The air might not be warm enough to melt snow on top of glaciers, but warm ocean currents are thawing the underbellies of floating ice sheets in Antarctica say NASA and BAS researchers.
Using a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves, researchers from NASA and the British Antarctic Survey (BAS) concluded that 20 of the 54 ice sheets are melted by warm ocean currents.
Most reside in West Antarctica where inland glaciers flowing down to the coast and feeding into these ice shelves have accelerated. This ocean-driven thinning is responsible for the most widespread and rapid ice losses.
“We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt,” said Hamish Pritchard, lead author from the BAS. “The oceans can do all the work from below.”
NASA’s ICESat – Ice, Cloud and land Elevation Satellite – mapped the changing thickness of most floating ice shelves in Antarctica using a laser instrument. It took 4.5 million surface height measurements between October 2003 and October 2008. Researchers measured how the ice shelf height changed over time, running computer models to discard changes due to natural snow accumulation and compaction, and tidal variables.
“This study demonstrates the power of space-based laser altimetry for understanding Earth processes,” said Tom Wagner, cryosphere program scientists from NASA. “Coupled with NASA’s portfolio of other ice sheet research, we get a comprehensive view of ice sheet change that improves estimates of sea level rise.”
The research published in Nature also links the observed increase in melting that occurs on the underbelly of a glacier or ice shelf – known as basal melt – with changes in wind pattern.
“Studies have shown Antarctic winds have changed because of changes in climate,” Pritchard said. “This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”
ICESat operated between 2003 and 2009 and was the first satellite specifically designed to use laser altimetry to study the Polar Regions. It will be replaced by ICESat-2, which is scheduled for launch in 2016.