125,000 YEARS AGO
By Paul Voosen Jul. 10, 2020 , 3:50 PM
Scientists have long suspected that 125,000 years ago, the West Antarctic Ice Sheet collapsed, drowning a world not much warmer than today in 3 meters of rising tides. But hard evidence of whether such a collapse occurred—and if it did, how fast the melt went—has remained scarce.
Next week, the National Science Foundation will fund a 5-year project, costing more than $3 million, that will seek evidence of this collapse from gases trapped in tiny bubbles encased in a 2.5 kilometer-long tube of ice. The core drilling, likely to start in 2023, will target Hercules Dome, an expanse of ice 400 kilometers from the South Pole. Hercules sits at the saddle between the continent’s western and eastern ice sheets; if the western one collapsed, “Hercules Dome would be sitting on the waterfront, so to speak,” says Eric Steig, the project’s principal investigator and a glaciologist at the University of Washington, Seattle.
The Eemian, the last warm period between the ice ages, lasting from 129,000 to 116,00 years ago, is one of the best analogs for modern Earth. Temperatures were about 1° warmer than now, yet sea levels were 6 meters to 9 meters higher. And recent work, some still unpublished, has suggested much of this melt must have come from Antarctica.
If the ice collapsed, then the gases trapped at Hercules Dome would capture such a shift. It would be as if a set of protective mountains suddenly dropped away, exposing the Hercules ice to the warm storms that regularly strike Antarctica’s edge before petering out inland. Sodium would spike, and variations in oxygen isotopes would capture the warmer, wetter weather. And not only could the ice core capture whether the melt happened—it might also say how fast it occurred, Steig says, a hugely important variable for projections of future sea-level rise.
Much of the land in western Antarctica sits below sea level, leaving the ice on top at risk of melt from intruding warm ocean waters, and glaciers fringing it are retreating fast. Some scientists fear such a collapse is already unstoppable, which has prompted climate scientists to attack the question from all angles: NSF and U.K. government are supporting an expansive study of the western glacier most at risk of collapse, Thwaites, while marine drilling has targeted past evidence of collapse in the sediments off of the continent’s shore.
One reason the Hercules project was funded now, even though drilling remains years away, is that it will include community workshops to develop scientific proposals for other ways the core might be used. Deep ice drilling is a tight-knit, homogenous group; Steig and NSF hope these workshops will help bring in scientists “beyond the usual suspects,” he says.
doi:10.1126/science.abd7704
Paul Voosen is a staff writer who covers Earth and planetary science.
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