Study sheds light on the future of the massive Thwaites Glacier.
The world’s largest ice caps may be less at risk of sudden collapse than expected, new findings from the University of Michigan show.
The study, published in Science, included the simulation of the disappearance of the Thwaites Glacier from West Antarctica, one of the largest and most unstable glaciers in the world. The researchers modeled the collapse of varying heights of ice cliffs, almost vertical formations that occur where glaciers and ice shelves meet the ocean. They discovered that instability does not always lead to rapid disintegration.
“What we found is that over long periods of time, ice behaves like a viscous fluid, much like a pancake spreading out in a frying pan,” said Jeremy Bassis, associate professor of science and technology. of climate and space engineering at UM. “So the ice is expanding and thinning faster than it can fail and that can stabilize the collapse. But if the ice cannot thin out fast enough, then you have the possibility of a rapid glacier collapse. “
Researchers combined for the first time the variables of ice breakage and ice flow, finding that stretching and thinning of ice, as well as strengthening of trapped chunks of ice, can moderate the effects of l instability of the sea ice cliff induced by the fracture.
The new findings add a nuance to a previous theory called sea ice cliff instability, which suggested that if the height of an ice cliff reaches a certain threshold, it can suddenly disintegrate under its own weight in a chain reaction. of ice fractures. The Thwaites Glacier in Antarctica, sometimes referred to as the “Doomsday Glacier,” is approaching this threshold and could contribute nearly 3 feet to sea level rise in the event of a complete collapse. At 74,000 square miles, it is roughly the size of Florida and is particularly sensitive to climate and ocean changes.
The research team also found that icebergs that crack and fall from the main glacier in a process known as “iceberg calving” can actually prevent, rather than contribute to, catastrophic collapse. If the chunks of ice get stuck on outcrops on the ocean floor, they can put back pressure on the glacier to help stabilize it.
Bassis notes that even if the glacier does not collapse catastrophically, the exposure of a high cliff could still trigger a retreat of a few kilometers per year, the equivalent of the length of about twenty sites. football, which would make a significant contribution to future sea level rise.
How fast is the sea level rising?
While it is clear that Thwaites and other glaciers are melting, the speed of their disappearance is of great interest to coastal areas as they develop strategies to adapt and build resilience. But predicting the retreat of glaciers is an incredibly complex endeavor, as they are affected by the interplay of a myriad of factors – the stress and strain of billions of tons of moving ice, changes in air temperature and of water and the effects of liquid water flow. on ice, to name a few.
As a result, predictions of the collapse of the Thwaites Glacier range from a few decades to several centuries. The new study, says Bassis, is an important step towards producing accurate and actionable predictions.
“There is no doubt that the sea level is rising and that this will continue in the decades to come,” Bassis said. “But I think this study offers hope that we are not approaching a complete collapse – that there are measures that can ease and stabilize things. And we always have the opportunity to make a difference by making decisions on things like energy emissions, methane and CO2.
The fate of the Antarctic and Greenland ice caps
In addition to Bassis, the research team includes UM graduate student research assistant Brandon Berg, and Anna Crawford and Doug Benn of the University of St. Andrews.
Crawford says the study’s results will also be useful in predicting the fate of other glaciers and ice formations in the Arctic and Antarctic.
“This important information will inform future research on the retreat of the Thwaites Glacier and other large outlet glaciers from the West Antarctic ice sheet that are likely to retreat due to the ice cliff breaking and the instability of the sea ice cliff, ”she said. “They highlight the conditions that facilitate recoil, demonstrate the terminal’s stabilizing potential, and show how sea ice can actually slow down the collapse process.”
Bassis says the research team is already working to further refine their models by incorporating additional variables that affect glacial retreat, including how the shapes of individual glaciers affect their stability and the interaction between glacial ice and ice. liquid ocean surrounding it.
“The ocean is still there, sort of tickling the ice in a very complex way, and we’ve only known for a decade or two how important that is,” he said. “But we’re starting to understand that this is causing a lot of the changes we’re seeing, and I think this will be the next big frontier in our research.”
Reference: “Transition to marine ice cliff instability controlled by ice thickness gradients and velocity” by JN Bassis, B. Berg, AJ Crawford and DI Benn, June 18, 2021 Science.
DOI: 10.1126 / science.abf6271
The study is part of the International Thwaites Glacier Collaboration. The research was supported by the DOMINOS project, a component of the International Thwaites Glacier Collaboration, and by the National Science Foundation (grant number 1738896) and the Natural Environment Research Council (grant number NE / S006605 / 1).