The sudden and complete drainage of meltwater on top of the Greenland ice sheet has been observed by scientists for the first time giving them a clue to the acceleration of glaciers to the sea.
Researchers have found draining of surface meltwater can accelerate slow-moving glaciers by 50-100 percent. Photo: Flying over ice sheets. Credit: oliptang/Flickr
Each year thousands of lakes form on top of Greenland’s glaciers during the warmer months as sun and warmer air unite to melt surface ice. However the sudden drainage from the top to the bottom of the ice sheet through vast cracks in the ice has shown that the lakes can act as a lubricant for glaciers.
“We found clear evidence that supraglacial lakes—the pools of meltwater that form on the surface in summer—can actually drive a crack through the ice sheet in a process called hydrofracture,” said glaciologists Sarah Das, an assistant scientist in the Woods Hole Oceanographic Institution (WHOI) Department of Geology and Geophysics.
“If there is a crack or defect in the surface that is large enough, and a sufficient reservoir of water to keep that crack filled, it can create a conduit all the way down to the bed of the ice sheet,” she said.
However though playing an important role in ice dynamics, researchers found that the drainage of meltwater would be only a minor contributing factor to increased sea levels.
"...the new findings indicate that while surface melt plays a substantial role in ice sheet dynamics, it may not produce large instabilities leading to sea level rise," said the University of Washington's Ian Joughin. "There are still other mechanisms that are contributing to the current ice loss and likely will increase this loss as climate warms."
The two wrote that draining meltwater can increase the speed of ice flow in slow-moving regions of the ice sheet by 50-100 percent.
"It's hard to envision how a trickle or a pool of meltwater from the surface could cut through thick, cold ice all the way to the bed," wrote Das.
"For that reason, there has been a debate in the scientific community as to whether such processes could exist, even though some theoretical work has hypothesised this for decades."
Scientists were able to capture the draining of one ice sheet in 2006, "...that had once covered 5.6 square kilometres (2.2 square miles) of the surface and held 0.044 cubic kilometres (11.6 billion gallons) of water," according to the Woods Hole Oceanographic Institution.
"Like a draining bathtub, the entire lake emptied from the bottom in 24 hours, with the majority of the water flowing out in a 90-minute span. The maximum drainage rate was faster than the average flow rate over Niagara Falls," the scientists said in their report.
The research led by Das and Joughin is published in this week's Science Express journal with further publication of the papers in the May 9 edition of Science.
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