Sub-ice environments are biologically active and converting organic material to methane
By Summit Voice
SUMMIT COUNTY — Climate researchers have long warned that stores of organic material in the Arctic will release vast amounts of heat-trapping methane as the atmosphere warms.
Now, a new study shows that Antarctica is another potentially huge source of methane. As much as 50 percent of the West Antarctic ice sheet may be covering old organic matter in sedimentary basins — and that organic matter may have been converted to methane by micro-organisms living under oxygen-deprived conditions.
The methane could be released to the atmosphere if the ice sheet shrinks and exposes these old sedimentary basins, the study concludes.
“This is an immense amount of organic carbon, more than ten times the size of carbon stocks in northern permafrost regions,” said team leader professor Jemma Wadham, from the University of Bristol’s School of Geographical Sciences. “Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolized to carbon dioxide and methane gas by microbes.”
Through modeling, the scientists determined that conditions under the ice favor the accumulation of frozen methane, trapped with the structure of water molecules, where it could easily be released in a warmer climate regime.
The total amount of methane (frozen and free methane gas) could be as much 400 billion tons, a similar order of magnitude to some estimates made for Arctic permafrost. The predicted shallow depth of these potential reserves also makes them more susceptible to climate forcing than other methane hydrate reserves on Earth.
“It’s not surprising that you might expect to find significant amounts of methane hydrate trapped beneath the ice sheet. Just like in sub-seafloor sediments, it is cold and pressures are high which are important conditions for methane hydrate formation,” said Dr. Sandra Arndt, a NERC fellow at the University of Bristol.
If substantial methane hydrate and gas are present beneath the Antarctic Ice Sheet, methane release during episodes of ice-sheet collapse could act as a positive feedback on global climate change during past and future ice-sheet retreat.
“Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica, because they may have far greater impact on Earth’s climate system than we have appreciated in the past,” said Professor Slawek Tulaczyk, a glaciologist with the University of California, Santa Cruz.