April 17, 2012
Greenland Slipping Away
Massive releases of meltwater from surface lakes may be causing Greenland to slide ever faster into the ocean, according to a new study by the University of Colorado Boulder-based Cooperative Institute for Research in Environmental Sciences (CIRES).
Researchers say these actions could increase sea-level rise, having a direct impact on 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 new study with Yu-Li Liang, a CU-Boulder computer science doctoral student.
According to a press release on the matter, meltwater pools and gathers into lakes on the ice sheet´s surface during the summer months, building pressure beneath the surface. When this pressure gets high enough, the ice will fracture beneath the lake, causing what the CU researchers call a vertical drainpipe, which in turn will cause “a huge burst of water” to quickly pulse to the bed of the ice sheet.
Using satellite images and new software used to recognize features in the ice, the team monitored almost 1,000 lakes on an ice sheet the size of Connecticut. For more than 10 years the team studied these lake and discovered “catastrophic” lake drainages as the weather becomes warmer. In fact, the drainages were 3.5% more likely to occur in the warmest months than when it was at its coldest.
The amount of water being drained beneath these sheets of ice is enormous. According to the CU-Boulder team, a typical catastrophic lake drainage can dump about 1 million cubic meters of meltwater-roughly the amount of water to fill 4,000 Olympic sized swimming pools-underneath the ice sheet within a day or two. There, the meltwater can cause the ice sheets to slide around like snow on a hot tin roof. This could cause the sheet to slide into the ocean, thus accelerating the sea-level rise associated with climate change.
There may not be all bad news, however. The massive water drainages could also carve out pathways or “sewers” beneath the glaciers, effectively routing the water back to the ocean without lubricating the ice sheets.
“This would drain the ice sheet´s water, making less water available for ice-sheet sliding,” Colgan said.
Since the scenario could go either way, Colgan says it´s now important to understand how the ice will work under different models and to prepare the surrounding communities for sea-level change.
To conduct their study, the researchers developed new software capable of spotting these supraglacial lakes in satellite images, determining their size and where they appear. “Previously, much of this had to be double-checked manually,” Colgan said. “Now we feed the images into the code, and the program can recognize whether a feature is a lake or not, with high confidence and no manual intervention.”
The software could be useful in future studies as other teams attempt to measure lake drainages and sea-level rise.
Image Caption: A surface or "supraglacial" lake on the Greenland Ice Sheet. (Photo by Konrad Steffen)