Evidence buried in Greenland’s bedrock shows the island’s massive ice sheet melted nearly completely at least once in the last 2.6 million years. This suggests that Greenland’s ice may be less stable than previously believed.
(From Scientific American / by Alexandra Witze)– “Our study puts Greenland back on the endangered ice-sheet map,” says Joerg Schaefer, a palaeoclimatologist at the Lamont-Doherty Earth Observatory in Palisades, New York, and co-author of a paper published on December 7 in Nature.
A second paper in the same issue paints a slightly different view of the ice sheet’s past stability. A group led by Paul Bierman, a geomorphologist at the University of Vermont in Burlington, found that ice covered eastern Greenland for all of the past 7.5 million years. Experts say the two papers do not necessarily contradict one another: at times, nearly all of Greenland’s ice could have melted (as seen by Schaefer’s team) while a frosty cap remained in the eastern highlands (as seen by Bierman’s group).
If all of Greenland’s ice melted, it would raise sea levels by seven metres. Models suggest that Greenland could become ice-free as soon as 2,500 years from now, depending on the concentration of greenhouse gases in the atmosphere.
The latest papers add to a growing understanding of how Greenland’s ice has shifted over millions of years. Both studies used radioactive isotopes of beryllium and aluminium to estimate how long the island’s bedrock was exposed to the atmosphere—as cosmic rays pummel rock, they produce radionuclides such as beryllium-10 and aluminium-26. By counting those radionuclides in the topmost rock, researchers can estimate how long the surface was exposed to cosmic rays—that is, not shielded by thick ice.
Schaefer’s team analysed bedrock collected from the very bottom of the hole drilled for the GISP2 ice core, which was completed in central Greenland in 1993. “We just asked the surface, ‘Have you been ice free or not?’” says Schaefer. “It clearly told us, ‘I have been ice free.’”
Read the full article here: https://www.scientificamerican.com/article/greenland-once-lost-nearly-all-its-ice-and-could-again/