Arctic boulders confirm that glaciers are thinning

February 29th, 2008 - 11:04 am ICT by admin  

London, Feb 29(IANS) Huge boulders could enable scientists to predict the contribution of the West Antarctic Ice Sheet (WAIS) to sea level rise, according to the latest issue of Geology. These boulders - deposited by three glaciers in the Amundsen Sea region - are currently being studied by scientists from the British Antarctic Survey (BAS), Durham University and Germany’s Alfred Wegener Institute.

And the conclusion is inescapable - these glaciers are thinning at a rate of 1.6 metres a year since 1990, whereas they were thinning at an average of two to four centimetres a year for some 15,000 years before that.

Currently the focus of intense international attention, the region is changing faster than anywhere else on the WAIS and has the potential to raise sea-level by 1.5 metres.

Analysis of the boulders has also enabled the scientists to start constructing a long-term picture of glacier behaviour in the region.

One task was to put recent ice sheet changes into a historical context, and determine if these are part of a natural retreat since the end of the last glacial period (about 20,000 years ago), or if they are a result of recent human-induced climate change.

Co-author Joanne Johnson of BAS said: “Until now we didn’t know much about the long-term history of this part of the WAIS because the region is incredibly remote and inaccessible.

“Our geological findings add a new piece to the jigsaw and will be used for improving computer models - the most important tools we have for predicting future change.”

Initial results show that Pine Island Glacier has thinned by around four centimetres per year over the past 5,000 years, while Smith and Pope Glaciers thinned by just over two centimetres per year during the past 14,500 years.

These rates are more than 20 times slower than recent changes: satellite, airborne and ground based observations made since the 1990s show that Pine Island Glacier has thinned by around 1.6 metres per year in recent years.

The scientists reached their conclusions by investigating how long the boulders have been exposed to cosmic radiation rather than being shielded by ice or sediment.

Co-author Mike Bentley from University of Durham said: “When rocks are left high and dry by thinning glaciers they are exposed to high energy cosmic rays which bombard the rock.

“This creates atoms of particular elements that we can extract and measure in the laboratory - the longer they have been exposed the greater the build-up of these elements.”

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