West Antarctic Ice Sheet Changed Rapidly in Response to Climate Warming in the Past
20.03.2009 - Logistics, Water & Oceans, Land & Geology, Ice & Snow, Other, Antarctic
New studies from the five-nation ANDRILL (ANtarctic geologicalDRILLing) project, which have been published in the 19 March edition ofNature, show that a slight rise in atmospheric concentrations of carbondioxide may affect the stability of the West Antarctic Ice Sheet (WAIS).
The first of the two studies is based on investigations conducted on a 1,280-metre long sedimentary rock core taken from beneath the sea floor under the Ross Ice Shelf during the first ANDRILL research programme, the McMurdo Ice Shelf (MIS) Project. The information obtained from the core suggests that changes in the Earth's rotational axis have played a major role in ocean warming, which has driven repeated cycles of growth and retreat of the WAIS during the Pliocene Era, between 2 and 5 million years ago. This suggests ocean temperatures have played a major role in the expanse and retreat of the WAIS.
The sedimentary record shows that under global warming conditions similar to those projected to occur over the next 100 years, ice shelves, which protect the ice sheet, could shrink and disappear, making them more vulnerable to melting. "If the current warm period persists, the ice sheet could diminish substantially or even disappear over time," said Ross Powell, professor of geology at Northern Illinois University. "This would result in a significant sire in sea levels."
According to Tim Naish, director of Victoria University of Wellington's Antarctic Research Centre. "It also appears that when atmospheric carbon dioxide concentrations reached 400 parts per million around four million years ago, the associated global warming amplified the effect of the Earth's axial tilt on the stability of the ice sheet." Current atmospheric concentrations of carbon dioxide are approaching 400 ppm.
A second study within the ANDRILL programme, led by David Pollard of Pennsylvania State University and Rob DeConto of the University of Massachusetts, reports results of computer models of the ice sheets, which show that each time the WAIS collapsed, some of the margins of the East Antarctic Ice Sheet also melted. The combined effect was a global sea level rise of 7 meters above present-day levels.
