Where Thick Ice Sheets in Antarctica Meet the Ground, Small Changes Could Have Big Consequences
Scientists studying the physics and thermodynamics of Antarctica’s ice sheets say they’ve discovered a potential new weak spot that could accelerate melting and sea level rise over the next several hundred years.
The international team of researchers modeled how the giant slabs of ice behave where they meet the ground, sometimes thousands of feet below the surface, and the results suggested that just a little bit of thawing could make the region a big new source of sea level rise, said Eliza Dawson, a Ph.D. candidate at Stanford’s radio glaciology lab who led the study published today in Nature Communications.
There’s very little research on what happens at the bottom of the ice in the remote region, but clear signs in ancient climate records that there can be big changes in that basal state over the span of a few centuries, she said, adding that it’s important to understand that there are important differences within the various ice fields.
Fast-flowing glaciers reaching the sea have been studied, she said, “but in between, there are frozen patches, sometimes separating them and interweaving them. And no one has really looked at what if some of those frozen patches thaw, and how that could affect the total mass loss,” she added.
History shows there are ice streams flowing from land to sea that have turned on and off, said co-author Dustin Schroeder, with the Stanford University radio glaciology research group. “There’s areas that used to flow quickly that have stagnated.” But models don’t show exactly how the ice goes from being frozen fast to flowing quickly. The temperatures at the base of the ice sheet may hold the answer, he added.
When the team modeled thawing of the frozen patches,the George V coast region, which includes Wilkes Basin, stood out. “Which I think is probably the most interesting result,” said Dawson. The Wilkes Basin’s ice volume is similar to West Antarctica’s Thwaites Glacier, which is now known to be very vulnerable to melting,” she added.
“It’s a really massive region that could contribute a lot to sea level rise if somehow that volume of ice were to be discharged” from the land to the sea, she said. “And I found that there were some patches near the Wilkes subglacial basin that appear to be frozen but close to falling.”
‘One-Sided Uncertainties’ Prevail
Uncertainties about sea level rise are “largely one-sided,” said Penn State University geoscientist Richard Alley, who was not involved in the new research, meaning there hasn’t been any recent research suggesting that ice melt and sea level rise won’t be as bad as thought. The new paper focuses on one of the big uncertainties—what happens at the base of the ice sheet, he said.
“Suppose you started an ice sheet in a really cold place,” he said. “The bed initially would be frozen, with the ice sticking to it strongly.” But like a partially defrosted old-school refrigerator, the ice slides out pretty easily when there is a bit of water in the mix, he added.
One factor that could create more heat is “a positive feedback in ice dynamics, whereby enhanced ice deformation releases more deformational heat, which makes the ice softer, which further enhances ice deformation,” said William Colgan, a glaciologist with the Geological Survey of Denmark and Greenland.
“I can say, yup, the specter of widespread basal thaw looms large over ice-sheet stability,” he said. “I guess the biggest uncertainty in a study like this might be where is the ice bed frozen today?” Other research in Greenland shows “we don’t know that terribly well … and when your initial condition is off, your projection is off,” he said.
“I can add that the freeze-thaw point at the bed of an ice sheet is one of those thresholds where, when crossed, the timescales and dynamics of governing processes change dramatically,” added Nanna Karlsen, also a glaciologist with the Geological Survey of Denmark and Greenland. “In that respect, it is not surprising that areas considered to be frozen today will respond the most to a change in conditions at the bed. The findings are important because they highlight how a seemingly docile part of Antarctica may yet play an important role in future sea-level rise.”
More Nasty Climate Feedback
What happens where the ice meets the ocean could also ultimately affect the seemingly impervious deep ice sheets, added Alley. As floating coastal ice shelves thin, it could speed the flow of land-based ice, and the increasing speed could generate friction and heat that could thaw some of the patches where the ice sheets are frozen to the ground, he said. Overall, the new study gives “additional documentation on the idea that the uncertainties about sea-level rise are largely one-sided.”
Dawson, the study’s lead author from Stanford, said that there have been very few observations of the ice shelves in this region, particularly when compared to the Thwaites Glacier, which has been far more extensively studied. “There’s a lot of very fundamental questions about how the ocean circulation could interact with the ice shelves in those regions (of East Antarctica), and how much it could be warming, and how the ice streams and outlet glaciers in this region might be responding,” she said.
Recent paleoclimate research shows there has been previous retreat in the Wilkes Basin area. “But how it might be evolving right now, and how vulnerable it might be to warm waters, is challenging without having a new kind of field campaign to go into these areas and collect more data,” she said. More research, using sensitive radar and other instruments, is planned to get more data from the critical areas, she added.
Co-author Elisa Mantelli, an ice sheet dynamics expert and lecturer at the Institute for Marine and Antarctic Studies at the University of Tasmania in Hobart, said it’s important to remember that the study doesn’t say that the current warming of the atmosphere will suddenly heat up the base of the ice sheet.
“That’s not how an ice sheet works,” she said. “The key message to convey is that changes in ice flow can change the thermal state of the ice.” The findings don’t point to an imminent tipping point, she added. “But there are some of these tipping points that are related to how heat is produced at the base,” she said.
Those points are not well-resolved, she added. “We just don’t know the consequences.”
Colgan, the Denmark and Greenland-based ice scientist, said the new study “joins a growing chorus saying ‘It’s the bed, stupid,’ meaning that we really need to take a hard look at how to address our poor scientific understanding of today’s basal conditions.”
That, he added, is needed “before we can really constrain the currently gaping probability of ice-sheet collapse.”