A paper on the subject by Scambos and Jennifer Bohlander of the University of Colorado-headquartered National Snow and Ice Data Center, Mark Fahnestock of the University of Maryland and Christine Hulbe of NASA's Goddard Space Flight Center in Greenbelt, Md., appeared in the January issue of the Journal of Glaciology. The shelf retreats that have occurred so far have had few consequences for sea-level rise, but breakups in some other areas like the Ross Ice Shelf could lead to increases in ice flow off the Antarctic and cause sea level to rise. Floating ice shelves, which account for about 2 percent of Antarctic ice, typically undergo cycles of advance and retreat over many decades. While scientists have known that meltwater fills crevasses and enlarges the cracks, this is the first study to explain the physics linking ice-shelf viability and meltwater ponds. The extra outward pressure of the water counteracts the internal pressure holding the ice together, according to the scientists' conclusions.
Crevasses routinely form on the landward side of the shelf.
Satellite observations of melted water on the ice surfaces provide important clues to the water pressure theory, said Fannestock. After analyzing images of the Larsen Ice Shelf over the past two decades, he deduced the years with the longest duration of surface meltwater corresponded to the years of major shelf breakup events. The melt season during the 1995 Larsen Ice Sheet retreat was more than 80 days long - about 20 days longer than average. The researchers believe the splintered remains are likely held together by bridges between crevasses until a combination of winds, tides and another season of melting lead to a breakup. The process can be expected to be more widespread if Antarctic summer temperatures continue to increase.