New map reveals state of Greenland ice sheet

A new map has provided the key to predicting how the Greenland ice sheet is faring. Created in collaboration with researchers at NASA, the map is the first to show which parts are thawed.

Greenland’s thick ice sheet insulates the bedrock from the cold temperatures at the surface. The bottom of the ice is often tens of degrees warmer than the top, because it is slowly warmed by heat from Earth’s depths.

Knowing what type of ground this ice lies on is essential for predicting how it will flow in the future. Now, a new study has aggregated different methods of determining the ground type to assess the Greenland ice sheet’s basal thermal state. It will show whether the bottom of the ice is melted or not.

“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.

He explained that if the ice at the bottom is at the melting-point temperature, or thawed, there could be enough liquid water for the ice to flow faster and affect how quickly it responds to climate change.

For this study, the research team combined four different approaches. First, they examined results from eight recent computer models of the ice sheet, which predict bottom temperatures.

They then studied the layers that compose the ice sheet itself; looked at where the ice surface speed measured by satellites exceeded its “speed limit”, or the maximum velocity at which the ice could flow but remain frozen to the rock beneath it; and studied imagery from the Moderate Resolution Imaging Spectroradiometers on the NASA Terra and Aqua satellites, looking for rugged surface terrain that usually indicates ice sliding over a thawed bed.

“Each of these methods has strengths and weaknesses. Considering just one isn’t enough. By combining them, we produced the first large-scale assessment of Greenland’s basal thermal state,” MacGregor said.

The team’s results determined that the bed is likely thawed under Greenland’s southwestern and northeastern ice drainages, but frozen in the interior and west of the ice sheet’s central ice divide. For a third of the ice sheet, there was not enough data available to determine its basal thermal state.

MacGregor described the research map as an “essential effort” but “just one step in fully assessing the thermal state of the bottom of Greenland’s ice sheet.”

Photo credit: NASA’s Earth Observatory/ CC BY 2.0

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