A new study from Stanford University has found that if the frozen bottom of the East Antarctic, currently under miles-thick glacial ice, were to thaw at the land interface, glaciers that presently do not contribute to sea level rise could become a new and significant source.
Besides ice fracture, calving, and surface melting, this new phenomenon of thawing at the bedrock threatens to make an already complicated process of ice loss even direr.
Antarctica is approximately the size of the continental United States. The area of vulnerability where small changes at the bedrock could create enormous problems for global coastlines is the size of California, the researchers noted in their introduction.
The temperature where the ice sheet meets the ground is known as the basal temperature. That area must stay frozen as it inhibits ice from sliding, ice flow, and sub-glacial melt at the base.
The study mentions that "Temporal changes in the basal thermal state can involve two processes: basal thawing and refreezing. While both processes can affect the behavior and evolution of ice sheets, here we focus on whether basal thawing could impact the century-scale evolution of the ice sheet mass balance. To distinguish the parts of the bed that could be vulnerable to thawing, we introduce the term thawable to refer to regions where the bed is frozen but within a few degrees below the" PMP or pressure melting point, where friction can create enough energy to melt the bottom.
Danielle Torrent Tucker writes the presser for Stanford.
The simulations were built on recent theoretical work showing that basal thaw could occur over short time scales. Using numerical ice sheet models, the study co-authors tested hypotheses about whether the onset of such thaw could lead to significant ice loss within a 100-year period. They found that triggering thaw led to mass loss in regions of the ice sheet that are not usually associated with instability and sea-level contributions at that time scale.
“There really has been little to no continental-wide work that looks at the onset of thawing – that transition from frozen ice to ice at the melting point, where a little bit of water at the bed can cause the ice to slide,” said lead study author Eliza Dawson, a PhD student in geophysics. “We were interested in learning how big an effect thawing could have and what regions of the ice sheet were potentially most susceptible.”
The researchers modeled temperature changes at Antarctica’s base according to shifts in friction caused by the ice sheet sliding over the land beneath it. The simulations revealed 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 the Wilkes Basin as capable of becoming a leading sea-level contributor if thawing were to occur – a feature comparable in size to the rapidly evolving and likely unstable Thwaites Glacier in West Antarctica.
West Antarctica has massive marine extensions extending for miles out in the ocean; East Antarctica ice covers the land. However, with warm water upwelling and melting from below, the smaller ice shelves underbellies in East Antarctica are as vulnerable to disintegration as those in the west. The land glaciers in the east are at risk of thawing at the base and sliding into the ocean, per the study. This is new.
Bob Berwyn always does excellent work on climate issues. His post in Inside Climate News is no exception.
He writes Where Thick Ice Sheets in Antarctica Meet the Ground, Small Changes Could Have Big Consequences:
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.”
The below graphic includes melt from the Antarctic and Greenland. It highlights what a gigaton of meltwater looks like.
Some good news.