Antarctic Ice Sheet may be more stable than thought
15 March 2011, by Tamera Jones
A detailed study has revealed that the giant West Antarctic Ice Sheet may have remained intact for at least 200,000 years, even though there was a particularly warm period – called an interglacial – about 125,000 years ago.
Whether or not a warmer climate will melt the ice sheet and raise sea levels by several metres is one of the most hotly contested debates in climate science.
During the interglacial, global temperatures were around 2° Celsius warmer than today. Evidence from higher than expected tropical coral reefs and deep sea cores suggest sea levels were anything from four to six metres higher during this warm period than they are today.
'Some models of that past climate suggest sea levels were much higher during that time than they are now, and some of that water would have to have come from this giant freshwater body of ice – suggesting the ice sheet is vulnerable to melting at warmer global temperatures,' says Dr Chris Fogwill, from the University of Exeter, lead author of the study.
'The water had to come from somewhere and the Greenland and West Antarctic Ice Sheets are the most likely candidates,' echoes Professor David Sugden from the University of Edinburgh, co-author of the latest study published in Palaeogeography, Palaeoclimatology, Palaeoecology.
Ice sheet may be more resilient
But the study by Fogwill, Sugden and colleagues from the universities of Edinburgh and Durham suggests the West Antarctic Ice Sheet may be more resilient to warmer temperatures that they thought. While the ice sheet may have fluctuated in thickness over the last 200,000 years, it doesn't seem to have melted completely.
The researchers studied rocks carried and left behind by the ice sheet thousands of years ago, called moraines, in the Heritage Mountain Range in West Antarctica.
Chris Fogwill about to sample rock deposited when ice in the Heritage Range was thicker than today.
They used a technique called cosmogenic dating which relies on cosmic radiation left over from the Big Bang, when scientists think the universe started. When cosmic rays hit some elements, they generate new isotopes, or new forms of the same chemical element. So when rocks in moraines are exposed to these rays, the isotopes build up – this is what Sugden, Fogwill and their colleagues measured.
Earlier cosmogenic isotope studies have shown 'a real mix of ages for the rocks in the moraines,' says Sugden. 'The theory put forward was that maybe these rocks had been exposed, picked up by the ice and then re-deposited.'
But by measuring the ratio of two different cosmogenic nuclides, Aluminium-26 and Beryllium-10, the researchers found that the rocks hadn't been reburied at all.
Their results led them to hypothesize that the ice sheet's central dome has remained intact for at least 200,000 years, and possibly for as long as 400,000.
Despite the obvious implications of this finding – that the West Antarctic Ice Sheet might not be as sensitive to climate change as scientists thought – Sugden is keen to point out that it is just a theory that needs a lot of further testing.
'We need to understand the exact process that builds blue-ice moraines and we'd really like to get more specific data to test our theory,' he adds. 'Working in Antarctica is challenging and expensive, but you have to go back to the same places to build up a solid story.'
Christopher J. Fogwill, Andrew S. Hein, Michael J. Bentley and David E. Sugden, Do blue-ice moraines in the Heritage Range show the West Antarctic ice sheet survived the last interglacial?, Palaeogeography, Palaeoclimatology, Palaeoecology, published online 4 February 2011, doi:10.1016/j.palaeo.2011.01.027
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