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Lakes on the Greenland ice sheet can drain a lot of water even in winter



Lakes on the Greenland ice sheet can drain a lot of water even in winter

Every summer, as the weather warms, lakes are formed on the surface of the Greenland ice sheet. They exist for weeks or months, but may be lost within hours due to hydraulic fracturing, transferring millions of cubic meters of water and heat to the bottom of the ice sheet. Now, researchers at the University of Cambridge have used satellites to “see in the dark”

; and show that these lakes may also be lost in winter. Credit: Ian Willis

For the first time, researchers used satellite data to “look in the dark”, which shows that lakes on the Greenland ice sheet will be lost in winter. This discovery has an impact on the speed of the world’s second largest ice sheet flowing to the ocean.

Researchers from the University of Cambridge used radar data from the European Space Agency satellite to show that even in the absence of heat from the sun, these lakes can release large amounts of water to the bottom of the ice sheet. These “drainage events” are believed to play an important role in accelerating the movement of ice by lubricating the ice from below.

In summer, through the combination of direct field observation and optical satellite data that requires sunlight, previous studies on drainage lakes have been conducted in summer.

The method developed by the Cambridge researchers uses radar “backscattering” (the reflection of waves from the launch site back to the satellite) to detect changes in the lake in Greenland that is almost completely dark in winter.

The results are reported in the magazine CryosphereThis means that the “piping system” under the Greenland ice sheet will not only slowly leak the water from last summer, but even in the depths of the Arctic winter, due to the large amount of surface lake water cascades, it can be “recharged” to the ice sheet. bottom

Many previous studies have shown that the Greenland Ice Sheet is losing quality due to melting and runoff, and the rate of loss is accelerating.

Dr. Ian Willis, a co-author of the Scott Polar Institute at Cambridge University, said: “One of the unknown factors in predicting the future of ice sheets is how fast the glacier moves? (SPRI). “The key control over the speed of glacier movement is The amount of melt water that reaches the bottom of the ice sheet is what we do. “

Every summer, as the weather warms, lakes are formed on the surface of the Greenland ice sheet. They exist for weeks or months, but may be lost within hours due to hydraulic fracturing, transferring millions of cubic meters of water and heat to the bottom of the ice sheet. The affected area includes sensitive areas inside the ice sheet, where the impact on ice flow may be significant.

Corinne Benedek, a co-author from SPRI, said: “It has always been thought that these lakes drain water only in summer, only because it warms and the sun causes the ice to melt.” In winter, it is very dark and the surface is frozen. We believe that the filling of the lake is the cause of the final drainage of the lake, but this is not always the case.”

Benedek, currently a doctorate. She is a graduate student of SPRI. She is a master student. When studying satellite thermal data, she was first interested in what happened to the surface lake in winter.

She said: “Thermal data shows that liquid water can survive in lakes throughout the winter.” “Previous research using airborne radar also found that lakes are buried a few meters below the surface of the ice sheet in summer and summer. All this makes me Begin to think about the way to observe lakes throughout the year. We usually use optical satellite images to observe that there are no lakes in winter or even on cloudy days.”

Benedek and Willis developed a method of using Sentinel-1 satellite data using a type of radar called synthetic aperture radar (SAR). The wavelength of SAR allows observation through clouds and in the dark. Ice and water use SAR readings differently, so they developed an algorithm that can track when a sudden change in SAR backscatter occurs.

In the three winters, they identified six lakes, which have been draining during the winter months. These lakes are frozen underground lakes or surface lakes. The algorithm was able to identify significant changes in the backscattering characteristics of the lake between one image and the next image recorded 12 days later.

The SAR data was backed up along with other optical data from the previous autumn and the following spring, which confirmed that the lake area of ​​the six drainage lakes was greatly reduced. For these three lakes, optical data and data from other satellites were used to show that the lake covered with ice and snow had collapsed several meters, again confirming that the water had been drained.

Benedek said: “The first lake I found was surprising.” “It took me a while to be sure that what I saw was what I got. We used ground elevation data before and after the event to confirm our thoughts. Now. We know that winter is a possibility, but we don’t yet know how often it happens.”

Willis said: “Glaciers slow down in winter, but they are still moving.” “This movement must have caused cracks in some places to drain some lakes. We don’t know this kind of winter lake drainage How widespread is the phenomenon, but it may have important implications for both the Greenland ice sheet and icebergs. In other parts of the Arctic and Antarctica.”


Researchers have discovered more than 50 lakes under the Greenland ice sheet


More information:
Rosamond J. Tutton et al., a low-cost method for monitoring the snowfall characteristics of remote field sites, Cryosphere (2021). DOI: 10.5194/tc-15-1-2021

Provided by Cambridge University



Citation: Even in winter (2021, March 31) in the winter retrieved from https://phys.org/news/2021-03-lakes-greenland-ice-sheet-huge on April 1, 2021, Greenland Lakes on ice sheets may also discharge large amounts of water. .html

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