Thwaites Glacier in West Antarctica.
NASA/ZUMA Wire/Shutterstock
Underwater “storms” are melting the ice shelf protecting the Thwaites Doomsday Glacier in Antarctica, raising fears that we may be underestimating future sea level rise.
These storm vortices, up to 10 kilometers wide, making them “submesoscale,” begin to swirl when waters of different densities or temperatures collide in the open ocean, similar to hurricanes formed by the mixing of air bodies in the atmosphere. And like hurricanes, some of them rush towards the coast, which in Antarctica is mainly made up of ice shelves – floating extensions of glaciers that extend tens of kilometers into the sea.
“They move so much that it’s really hard to stop them,” says Mattia Poinelli at the University of California, Irvine. “So the only way they can get away is to just be trapped under the ice.”
Modeling by Poinelli and colleagues found that these submesoscale features were responsible for one-fifth of the total melting of the Thwaites and neighboring Pine Island ice over a nine-month period. This is the first study to quantify the impact of these storms on the entire ice shelf.
Ice shelves slow the slide of glaciers into the sea and protect them from wave erosion. The vulnerable Thwaites Glacier loses 50 billion tons of ice every year and could raise sea levels by 65 centimeters if it collapses.
In the waters around Antarctica, several hundred meters of colder, fresher water sit on top of warmer, saltier deep water. If a storm enters a cavity beneath an ice shelf, its vortex pushes cold surface water away from the center of the vortex, drawing warm, deep water upward into the resulting void and melting the ice shelf from the bottom up.
This starts a feedback loop in which the cold fresh water released by the melt interacts with the warm salt water, increasing the rotation of the underwater storm, causing even more melting.
In 2022, a deep-sea float measuring temperature, salinity and pressure was “caught” by a large rotating eddy that became lodged beneath the Stancombe-Wills Ice Tongue elsewhere on the Antarctic coast. With data later collected from the captured float, Katherine Hancock at Florida State University and her colleagues rated that the vortexes cause the melting of 0.11 meters annually under this ice tongue.
“This shows that the concept of a vortex rotating underneath an ice shelf is important,” Hancock says.
The smaller, submesoscale storms in Poinelli's study likely have a similar effect, she said, suggesting that swirling bodies of water of varying scales are melting significant amounts of ice. “This needs to be better quantified,” Hancock says.
As the climate warms and fresh meltwater from Antarctica increases, undersea storms are likely to intensify, potentially causing more sea level rise than we currently expect.
Thiago Dotto The UK's National Oceanography Center says the “striking” new findings require more observations from beneath the ice shelves.
“Given current changes in wind patterns and sea ice around Antarctica, how much are we really losing by not monitoring these small scales?” he asks.
Topics:
