A cause of rapid ice melting in Greenland is discovered by researchers.

Researchers from the University of California, Irvine and NASA’s Jet Propulsion Laboratory have discovered a new way in which the ice and ocean interact at Petermann Glacier in northwest Greenland. The scientists found that Petermann Glacier’s grounding line, where ice detaches from the bed and begins to float in the ocean, shifts substantially during tidal cycles, allowing warm seawater to intrude and melt ice at an accelerated rate. This previously unseen phenomenon could mean that the magnitude of future sea level rise caused by polar ice deterioration has been vastly underestimated by the climate community, according to the researchers. The UCI/NASA team used satellite radar data from three European missions for the study. Their findings are published in Proceedings of the National Academy of Sciences.

“Petermann’s grounding line could be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers as tides come in and out,” said lead author Enrico Ciraci, UCI assistant specialist in Earth system science and NASA postdoctoral fellow. “This is an order of magnitude larger than expected for grounding lines on a rigid bed.” Previous thinking was that grounding lines beneath ocean-reaching glaciers did not migrate during tidal cycles nor experience ice melting. However, warm ocean water intrudes beneath the ice through preexisting subglacial channels, with the highest melt rates occurring at the grounding zone.

As Petermann Glacier’s grounding line retreated nearly four kilometers between 2016 and 2022, warm water carved a 670-foot-tall cavity in the underside of the glacier, and that abscess remained there throughout 2022. “These ice-ocean interactions make the glaciers more sensitive to ocean warming,” said senior co-author Eric Rignot, UCI professor of Earth system science and NASA JPL research scientist. “These dynamics are not included in models, and if we were to include them, it would increase projections of sea level rise by up to 200 percent—not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica.”

The PNAS paper stresses that the Greenland ice sheet has lost billions of tons of ice to the ocean in the past few decades, with most of this loss caused by warming of subsurface ocean waters, a product of Earth’s changing climate. Exposure to ocean water melts the ice vigorously at the glacier front and erodes resistance to the movement of glaciers over the ground, causing the ice to slide more quickly to the sea.

 

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