Thanks to the deployment of an underwater robot under a rapidly melting ice shelf in Antarctica, scientists have uncovered
new clues as to how it is melting
.
The findings will help assess the threat that this and other ice shelves pose to long-term sea level rise.
The overall melting of the bottom of the Thwaites Shelf in West Antarctica was less than expected from estimates derived from computer models, the researchers said.
But they also found that
the rapid melting was taking place in unexpected places
: a series of terraces and cracks that extended deep into the ice.
The results do not alter the fact that the Thwaites is one of the fastest receding and least stable Antarctic ice shelves, and the one of greatest concern when it comes to sea level rise.
Nor do the forecasts change that the collapse of the platform and the glacier of which it is a part would cause a rise of half a meter over several centuries.
Members of the British Antarctic Survey team drilling a hole in the Thwaites Ice Shelf, Antarctica.
(Icefin/ITGC/Schmidt via The New York Times)
According to one of the scientists, Peter ED Davis, an oceanographer with the British Antarctic Survey, the research "tells us much more about the processes driving the Thwaites retreat."
The results, published Wednesday in the journal Nature, will be used to refine models that predict the long-term future of Thwaites.
The research is part of a larger effort, the US-British sponsored International Thwaites Glacier Collaboration, to better understand what's going on in the Thwaites.
The ice shelf is the floating tongue of the
Thwaites Glacier, a river of ice the size of Florida
that helps keep one of Antarctica's two massive ice sheets at bay.
The waters surrounding Antarctica are warming as a result of climate change, and as this warm water flows under the shelf, the ice underneath melts and the shelf thins.
The so-called bottom line, the area where the floating ice meets the bedrock, has been receding as the shelf has lost ice, moving about 12 kilometers inland in the last two decades.
The new findings were published in two papers in Nature: Davis was lead author on one, and Britney E. Schmidt, a geophysicist at Cornell University, was lead author on the other.
The researchers camped out on the ice during the Antarctic summer of 2019-20, often in extreme cold and windy conditions, and used hot water to drill several holes through 600 meters of ice to the ocean below, not far from the sea. ground line.
Davis and his team lowered instruments into the water to measure its temperature, salinity and other characteristics.
Although they found that
the water was well above freezing
, the slow current and the layering of water with varying levels of salinity prevented mixing, which would have added more heat and melted more ice.
Alastair Graham, an oceanographer at the University of South Florida who has studied the historical retreat of the Thwaites ice but was not involved in these two studies, said the Davis team's work showed that "there is a lot of heat working its way up to the stranding zone. of Thwaites".
"However, not all of that ocean heat turns into ice melt," he said.
The star of the show was the
underwater robot, named Icefin
, designed, built, and operated by Schmidt and his team.
A cylinder 9 inches in diameter and about 12 feet long, carrying cameras, sonar, and other instruments, as well as thrusters for propulsion.
Schmidt slowly "drove" the apparatus along a long cable that carried signals from the surface.
Icefin explored steep-sided cracks and terraces at the bottom of the ice, finding rapid melting there, as the near-vertical orientation of the sidewalls allowed mixing and added more heat to the ice.
Sometimes Icefin allowed researchers to measure what was happening just inches from the ice.
Seeing those ice faces up close and their orientation was puzzling, she said, "and trying to figure it out has been a big part of the story."
Like Davis, Schmidt said the findings provided important context for what's happening on Thwaites Glacier.
"It's not about 'hot water equals X amount of melt,'" she said.
"It's 'hot water plus process X means fusion.'"
Because there is generally less melting at the bottom, but the Thwaites is still unstable, he said, "it means it actually takes a lot less than we thought to push these things out of balance."
"It doesn't mean things are better," Schmidt added.
"It means that things are different."
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