The bases of ice sheets are in contact with solid bedrock. Natural heat emanating from this bedrock slowly thaws out the icy base, which is insulated from the cold atmosphere by the thick ice on top of it. If the bases become too lubricated, the ice on top will flow faster – and, more often than not, end up in the sea, where it will directly contribute to rising sea levels.
Measuring the thermal state of the underlying sides to ice sheets is actually incredibly difficult. Less than two dozen boreholes have permitted researchers to make direct measurements, so for this study, more indirect techniques were required.
All in all, eight computer simulations, ground-penetrating radar surveys, measurements of the ice surface movement speed, and detailed satellite imagery of the surface terrain were taken into account. The end result was a painstakingly detailed subglacial map – the first of its kind. Although there’s a lot more work to be done to improve its resolution, this represents an important first step.
“I call this the piñata, because it's a first assessment that is bound to get beat up by other groups as techniques improve or new data are introduced,” MacGregor added. “But that still makes our effort essential, because prior to our study, we had little to pick on.”
A recent CryoSat analysis revealed that between 2011 and 2014, the Greenland Ice Sheet lost one trillion tonnes (1.1 trillion tons) of ice. This contributed to a degree of sea level rise that was twice the average of that observed during the preceding two decades. Faster flowing ice at its peripheries will only exacerbate this problem further.
The Greenland Ice Sheet flowing into a valley. NASA/María José Viñas