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Lakes on Greenland Ice Sheet can drain huge amounts of water, even in winter

UNIVERSITY OF CAMBRIDGE

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IMAGE
IMAGE: LAKES FORM ON THE SURFACE OF THE GREENLAND ICE SHEET EACH SUMMER AS THE WEATHER WARMS. THEY EXIST FOR WEEKS OR MONTHS BUT CAN DRAIN IN A MATTER OF HOURS… view extra CREDIT: IAN WILLIS

Using satellite tv for pc information to ‘see in the dark’, researchers have proven for the primary time that lakes on the Greenland Ice Sheet drain throughout winter, a discovering with implications for the pace at which the world’s second-largest ice sheet flows to the ocean.

The researchers, from the University of Cambridge, used radar information from a European Space Agency satellite tv for pc to indicate that even when the warmth from the Sun is absent, these lakes can discharge massive amounts of water to the bottom of the ice sheet. These ‘drainage events’ are thought to play a major position in accelerating the motion of the ice by lubricating it from beneath.

Previous research of draining lakes have all been carried out throughout the summer time months, by way of a mix of direct discipline observations and optical satellite tv for pc information, which requires daylight.

The strategy developed by the Cambridge researchers makes use of the radar ‘backscatter’ – the reflection of waves again to the satellite tv for pc from the place they have been emitted – to detect adjustments in the lakes throughout the winter months, when Greenland is in near-total darkness.

The outcomes, reported in the journal The Cryosphere, suggest that the ‘plumbing’ system beneath the Greenland Ice Sheet doesn’t simply slowly leak water from the earlier summer time, however even in the depths of the Arctic winter, it can be ‘recharged’, as massive amounts of floor lake water cascade to the bottom of the ice sheet.

Many earlier research have proven that the Greenland Ice Sheet is dropping mass, and the speed of loss is accelerating, as a consequence of melting and runoff.

“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,” stated co-author Dr Ian Willis from Cambridge’s Scott Polar Research Institute (SPRI). “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 kind on the floor of the Greenland ice sheet every summer time because the climate warms. They exist for weeks or months however can drain in a matter of hours as a consequence of hydrofracturing, transferring tens of millions of cubic metres of water and warmth to the bottom of the ice sheet. The affected areas embody delicate areas of the ice sheet inside the place the influence on ice circulate is doubtlessly massive.

“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,” stated co-author Corinne Benedek, additionally from SPRI. “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.”

Benedek, who’s at present a PhD candidate at SPRI, first took an interest in what occurs to floor lakes in the winter whereas she was a Master’s scholar learning satellite tv for pc thermal information.

“The thermal data showed me that liquid water can survive in the lakes throughout the winter,” she stated. “Previous studies using airborne radar had also identified lakes buried a few metres beneath the surface of the ice sheet in the summer. Both of these things got me thinking about ways to observe lakes all year long. The optical satellite imagery we normally use to observe the lakes isn’t available in winter, or even when it’s cloudy.”

Benedek and Willis developed a technique utilizing information from the Sentinel-1 satellite tv for pc, which makes use of a kind of radar known as artificial aperture radar (SAR). SAR capabilities at a wavelength that makes it potential to see by way of clouds and in the darkish. Ice and water learn otherwise utilizing SAR, and they also developed an algorithm that tracks when sudden adjustments in SAR backscatter happen.

Over three winters, they recognized six lakes which appeared to drain over the winter months. These lakes have been buried lakes or floor lakes that have been frozen over. The algorithm was in a position to determine the place the backscatter traits of the lake modified markedly between one picture and the following one recorded 12 days later.

The SAR information was backed up with further optical information from the earlier autumn and subsequent spring, which confirmed that lakes areas shrank significantly for the six drained lakes. For three of the lakes, the optical information in addition to information from different satellites was used to indicate the snow- and ice-covered lakes collapsed, dropping by a number of metres, once more confirming the water had drained.

“The first lake I found was surprising,” stated 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.”

“Glaciers slow down in the winter, but they’re still moving,” stated 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.”

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