A new view of Greenland’s melting glaciers

NASA researchers have helped produce the first map showing what parts of the bottom of the massive Greenland Ice Sheet are thawed — key information in better predicting how the ice sheet will react to a warming climate.

Greenland’s thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than the top, because the ice bottom is slowly warmed by heat coming from Earth’s depths. Knowing whether Greenland’s ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future, But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Now, a new study synthesizes several methods to infer the Greenland Ice Sheet’s basal thermal state — whether the bottom of the ice is melted or not — leading to the first map that identifies frozen and thawed areas across the whole ice sheet.

“We’re ultimately interested in understanding how the ice sheet flows and how it will behave in the future,” said Joe MacGregor, lead author of the study and a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “If the ice at its bottom is at the melting-point temperature, or thawed, then there could be enough liquid water there for the ice to flow faster and affect how quickly it responds to climate change.”

From their analysis, MacGregor and his colleagues determined that the bed is likely thawed under Greenland’s southwestern and northeastern ice drainages, while it’s frozen in the interior and west of the ice sheet’s central ice divide. For a third of the Greenland ice sheet, there’s not enough data available to determine its basal thermal state.

MacGregor said the team’s map is just one step in fully assessing the thermal state of the bottom of Greenland’s ice sheet.

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