Wednesday :: Apr 23, 2008

Toward Collapse


by Turkana

Nature:

Joanne Johnson's first chance to explore the fastest-melting glaciers of the West Antarctic Ice Sheet came unexpectedly, nearly two years ahead of schedule. But it was also overdue.

Satellite data and ground-based measurements had raised alarms that fast-flowing glaciers near Pine Island Bay could disintegrate completely, raising global sea levels by a metre. Yet Johnson, whose work has now validated concerns that the glaciers there are melting rapidly, was the first to set foot on the region's rocky bluffs in four decades....

The crucial clues were beryllium-10 and certain other isotopes, formed in the granite when boulder-bearing glacial currents shrank back from mountaintops and left the rocks high and dry — and exposed to cosmic rays from space. As the isotopes accumulate over time in ice-free rock, they provide a measure of when — and how quickly — the glaciers thinned. Lacking that historic perspective, scientists couldn't be sure that the melting seen today is much different from the ice sheets' past behaviour....

The recently published analyses (Geology 36, 223–226; 2008) show that the glaciers have been thinning for at least 14.5 thousand years at approximately 2.3–3.8 centimetres per year, on average. Contrasted with the 1.6-metre-per-year deglaciation detected by satellite from 1992 to 1996, Johnson's results support fears that global warming is pushing the glaciers toward collapse. The sparse initial measurements will be filled in by forthcoming data, including some from Johnson's colleagues, who have just returned to find the sea ice much tamer.

Turkana :: 8:11 PM :: Comments (13) :: Digg It!