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Climate: Study redefines Greenland Ice Sheet topography, finds greater risk of fast melting

How fast will the Greenland Ice Sheet melt? Map courtesy Change in Elevation over Greenland ICESat's precise elevation change measurements, combined with information from other technologies, are producing a comprehensive look at the behavior of Earth’s ice sheets -- critical for quantifying forecasts of sea level rise. Scientists used ICESat data to show changes in elevation over the Greenland ice sheet between 2003 and 2006. White regions indicate a slight thickening, while the blue shades indicate a thinning of the ice sheet. Gray indicates areas where no change in elevation was measured.  Credit: NASA Goddard's Scientific Visualization Studio

How fast will the Greenland Ice Sheet melt?
Credit: NASA Goddard’s Scientific Visualization Studio.

STAFF REPORT

FRISCO — New data on Greenland’s rugged shoreline topography doesn’t bode well for coastal cities around the world. A series of deep canyons stretching for miles under the Greenland Ice Sheet will enable warming ocean water to flow beneath the ice, accelerating melting and sea level rise, according to a new study published in the journal Nature Geoscience.

The bedrock canyons sit well below sea level, meaning that as subtropical Atlantic waters hit the fronts of hundreds of glaciers, those edges will erode much further than had been assumed and release far greater amounts of water, the study found.

“We anticipate that these results will have a profound and transforming impact on computer models of ice sheet evolution in Greenland in a warming climate,” the researchers from the University of California, Irvine and NASA concluded.

“Operation IceBridge vastly improved our knowledge of bed topography beneath the Greenland Ice Sheet,” said co-author Eric Rignot of UC Irvine and NASA’s Jet Propulsion Laboratory. “This new study takes a quantum leap at filling the remaining, critical data gaps on the map.”

Ice melt from the subcontinent has already accelerated as warmer marine currents have migrated north, but older models predicted that once higher ground was reached in a few years, the ocean-induced melting would halt. Greenland’s frozen mass would stop shrinking, and its effect on higher sea waters would be curtailed.

“That turns out to be incorrect. The glaciers of Greenland are likely to retreat faster and farther inland than anticipated – and for much longer – according to this very different topography we’ve discovered beneath the ice,” said lead author Mathieu Morlighem, a UCI associate project scientist. “This has major implications, because the glacier melt will contribute much more to rising seas around the globe.”

To obtain the results, Morlighem developed a breakthrough method that for the first time offers a comprehensive view of Greenland’s entire periphery. It’s nearly impossible to accurately survey at ground level the subcontinent’s rugged, rocky subsurface, which descends as much as 3 miles beneath the thick ice cap.

Since the 1970s, limited ice thickness data has been collected via radar pinging of the boundary between the ice and the bedrock. Along the coastline, though, rough surface ice and pockets of water cluttered the radar sounding, so large swaths of the bed remained invisible.

Measurements of Greenland’s topography have tripled since 2009, thanks to NASA Operation IceBridge flights. But Morlighem quickly realized that while that data provided a fuller picture than had the earlier radar readings, there were still major gaps between the flight lines.

To reveal the full subterranean landscape, he designed a novel “mass conservation algorithm” that combined the previous ice thickness measurements with information on the velocity and direction of its movement and estimates of snowfall and surface melt.

The difference was spectacular. What appeared to be shallow glaciers at the very edges of Greenland are actually long, deep fingers stretching more than 100 kilometers (almost 65 miles) inland.

 

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