The weakening of the ice shelf caused the acceleration of the crucial Antarctic glacier

A large and rapidly melting glacier in West Antarctica has expanded dramatically since 2017. This may be a sign that the floating ice shelf in front of it is no longer helping to hold the ice back.

Pine Island Glacier is the fastest flowing glacier in Antarctica and the largest contributor to sea level rise of all Antarctic glaciers. It is a key part of the West Antarctic Ice Sheet, which holds enough ice to raise global sea levels by 5.3 meters if it melted completely.

The Pine Island Ice Shelf lies in front of the glacier and juts out over the ocean. It is thought to play a key role in holding inland ice and protecting it from warm water, supporting an amount of ice equivalent to 51 centimeters of sea level rise.

The instability of the Pine Island Glacier and the neighboring Thwaites Glacier, nicknamed the Doomsday Glacier, poses a major threat to the long-term viability of the wider West Antarctic Ice Sheet.

Sarah Wells-Moran at the University of Chicago and her colleagues tracked the movement of the Pine Island Glacier using images from the Copernicus Sentinel-1 satellite and observations from the early 1970s.

The glacier’s speed increased from 2.2 kilometers per year in 1974 to 4 kilometers per year by 2008. It then jumped to nearly 5 kilometers per year between 2017 and 2023, a 20 percent increase in six years and a 113 percent increase since 1973.

Between 1973 and 2013, the rate of ice discharge from Pine Island Glacier increased by more than three-quarters.

These changes led to a dramatic retreat of the glacier’s grounding line, the point at which the ice shelf begins to float rather than rest on the sea floor, by more than 30 kilometers.

The team compared these observations with computer models and concluded that the rapid acceleration occurred as a result of the ice shelf thinning and breaking up as warmer seawater encroached further along its underside. The sides of the ice shelf separated from the surrounding ice, “unzipping” the shelf edges, Wells-Moran and her colleagues write.

They concluded that the Pine Island Ice Shelf “now provides negligible ice support upstream”, which has accelerated the loss of ice from West Antarctica.

Sue Cook at the University of Tasmania in Australia argue that calving—the breakup of ice at the front of the ice shelf—is insufficient to explain the glacier’s acceleration. “The most likely cause is increased damage to the shear edges of the glacier,” he says. “This study helps confirm this mechanism.”

Ted Scambos at the University of Colorado say warm ocean water can reach the edges of the ice shelf, where it juts out into Pine Island Bay, a glacier-carved fjord. “With the loss of the ice shelf, ocean circulation in the fjord is likely to accelerate and the intensity of circulation near where the glacier is anchored to the bedrock will increase,” says Scambos.

Nerilie Abramova from the Australian Antarctic Division says the study helps demonstrate how much and how quickly the Pine Island Glacier is failing. “There is no doubt that ice loss from this region will continue to affect the world’s coastlines for decades and centuries to come,” says Abram.

Northern lights, fjords and glaciers: Svalbard and Tromso, Norway

Join an exciting arctic adventure in Norway where you can delve into the science behind the aurora borealis, arctic ecosystems and human adaptation to extreme northern environments.

topics: