Petermann Glacier in the far north of Greenland was found to have a bad case of cheeseification in its ice as warm ocean tides have tunneled from the grounding line up towards the ice surface. One cavity was as tall as a sixty-seven-floor-high skyscraper between 2016 and 2022. Six freaking years! Gobsmacking damage to the ice in such a short period.
Petermann is a marine-terminating glacier that is 43 miles long and 9.3 miles wide. Despite heavy snowfall levels on top of the glacier, eighty percent of its mass loss results from meltwater at the bottom of the glacier from warm ocean tides. The glacier’s fjord and the nearby Nares Strait have been a mystery for decades. Still, a new study has found that warm deepwater upwelling and waves rapidly melt Petermann and likely other glaciers in Greenland and even Antarctica. The findings suggest that the sea level rise magnitude from the polar ice caps is seriously underestimated.
"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."Seth Borenstein writes for the AP:
Daily tides stoked with increasingly warmer water ate a hole taller than the Washington Monument at the bottom of one of Greenland's major glaciers in the last couple years, accelerating the retreat of a crucial part of the glacier, a new study found.
And scientists worry that the phenomenon isn't limited to this one glacier, raising questions about previous projections of melting rates on the world's vulnerable ice sheets.
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The study looks at the all-important grounding line area of glaciers on ice sheets. That's the point where glaciers go from being on land to floating on water. Previous studies show it's also a key spot for rapid ice loss.
At remote Petermann, where few people have been and there are no base camps, that grounding line zone is more than six-tenths of a mile (1 kilometer) wide and could be as much as 3.7 miles (6 kilometers) wide, the study said.
Scientists used to think the daily tides weren't a big deal on melt. The snow added on top of the glacier compensated for the tides moving further in, said Rignot, the day before he left for an expedition to Petermann.
But with an ocean that's warmer because of climate change the tides became “a very powerful mechanism,” Rignot said.
From the University of California, Irvine presser:
Using satellite radar data from three European missions, the UCI/NASA team learned that Petermann Glacier's grounding line—where ice detaches from the land bed and begins floating in the ocean—shifts substantially during tidal cycles, allowing warm seawater to intrude and melt ice at an accelerated rate. The group's results are the subject of a paper 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."
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 knowledge that warm ocean water intrudes beneath the ice through preexisting subglacial channels, with the highest melt rates occurring at the grounding zone.
The mega-canyon empties into the Petermann fjord.