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Phoenix666 writes:

Surface meltwater that drains to the bed of the Greenland Ice Sheet each summer causes changes in ice flow that cannot be fully explained by prevailing theories. Now a multinational, multidisciplinary team led by ice sheet modelers at Los Alamos National Laboratory is exploring how changes in extensive, sediment-choked subglacial "swamps" actually explain why the ice sheet's movement slows down in late summer and winter.

"The drainage system beneath the Greenland Ice Sheet controls how fast the ice flows towards the sea and ultimately contributes to sea-level change," said Matthew Hoffman, lead author on the project and an ice-sheet modeler at Los Alamos. "For more than a decade it's been known that the ice flow more than doubles in speed in many regions during summer, as surface melt drains to the bed and lubricates the motion. This acceleration sends ice to the sea faster. However, the motion also slows down in late summer, fall, and winter, which largely offsets the summer speedup. Exactly why it slows down as much as it does and for as long as it does has not been clear."

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