Staggering sums of methane could be trapped under Antarctic ice. Antarctic methane stores could be equivalent to, or as much as ten times greater than, Arctic methane stores, which are known triggers of accelerated global warming. Before the climate cooled 35 million years ago, large amounts of organic matter were produced by abundant plant growth and accumulated in Antarctic basins now covered with ice. Low oxygen conditions under the ice have been favorable for biological processes to convert organic matter into methane and for the ice to trap it. As the Antarctic ice cap flows into the sea, if the climate warms enough, a fraction of the stored methane would be released to the atmosphere. Because methane is a more potent greenhouse gas than CO2 and because the atmospheric processes that convert methane to CO2 could be overwhelmed by the sudden release of large amounts of methane, this could be a catastrophic event.
No one has drilled the ice covered sediments to determine the amounts of gas, but
laboratory and model studies have shown that it could have been produced by bacterial degradation of organic matter and trapped as methane ice (clathrates).
Large sedimentary basins containing marine sequences up to 14 kilometres thick2 and an estimated 21,000 petagrams (1 Pg equals 1015 g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model3 and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica.
The potential amount of methane under the ice is staggering. If just 10% of the calculated amount present would escape to the atmosphere a rapid acceleration in climate warming would occur.
Half the West Antarctic ice sheet and a quarter of the East Antarctic sheet lie on pre-glacial sedimentary basins containing around 21,000bn tonnes of carbon, said the scientists, writing in the journal Nature.
British co-author Prof Jemma Wadham, from the University of Bristol, said: "This is an immense amount of organic carbon, more than 10 times the size of carbon stocks in northern permafrost regions.
"Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolised into carbon dioxide and methane gas by microbes."