According to foreign media reports, researchers have used satellite data "observations in the dark" to prove for the first time that lakes on the Greenland ice sheet will dry up in winter. Speed is of great significance. Researchers from University of Cambridge used radar data from ESA satellites to conclude that even without the heat of the sun, these lakes would discharge large amounts of water to the bottom of the ice sheet.
These "drainage events" are believed to have played an important role in accelerating the movement of ice.
Previous studies on lake drainage were carried out in summer. Researchers conducted their work through direct field observation and combined with optical satellite data, but all this requires daylight.
The method developed by researchers at the University of Cambridge uses radar "backscattering"-waves reflected from the launch site to the satellite-to detect changes in the lake during the winter months when Greenland is almost completely dark .
Many previous studies have shown that the quality of the Greenland ice sheet is declining and the rate of decline is accelerating due to melting and runoff .
Dr. Ian Willis from the Scott Polar Research Institute (SPRI) of the University of Cambridge is one of the co-authors of the study. He pointed out: "In predicting the future of ice sheets, an unknown factor is the speed at which glaciers move - whether they Will accelerate, if so, how fast. The key to controlling the speed of glaciers is the amount of melt water reaching the bottom of the ice sheet, and this is the starting point for our work."
Every summer, as the weather warms, Greenland Lakes will form on the surface of ice sheets. They can exist for weeks or months, but due to hydraulic fracturing, they can drain in a few hours and transfer millions of cubic meters of water and heat to the bottom of the ice sheet. The affected areas include sensitive areas inside the ice sheet, where the impact on ice flow may be significant.
"People have always thought that these lakes only dry up in summer for a simple reason.Because the weather is warm, the sun will cause the ice to melt," said Corinne Benedek, one of the authors of the paper, also from Spree. "In winter, it is very dark and the surface freezes. We believe that the siltation of lakes is the cause of their final drainage, but this is not always the case... Thermal data tells me that liquid water can exist in lakes throughout the winter. Previous research using airborne radar also found lakes buried a few meters below the surface of the ice sheet in summer. These two things made me think about how to observe the lake throughout the year. The optical satellite images that we usually use to observe lakes are not available in winter, even when it is cloudy.
For this reason, Benedek and Willis developed a method using data from the Sentinel-1 satellite, which uses a radar called synthetic aperture radar ( SAR ). The effective wavelength of synthetic aperture radar allows people to Penetrate clouds in the dark. Because ice and water have different readings when using SAR, they developed an algorithm that can track sudden changes in SAR backscattering.
In the past three winters, research The personnel found six lakes that seemed to dry up in winter. These lakes were underground lakes or surface lakes covered by ice. The algorithm was able to identify the backscatter characteristics of the lake in one image and the next recorded 12 days later. Places where significant changes have occurred between the images.
Additional optical data from the fall of the previous year and the following spring supported the SAR data, which confirmed that the lake area of these six dried-up lakes was greatly reduced. For three of them, optical The data and other satellite data were used to show that the ice-covered lake collapsed and it dropped a few meters, which once again confirmed that the lake has dried up.
"The first lake I found was surprising," Benedek said. "I spent a lot of money." It took a while to make sure that I thought what I saw was really what I saw. We used the surface elevation data before and after the event to confirm our ideas. We now know that lake drainage may occur in winter, but we don’t yet know how often this happens.
Willis pointed out: "Glaciers will slow down in winter, but they are still moving. This movement must have caused cracks in some places and caused some lakes to dry up.Although we don't know how common lake drainage is this winter, it may have an important impact on the Greenland ice sheet, Arctic and other parts of Antarctica. ”
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