses the overlying thousands of meters thick ice layer faced upward.

Disintegration of the Amundsen sector

→ Main article : Pine Island Glacier

In May 2014, two research teams came up with the forecast that the Amundsen sector of the West Antarctic ice sheet could collapse in the next 200 to 1000 years, which would contribute more than one meter to the rise in sea levels . For several of the glaciers flowing into the Amundsen Sea , radar observations of the tidal fluctuations by the satellites ERS-1 and -2 showed a retreat of the so-called grounding lines from which the ice swims. In particular, the retreat of the baseline of the 100 km wide Thwaites Glacier , whose behavior the second group of researchers simulated on the computer, accelerated . In the same month a third group published an analysis of historical episodes of rapid flow of glaciers and ice sheets, from which a consistent time horizon for the collapse of the Thwaites Glacier emerged, but for the narrower Pine Island Glacier with its pronounced side valleys a stabilization after a temporary one Acceleration.

Web links

• First Map of Antartica's Moving Ice earthobservatory.nasa.gov, accessed August 23, 2011

Individual evidence

1. ↑ ^{a b} Peter T. Fretwell et al .: Bedmap2: improved ice bed, surface and thickness datasets for Antarctica. The Cryosphere 7, 2013, doi: 10.5194 / tc-7-375-2013 (free full text).
2. ^ HowStuffWorks: The World's Water.
3. ↑ Eric Rignot et al .: Four decades of Antarctic Ice Sheet mass balance from 1979-2017 . In: Proceedings of the National Academy of Sciences . 2019, doi : 10.1073 / pnas.1812883116 .
4. ↑ Two degrees of ocean warming were enough in the past to destabilize Antarctica - PIK Research Portal. Accessed February 16, 2020 . 
5. ↑ 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 .
6. ↑ Antarctic glaciers also grow from below Spektrum.de, March 4, 2011
7. ^ Antarctic ice sheet built from bottom BBC, March 3, 2011
8. ↑ Eric Rignot et al .: Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011. Geophysical Research Letters 41, 2014, doi: 10.1002 / 2014GL060140 (free full text).
9. ^ Ian Joughin et al .: Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica. Science, 2014, doi: 10.1126 / science.1249055 .
10. ↑ Johan Kleman, Patrick J. Applegate: Durations and propagation patterns of ice sheet instability events. Quaternary Science Reviews 92, 2014, doi: 10.1016 / j.quascirev.2013.07.030 (free full text).