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Lakes on the Greenland Ice Sheet are draining in the winter

For the first time, researchers have confirmed that lakes on the Greenland Ice Sheet drain enormous amounts of water, even during the wintertime. The new study from the University of Cambridge raises new concerns about how fast the ice sheet is flowing into the ocean. 

The investigation was focused on radar data from a European Space Agency satellite. The experts found that even without heat from the Sun, lakes on the Greenland Ice Sheet often discharge large amounts of water to the base of the ice sheet. 

The “drainage events” are thought to play a significant role in accelerating the movement of the ice by lubricating it from below.

“Glaciers slow down in the winter, but they’re still moving,” said study co-author Dr. Ian Willis. “It must be this movement that causes fractures to develop in certain places allowing some lakes to drain.” 

“We don’t yet know how widespread this winter lake drainage phenomenon is, but it could have important implications for the Greenland Ice Sheet, as well as elsewhere in the Arctic and Antarctic.”

The experts developed a new approach to detect changes in the lakes during the winter, when Greenland is in near-total darkness. This method uses the radar “backscatter,” which is the reflection of waves back to the satellite from where they were emitted.

The study revealed that even in the depths of the Arctic winter, large amounts of surface lake water periodically cascade to the base of the ice sheet.

“One of the unknowns in terms of predicting the future of the ice sheet is how fast the glaciers move – whether they will speed up and if so, by how much,” said Dr. Willis.

“The key control on how fast the glaciers move is the amount of meltwater getting to the bottom of the ice sheet, which is where our work comes in.”

Lakes form on the Greenland Ice each summer. While the lakes can persist for weeks or even months, they can also drain in a matter of hours due to hydrofracturing. 

The draining lakes transfer millions of cubic meters of water and heat to the base of the ice sheet. According to the experts, affected areas include sensitive regions of the ice sheet interior where the impact on ice flow is potentially large.

“It’s always been thought that these lakes drained only in the summer, simply because it’s warmer and the sun causes the ice to melt,” said study co-author Corinne Benedek. 

“In the winter, it’s dark and the surfaces freeze. We thought that the filling of the lakes is what caused their eventual drainage, but it turns out that isn’t always the case.”

The researchers analyzed data from the Sentinel-1 satellite, which uses a type of radar called synthetic aperture radar (SAR). Over three winters, the team identified six lakes which appeared to drain over the winter months.

“The first lake I found was surprising,” said Benedek. “It took me a while to be sure that what I thought I was seeing was really what I was seeing.” 

“We used surface elevation data from before and after the events to confirm what we were thinking. We know now that drainage of lakes during the winter is something that can happen, but we don’t yet know how often it happens.”

The study is published in the journal The Cryosphere.

By Chrissy Sexton, Staff Writer

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