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.
The rapid melt seen in this study was in the far northwest of Greenland on Petermann Glacier. If it is happening in the rest of Greenland and the even bigger Antarctic ice sheet, then global ice loss and the sea level rise could jump as much as twice as fast as previously thought, according to the study in Monday’s Proceedings of the National Academy of Sciences.
“It’s bad news,” said study author Eric Rignot, a glaciologist at University of California Irvine. “We know the current projections are too conservative.”
He said this newly found consequence of tidal activity “could potentially double the projections” of global melt.
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.
“The sea water actually goes much farther beneath the grounded ice (than previously thought), kilometers, not hundreds of meters,” Rignot said. “And that water is full of heat and able to melt the glaciers vigorously. And it’s kind of the most sensitive part of the glacier.”
The study provides strong evidence that models need to include these tidal effects deep inland, said Pennsylvania State University glaciologist Richard Alley, who wasn’t part of this study.
