Richard Alley, a geoscientist at Pennsylvania State University in University Park, said that De Angelis and Skvarca's evidence for glacial surge is pretty good given the fact that a long-term record on the rate of flow of these glaciers does not exist. The Argentine scientists simply looked forand foundtelltale signs of glacial surge.
"Nature might have caused a surge naturally at about the time of an ice shelf breakup. But nature is highly unlikely to have caused a bunch of surges at almost the same time unless they are related to the ice shelf breakup," he said. "The authors found such features. So it appears that the ice shelf breakup and ice flow speedup did occur together."
Balance of Forces
De Angelis and Skvarca say their find is significant because it shows that at least for some glaciers, ice shelves do act as barriers that prevent them from spilling into the sea. This finding, they say, is directly linked to the debate over the stability of the West Antarctic Sheet and its sensitivity to ice shelf disintegration.
Ted Scambos, a research scientist at the National Snow and Ice Data Center in Boulder, Colorado, said that much of this debate centers on defining the balance of forces that prevent glaciers from spilling into the ocean. The braking ability of ice shelves is one force. Another is the bed upon which the glacier rests.
"Different characteristics of the bed have a big effect on how a glacier moves and how fast it would move if you remove the back-stress [such as an ice shelf]," he said. "People have also debated how much back-stress is within the glacier itself."
For example, if the glacier is frozen to its bed, the removal of an ice shelf would not have much of an effect on the glacier's velocity, said Alley. But if the glacier rests on a slippery bed of mud, the loss of an ice shelf sheet could cause a glacier to accelerate. There are also cases where the bed is already so slippery that that the glacier is essentially floating on the bed but held back because of other factors such as being frozen to side walls.
"Telling where the ice goes from having a non-slippery to slippery to too-slippery bed is not all that easy," said Allen. "We know a lot, are learning more, but a clear answer is not yet in hand."
SOURCES AND RELATED WEB SITES