The goal of this project is to develop a two-dimensional, basin-scale model for the deep sediment biosphere with methane dynamics to provide a better picture of the distribution of hydrates on the sea floor and their vulnerability to warming of the deep ocean, thus integrating methane hydrates into the global carbon cycle.
University of Chicago – Chicago, IL 60637
University of California Berkeley – Berkeley, CA
Large but poorly quantified amounts of methane are trapped in the sediments beneath the sea floor, frozen into a form of water ice called clathrate or hydrate. The hydrates could be vulnerable to melting with a temperature increase of a few degrees Celsius (°C) [Buffett and Archer, 2004], an increase which is achievable given the available inventories of fossil fuel carbon for combustion. The hydrate carbon reservoir has probably grown in size over millions of years within the context of gradual ocean cooling, but a release of carbon from the hydrate pool due to melting could take place on a time scale of millennia.
The melting temperature of hydrate increases with pressure, and temperature in the ocean decreases with pressure (depth), so hydrate becomes increasingly stable with increasing ocean depth in the presence of methane gas [Kvenvolden, 1993]. Absence of methane gas in the open ocean, however, means that most of the hydrates are found in the sediment.
Within the sediment column, the temperature increases with depth, so that at a depth of typically a few hundred meters below the sea floor, the temperature exceeds the melting threshold. Therefore, the term hydrate stability zone generally refers to the sediment column from the sea floor down to the melting depth a few hundred meters below the sea floor. Climate warming primarily affects hydrate stability near the base of the stability zone, where temperatures approach the melting point. The sediment column provides a thermal buffer that slows the response of the hydrates to climate warming by many centuries. A change in sea level might also affect the stability of hydrates by altering the pressure. Sea level rise in the future would tend to stabilize the hydrates in the coming centuries, whereas warming would de-stabilize them.
The impact of melting oceanic hydrates on climate depends on whether the carbon reaches the atmosphere in the form of methane. If methane is released on a time-scale which is long relative to its atmospheric lifetime (decade), the result would be an increase in the steady-state concentration of methane in the atmosphere. The oxidation product of methane is CO2, another greenhouse gas although a weaker one. In contrast to methane (a transient chemical species) CO2 accumulates in the atmosphere, ultimately taking hundreds of thousands of years to be consumed by weathering reactions with igneous rocks. Methane that dissolves in the deep ocean would be oxidized to CO2 within a few years [Valentine et al., 2001], in which form it would ultimately equilibrate with the atmosphere, releasing some 15%-25% of the carbon to the air.
No mechanism has been proposed by which more than a Gton or so of methane could be released to the atmosphere within a few years, generating a significant transient spike of atmospheric methane concentration. The more likely impact of a melting hydrate reservoir is, therefore, a long-term, chronic methane source, elevating atmospheric methane and contributing to the total CO2 load on the atmosphere.
The bottom-line question which this project aims to address is whether the methane released from melting hydrates in the sediment column is likely to escape into the ocean or the atmosphere, or remain in place below the sea floor.
The project will serve to provide an improved understanding of the mechanisms responsible for methane cycling within the deep sediment column, thus providing constraints on the potential for hydrate response to climate change and the role of hydrates in the global carbon cycle.
The project has been completed. The final report is available below under "Additional Information".
Phase 1 - $171,126
Phase 2 - $231,224
Phase 3 - $237,924
Planned Total Funding - $640,274
Phase 1 - $43,669
Phase 2 - $58,895
Phase 3 - $60,629
Planned Total Funding - $163,193
NETL – Skip Pratt (Skip.Pratt@netl.doe.gov or 304-285-4396)
University of Chicago – David Archer (firstname.lastname@example.org or 773-702-0823)
University of California Berkeley – Bruce Buffett (email@example.com or 510-559-8167)
If you are unable to reach the above personnel, please contact the content manager.
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].
Final Project Report [PDF-16.8MB] April, 2012
Technology Status Assessment [PDF-31KB]