Potential methane reservoirs beneath Antarctica

TLDR: The results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed, and calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost.

Abstract: On the basis of data from other subglacial environments and simulations of the accumulation of methane hydrate in Antarctic sedimentary basins, it seems there could be unsuspected, large stores of methane beneath the Antarctic Ice Sheet. The ice-covered parts of Antarctica are known to be a reservoir of metabolically active microbial cells and organic carbon, but the potential for microorganisms to support the degradation of organic carbon to methane beneath the ice has not yet been evaluated. In this paper, Jemma Wadham and colleagues numerically simulate the accumulation of methane in Antarctic sedimentary basins. Their findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane inventory that could act as a positive feedback on global climate change during episodes of ice-sheet collapse. Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon1. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. 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. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. 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.