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Polar Ice Melt Causes Global Shifts in Earth’s Crust, Harvard Grad Finds

Hoffman Laboratory houses the Department of Earth and Planetary Sciences.
Hoffman Laboratory houses the Department of Earth and Planetary Sciences. By Ryan N. Gajarawala
By Justin Lee, Crimson Staff Writer

As ice sheets melt in Greenland and the Antarctic, the water that is generated shifts the planet’s crust on a global scale, reveals a new theoretical model by a researcher who recently completed her Ph.D at Harvard.

Sophie L. Coulson, who received her doctorate in Earth and Planetary Sciences in May, and other researchers at the Los Alamos National Laboratory, where she is now a fellow, published their findings in the peer-reviewed journal Geophysical Research Letters last month.

As a result of climate change, the global melting rate has starkly increased over the past two decades. Motion in the planet’s crust as a result of such meltage has been previously observed on a regional scale, directly beneath ice masses.

By analyzing satellite data from 2003 to 2018 to measure the crust’s shift, Coulson and her group predicted that the impact occurs at the global level.

“People have spent a lot of time focusing on the area directly around and beneath the ice sheet so it’s been known for a long time that beneath Antarctica and beneath Greenland, you have these significant 3D motions,” Coulson said in an interview. “I don’t think people were necessarily aware that these things are occurring thousands of kilometers away from the centers of ice melt.”

Melting ice causes multiple processes that generate the complex 3D motion at Earth’s surface, Coulson said.

First, the water from the ice sheet is moved into the global ocean, increasing the sea level. Meltage also reduces the mass of the ice and the load on the crust below the ice sheet, causing it to rebound, which shifts the surrounding crust, she explained.

Finally, there is a gravitational effect. As the ice sheet loses mass, the gravitational attraction that pulls water toward it is reduced, leading to a “counterintuitive” decrease in sea level near the ice sheet that has just melted.

Coulson said that this research has implications for GPS measurements, which are used widely to monitor things such as large scale tectonic activity, earthquakes, and volcanoes.

“People had already been doing a correction for this ice sheet loading process nearby, but in places like the continental U.S., they didn’t necessarily realize that they needed to be correcting for that signal,” Coulson said. “We need to look back at those previous studies that use these GPS measurements and make sure we have a correction in there.”

For Coulson and her research group at Los Alamos, the next steps are to empirically confirm the theoretical model’s predictions.

“We want to look at the data and say, ‘Okay, so we’ve predicted these signals, can we actually find them in this data that we’re analyzing?’” Coulson said.

—Staff writer Justin Lee can be reached at justin.lee@thecrimson.com.

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