The Antarctic Ice Sheet could be an overlooked but important source of methane, a potent greenhouse gas, according to a report in Nature by an international team of scientists. The new study demonstrates that old organic matter in sedimentary basins located beneath the Antarctic Ice Sheet 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.
It is easy to forget that before 35 million years ago, when the current period of Antarctic glaciations started, this continent was teeming with life. Some of the organic material produced by this life became trapped in sediments, which then were cut off from the rest of the world when the ice sheet grew. Our modeling shows that over millions of years, microbes may have turned this old organic carbon into methane.—Coauthor Slawek Tulaczyk, a professor of Earth and planetary sciences at UC Santa Cruz
The science team estimated that 50% of the West Antarctic Ice Sheet (1 million square kilometers) and 25% of the East Antarctic Ice Sheet (2.5 million square kilometers) overlies pre-glacial sedimentary basins containing about 21,000 billion metric tons of organic carbon.
The researchers numerically simulated the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model. They found that sub-ice conditions favor the accumulation of methane hydrate (that is, methane trapped within a structure of water molecules, forming a solid similar to regular ice).
They also calculated that the potential amount of methane hydrate and free methane gas beneath the Antarctic Ice Sheet could be up to 4 billion metric 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.
Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.—Wadham et al.
This research is a collaborative venture between the University of Bristol (UK), The University of California, Santa Cruz (USA), The University of Alberta, Edmonton, and the University of Utrecht (The Netherlands). It was funded principally by the Natural Environment Research Council (UK), the Leverhulme Trust (UK) with additional funds from the National Science Foundation (USA), the Natural Science and Engineering Research Council of Canada and the Netherlands Organization for Scientific Research (NWO).
J. L. Wadham, S. Arndt, S. Tulaczyk, M. Stibal, M. Tranter, J. Telling, G. P. Lis, E. Lawson, A. Ridgwell, A. Dubnick, M. J. Sharp, A. M. Anesio & C. E. H. Butler (2012) Potential methane reservoirs beneath Antarctica. Nature 488, 633–637 doi: 10.1038/nature11374