Geophysicists from the United States and Sweden have discovered ice blocks as tall as city skyscrapers at the very bottom of the Greenland Ice Sheet. The discovery may help scientists understand more about how ice sheets behave and how they will respond to a warming climate.
Distribution of the newly discovered ice structures (black color) in northern Greenland. Image credit: Robin E. Bell et al.
While mapping the Gamburtsev Subglacial Mountains in Antarctica in 2008-09, Dr Robin Bell of Columbia University and her colleagues discovered melting and refreezing along ridges and steep valley walls of the range.
Though researchers had long known that pressure and friction can melt the bottom of ice sheets, no one knew that refreezing water could deform the layer-cake structure above.
In a 2011 study, the team proposed that ice sheets can grow from the bottom up, not just from the top-down accumulation of falling snow.
The new study, published in the journal Nature Geoscience, builds on the findings from Antarctica by linking the bottom features to faster ice sheet flow.
Dr Bell and her colleagues looked at Petermann Glacier in the north of Greenland. They discovered that the glacier is sweeping a dozen large features with it toward the coast as it funnels off the ice sheet. One feature sits where satellite data has shown part of the glacier racing twice as fast as nearby ice.
The scientists suggest that the refreeze process is influencing the glacier’s advance hundreds of miles from where Petermann floats onto the sea.
“We see more of these features where the ice sheet starts to go fast. We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow,” explained Dr Bell, who is the first author on the study.
The team estimates that the ice structures cover about 1/10 of northern Greenland, becoming bigger and more common as the ice sheet narrows into ice streams, or glaciers, headed for the sea.
As meltwater at the bottom refreezes over hundreds to thousands of years, the scientists believe it radiates heat into the surrounding ice sheet, making it pick up its pace as the ice becomes softer and flows more easily.
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Robin E. Bell et al. Deformation, warming and softening of Greenland’s ice by refreezing meltwater. Nature Geoscience, published online June 15, 2014; doi: 10.1038/ngeo2179
