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Greenland's ice sheet may be more vulnerable to melting than previously thought, say scientists. A new study has reassessed the shape of the great fjords down which glaciers drain to the ocean. It finds them to be far deeper and to stretch further back inland than was recognised in earlier research.
Dr Mathieu Morlighem told the Nature Geoscience journal that this could expose the glaciers to more prolonged erosion by warm seawaters. "We know that many of these Greenland glaciers are accelerating and that their fronts are retreating because of the action of warmer ocean waters," he said.
"And because we now know these canyons are far longer than we thought, it means the ice forms can retire much further back, before rising on to land where they won't be in contact with the ocean anymore."
The usual way to map the thickness of glaciers and the position of the underlying rockbed is to make surveys with airborne ice-penetrating radar. But acquiring such data sets is both expensive and difficult. Even in those locations where radar has been used, the rugged terrain under the ice can often give a very cluttered picture. And in places where melt water sits on top of the glacier, the radar pulse is simply deflected away from the ice body.
"Older models predicted that these glaciers would soon retreat on to higher ground and would stabilise, and so the contribution to sea-level rise from the Greenland ice sheet would be limited," said Dr Morlighem.
"But the problem is that these models were based on rockbed topography that was not accurate enough. With our new bed topography, we can expect the predictions for the Greenland ice sheet's contribution to sea-level rise to be changed."