Underwater ‘storms’ melt ice floes on ‘apocalyptic’ glacier

Underwater ‘storms’ are melting the ice shelf protecting the ‘doomsday’ Thwaites Glacier in Antarctica, raising concerns that we may underestimate future sea level rise.

Measuring up to 10 kilometers wide – making them “sub-mesoscale” features – these storm-like vortices begin to swirl when waters of different density or temperature collide in the open ocean, much like hurricanes form through the mixing of air bodies in the atmosphere. And like hurricanes, some of them head toward the coast, which in Antarctica is largely made up of ice shelves – the floating extensions of glaciers that extend dozens of kilometers into the sea.

“They move so much and it’s really hard to stop them,” says Mattia Poinelli of the University of California, Irvine. “So the only way for them to get out is to get stuck under the ice.”

Poinelli and colleagues’ modeling showed that these submesoscale features were responsible for a fifth of the total ice melt on Thwaites and neighboring Pine Island over nine months. This is the first study to quantify the impact of these storms on an entire ice floe.

Ice shelves slow the sliding of glaciers into the sea and protect them from wave erosion. The vulnerable Thwaites Glacier loses 50 billion tonnes 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 lie above deeper, warmer, saltier waters. If a storm becomes trapped in the cavity beneath an ice shelf, its vortex pushes cold surface water outward, away from the center of the vortex, pulling the warm, deep water into the resulting void and melting the ice shelf from the bottom up.

This triggers a feedback loop in which the cold, fresh water released by this melt interacts with the warm, salty water to intensify the rotation of the underwater storm, causing even greater melting.

In 2022, a deep-water float measuring temperature, salinity and pressure was “captured” by a large rotating eddy that became trapped beneath the Stancomb-Wills ice tongue at another location along the Antarctic coast. Using data later collected from the captured float, Cathrine Hancock of Florida State University and colleagues estimated that the eddies cause 0.11 meters of melting beneath this tongue of ice each year.

“This shows that the concept of a rotating vortex beneath an ice shelf is important,” says Hancock.

The smaller subscale storms in the Poinelli study likely have a similar effect, she says, suggesting that swirling bodies of water at different scales are melting significant amounts of ice. “These need to be better quantified,” says Hancock.

As the climate warms and more fresh meltwater flows from Antarctica, underwater storms are likely to intensify, potentially causing greater sea level rise than currently expected.

Tiago Dotto of the UK’s National Oceanography Center says the “stunning” new results call for more observations beneath ice shelves.

“Given current changes in wind and sea ice patterns around Antarctica, how much are we really missing by not observing these small scales? » he asks.