Tuesday, June 10, 2008

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Larsen Ice Shelf

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The ice along the Antarctic Peninsula has been observed to be disappearing in a series of retreats over the past 30 years. Climate in this area is warming at approximately 0.5 degrees Celsius per year following a trend that is believed to have been occurring for at least the past 50 years Generally this retreat has occurred as icebergs break away from the oceanward edge of the ice.

More recently a new pattern has been observed. Scientists have been closely monitoring the Larsen Ice Shelf since 1995 when a large portion of it (Larsen A) dramatically disintegrated. In 2002 another similar event occurred at Larsen B (see image series below). In contrast to the slower pattern of calving - where pieces of ice break away at the edge of the shelf – these two events occurred over a large area and in a relatively short period of time. In the case of Larsen B 3,250 square kilometers of the ice shelf shattered into a plume of 1000s of icebergs in a little over a month. Over the last 5 years approximately 40 per cent of Larsen B has disintegrated--5,700 square kilometers. Larsen A is believed to have been in place for over 2000 years at the time of its collapse and Larsen B is thought to have been still older.

Scientists have developed a theory to explain this new phenomenon of catastrophic collapse which links it to summertime warming and the pooling of melted water on the surface of the ice shelf. The pooling water is believed to accelerate the expansion of crevasses and lead to the breakdown of the ice shelves. In the case of Larsen B, ponds of melt water can be seen in the remote sensing images taken shortly before the collapse occurs, lending credence to this theory. Melt-water ponds can now be seen forming on Larsen C in more recent images suggesting the potential for a similar collapse there in the future.

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