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Variability of the West Antarctic Ice Sheet Over the Past 5 Million Years
A warming of ocean temperatures by five degrees Celsius could prompt the collapse of the West Antarctic ice sheet (WAIS), according to models published in Nature this week. The models show that such a catastrophic collapse has occurred several times in the recent past over geologically short timescales.
Scientists are concerned that the WAIS is currently unstable – any small change in temperature could lead to rapid disintegration and eventual collapse. Projections of any future break-ups are limited by a lack of understanding of past variations and their underlying forcing mechanisms. Isotopic records from deep sea sediment cores have given an indication of prior collapses during the warm early Pliocene (3-5 million years ago), but until now models have not been able to simulate such changes.
David Pollard and Robert DeConto use a combined ice sheet and ice shelf model in order to simulate Antarctic ice sheet variations over the past five million years so they could track the ‘grounding line’ – the junction between grounded ice sheet resting on bedrock, and floating ice shelves that are sustained by flow from the ice sheet. The results show that during this time, the WAIS transitioned between full, intermediate and collapsed states in only a few thousand years.
In a related paper, Tim Naish and colleagues analyse an ocean sediment core beneath the marine-based Ross Ice Shelf to investigate the relationship between orbital cycles and the pattern of collapse of the WAIS. They found evidence that the WAIS periodically collapsed during the early Pliocene, a time when atmospheric carbon dioxide was similar to, or slightly higher than, present day levels. The pattern of collapse suggests an influence of 40,000-year cycles in the tilt of Earth’s rotational axis.
Embargoed until:
18-Mar-2009 14:00 US Eastern time | 18:00 London time
19-Mar-2009 03:00 Japanese time | 05:00 Australian Eastern time
March 23rd, 2009 at 7:18 am
How long? I thought it was going to happen next week.
I guess Al Gore has been visiting Antarctica lately.