June 17, 2024

Microscopic changes in the ice determine the flow speed of entire glaciers!

Glacier flow speeds can range from a few meters to kilometers per year and thus represent uncertainty in forecasts
Lisa Syed

Lisa Syed 5 minutes

As the ice caps and glaciers melt, huge amounts of water flow into the sea – and as a result, sea levels rise to a previously unimaginable extent. Researchers have now A new model for melting glaciers It was developed to better predict sea level rise. The study by MIT scientists shows that glacial flow depends on microscopic defects in the ice.

With the Glacier flow It refers to the movement of glacial ice from the top or center of the ice sheet to the edges. There the ice breaks up and melts into the ocean. There are measurements such as ice flow or flow velocity that can be used to determine the speed of movement of glaciers.

Those in Proceedings of the National Academy of Sciences published Stady He came to the conclusion that the speed of the glacier’s flow could be estimated Depending on the type of microscopic defects the ice is susceptible to. Scientists have developed a new model of glacier flow using the relationship between micro- and macro-level deformation.

Microscale and macroscale behavior

“This study shows that Effects of microscopic processes on macroscopic behavior“It’s a lot of fun,” says Meghna Ranganathan, study leader in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and now a postdoctoral fellow at the Georgia Institute of Technology. “These mechanisms occur at the level of water molecules and may ultimately affect the stability of the West Antarctic ice sheet.”

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“In general, glaciers are accelerating their growth, and there are a lot of variations on this,” adds Brent Minshew, co-author of the study and associate professor at EAPS. “This is the first study to take the step from the laboratory to the ice sheets and get started To evaluate the stability of ice in the natural environment. “This will ultimately contribute to our understanding of the potential for catastrophic sea level rise.”

Global warming and the accelerated melting of glaciers have led to a rapid rise in sea levels. the Loss of polar ice Although it contributes significantly to increasing water masses, it is also The greatest uncertainty in forecasts.

Two mechanisms make the ice flow

“Part of this is the problem of scaling,” Ranganathan explains. “Many of the basic mechanisms that lead to ice flow occur on a scale so small that we can’t see it. We wanted to know exactly Which microphysical processes control ice flow?Which is not taken into account in sea level rise models.

The team’s new study builds on previous experiments conducted by the University of Minnesota in the 2000s that examined… How small shards of ice deform when they are physically pressed and compressed. Two microscopic mechanisms by which ice begins to flow have been discovered: dislocation creep, in which particle-sized cracks move across the ice, and grain boundary sliding, in which individual ice crystals slide against each other, causing the boundaries between them to move across the ice. Ice.

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As a result, the sensitivity of ice to stress or its flow potential depends on which of the two mechanisms prevails. In particular, ice reacts More sensitive to stress when Microscopic defects are most likely due to dislocation creep Which results from the sliding of grain boundaries.

Glacier
Results at the microstructural level allow for more reliable predictions of glacier flow speed. Image: Pixabay

Ranganathan and Mincio realized this The results at the microscopic level help understand the flow of glaciers It can change over larger glacial scales.

“Current models of sea level rise assume a single value for the sensitivity of ice to pressure and keep this value constant across the entire ice sheet,” Ranganathan said. “These experiments have shown that In fact, ice sensitivity varies widely depending on which of these mechanisms is in operation“.

“If climate change causes glaciers to shrink, this could affect the sensitivity of ice to stress,” Ranganathan says. The future instabilities expected in Antarctica can now be better predicted using the new model.

source:

Ranganathan, Meghana, and Minchu, Brent (2024): The modified viscous flow law for natural glacial ice: extending from laboratories to ice sheets. Proceedings of the National Academy of Sciences, 121 (23). https://hdl.handle.net/1721.1/155148