Determine the potential impacts of gas hydrate instability in terms of the release of methane into seafloor sediments, the ocean and the atmosphere.
University of California, San Diego (Scripps Institution of Oceanography) – manage geochemical, hydrological and sedimentological investigations
Texas A&M University – manage field monitoring program
La Jolla, California 92093
This project will monitor, characterize, and quantify the rates of formation and dissociation of methane gas hydrates at and near the seafloor in the northern Gulf of Mexico, and determine linkages between formation/dissociation and physical/chemical parameters of the deposits over the course of a year. The stability and response of shallow gas hydrates to temperature and chemical perturbations will be monitored in situ, and localized seafloor and water column environmental impacts of hydrate formation and dissociation characterized. The following will be determined: 1) The equilibrium/steady state conditions for structure II methane gas hydrates at the field site,2) whether the system is in dynamic equilibrium and the local hydrology is characterized by steady state episodic fluid flow, and 3) how fluid fluxes and fluid composition work together to dynamically influence gas hydrate stability.
This project is designed to increase understanding of the effects of environmental changes on the stability of naturally occurring gas hydrates on the seafloor. This work will help determine the potential environmental impacts of gas hydrate instability which can release methane into seafloor sediments, the ocean, and the atmosphere. The chemistry and structure of the hydrates, the composition of the overlying seawater, and the chemistry, mineralogy and hydrology of nearby sediments and pore waters are being characterized in detail. This project will also provide knowledge that is necessary for the future success of hydrate energy development, planning safe deep-water drilling operations, and preventing sediment slides in areas where gas and/or oil pipelines exist or where drilling is in progress.
Previous observations at Gulf of Mexico field sites suggest that gas hydrates on the seafloor form and dissociate in cycles over periods of several weeks to several months. Many factors, including biochemistry, subsurface hydrology, and temperature play a role in these cycles. Unfortunately, data on the kinetics of natural gas hydrate formation and dissociation in the marine environment are lacking. This project is designed to collect and analyze such data.
This project (informally called the Gas Hydrate Observation, Sampling, and Tracer Study or GHOSTS) is in the final year of a three-year cooperative agreement. The first of two research cruises took place June 6-14, 2002 aboard the R/V Seward Johnson. Two sites, Green Canyon 185 (Bush Hill) and Green Canyon 234, were selected for study based on their well-mapped and well-characterized shallow gas hydrate outcrops.
Using the Johnson Sea Link submersible, core and water samples were collected, time-lapse video and temperature recorders were installed, and geochemical and hydrological monitoring equipment was deployed to collect data during the following year. These instruments provided a record of pore fluid and bottom-water chemical and isotopic compositions, seafloor temperatures, and sediment fluid flow rates. They also recorded a visual record of hydrate responses and changes on the seafloor that occur as a result of environmental variations. A second cruise to retrieve the equipment took place in August 2003.
A time-lapse digital camera assembly installed on the seafloor recorded hourly images of the growth or dissolution of an exposed hydrate deposit. The assembly was equipped with a synoptic temperature recorder.
The fluids and samples retrieved during the 2003 cruise currently reside at the shore-based laboratory at Scripps Institution of Oceanography. An extensive array of geochemical, isotopic, mineralogical, and structural analyses of the gas hydrate, vent water, pore fluid, and sediment samples have been completed . Analyses of petroleum and other high carbon number organic compounds were conducted at Texas A&M. The collective geochemical data from this cruise will provide essential information on the coupling of the ocean and sub-seafloor thermal regime, on heat transfer between the ocean and the sub-seafloor, and on the amount of methane and other low-carbon number organic species that are required to form additional gas hydrates or stabilize existing deposits. The following conclusions can be drawn from the research activities and the subsequent analyses:
All work on this project has been completed. The project final report is available below under "Additional Information".
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 Report [PDF-1.2MB] - June, 2006
Kastner, M., D. Bartlett, I. MacDonald, and E. Solomon, 2005, CH4 fluxes across the seafloor at three distinct gas hydrate fields: impacts on ocean and atmosphere chemistry, Trondheim, Norway, Proceedings of the Fifth International Conference on Gas Hydrates, Volume 3, p. 709-714.
Solomon, E., M. Kastner, H. Jannasch, Y. Weinstein, and G. Robertson, 2005, Insights into the dynamics of in situ gas hydrate formation and dissociation at Bush Hill gas hydrate field, Gulf of Mexico, Trondheim, Norway, Proceedings of the Fifth International Conference of Gas Hydrates, Volume 3, p. 947-953.
Kastner, M., D. Bartlett, I. MacDonald, and E. Solomon, 2005, CH4 fluxes across the seafloor at three distinct gas hydrate fields: impacts on ocean and atmosphere chemistry, Trondheim, Norway, Fifth International Conference on Gas Hydrates, June 13-16.
Kastner, M., C. Solem, D. Bartlett, I. MacDonald, and D. Valentine, 2003, The extent of CH4 emission and oxidation in thermogenic and biogenic gas hydrate environments, American Geophysical Union Fall Meeting, December 8-12.
Solomon, E., M. Kastner, H. Jannasch, Y. Weinstein, G. Robertson, and A. Aubrey, 2004, Long-term continuous monitoring of fluid chemistry and flux at the Bush Hill gas hydrate field, Gulf of Mexico, using a new flowmeter, the MOSQUITO, American Geophysical Union, Fall Meeting, December 13-17.
Solomon, E., M. Kastner, H. Jannasch, Y. Weinstein, and G. Robertson, 2005, Insights into the dynamics of in situ gas hydrate formation and dissociation at Bush Hill gas hydrate field, Gulf of Mexico, Trondheim, Norway, Fifth International Conference of Gas Hydrates, June 13-16.
Weinstein, Y., M. Kastner, and H. Jannasch, 2003, The MOSQUITO: a new sampler for monitoring fluid and solute fluxes between the sediment and the ocean, EGS-AGU-EUG Joint Assembly Meeting, Nice, France, April 6-11.