Glaciers all over Antarctica are in trouble as ice there rapidly melts. There’s no Antarctic glacier whose fate is more consequential for our future than the Thwaites Glacier, and new research shows that things aren’t looking good for it.
Researchers have known that the Thwaites Glacier is in trouble due to encroaching warm waters, but they’d never actually analysed data from beneath the glacier’s float ice shelf — until now. A new study published in Science Advances on Friday presents the first-ever direct observations of what’s going under the infamous ice shelf, including the temperature and salinity of the water that’s flowing under it as well as the strength of the current.
What they found is pretty troubling. The authors explain that the supply of warm water to the glacier’s base is larger than scientists previously believed, which means it’s even more unstable than we thought. Given that it’s often called the “doomsday glacier,” that’s particularly ominous.
Thwaites glacier a broad, vast hunk of ice that flows from the West Antarctic ice sheet into Pine Island Bay, a part of the Amundsen Sea. The 92,000-square-kilometre ice shelf is disappearing faster than any other one in the region in large part because of the waters circulating beneath it and wearing away at its base. If it collapses completely, it could have a devastating effect on global sea level rise.
The new study is based on field observations from 2019 when a team of two dozen scientists sent an autonomous orange submarine named Ran down underneath Thwaites. For 13 hours, the underwater vehicle travelled around two deep troughs beneath the glacier that funnel warm water toward it. As it did, the vehicle captured data showing that warm water — warm for a glacier, at up to 1.05 degrees Celsius — is swirling around the glacier’s crucial “pinning points,” or the points of contact where the ice shelf meets the bedrock that holds it in place. This warm water is melting away these crucial holds, making room for cracks and troughs in ice that can make the shelf all the more unstable.
“The worry is that this water is coming into direct contact with the underside of the ice shelf at the point where the ice tongue and shallow seafloor meet,” Alastair Graham, associate professor of geological oceanography at the University of Southern Florida and study co-author, who was on the research expedition to the glacier, wrote in an email. “This is the last stronghold for Thwaites and once it unpins from the sea bed at its very front, there is nothing else for the ice shelf to hold onto. That warm water is also likely mixing in and around the grounding line, deep into the cavity, and that means the glacier is also being attacked at its feet where it is resting on solid rock.”
The discovery of warm water confirms previous concerns from a separate project, wherein another group of 100 scientists drilled a hole 600 metres into the glacier.
“This study fills in critical gaps in our knowledge in this area and will undoubtedly allow for major advances in the modelling of this system, and thus improved projections,” David Holland, a glaciologist from New York University who worked on the previous study but not the newer one, wrote in an email.
As the submarine moved around one of the troughs, it also captured data showing low-salinity water in the area 1,050 metres below the ice shelf. That salinity level it showed matches that of the neighbouring Pine Island Bay. Scientists previously thought this part of the glacier was protected from the bay’s currents by a thick underwater ridge. But it seems they were wrong — the findings indicate it’s flowing into the trough freely. That closely links its fate to the bay more than climate models currently account for.
It’s not just Pine Island Bay’s encroaching warm waters we have to worry about, either. Using the submarine’s readings, the authors also mapped out the channels along which warm water is getting transported toward Thwaites Glacier. They found more warm water is also surging in from along the continental shelf.
“Thwaites is really being attacked by the ocean from all sides,” said Graham.
All this has very serious consequences for those living along the coast. Thwaites Glacier’s collapse would raise sea levels by 0.5 to 0.9 metres, and could also trigger an even worse chain of events because it could initiate the collapse of another nearby imperiled ice shelf, the Pine Island Glacier. Together, these shelves act as a braking mechanism on land ice that, if released into the open waters, could push seas up to 3.1 metres, overwhelming coastal cities around the world.
Over the past four decades, Graham explained, satellite data has shown that the glacier has been flowing into the ocean much more quickly. Sure, it replenishes some of it when fresh snow falls and gets compacted into new ice, but that’s not happening quick enough to make up for its losses.
To learn more about this process, scientists are trying to learn as much as they can about the glacier. Sending a submarine underneath it marks a big, groundbreaking step. But there’s still a lot of uncertainty about how quickly it’s edging toward collapse.
The study illustrates the importance of climate adaptation measures, including weighing the potential benefits of having communities retreat away from coasts. That’s especially true because Graham said that it’s not entirely clear whether or not the Thwaites’ demise is preventable.
“We might (and I stress might) have already reached and passed a point where there is really no turning back for Thwaites, no matter what we as humans do to our climate,” Graham.
Graham knows how scary this is firsthand since he lives on the Florida Gulf Coast. But not all is lost.
“There may be physical mechanisms that we are yet to uncover that could help Thwaites stabilise and ‘doomsday’ may never come,” he said.