A major glacial formation in Antarctica is shrinking, a report in Science reveals today -- but questions still remain about the speed at which ice sheet thinning is taking place.
Scientists at University College London (UCL) and the British Antarctic Survey have used satellite data to show that the interior of the West Antarctic Ice Sheet (WAIS) is thinning inland.
Since 1992, 31 cubic kilometers of ice has been lost from its interior. The loss can be pinpointed to the fast-flowing Pine Island Glacier -- the largest glacier in West Antarctica -- which transports ice from the deep interior of the ice sheet to the ocean.
Occupying what many visitors to Antarctica consider to be one of its remotest spots -- visits by man can be numbered by the handful -- the Pine Island Glacier is up to 2500 meters thick with a bedrock over 1500 meters below sea level.
The glacier, scientists now say, has retreated by over 5 kilometers inland as a consequence of the thinning. This adds further weight to the argument that small changes at the coast of the Antarctic continent -- such as the effects of global warming -- may be transmitted rapidly inland, leading to an acceleration of sea level rise.
Using high precision radar measurements from the ERS satellite altimeter -- accurate to within 20 centimeters -- the height of the WAIS has been mapped at regular intervals since 1992.
The data revealed a clear pattern of ice thinning within a 5000 square kilometer section of the Pine Island Glacier drainage basin during the past 8 years.
A map of glacial velocity, much of which was previously uncharted, was constructed using ERS SAR interferometry in order to clarify which regions within the vast section were actually thinning.
The combination of these two datasets -- derived from separate instruments on board the same satellite -- showed that the ice has thinned to as much as 10 meters and was restricted to the fastest flowing sections of the glacier.
Professor Duncan Wingham at University College London insists that the success of the research lies in the performance of the ERS satellite radar:
"The extreme precision which satellite measurements can now make of the Earth's surface allows us to see the internal changes in the Antarctic Ice Sheet for the very fist time."
The scientific team believes that their results point unambiguously to thinning in this part of the Antarctic Ice Sheet and are associated with the flow of ice from the interior.
If the present rate of thinning continues, the team believes that the Pine Island Glacier will be lost to the ocean within a few hundred years. Dr. Andrew Shepherd of UCL said:
"For the past 25 years there has been speculation about whether a retreat of a West Antarctic glacier could acclerate ice flow from its interior, producing a rise in sea level. We have shown for the first time that such a retreat is indeed occurring.
"It is of paramount importance to determine whether the thinning is accelerating. Our present theoretical understanding is not sufficient to firmly predict the future evolution of the Pine Island Glacier."
(Reference: Inland Thinning of Pine Island Glacier, West Antarctica; A. Shepherd, D.J. Wingham, J.A.D. Mansley, H.F.J. Corr, Science, February 2nd, 2001.)
Images of Pine Island Glacier, from /Science