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An inside look at Greenland's melting surface ice
Aug 06, 2012 | by Jack Williams | The Washington Post
Greenland’s big mid-July “melt” gave a few polar scientists a chance to study a rare warming event as it was happening. Previously they’d seen such warming only as small sections of ice cores pulled up from 165 feet below the 656,000-square-miles ice sheet that covers roughly 85% of Greenland.
“I have been studying melt layers (seen in ice cores) for the past year” says Kaitlin Keegan, a PhD degree student in polar science at Dartmouth. “I have lots of ideas about (ice sheet) melt” she says. “You couldn’t hope for anything better than to be studying melt in Greenland at the time when it’s happening.”
When temperature rose above 32 degrees each day from July 11 through 14 at the National Science Foundation’s Summit, Greenland, Observatory, polar scientists realized they were seeing a kind of warming that had last occurred in 1889...
...Keegan began studying the 1889 melt last year when she saw a one-centimeter (0.39 inch) part of an ice core that “is mostly transparent like an ice cube.” The core above and below this area is much less dense firn.
“When comparing this layer to the brightness and darkness of other firn layers, it is definitely more bright,” Keegan says. “You can imagine that light can transmit fairly straight through an ice cube but not a snow cone or shaved ice. Also, in the firn you can easily see different grains whereas [in] the ice layer you cannot [just like you cannot see the grains in an ice cube]. It’s definitely the appearance that attracted me to studying the layer. It’s just so very different than the rest of the core.”
After seeing the layer of clear ice, talking about it with other scientists and reviewing the scientific literature, she “realized that what happened in 1889 was a widespread melt event. The study of this melt event, and other smaller, local melt events, will be one chapter of my PhD thesis.”
Until this July, Keegan and other scientists studying the 1889 melt and similar events in the past were confined to what they could tease out from small cross sections of ice cores. “This makes it hard to understand how the melt layer formed and how evenly distributed it is,” Keegan says.
“The most interesting part of being at Summit Station just after the melting is that the melt layer formation could be observed,” she says. “This presents a unique opportunity for us to understand how previous melt events occurred.”
Mary Albert, one of Keegan’s two PhD advisors, who is also executive director of the U.S. Ice Drilling Program Office, says: “One real coincidence with the current melt is the timing relative to a paper Kaitlin and I have been working on.
“We are finishing a paper—telling the interesting story of the 1889 layer―we started on that before we went to Summit,” Albert says. “The melt that then occurred at Summit is pure serendipity with our investigation of the 1889 event. Our investigation of the 1889 ice layer centers on ‘why’―there are lots of warm spells when the snow does not melt at Summit—why did it melt then? Summit is right on the edge and we’re in the process of explaining in this paper what happened.”
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