Glacial Meltwater Pooling At Base Of Greenland Ice Sheet, "Slushifying" It En Route To Ocean
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It was thought that the water quickly flowed between ice and rock and out to sea, with little impact on the bottom ice layers. But a new study suggests the story isn’t so simple. In a serendipitous discovery, a team of scientists has found a lake at the bottom of the ice where the relatively warm meltwater pools and makes the ice around it slushier. Ultimately, that could make the ice flow faster to the ocean.
The finding, detailed in the Jan. 22 issue of the journal Nature, suggests that this process could be important to more accurately modeling how Greenland will respond to climate change and contribute to the already 8 inches of global sea level rise since 1900. Greenland holds enough ice to raise global sea levels by 24 feet, and how much and how quickly it melts could change projections of future sea level rise, which the Intergovernmental Panel on Climate Change puts between 10 and 32 inches by 2100, including contributions from Greenland’s glaciers.
As happens so often in science, Mike Willis wasn’t actually looking for what he ended up discovering. The glaciologist was combing through satellite and GPS data to see what small, local effects could be clouding satellite measurements of larger changes in Earth’s gravity from ice loss. What he did not expect to find was a hole twice the size of Central Park in a small ice cap in the northern reaches of Greenland. “What the heck is that?” he thought when he saw it. He didn’t think he could possibly be the first person to have spotted it. “Surely someone’s noticed a gigantic hole in northern Greenland before,” he said, but there were no records of it.
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What Willis’s discovery suggests is that the meltwater that flows down from the ice sheet’s surface doesn’t have just a fleeting encounter with the base of the ice. Instead, “it pauses on its rush to the ocean,” Bell said, in the subglacial lake. Because that meltwater has been warmed by the sun’s rays and the comparatively warm atmosphere, it is far warmer than the basal ice. The pause means the meltwater has time to transfer heat to the ice, making it “gooier,” in Bell’s words, and gooier ice is “going to flow faster in the long term,” Willis said. Other recent findings of Bell’s — that refreezing meltwater can warp the bottom of the ice sheet — combine with the new study to show “there’s a richer range of processes that can happen at the bottom of the ice sheet than we thought,” Bell said. So scientists have further to go to understand everything that’s influencing the ice sheet’s flow.
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http://www.climatecentral.org/news/surprise-lake-sheds-light-on-underbelly-of-greenland-ice-18580
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