Ghost Mountains

The discovery of numerous large ice structures within Antarctica’s Dome A region, the site of the buried ghost mountains, reveals new understanding about ice sheet growth and movement that is essential for predicting how the ice sheet may change as the Earth’s climate warms. The Gamburtsev Mountain Range is a subglacial mountain range located in Eastern Antarctica. The range was discovered by the 3rd Soviet Antarctic Expedition in 1958 and is named for Soviet geophysicist Grigoriy A. Gamburtsev. It is approximately (750 miles long, and the mountains are believed to be about 8,900 feet high, although they are completely covered by over 600 meters (2,000 ft) of ice and snow. The Gamburtsev Mountain Range is currently believed to be about the same size as the European Alps.

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Reporting this week in the journal Science a six-nation group of scientists studying the Gamburtsev Subglacial Mountains describe how these remarkable structures form.  Typically ice sheets grow when layers of snow are deposited on the surface, but the researchers found startling new evidence of growth at the base. Widespread re-freezing of large volumes of water to the underside of the ice sheet modifies its structure. In some places this process can account for up to half the ice sheet’s thickness, and the growth caused by refreezing may be comparable to that occurring at the surface.

Ground-penetrating radar results from 2008 and 2009 have made possible earlier the most detailed physical ground images yet of the Gamburtsev Mountains—and it’s a surprisingly serrated range.  The ice structures are now another amazing part of the picture.

Lead Author, Dr Robin Bell of Columbia University’s Lamont-Doherty Earth Observatory says, “We usually think of ice sheets like cakes - one layer at a time added from the top. This is like someone injected a layer of frosting at the bottom - a really thick layer. Water has always been known to be important to ice sheet dynamics, but mostly as a lubricant. As ice sheets change, we want to predict how they will change. Our results show that models must include water beneath.”

Co-Author Dr Fausto Ferraccioli, from British Antarctic Survey says, "This International Polar Year study provides a unique view on the interactions between subglacial water and ice sheet structure in East Antarctica. Understanding these interactions is critical for the search for the oldest ice and also to better comprehend subglacial environments and ice sheet dynamics. Incorporating these processes into models will enable more accurate predictions of ice sheet response to global warming and its impact on future sea-level rise".  

The refrozen structures form because the vast Antarctic ice sheet acts like blanket trapping geothermal heat from the Earth beneath. This heat, combined with the great pressure from the overlying ice allows ice to melt at the base. When under the ice this water can be pushed uphill, towards mountain ridges where the ice sheet is thinner. This thinner and colder ice refreezes the water, creating the spectacular structures observed close to the base of the ice sheet.

The researchers theorize that this process explains the re-frozen structures appearing at the heads of valleys beneath the ice sheet. This new ice at the base pushes older ice closer to the surface, making the ancient layered record of climate embedded in the ice easier for researchers to reach.

For further information:  http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=1421