Reactive transport modeling of oceanic gas hydrate instability and dissociation in response to climate change

Authors: Matthew T. Reagan and George J. Moridis

Venue: 6th International Conference on Gas Hydrates 2008, Vancouver, British Columbia, July 9-12, 2008 (http://www.icgh.org [external site])

Abstract: Paleoceanographic evidence has been used to postulate that methane from oceanic hydrates may have had a significant role in regulating past global climate. The implication is that global oceanic deposits of methane gas hydrate is the main culprit for a sequence of rapid global warming affects that occurred during the late Quaternary period. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, is poorly understood. To determine the fate of the carbon stored in these hydrates, we performed coupled thermo-hydrological-chemical simulations of oceanic gas hydrate accumulations subjected to temperature changes at the seafloor, and assessed the potential for methane release into the ecosystem. Our modeling analysis considered the properties of benthic sediments, the saturation and distribution of the hydrates, the ocean depth, the initial seafloor temperature, and the effects of benthic biogeochemical activity. The results show that while many deep hydrate deposits are indeed stable during periods of rapid ocean temperature changes, shallow deposits (such as those found in arctic regions or in the Gulf of Mexico) can undergo rapid dissociation and produce significant carbon fluxes over a period of decades. These fluxes may exceed the ability of the seafloor environment (via anaerobic oxidation of methane and the formation of carbonates) to sequester the released carbon. This model will provide a source term to regional or global climate models in order to assess the coupling of gas hydrate deposits to changes in the global climate.

Related NETL Project
This presentation is related to the NETL project ESD07-014, “Interrelation of Global Climate and the Response of Oceanic Hydrate Accumulations.” The primary objectives of this project are to: 1) investigate the effect of rising water temperatures on the stability of oceanic hydrate accumulations, 2) estimate the global quantity of hydrate- originating carbon that could reach the upper atmosphere as CH4 or CO2 thus affecting global climate, 3) quantify the interrelationship between global climate and the amount of hydrate-originating carbon reaching the upper atmosphere focusing on the potential link between hydrate dissociation and cascading global warming and 4) to test the discharge phase of the Clathrate Gun Hypothesis which stipulates large-scale hydrate dissociation and gas release and rapid warming over very short geological periods.

Project Contacts
NETL – Richard Baker (richard.baker@netl.doe.gov or 304-285-2714)
LBNL – George Moridis (GJMoridis@lbl.gov or 510 486-6709)