The melting of Greenland ice is one of the processes associated with current climate change that is of most concern to the scientific community and the world in general, among other reasons because it will have a notable impact on the rise in sea level on a planetary scale. Ice loss from Greenland's land cover has accelerated in recent years beyond what was predicted by climate models and more than expected from the increase in temperature already recorded. Last week we reported the results of a study showing that global warming increases the presence of black algae in Greenland and this, in turn, increases melting ice.
A new study led by experts from the University of California at Irving (United States) now presents the existence of an interaction process between seawater and ice that could complete the explanation for this acceleration in melting in Greenland.
The discovery became apparent while researchers from the University of California and NASA's Jet Propulsion Laboratory were conducting a study of the Petermann Glacier in northwestern Greenland. The glaciologists on this team explain that their findings could mean that the climate community has been vastly underestimating the magnitude of future sea level rise caused by the deterioration of polar ice.
Using satellite radar data from three European missions, the UCI/NASA team learned that the grounding line of the Petermann Glacier, where the ice breaks away from the Earth's bed and begins to float in the ocean, changes substantially during the cycles of tidal, allowing warm seawater to come in and melt the ice at an accelerated rate. The group's results are the subject of a paper published in the Proceedings of the National Academy of Sciences.
"The Petermann grounding line could be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers as the tides come in and out," said lead author Enrico Ciraci, an assistant specialist at the UCI in Earth System Science and NASA Postdoctoral Fellow. "This is an order of magnitude higher than expected for grounding lines on a rigid bed."
He said the traditional view of grounding lines beneath ocean-reaching glaciers was that they did not migrate during tidal cycles, nor did they experience ice melt. But the new study replaces that thinking with the knowledge that warm ocean water intrudes beneath the ice through pre-existing subglacial channels, with the highest melt rates in the landfall zone.
The researchers found that when the Petermann Glacier's ground line receded nearly 4 kilometers between 2016 and 2022, warm water carved a 670-foot-tall cavity at the bottom of the glacier, and that abscess remained there throughout 2022.
"These ice-ocean interactions make glaciers more sensitive to ocean warming," said co-lead author Eric Rignot, a UCI professor of Earth system sciences and NASA JPL research scientist. "These dynamics are not included in the models, and if we did include them, they would increase projections of sea level rise by as much as 200 percent, not just for Petermann but for all ocean-terminating glaciers, which is the largest part of northern Greenland and all of Antarctica".
The Greenland ice sheet has lost billions of tons of ocean ice in recent decades, the PNAS paper highlights, with most of the loss caused by warming ocean groundwater, a product of change Earth's climate. Exposure to ocean water vigorously melts the ice on the glacier front and erodes the resistance to glacier movement above ground, causing the ice to slide more rapidly toward the sea, according to Rignot.
