The hydrate hazard - A moderate increase in sea-floor temperature could trigger … widespread release

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http://www.nature.com/climate/2009/0902/full/climate.2009.2.html

Research Highlights

Nature Reports Climate Change
Published online: 15 January 2009 | doi:10.1038/climate.2009.2

The hydrate hazard

Anna Armstrong

http://dx.doi.org/10.1029/2008JC004938">J. Geophys. Res. doi:10.1029/2008JC004938 (2008)

A moderate increase in sea-floor temperature could trigger the widespread release of methane from ocean hydrates, finds new research. Large quantities of the potent greenhouse gas are stored beneath the sea in solid crystalline structures, known as hydrates, that could potentially be destabilized by ocean warming.

Matthew Reagan and George Moridis of the Lawrence Berkeley National Laboratory in Berkeley, California, used computer simulations to examine the effect of 100 years of moderate ocean warming on the stability of deep and shallow ocean hydrates. They found that deep ocean deposits remained stable over the 100-year period, but that shallow ocean deposits were highly unstable, releasing significant quantities of dissolved and gaseous methane in response to just 1 °C of warming at the sea floor. Of the shallow deposits examined, cold hydrates, representative of the Arctic continental shelf, released nearly three times more methane than those representative of warm regions such as the Gulf of Mexico.

An increase in deep-sea pressure resulting from sea level rise would delay methane release but would not prevent its inevitable escape into the sea, say the researchers. Given that the release of methane could amplify climate change, the authors call for a detailed assessment of the hydrate hazard.

http://www.agu.org/pubs/crossref/2008/2008JC004938.shtml

Dynamic response of oceanic hydrate deposits to ocean temperature change

Matthew T. Reagan

Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA

George J. Moridis

Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA

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Vast quantities of methane are trapped in oceanic hydrate deposits. Because methane is a powerful greenhouse gas (about 26 times more effective than CO₂), there is considerable concern that a rise in the temperature of the oceans will induce dissociation of oceanic hydrate accumulations, potentially releasing large amounts of carbon into the atmosphere. Such a release could have dramatic climatic consequences because it could amplify atmospheric and oceanic warming and possibly accelerate dissociation of the remaining hydrates. This study assesses the stability of three types of hydrates (case I, deep-ocean deposits; case II, shallow, warm deposits; and case III, shallow, cold deposits) and simulates the dynamic behavior of these deposits under the influence of moderate ocean temperature increases. The results indicate that deep-ocean hydrates are stable under the influence of moderate increases in ocean temperature; however, shallow deposits can be very unstable and release significant quantities of methane under the influence of as little as 1°C of seafloor temperature increase. Less permeable sediments, or burial underneath layers of hydrate-free sediment, affect both the rate of hydrate dissociation and methane transport to the seafloor but may not prevent methane release. Higher-saturation deposits can produce larger methane fluxes with the thermodynamics of hydrate dissociation retarding the rate of recession of the upper hydrate interface. These results suggest possible worst case scenarios for climate-change-induced methane release and point toward the need for detailed assessment of the hydrate hazard and the coupling of hydrate-derived methane to regional and global ecosystems.

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Received 30 May 2008; accepted 13 October 2008; published 24 December 2008.

Citation: Reagan, M. T., and G. J. Moridis (2008), Dynamic response of oceanic hydrate deposits to ocean temperature change, J. Geophys. Res., 113, C12023, doi:10.1029/2008JC004938.