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Environmental Geosciences, V.
Gaseous emission rates from natural petroleum seeps in the Upper Ojai Valley, California
1Department of Earth Science, University of California, Santa Barbara, California 93106; present address: 2100 Main St, Suite 150, Huntington Beach, California 92648; [email protected]
2Graduate Program in Marine Science, University of California, Santa Barbara, California 93106; [email protected]
3Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, California 93106; [email protected]
4Department of Earth Science and Institute for Crustal Studies, University of California, Santa Barbara, California 93106; [email protected]
5Department of Earth Science and Institute for Crustal Studies, University of California, Santa Barbara, California 93106; [email protected]
Marlene Duffy is a senior staff geologist at Geosyntec Consultants. Duffy holds an M.S. degree in geological sciences from the University of California at Santa Barbara (2004). She currently works on a variety of projects involving groundwater evaluation.
Frank Kinnaman is a graduate student researcher in the Marine Sciences Department at University of California at Santa Barbara. His graduate research as a member of the Valentine Group is focused on the microbial geochemistry of hydrocarbon seep environments, particularly the consumption of natural gas in marine sediments.
David L. Valentine is an associate professor of earth science at the University of California at Santa Barbara. His research interests center on biogeochemical processes including those impacting hydrocarbons. Valentine holds a Ph.D. in earth systems science from the University of California at Irvine (2000).
Edward A. Keller is a professor at the University of California at Santa Barbara in the Department of Earth Science and Program of Environmental Studies. His research is focused on active tectonics centered on the western transverse ranges of southern California and hydrologic studies of basic river processes, high-magnitude flood deposits, channel form, and process, and river restoration and management.
Jordan F. Clark (B.S., Yale University; Ph.D., Columbia University) is an associate professor at the University of California at Santa Barbara in the Department of Earth Science and Program of Environmental Studies. His research is focused on understanding geochemical interactions that occur near the Earth's surface and the effects of external anthropogenic and climatic forcing on these interactions. For more than a decade, his research group at University of California at Santa Barbara has been examining the fate of methane and other gases emitted by natural hydrocarbon seeps.
Dan Tanner of Vintage Petroleum granted permission to conduct the fieldwork on company property. We thank J. R. Boles and B. P. Luyendyk for helpful discussions and R. W. Klusman, K. A. Kvenvolden, A. Y. Huc, and J. S. McColloch for careful reviews of an earlier revision of this manuscript. This research was supported by the University of California Energy Institute. Additional funding for D. Valentine and F. Kinnaman was provided by the National Science Foundation through the CAREER program in chemical oceanography (OCE-0447395). This is contribution 0789 of the Institute for Crustal Studies at the University of California, Santa Barbara.
The atmospheric fluxes of methane (CH4), carbon dioxide (CO2), and reactive organic gases (ROGs) were determined for natural terrestrial petroleum seeps in the Upper Ojai Valley, California, by measuring the emission rates from five vents and scaling these measurements with the known distribution of seeps within the valley. The Upper Ojai Valley seeps emit about 55 m3/day (1942 ft3/day) of gas, of which about 15 m3/day (529 ft3/day; 3.6 Mg/yr) is CH4, about 40 m3/day (1412 ft3/day; 27 Mg/yr) is CO2, and less than 0.05 m3/day (1.765 ft3/day; 0.04 Mg/yr) are ROGs. CH4 and ROG fluxes in the Upper Ojai Valley are, respectively, three and five orders of magnitude less than at the well-characterized Coal Oil Point field, a large offshore seep field located approximately 70 km (43 mi) to the west of the valley. The CO2 flux from these two fields is about the same. The compositions and 13C values of seep and reservoir gases were also quantified and indicate extensive biodegradation of gaseous hydrocarbons and the input of isotopically enriched CO2 during ascent from the reservoir. Unlike the nearby CH4-dominated marine seeps, the largest percentage of gas emitted by seeps in the Upper Ojai Valley is CO2.
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