Caltech researchers have analyzed nine years of satellite radar data to quantify how the collapse of floating ice shelves accelerates the flow of Antarctica's Pine Island Glacier, the continent's largest contributor to sea-level rise. The study, published in the Proceedings of the National Academy of Sciences, examines observations from the European Space Agency's Sentinel-1 satellites spanning 2015 to 2024.
The Pine Island Glacier currently flows into the ocean at roughly 4.8 kilometers per year, a velocity that has increased more than 100 percent since 1973. A major calving event in 2017, when a large section of the ice shelf broke away, corresponded with a further 20 percent speedup in glacier flow.
Ice shelves act as buttresses, providing a "cork in a bottle" effect that restrains the land-based glacier behind them. The new analysis shows that losing this buttressing stress transfers additional force to the glacier's shear margins — the zones where the ice grinds against rocky outcroppings along its sides.
These shear margins normally supply frictional drag that slows the glacier. However, the data indicate that the 2017 calving event intensified pre-existing damage in the shear margins, creating a feedback loop: faster flow increases stress on the margins, causing more damage, which further reduces friction and allows yet more acceleration.
By 2020, the glacier appeared to have become completely decoupled from its damaged shear margins, effectively losing a primary braking mechanism. Lead author Sarah Wells-Moran, a former student in professor Brent Minchew's group, notes that this observational record provides a rare benchmark for testing numerical models of ice-sheet retreat.
Minchew emphasizes that the difference between manageable and extreme sea-level scenarios hinges on the behavior of the West Antarctic Ice Sheet, particularly Pine Island and neighboring Thwaites Glacier. Roughly one-third of the global population lives near coastlines, and every centimeter of rise could displace an estimated 1.5 million people.
The research team is now investigating whether natural healing processes within the ice could be leveraged to slow mass loss and stabilize the ice sheets. Funding for the work came from the National Science Foundation.
The paper, titled "Near-total loss of buttressing stresses observed on Pine Island Ice Shelf, West Antarctica," was co-authored by Wells-Moran, Minchew, and Bryan Riel of Zhejiang University.
Models of Glacial Collapse in Antarctica Improve Predictions of Sea-Level Rise
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