Largest Arctic ice shelf breaks up, draining freshwater lake
"Warwick Vincent and Derek Mueller of Laval University in Quebec City, Quebec, and Martin Jeffries of the University of Alaska Fairbanks have studied the Ward Hunt Ice Shelf on site and through RADARSAT imagery and helicopter overflights. They report in the journal Geophysical Research Letters that a three decade long decline in the Ward Hunt Ice Shelf culminated in its sudden break-up between 2000 and 2002. It fragmented into two main parts with many additional fissures. It also calved a number of ice islands, some of which are large enough to pose a danger to shipping and to drilling platforms in the Beaufort Sea.
An immediate consequence of the ice shelf's rupture was the loss of almost all of the freshwater from the northern hemisphere's largest epishelf lake, which had been dammed behind it in 30 kilometer [20 mile] long Disraeli Fiord. An epishelf lake is a body of mostly freshwater trapped behind an ice shelf. The freshwater layer in the Disraeli Fiord measured 43 meters [140 feet] in depth and lay atop 360 meters [1,200 feet] of denser ocean water. The loss of fresh and brackish water has affected a previously reported unique biological community, consisting of both freshwater and marine species of plankton. The breakup of the ice shelf has also reduced the habitat available for cold-tolerant communities of microscopic animals and algae that live on the upper ice surface."
Mueller, Vincent, and Jeffries attribute the disintegration of the Ellesmere Ice Shelf and the breakup of the Ward Hunt Ice Shelf to the cumulative effects of long-term warming since the 19th century. The precise timing and pattern of fracturing of the climate-weakened ice shelf may have been influenced by freeze-thaw cycles, wind, and tides, they say. Other factors may include changes in Arctic Ocean temperature, salinity, and flow patterns, they add.
Though the process has been going on since the 1800s recent data collection indicates that it may be accelerating in the region. Other regions have different histories and as noted above water temperature, salinity, currents, winds and tides are all part of this complex system, but the suspicion that there are human influences on this process lingers.
posted by back40 |
9/22/2003 01:27:00 PM
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