Effects of Seafloor Temperature on the Distribution of Methane Hydrate (Poster)

Authors: Gu, Guangsheng (speaker), Bhatnagar, Gaurav, Dickens, Gerald R., Chapman, Walter G., and Hirasaki, George J., Rice University; Colwell, Frederick S., Oregon State University.

Venue: American Geophysical Union’s fall meeting in San Francisco, CA, December 10–14, 2007 (http://www.agu.org/meetings/fm07/ [external site]).

Abstract: Deep ocean temperatures were 10–15 °C warmer than present day during the Early Cretaceous and Early Paleogene. Such temperatures would impact the distribution of gas hydrate in marine sediment. Clearly, the vertical extent of the Gas Hydrate Stability Zone (GHSZ) and the overall volume of sediment hosting gas hydrates at shallow water depths would be smaller than they are today. Several authors have taken this to mean that overall amounts of gas hydrate and methane in marine sediments were much smaller in ancient warm oceans. However, this inference may be incorrect. In any case, it has not been appropriately evaluated. Researchers in this project have developed a one-dimensional numerical model that describes the formation and distribution of methane hydrate in marine sediment on geological time scales. They modified this model to examine the effect of changing seafloor temperature from 3 to 18 °C in cases where microbial activity supplies most of the methane. Predictably, the temperature increase shifts the methane solubility curve in marine sediment and decreases the depth of the GHSZ. Less obvious but more important are temperature effects on the flux of seafloor organic carbon and the rate of methanogenesis. In some cases, increased seafloor temperature results in decreased amounts of methane hydrate. However, in other simulations, when seafloor organic fluxes and biogenic reaction rates increase significantly, amounts of methane hydrate can be higher than modeled for the present day. It is possible that, during times of warm oceans, greater amounts of organic carbon enter the seafloor, microbes make methane from this carbon at much faster rates, and gas hydrate quantities exceed those of today. These somewhat counterintuitive results may help to explain certain observations during warm climates.

Related NETL Project
The proposed research of the related NETL project DE-FC26-06NT42960, “Detection and Production of Methane Hydrate,” is to improve the understanding of regional differences in gas hydrate systems from three perspectives: as an energy resource, as a geohazard, and as a long-term influence on global climate.

NETL Project Contacts
NETL – Rick Baker (richard.baker@netl.doe.gov or 304-285-4714)
Rice University – Dr. George Hirasaki (gjh@rice.edu or 713-348-5416)