Cause of fast ice melting in Greenland uncovered by researchers

While conducting a study on the Petermann Glacier in northwest Greenland, researchers at the University of California, Irvine and NASA’s Jet Propulsion Laboratory discovered a previously unseen way in which ice and ocean interact. The glaciologists said their findings could mean that the climate community has greatly underestimated the future rise in sea level caused by the deterioration of polar ice.

Using satellite radar data from three European missions, the UCI/NASA team has learned that Petermann Glacier’s ground line—where ice breaks off the Earth’s floor and begins to float into the ocean—changes dramatically during tidal cycles, allowing warm seawater to intrude and melt ice at accelerated rate. The group’s findings are the subject of research published in Proceedings of the National Academy of Sciences.

“The Petermann grounding line can be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers with the entry and exit of the tides,” said lead author Enrico Ciraci, UCI associate specialist in Earth System Sciences and postdoctoral fellow at NASA. “This is an order of magnitude greater than would be expected for grounding lines on a solid bed.”

He said the traditional view of grounding lines under glaciers that reach the ocean is that they did not migrate through tidal cycles, and did not experience ice melt. But the new study replaces this thinking with the knowledge that warm ocean water infiltrates under the ice through pre-existing subglacial channels, with the highest rates of melt occurring in the grounding zone.

The researchers found that as Petermann Glacier’s ground line retreated nearly 4 kilometers — two and a half miles — between 2016 and 2022, warm water carved a 670-foot-high cavity into the glacier’s lower side, and that fissure remained there throughout 2022.

“These ocean-ice interactions make glaciers more sensitive to ocean warming,” said co-senior author Eric Rignot, professor of Earth system sciences at UCI and a NASA JPL research scientist. “These dynamics were not built into the models, and if we did include them, it would increase projections of sea level rise by as much as 200 percent — not just for Petermann but for all the glaciers that end in the ocean, which is in most of northern Greenland and all of Antarctica.”

The Greenland Ice Sheet has lost billions of tons of ice to the ocean in the past few decades PNAS Leaf stresses, with most losses caused by warming of the ocean floor waters, which is a product of Earth’s changing climate. Exposure to ocean water causes ice to melt more aggressively at the glacier front and undermines the resistance to movement of glaciers above land, causing the ice to slide more quickly out to sea, according to Renott.