Oceanic gas hydrate dissociation in response to climate change and the fate of hydrate-derived methane

Authors: Matthew T. Reagan and George J. Moridis

Venue: 2008 AGU Fall Meeting, December 15-19, 2008 in San Francisco, California www.agu.org

Abstract: Paleoceanographic evidence has been used to postulate that methane from oceanic hydrates may have had a significant role in regulating past global climate. However, the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes, like those predicted under future climate change scenarios, has only recently been investigated, and the fate of the hydrate-derived methane is still unclear. The release of methane from oceanic deposits is controlled and constrained by coupled heat transfer, fluid flow, and thermodynamic processes; this methane may interact with benthic biogeochemical systems before reaching the seafloor. In this work, computational simulations of hydrate dissociation in oceanic sediments have been coupled to models of sediment biogeochemistry. Important considerations include dynamic exchange of methane in the aqueous and gas phases within the chemically active zone, transport of reaction products through the sediment, the effects of depth and temperature, the properties of the hydrate-bearing sediments, and the one- and two-dimensional configuration of the hydrate deposit itself. This coupled model establishes bounds for benthic methane oxidation (and possibly, sequestration of the carbon as solid carbonate) for potential hydrate release scenarios and provides the first assessment of the fate of hydrate-derived methane released due to climate change.

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 – Sandra L. McSurdy (sandra.mcsurdy@netl.doe.gov 412 386-4533)
Lawrence Berkeley National Laboratory. – George Mordis (GJMoridis@lbl.gov or 510 486-6709)