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Monday, November 3, 2008

Ice Under Fire: Antarctica

The disintegrating face of the Müller Ice Shelf, Lallemand Fjord, Antarctic Peninsula, 67° South, April 2, 1999. This small shelf, fed by glaciers from the Loubet Coast, has been receding recently after growing over a 400-year cooling period. Like other receding ice shelves such as the larger Larsen, it may be a sensitive monitor of rising regional temperatures. The Larsen Ice Shelf lost a 1200 square mile section early in 2002. Earlier in the 1990's other huge sections of this shelf disintegrated. In 2003 Argentine glaciologists reported that the land-based glaciers exposed by the removal of those sections had surged rapidly into the ocean. Thus, although ice shelves are floating and do not add to sea level when they melt or break up, land based glaciers released by such events definitely will add to sea level.

Another view of the Müller Ice Shelf calving rapidly (right). Across the Peninsula, seven monitored ice shelves have declined by a total of about 13,500 km2 since 1974, according to the National Snow and Ice Data Center. This is nearly the area of Connectcut. On the Larsen shelf (satellite view left), about 3,250 km2 of shelf in area B disintegrated in a 35-day period beginning on 31 January 2002. Eugene Domack, Hamilton College geologist, and others believe this portion of the shelf may have been stable for about 12,000 years before this year's collapse.

Technicians for the National Science Foundation on the rear deck of the research vessel, Nathaniel B. Palmer, prepare a kasten core device to lower into sediment near the Müller Ice Shelf. This is during a study by Dr. Eugene Domack, funded by the National Science Foundation, on the history of climate in peninsular Antarctica. All ice shelves in the area have been receding, but because they were already floating they do not raise sea level. The concern is that landed glaciers behind the shelves may be next to begin rapid retreat, which would raise ocean levels.

This mile-long ice cliff of Marr Ice Piedmont, Anvers Island, has receded about 500 meters since the mid 1960s. The cliff's previous position was to the left of the line of ice floating in the harbor and extended to the headland at the extreme upper left. The regional temperature has increased 5° C in winter over the past 50 years. This reduces seasonal icepack, disrupts growth of krill and changes conditions on penguin rookeries.

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