Washington: Greenland ice sheet may be sliding faster into the ocean because of massive releases of meltwater from surface lakes, a new study suggests.
Such lake drainages may affect sea-level rise, with implications for coastal communities, according to researchers at the University of Colorado Boulder-based Cooperative Institute for Research in Environmental Sciences.
“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,” said CIRES research associate William Colgan, who co-led the new study with CU-Boulder computer science doctoral student Yu-Li Liang.
During 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,” explained Colgan.
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 years.
During a typical catastrophic lake drainage, about 1 million cubic meters of meltwater -- which is equivalent to the volume of about 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 that abuts underlying rock, 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 sub-glacial “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 said.
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 said.
Finding out which scenario is correct is a pressing question for climate models and for communities preparing for sea-level change, he said.
The study has been published online by the journal Remote Sensing of the Environment.
First Published: Tuesday, April 17, 2012, 12:45