Dissociation of Cascadia margin gas hydrates in response to contemporary ocean warming

Abstract

Gas hydrates, pervasive in continental margin sediments, are expected to release methane in response to ocean warming, but the geographic range of dissociation and subsequent flux of methane to the ocean are not well constrained. Sediment column thermal models based on observed water column warming trends offshore Washington (USA) show that a substantial volume of gas hydrate along the entire Cascadia upper continental slope is vulnerable to modern climate change. Dissociation along the Washington sector of the Cascadia margin alone has the potential to release 45-80 Tg of methane by 2100. These results highlight the importance of lower latitude warming to global gas hydrate dynamics and suggest that contemporary warming and downslope retreat of the gas hydrate reservoir occur along a larger fraction of continental margins worldwide than previously recognized.

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

“…It is not possible to know what percentage or amount of NGH was converted during the early or subsequent thinning of the GHSZ, but we can postulate that significant amounts of low-salinity water and free gas were produced as a result of NGH dissociation (Max et al, 2006) and that considerable amounts of low salinity water may still be held within the sediment. Although more quantitative estimates for NGH products, such as those conducted in Svalbard and the Cascadia margin (Berndt et al, 2014;Hautala et al, 2014), remain to be carried out for the Mediterranean (Max & Johnson, 2016), conversion of a large amount of NGH into lowsalinity water and gas is highly likely.…”

A science plan for carbon cycle research in North American coastal waters. Report of the Coastal CARbon Synthesis (CCARS) community workshop, August 19-21, 2014

“…Furthermore, it is well known that there are massive methane reserves in the sediments of the coastal ocean and that their stability is dependent on the temperature of bottom waters. The release of this methane may be underway along the U.S. east and west coasts as a result of ocean warming (Hautala et al, 2014;Phrampus and Hornbach, 2012), and there is the potential for further substantial releases globally over the coming centuries, though the uncertainties are large (Archer et al, 2009). Finally, much work needs to be done to examine the net "blue carbon" benefits of tidal wetlands, which sequester CO 2 but emit CH 4 (Weston et al, 2014).…”

Geological Hazards

“…Sediment column thermal models, based on observed water column warming trends offshore Washington (USA), show that substantial volume of gas hydrate along the entire Cascadia upper continental slope is vulnerable to modern climate change. Dissociation along the Washington sector of the Cascadia margin alone has the potential to release 45-80 Tg of methane by 2100 (Hautala et al, 2014).…”