What is it about?
Picture a grotto: a low cave containing a lake of still water. In certain parts of Southeast Greenland, liquid water sits inside the glacier, similar to a 0° grotto. These glacial aquifers exist in the top hundred feet of the glacier, where summertime meltwater is trapped by huge wintertime snow drifts. Directly downhill of one such aquifer, we found a number of wide crevasses. This suggests that the aquifer water flows, invisibly under the snow, into these crevasses. Using a new, physically based fracture-mechanics model that predicts the shape and size of water-filled crevasses, we found that the water fractures the crevasses all the way to the bottom of the ice sheet, half a mile below. Thus, the crevasses give the aquifer water an easy path (under the ice sheet) to the global ocean. Without the aquifer and crevasses, this water would not reach the ocean.
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Why is it important?
Most ice-sheet / climate models generally assume that meltwater runs off into the global ocean, raising sea levels. We did not know whether this was true of meltwater in the glacier aquifer -- does it reach the sea via the ice-sheet bed, or does it refreeze within the ice sheet? We have now shown that meltwater in our study area *does* reach the ocean and contribute to global sea level, although there is a delay of some months to years as it travels through the aquifer - crevasse system.
Perspectives
I had developed a model for the fracture of crevasses over long time periods, but for a different project. At a conference, I learned that a separate research team, who specializes in the glacier aquifer, suspected that the water drained into crevasses, but could not tell whether the water reached the bottom of the ice sheet and, consequently from there, the global ocean. It was straightforward to adapt my model to answer this important question.
Kristin Poinar
NASA Goddard Space Flight Center
Read the Original
This page is a summary of: Drainage of Southeast Greenland Firn Aquifer Water through Crevasses to the Bed, Frontiers in Earth Science, February 2017, Frontiers,
DOI: 10.3389/feart.2017.00005.
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