While I do not normally post in this thread; however, the following Wadham et al 2012 paper cites the potential for large reservoirs of methane beneath the West Antarctic Ice Sheet, WAIS; while the Pollard et al 2015 article indicates that the WAIS could substantially collapse by 2100; which if it were to occur could release large amounts of methane from the WAIS seafloor in an abrupt manner:
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/nature11374http://www.nature.com/nature/journal/v488/n7413/full/nature11374.html?WT.ec_id=NATURE-20120830
Abstract: "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 carbon. 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 thick 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 model 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."
Pollard, DeConto & Alley (2015), indicate the possibility that a possible collapse of the WAIS could substantially collapse by 2100.
Pollard, D., DeConto, R.M. and Alley, R.B., (2015), "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth and Planetary Science Letters, Volume 412, 15 February 2015, Pages 112–121, doi:10.1016/j.epsl.2014.12.035http://www.sciencedirect.com/science/article/pii/S0012821X14007961
Abstract: "Geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years, at times reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies."