Lakes on the Greenland Ice Sheet can drain massive quantities of water even in winter – Watts Up With That?
CAMBRIDGE UNIVERSITY
Research news
PICTURE: SEA FORM ON THE SURFACE OF THE GRASSLAND ICE SHEET EVERY SUMMER WHILE THE WEATHER WARMS. THEY EXIST FOR WEEKS OR MONTHS, BUT CAN EXPIRE IN HOURS… show more CREDIT: IAN WILLIS
Using satellite data to see in the dark, researchers have shown for the first time that lakes on the Greenland Ice Sheet drain in winter. This has an impact on the speed at which the world’s second largest ice sheet flows into the ocean.
Cambridge University researchers used radar data from a European Space Agency satellite to show that these lakes can deliver large amounts of water to the base of the ice sheet even without solar heat. It is believed that these “drainage events” play an important role in accelerating the movement of the ice by lubricating it from below.
Previous studies of lake drainage were all conducted in the summer months through a combination of direct field observations and optical satellite data, which require daylight.
The approach developed by Cambridge researchers uses radar backscatter – the reflection of waves back towards the satellite from which they were emitted – to capture changes in the lakes during the winter months, when Greenland is nearly dark.
The results, published in The Cryosphere, suggest that the “plumbing” system beneath the Greenland ice sheet not only slowly drains water from the previous summer, but can also be “charged” in the depths of the arctic winter . , as large amounts of surface sea water cascade to the base of the ice sheet.
Many previous studies have shown that the Greenland ice sheet is losing mass and the rate of loss is accelerating due to melting and runoff.
“One of the unknowns in predicting the future of the ice sheet is how fast the glaciers are moving – whether they are accelerating, and if so, by how much,” said co-author Dr. Ian Willis from the Scott Polar Research Institute in Cambridge (SPRI). “The most important control over how fast the glaciers are moving is the amount of meltwater that gets to the bottom of the ice sheet. This is where our work comes in.”
In warmer weather, lakes form on the surface of the Greenland ice sheet every summer. They exist for weeks or months, but due to hydraulic fracturing, they can drain away in a few hours and transfer millions of cubic meters of water and heat to the base of the ice cover. Areas affected include sensitive areas of the interior of the ice sheet where the effects on ice flow can be large.
“It has always been assumed that these lakes are only drained in summer simply because it’s warmer and the sun is melting the ice,” said co-author Corinne Benedek, also from SPRI. “In winter it is dark and the surfaces freeze. We thought that the filling of the lakes was the cause of their eventual drainage, but it turns out that this is not always the case. “
Benedek, who is currently a PhD student at SPRI, first became interested in what happens to surface lakes in winter when she was studying satellite thermal data as a master’s student.
“The thermal data showed me that liquid water can survive in the lakes all winter,” she said. “Earlier studies with aerial radar had also identified lakes that were buried a few meters below the surface of the ice sheet in summer. Both of these made me think about ways to observe lakes all year round. The optical satellite images that we normally use to observe the lakes are not available in winter or even when it is cloudy. “
Benedek and Willis developed a method using data from the Sentinel-1 satellite that uses a type of radar called synthetic aperture radar (SAR). SAR works at a wavelength that allows you to see through clouds and in the dark. Ice and water read differently with SAR and developed an algorithm that tracks when sudden changes in SAR backscatter occur.
In three winters, they identified six lakes that appeared to drain during the winter months. These lakes were buried lakes or surface lakes that were frozen over. The algorithm was able to identify where the backscattering properties of the lake changed significantly between one image and the next, which was taken 12 days later.
The SAR data was backed up with additional optical data from the previous autumn and the following spring, which confirmed that the lake areas for the six drained lakes shrank significantly. For three of the lakes, the optical data, as well as data from other satellites, were used to show that the snow- and ice-covered lakes had collapsed and dropped several meters to reconfirm that the water had drained.
“The first lake I found was surprising,” said Benedek. “It took me a while to make sure that what I thought I was seeing was really what I was seeing. We used surface height data before and after the events to confirm what we were thinking. We now know that lake drainage can happen in winter, but we don’t yet know how often it happens. “
“Glaciers slow down in winter, but they’re still moving,” said Willis. “It has to be this movement that causes fractures to develop in certain places that allow 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. “
###
Like this:
Loading…
Comments are closed.