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| Earth on Sep 05, 2012

Massive methane gas stores could sit beneath Antarctica

If Antarctica’s ice sheets continue to thin as the climate warms, stores of the potent greenhouse gas could be released to the atmosphere, researchers say.

There could be a similar amount of methane stored beneath Antarctica’s vast ice sheets as there is trapped in the Arctic permafrost, researchers have discovered.

Photo credit: Anne Froehlich

If the white continent’s ice sheets continue to thin as the climate warms, stores of the potent greenhouse gas could be released to the atmosphere. This would lead to faster rises in temperature causing even more methane to be released, in a situation scientists call positive feedback.

The fact that the poles are the fastest-warming regions of the planet could make the problem even worse.

So far, researchers have focussed their attention on the fate of methane reserves trapped in the northern hemisphere in places like the Arctic permafrost. But recent research has revealed that beneath its ice sheets, Antarctica harbours micro-organisms and carbon left over from ancient marine sediments and other biomes that existed on the continent before the ice sheet grew 30 million years ago.

Not just that, but the low-oxygen conditions likely beneath the Antarctic ice sheets means it could well be home to micro-organisms that generate methane.

Professor Jemma Wadham from the University of Bristol is lead author of the study, published in Nature on August 30. He said:

People didn’t think there was life beneath Antarctica until around the 1990s. But over the last 10 years, researchers have discovered that there are microbes and organic carbon. And it’s remote from the atmosphere, so it’s a perfect place for methane-generating microbes to live.

Photo credit: SF Brit

In this latest study, Wadham together with UK, US and Canadian colleagues, set about testing the idea that methane could be produced beneath Antarctica’s ice sheets.

Their experiments revealed that such sub-ice environments are almost certainly biologically active. This means this organic carbon may have been metabolised by oxygen-deprived microbes, turning it into carbon dioxide and methane over tens of millions of years.

They calculate that 50 per cent of the West Antarctic Ice Sheet (WAIS) and 25 per cent of the East Antarctic Ice Sheet (EAIS) sits on top of ancient sedimentary basins, which contains an estimated 21,000 billion tonnes of carbon. The ice sheet formed on top of these deep layers of organic carbon. Wadham said:

This is an immense amount of organic carbon, more than ten times the size of carbon stocks in northern permafrost regions.

The researchers add that the carbon is buried in sediments several kilometres underneath the ice sheet.

Their experiment also revealed that there could be methane hydrates – an ice-like mixture of water and methane – just a few hundred metres below both ice sheets. Methane hydrate is stable at low temperatures and high pressure, but their relatively shallow depth in the Antarctic makes them more susceptible to changes in temperature resulting from climate change than other methane reserves in places like the Arctic or Siberia. Wadham said:

There’s a lot of uncertainty about how much methane hydrate is there and where it’s located. We’d like to do some detailed modelling at specific sites in Antarctica to get a better idea about where these methane stores are. It would also be good to get sample from shallow sub-ice sheet sediments to analyse them for methane. The 10-year plan would be to drill deeper in to sedimentary basins, but the technology to do this just isn’t there right now.