Wednesday, April 18, 2012

Is the Greenland Ice Sheet flushing itself away?

Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado-Boulder: Like snow sliding off a roof on a sunny day, the Greenland Ice Sheet may be sliding faster into the ocean due to massive releases of meltwater from surface lakes, according to a new study from the Cooperative Institute for Research in Environmental Sciences (CIRES) and the University of Colorado Boulder (CU). Such lake drainages may affect sea-level rise, with implications for coastal communities.

“This is the first evidence that Greenland’s supraglacial lakes have responded to recent increases in surface meltwater production by draining more frequently, as opposed to growing in size,” says CIRES research associate William Colgan, who co-led the study with CU’s Yu-Li Liang. The results were published online April 15 in Remote Sensing of Environment and will appear in the journal’s August issue.

During the summer, meltwater pools into lakes on the ice sheet’s surface. When the water pressure gets high enough, the ice fractures beneath the lake, forming a vertical drainpipe, and “a huge burst of water quickly pulses through to the bed of the ice sheet,” Colgan says.

The researchers used satellite images, along with innovative feature-recognition software, to monitor nearly 1,000 lakes on a Connecticut-sized portion of the ice sheet over a 10-year period. They discovered that as the climate warms, such catastrophic lake drainages are increasing in frequency. Catastrophic lake drainages were 3.5 times more likely to occur during the warmest years than the coldest.

During a typical catastrophic lake drainage, about 107 m3 of meltwater—equivalent to 4,000 Olympic swimming pools—funnels to the ice sheet’s underside within a day or two. Once the water reaches the ice sheet’s belly, it may turn the ice-bed surface into a Slip ‘n Slide, lubricating the ice sheet’s glide into the ocean. This would accelerate the sea-level rise associated with climate change.

Alternatively, however, the lake drainages may carve out subglacial “sewers” to efficiently route water to the ocean. “This would drain the ice sheet’s water, making less water available for ice-sheet sliding,” Colgan says. That would slow the ice sheet’s migration into the ocean and decelerate sea-level rise.

“Lake drainages are a wild card in terms of whether they enhance or decrease the ice sheet’s slide,” Colgan says. Finding out which scenario is correct is a pressing question for climate models and for communities preparing for sea-level change, he added...

Aerial view of Gothab, Glacial Ice flow, Greenland, shot by Susan M. Ottalini, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

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