Greenland Ice Sheet's Meltwater Channels Reveal More Complicated Picture

Things are more complicated in Greenland than we once thought. Scientists that are drilling and measuring the melt rates and ice sheet movement in Greenland have found that channels beneath the ice could make simplistic models inaccurate.

"Although the Greenland Ice Sheet initially speeds up each summer in its slow-motion race to the sea, the network of meltwater channels beneath the sheet is not necessarily forming the slushy racetrack that had been previously considered," said Matthew Hoffman, one of the scientists involved in the project, in a news release.

The researchers studied moulins, which are vertical conduits connecting water on top of the glacier down to the bed of the ice sheet, and boreholes. They found that subglacial channels ameliorate the speedup caused by water delivery to the base to the base of the ice sheet in the short term. However, by midsummer, the channels stabilize and are unable to grow any larger.

"Everyone wants to know what's happening under Greenland as it experiences more and more melt," said Ginny Catania, co-author of the new study. "The subglacial plumbing may or may not be critical for sea level rise in the next 100 years, but we don't really know until we fully understand it."

The Greenland's Ice Sheet's movement speeds up each summer and surface melt penetrates the ice through moulins and lubricates the bottom of the ice sheet. Yet direct observations of the subglacial drainage system are lacking. That's why scientists examined the bottom of the ice sheeth through boreholes. In the end, they found that Moulin water pressure does not lower over the latter half of the melt season. This revealed that there was a limited role of high-efficiency channels in subglacial drainage.

The findings reveal a previously unrecognized role of changes in hydraulically isolated regions of the bed in controlling evolution of subglacial drainage over the summer. This, in turn, can tell researchers a bit more about the rate of melt on the ice sheet.

The findings are published in the journal Nature.