Are we missing a crucial component of sea level rise?

Recent efforts using computer modeling to understand how melting ice in Antarctica will affect the planet’s oceans have focused on ice sheet geometry, fractures and surface melting – processes that could potentially trigger or accelerate ice sheet mass loss. Now Stanford University researchers have identified another process that could have a similarly significant impact on the future of the ice sheet: the thawing of the bed, known as basal thaw, at the interface between the land and the kilometer-thick ice sheet above.

The new study identifies areas that aren’t currently losing large amounts of mass but could be poised to experience some of the biggest contributors to sea level rise – like Thwaites Glacier – as they thaw. Antarctica is about the size of the United States, and vulnerable regions cover an area larger than California. The study was published on September 14th nature communication.

“You can’t necessarily assume that whatever is currently frozen will stay frozen,” said lead study author Dustin Schroeder, associate professor of geophysics at the Stanford Doerr School of Sustainability. “These regions may be underestimated potential contributors.”

Unusual suspects

The simulations were built on recent theoretical work showing that basal thawing can occur over short timescales. Using numerical ice sheet models, the study co-authors tested hypotheses about whether the onset of such a thaw could lead to significant ice loss within a 100-year timeframe. They found that triggering thaws led to mass loss in regions of the ice sheet not normally associated with instability and sea level contributions on this timescale.

“There was really little to no continental work that looked at the onset of thawing — the transition from frozen ice to ice at the melting point, where a little bit of water at the bed can make the ice slide,” said lead author of the study Eliza Dawson, Ph.D. Geophysics student. “We were interested in how strong the thawing could be and which regions of the ice sheet might be the most vulnerable.”

The researchers modeled temperature changes at the base of Antarctica according to frictional shifts caused by the ice sheet sliding across the land below. The simulations indicated that in East Antarctica, which is currently considered a relatively stable region compared to West Antarctica, the Enderby-Kemp and George V Land areas would be most sensitive to thawing at their beds. Within George V Land, they also highlighted that should a thaw occur, the Wilkes Basin could become a leading contributor to sea level – a feature comparable in size to the rapidly developing and likely unstable Thwaites Glacier in West Antarctica is.

“The entire community is really focused on Thwaites right now,” said Schroeder, who is also an associate professor of electrical engineering. “But some of the regions that are the usual suspects for big, impactful changes aren’t the most provocative and impactful areas in this study.”

temperature is important

Because of Antarctica’s location and extreme conditions, information about the ice sheet is sparse. Even less is known about the land beneath its frozen facade.

“Measuring the bed in these remote locations is a huge effort – we have the technology to do it, but you really have to pick the spot and sometimes it takes years, and field camps and special equipment to do that,” Schroeder said. “It’s difficult and expensive.”

To fill in the gaps in information, the researchers drew on the physics of how ice slides — how temperature changes affect the way the ice sheet flows and evolves. In follow-up work, the authors plan to develop and apply radar-based analysis approaches to study the temperature of the ice sheet in these critical areas.

“You need to know the regions where it matters, and that’s the transformative contribution of Eliza’s article,” Schroeder said. “It’s asking these general questions: does it matter? And if it matters, where? We hope this approach gives the community some prioritization of where to search and why, and to avoid hitting dead ends.”

sleeping giants?

Scientists don’t currently know which forces in the potentially vulnerable regions identified in this study are best able to trigger bedside thawing — or how quickly they might be able to do so. A possible driver could be changing ocean conditions, which is happening elsewhere in Antarctica.

“Warm seawater doesn’t necessarily reach these East Antarctic regions like it does in parts of West Antarctica, but it’s close by, so there’s a potential that could change,” Schroeder said. “When you look at the recent theoretical work showing that thermal processes at the bed are easy to activate – even spontaneously – it makes the short-term thawing of the ice sheet bed seem like a much simpler switch than we thought. “

The study shows that measuring, understanding and modeling the temperature at the base of ice sheets is important to understanding our future, since the greatest uncertainty in sea level rise projections is the contribution of processes that can alter the behavior of massive ice sheets Greenland and Antarctica.

“Further work will be required to further investigate these regions identified in this paper,” Dawson said. “Showing that bedside thawing can lead to mass loss of the ice sheet is a process that the community needs to understand and really start addressing — especially in these potentially vulnerable areas.”