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The hunt for ancient ice that witnessed West Antarctica’s collapse

Core from Hercules Dome site could reveal how susceptible the region’s ice is to warming.

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Mountains and land ice, Antarctic Peninsula

Many glaciologists see signs of runaway melting in West Antarctica.Credit: Mario Tama/Getty

Sometime this month, scientists in Antarctica plan to start up their snowmobiles and begin radar surveys of a thick ridge of ice called Hercules Dome. The dome — which sits 400 kilometres from the South Pole, between East and West Antarctica — could provide crucial clues to the future of the continent’s vast ice sheet.

The surveys are intended to guide the drilling of the United States’ next deep ice core. Glaciologists hope to retrieve a detailed climate record of a period 116,000 to 130,000 years ago, when temperatures as little as 1 °C warmer than today’s are thought to have driven the collapse of the West Antarctica’s ice.

A better understanding of what happened then could help scientists to predict the behaviour of West Antarctica as climate change intensifies. The pace at which the region’s glaciers are flowing to the sea has increased in recent years, and many scientists fear that rising temperatures have triggered runaway melting. West Antarctica’s ice contains enough water to raise sea levels by more than 3 metres.

“If the West Antarctic ice sheet collapsed, Hercules Dome would basically be waterfront property,” says Eric Steig, a glaciologist at the University of Washington in Seattle who is leading the project. He is hopeful that scientists will be able to see the signal of the region’s long-ago collapse in ice from the dome.

The US National Science Foundation (NSF) has given Steig and his colleagues nearly US$630,000 to conduct radar surveys of ice depth and structure across Hercules Dome. That work started in January. The $1.5-million drilling project could begin as soon as 2022, pending the agency’s approval.

“The Hercules structure will have served as witness to what the atmosphere and what the oceans were doing when the West Antarctic ice sheet collapsed,” says Mary Albert, a glaciologist at Dartmouth College in Hanover, New Hampshire, and head of the US Ice Drilling Program, which advises the NSF.

Tiny bubbles

Bad weather and unexpectedly rough terrain made it difficult to land the NSF’s Hercules cargo plane at Hercules Dome last year, limiting scientists’ ability to conduct radar surveys. Nonetheless, the University of Washington team managed to identify two potential drilling sites where the depth of the ice ranges from 1.6 to 2.8 kilometres, says glaciologist Knut Christianson, who is leading the radar surveys.

Modified from N. Holschuh/Univ. Washington. Data: I. M. Howat et al. Cryosphere 13, 665–674 (2019); D. Pollard & R. M. DeConto Nature 458, 329–332 (2009).

This year, he and his colleagues plan to spend around 30 days collecting data — helped along by a newly groomed ice runway. Christianson’s team is looking for ice that is solidly frozen all the way to Antarctic bedrock. That increases the odds that the researchers can recover air bubbles trapped in oldest layers of snow and ice, which accumulated while Earth was cycling through ice ages.

These air bubbles can reveal how the levels of greenhouse gases, trace gases and aerosols in the atmosphere changed from decade to decade, helping researchers to reconstruct past climate. Data from ancient ice at Hercules Dome could help reveal whether the West Antarctic ice sheet was intact 115,000 to 130,000 years ago, during a brief interlude between ice ages.

There is evidence that sea levels during that period were up to 9 metres higher than today’s — a phenomenon that Steig says is hard to explain without the loss of West Antarctica’s ice. But hard evidence for the ice sheet’s collapse has been tough to come by.

Cold case

Glaciologists had hoped to capture that ancient warm period in an ice core that they finished drilling in West Antarctica in 2011. But the core they extracted dated back only 68,000 years, possibly because the older ice had melted away. Models suggests there is little or no melting in the deepest ice layers at Hercules Dome, which are likely to be at least 150,000 years old.

“There may well be ice that is 2 million years old at the bottom,” Steig says. “I wouldn’t be surprised.” But it’s not clear how much information scientists can extract from such ancient, and often very compressed, ice.

Field team members prepare a snowmobile and grooming device at Hercules Dome, East Antarctica

Researchers unload equipment to begin grooming an ice runway at Hercules Dome.Credit: Knut Christianson

One of the biggest questions at Hercules Dome is how the weather there changed when the climate warmed 130,000 years ago, says Jeffrey Severinghaus, a palaeoclimatologist at the Scripps Institution of Oceanography in La Jolla, California. Climate models suggest that the collapse of West Antarctica’s ice changed air circulation across the region, creating stormier conditions at Hercules Dome.

Severinghaus’s research has shown that the prevalence of isotopes of krypton and other trace gases deposited in ice varies with atmospheric pressure. This suggests that scientists should be able to see evidence of storms in ice from Hercules Dome.

Drilling there could provide an unprecedented opportunity to determine what happened during a crucial period of Antarctica’s history, Severinghaus says. “This is a good analogue,” he adds, “for where humanity is headed right now.”

Nature 576, 193-194 (2019)

doi: 10.1038/d41586-019-03793-w

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