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Thinning, retreat of West Antarctic Glacier began in 1940s

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https://www.sciencedaily.com/releases/2016/11/161123140243.htm

New research by an international team shows that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s.

…The team concluded the date at which the grounding line retreated from a prominent seafloor ridge was in 1945 at the latest. The team also found that final ungrounding of the ice shelf from the ridge occurred in 1970.

Our results suggest that, even when climate forcing (such as El Niños, which create warmer water) weakened, ice-sheet retreat continued,” said James Smith of the British Antarctic Survey and lead author of an article appearing in the Nov. 23 issue of the journal, Nature.

The West Antarctic Ice Sheet is one of the largest potential sources of water that will contribute to rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line — which marks the boundary between grounded ice and floating ice shelf — is under way….

….The appearance of plutonium in the sediment marks the onset of above-ground testing of nuclear weapons in the 1950s, and indicates that ice-sheet retreat began before this time…..”Despite a return to pre-1940s climatic conditions in the ensuing decades, thinning and glacier retreat has not stopped and is unlikely to be reversible without a major change in marine or glaciological conditions,” Smith said. “A period of warming in the Antarctic shelf waters triggered a substantial change in the ice sheet, via the mechanism that we see today — that is, ocean-driven thinning and retreat of ice shelves leads to inland glacier acceleration and ice-sheet thinning.”

J. A. Smith,  et al. Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier. Nature, 2016; DOI: 10.1038/nature20136

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