This Antarctic giant is melting at a rapid rate, throwing billions of tons of ice into the ocean every year and raising global sea levels.
Now, a British-American team has surveyed the deep sea floor channels in front of the glacier that almost certainly provide warm water access to infiltrate and attack the underside of Thwaites.
It is information that will be used to try to predict the future of the ice stream.
“These channels have never been previously mapped with this kind of detail,” said Dr. Kelly, “and what we discovered is that they are in fact much larger than anyone would have thought – up to 600 meters deep. Think of six consecutive soccer fields.” Hogan from the British Antarctic Survey (BAS).
She told BBC News: “And because it is so deep and so wide – this allows a lot of water to reach the floating façade of the Twits and its melting, as well as the ice that falls on the sea floor.”
It is a majestic sight, with its blossoming façade, or “ice cliff,” as it rushes away into the sea and sets off huge icebergs. But satellite observations indicate that this glacier is melting at an accelerating rate.
In the 1990s, it was losing just over 10 billion tons of ice annually. Today, it is more than 80 billion tons. The melting is thought to be due to an influx of relatively warm bottom water being drawn from the wider ocean.
Currently, Thwaites’ ice loss contributes about 4% to the annual rise in global sea levels, with the potential to add 65 cm in total if the entire glacier collapses.
No one thinks this will happen in the short to medium term, but Thwaites is particularly vulnerable in a warming world, and scientists would like to know precisely how quickly any changes will occur.
Their scientists sailed a ship equipped with an echo-probe that reached the icy slopes of the glacier, to trace the shape of the sea floor below.
A plane was also moved back and forth across the rack to measure small differences in the force of gravity. These deflections reflect the ripples of the sea floor below the shelf.
Combined, the two datasets now provide the best view yet of the Thawites’ main terrain. They trace the path of a network of deep channels that cut across a ridge before they coalesce to form a main cavity under the ice shelf.
“The connected channels that we detailed in detail for the first time are the potential pathways for warm waters to enter the depths of the ocean and cause damage at that point where the iceberg remains anchored to the sea floor, as it begins to rise and float,” explained BAS Fellow Dr. Tom Jordan, “but also to melt The base of the ice shelf, which, if weakened, will make the ice flow faster at the source of the ice. “
Scientists need data from the real world to assemble their models so that they get realistic results when they run to simulate possible future behavior.
The new information is improving the volumes of the warm water introduction that may be considered possible under various scenarios.
When conducting the survey, scientists now have a better idea of the general roughness of the sea floor.
This tells them about the kinds of speeds the ice can achieve in a glacier as it slides through rocks and sediments. What the researchers produced, if you wanted to, was a kind of “stickiness indicator” to further restrict computer models.
Currently, the eastern side of the ice shelf is attached to a large ledge, which gives it stability. Dr Robert Larter of Bass says the current melting trend indicates that this situation will not last longer.
He told BBC News: “When the eastern ice shelf separates, the ice will spread, become thin, and eventually disintegrate, as we see happening now on the (central) glacier tongue.” “Even before an ice shelf disintegrates, loosening and rotating the ice shelf will reduce the supporting effect of the ice shelf on the glacier upstream, thus increasing the velocity of ice flow. This, in turn, will accelerate the glacier thinning and grounding retreat.”
British and American scientists had to temporarily suspend their investigations into Thwaites due to the Covid-19 crisis.
Teams were set to return to the glacier this Australian summer, but the remoteness of the location means the stakes are too high if anyone gets sick. Once the coronavirus outbreak is properly contained, scientists will return.
“It’s amazing that you go to a place like Thwaites to see the changes taking place right in front of your eyes,” said Dr. Hogan. “When we were there in 2019, we had direct access to the slopes of the ice shelf, and the reason we were able to do that and make our observations is that the icebergs and sea ice that has always existed throughout history is starting to disappear.”
The latest research has been published in two papers in The Cryosphere, and can be viewed here and here.
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Glacier, Thwaites Glacier, Antarctica, Nathaniel B. Palmer, British Antarctic Survey, Ice
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