Weakening ice shelf has caused crucial Antarctic glacier to accelerate

The significant and rapid melting of a glacier in West Antarctica has accelerated dramatically since 2017. This could be a sign that the floating sea ice 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 glaciers in Antarctica. It is a key part of the West Antarctic ice sheet, which contains enough ice to raise global sea levels by 5.3 meters if it completely melted.

The Pine Island Ice Shelf lies in front of the glacier and juts out into the ocean. It is thought to play a crucial role in retaining inland ice and protecting it from warm waters, strengthening an amount of ice equivalent to 51 centimeters of sea level rise.

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

Sarah Wells-Moran of 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 dating back to the early 1970s.

The speed of the glacier increased from 2.2 kilometers per year in 1974 to 4 kilometers per year in 2008. Then, between 2017 and 2023, it increased to almost 5 kilometers per year, an increase of 20% over six years and 113% since 1973.

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

These changes have resulted in a dramatic retreat of more than 30 kilometers in the glacier’s grounding line, the point at which the ice shelf begins to float rather than rest on the seafloor.

The team compared these observations with computer models and concluded that the rapid acceleration was due to the thinning and fracturing of the ice shelf, as warmer seawater reached farther along its underside. The sides of the ice shelf broke away from the surrounding ice, “opening up” the shelf margins, Wells-Moran and colleagues write.

They conclude that the Pine Island Ice Shelf “now provides negligible support to the upstream ice”, which has accelerated the loss of West Antarctic ice.

Sue Cook, of the University of Tasmania in Australia, says calving – the breaking up of ice at the front of the ice shelf – is not enough to explain the glacier’s acceleration. “The cause is most likely an increase in damage to the glacier’s shear margins,” she says. “This study helps confirm this mechanism.”

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

Nerilie Abram of the Australian Antarctic Division says the study helps demonstrate the scale and speed at which the Pine Island Ice Shelf is deteriorating. “There is no doubt that ice loss in this region will continue to impact the world’s coasts for decades and centuries to come,” says Abram.

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