Greenland Ice Sheet Is 'Happily Sliding Over a Surface That Theory Says It Shouldn't Be Able to Rapidly Slide Over'

A team of researchers from the University of Wyoming has uncovered an unusual process taking place on the Greenland ice sheet (GIS), which could have significant implications for how it responds to climate change.

The scientists found that the ice is rapidly sliding over a surface that theory suggests shouldn't allow such movement as it makes its way towards the edges of the mass, according to a study published in the journal Science Advances.

The GIS is the second largest body of ice in the world after the Antarctic ice sheet, covering around 660,0002 miles. Worryingly, the GIS has experienced record melting in recent years as global temperatures rise—a process that is contributing to sea-level rise around the globe.

While they may appear solid, all ice sheets—which are essentially giant glaciers—experience movement: ice flows downslope either through the process of deformation or sliding. The latest results suggest that the movement of the ice on the GIS is dominated by sliding, not deformation. This process is moving ice to the marginal zones of the sheet, where melting occurs, at a much faster rate.

"The study was motivated by a major unknown in how the ice of Greenland moves from the cold interior, to the melting regions on the margins," Neil Humphrey, a professor of geology from the University of Wyoming and author of the study, told Newsweek. "The ice is known to move both by sliding over the bedrock under the ice, and by oozing (deforming) like slowly flowing honey or molasses. What was unknown was the ratio between these two modes of motion—sliding or deforming.

"This lack of understanding makes predicting the future difficult, since we know how to calculate the flowing, but do not know much about sliding," he said. "Although melt can occur anywhere in Greenland, the only place that significant melt can occur is in the low altitude margins. The center (high altitude) of the ice is too cold for the melt to contribute significant water to the oceans; that only occurs at the margins. Therefore ice has to get from where it snows in the interior to the margins.

The team found that, surprisingly, the sliding is taking place over a hard bedrock and not softer material, such as mud, that usually acts as a lubricant.

"That's the kicker. The Greenland ice sheet is happily sliding over a surface that theory says it shouldn't be able to rapidly slide over," Humphrey said in a statement. "What's important is that, because of this, you get a lot of ice to the oceans or low altitudes where it can melt really fast. It's like a lump of molasses sliding off the continent. It just doesn't melt. It slides toward the ocean."

Nathan Maier, another author of the study from Wyoming, told Newsweek: "Our results of high sliding were totally unexpected. We typically think of these slow-moving regions resting on bedrock as having low rates of sliding, but surprisingly we found the highest fraction of surface motion due to sliding ever measured. This includes sliding measurements made on famously fast-moving outlet glaciers like Jakobshavn."

For the study, the scientists drilled hundreds of holes into the ice bed using the "fastest ice drill in the world," which is capable of boring 5,000 feet deep in eight hours. They then installed a network of more than 200 tilt sensors to collect data on the ice movement.

The researchers say that the latest results cast new light on our understanding of how Greenland's ice is moving, which could enable better predictions of future ice loss.

"The implications for having high sliding along the margin of the ice sheet means that thinning or thickening along the margins due to changes in ice speed can occur much more rapidly than previously thought," Maier said. "This is really important; as when the ice sheet thins or thickens it will either increase the rate of melting or alternatively become more resilient in a changing climate."

The Greenland ice sheet is more than 1.2 miles thick in most regions. If all of its ice was to melt, global sea levels could be expected to rise by about 25 feet. However, this would take more than 10,000 years at the current rates of melting.

Nevertheless, this is no reason to be complacent. In fact, recent studies suggest that Greenland's ice is melting at a faster rate than ever before.

"Mass loss from Greenland's [ice sheet] has been increasing and over the last decade is at its highest level ever recorded," Maier said. "There have been some really cool papers to come out recently that make this clear. One by Mouginot et al. in the journal Proceedings of the National Academy of Sciences looked at the mass loss over the last five decades and found that it increased six fold. This is a crazy statistic, which is not good for Greenland or sea-level rise."

Furthermore, this June, the ice sheet experienced a record melt event, according to the National Snow and Ice Data Center (NSIDC).

"Between June 11 and 20, an extensive area of the Greenland ice sheet surface melted," said a statement from the NSIDC. "At its peak on June 12, thawing climbed from the western and eastern coasts to elevations above 9,800 feet. High air pressure and clockwise circulation around the island brought warm air from the south and sunny conditions."

"While several recent years have had similar early widespread melt events, the event of June 11 to 20 reached a peak of just over 270,000 square miles, setting a record for this early in the melt season," the statement read. "Models estimate the amount of melted ice at approximately 80 billion tons for that period."

This article was updated to include additional comments from Nathan Maier and Neil Humphrey.

Greenland ice sheet
A glacier is seen from NASA's Operation IceBridge research aircraft along the Upper Baffin Bay coast on March 28, 2017 above Greenland. Mario Tama/Getty Images

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