CLARK, JORDAN F., Dept. of Geological Sciences, University of California, Santa Barbara, CA 93106; LIBE WASHBURN, Dept. of Geography, University of California, Santa Barbara, CA 93106; J. SCOTT HORNAFIUS, Mobil Oil Company, London WC2A-2EB, UK; and BRUCE P. LUYENDYL, Dept. of Geological Sciences, University of California, Santa Barbara, CA 93106

Abstract: Distribution and Source Strength of Dissolved Hydrocarbons from Natural Marine Seeps, Coal Oil Point, Santa Barbara, CA

Natural marine seeps near Coal Oil Point inject large quantities of dissolved hydrocarbons into the coastal ocean. Surveys of the resulting methane, ethane, and propane plumes in Sept. 1995 and Aug. 1996 show that hydrocarbons seep into stratified coastal waters creating complex plumes which extend for at least 12 km on density surfaces (s q = 24.5-26.0 kg m^-3). Earlier work has shown that sub-surface methane maxima in the upper waters of the southern California Bight are typically found between these density surfaces and extend 100s km offshore. We estimate that the total flux of methane into the water column above the Coal Oil Point seeps is 2 ´ 10¹⁰ g yr^-1, approximately equal to the total flux of dissolved methane to the atmosphere estimated earlier for the entire southern California Bight. These observations strongly support the inference of others that coastal sources which includes marine hydrocarbon seeps maintain the methane maximum observed off shore. Estimates of the global methane flux from coastal waters derived by extrapolating the flux from coastal California may be too large because of the anomalous amount of marine hydrocarbon seepage in these waters.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California