Oct 11, 2016

Greenland is melting from above and below — and scientists say they’re connected

Chris Mooney
Washington Post

There were no scientists around circa 11,000 years ago, when the great Laurentide Ice Sheet, which once covered much of present day North America, began to collapse in numerous stages and eventually dwindled into a collection of much smaller ice caps across Alaska and Canada, raising seas by tens of feet. So no one could observe all of the processes that, as the Northern Hemisphere warmed, led to its undoing.

Today, though, scientists studying the ice sheet covering Greenland — which survived when the Laurentide Ice Sheet didn’t — are watching something that may be highly analogous. And this time, they’re taking measurements.

As a result, what is coming into focus is that there appears to be a crucial interaction between ice melting on an ice sheet’s surface, forming into pools and lakes, and ice falling directly into the ocean where glaciers, extending out from the ice sheet’s center, terminate in often extremely deep waters. But precisely how they work together — and how much they could speed Greenland’s melt — is only beginning to reveal itself.

Two recent studies in Geophysical Research Letters each home in on different aspects of this linkage. And they do so by studying two apparently connected phenomena: The formation of sometimes vast lakes of meltwater on the ice sheet’s surface, and the release of huge “plumes” of meltwater beneath outlet glaciers that themselves are mostly submerged in the ocean.

One of the most remarkable features of Greenland’s melting — and this is probably true of all ice sheets — is the formation of what scientists term "supraglacial lakes"  on its surface. In Greenland, these lakes can be very large — with an area of 2 square miles in one case — and can also suddenly disappear, draining down into the depths of the ice sheet below.

That’s very bad, because researchers suspect that this drainage has what they often refer to as a lubricating effect on the bottom of the ice sheet, helping it slide toward the sea. But Greenland’s future should include many more of these kinds of lakes, say Ádám Ignéczi of the University of Sheffield in the United Kingdom and a group of colleagues at British and Belgian universities in one of the studies.