Irvine, Calif., May 19, 2014 ‚ÄĒ Greenland‚Äôs icy reaches are far more vulnerable to warm ocean waters from climate change than had been thought, according to new research by UC Irvine and NASA glaciologists. The work, published today in Nature Geoscience, shows previously uncharted deep valleys stretching for dozens of miles under the Greenland Ice Sheet.
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.
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‚Äôs frozen mass would stop shrinking, and its effect on higher sea waters would be curtailed.
‚ÄúThat turns out to be incorrect. The glaciers of Greenland are likely to retreat faster and farther inland than anticipated ‚Äď and for much longer ‚Äď according to this very different topography we‚Äôve discovered beneath the ice,‚ÄĚ said lead author Mathieu Morlighem, a UC Irvine associate project scientist. ‚ÄúThis has major implications, because the glacier melt will contribute much more to rising seas around the globe.‚ÄĚ
To obtain the results, Morlighem developed a breakthrough method that for the first time offers a comprehensive view of Greenland‚Äôs entire periphery. It‚Äôs nearly impossible to accurately survey at ground level the subcontinent‚Äôs 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‚Äôs 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 ‚Äúmass conservation algorithm‚ÄĚ 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 dramatic. 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.
‚ÄúWe anticipate that these results will have a profound and transforming impact on computer models of ice sheet evolution in Greenland in a warming climate,‚ÄĚ the researchers conclude.
‚ÄúOperation IceBridge vastly improved our knowledge of bed topography beneath the Greenland Ice Sheet,‚ÄĚ said co-author Eric Rignot of UC Irvine and NASA‚Äôs Jet Propulsion Laboratory. ‚ÄúThis new study takes a quantum leap at filling the remaining, critical data gaps on the map.‚ÄĚ
Other co-authors are Jeremie Mouginot of UC Irvine and Helene Seroussi and Eric Larour of JPL. Funding was provided by NASA.
The team also reported stark new findings last week on accelerated glacial melt in West Antarctica. Together, the papers ‚Äúsuggest that the globe‚Äôs ice sheets will contribute far more to sea level rise than current projections show,‚ÄĚ Rignot said.
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