The world's most spectacular marine hydrocarbon seeps (Coal Oil Point, Santa Barbara Channel, California): Quantification of emissions

We used 50 kHz sonar data to estimate natural hydrocarbon emission rates fi om the 18 km(2) marine seep field offshore from Coal Oil Point, Santa Barb ara, California. The hydrocarbon gas emission rate is 1.7 +/- 0.3 x 10(5) m 3d(-1) (including gas captured by a subsea seep containment device) and the associated oil emission rate is 1.6 +/- 0.2 x 10(4) Ld(-1) (100 barrels d( -1)). The nonmethane hydrocarbon emission rate from the gas seepage is 35 /- 7 td(-1) and a large source of air pollution in Santa Barbara County. Ou r estimate is equal to twice the emission rate from all the on-road vehicle traffic in the county. Our estimated methane emission rate for the Coal Oi l Point seeps (80 +/- 12 td(-1)) is 4 times higher than previous estimates. The most intense areas of seepage correspond to structural culminations al ong anticlinal axes. Seep locations are mostly unchanged from those documen ted in 1946, 1953, and 1973. An exception is the seepage field that once ex isted near offshore oil platform Holly. A reduction in seepage within a 1 k in radius around this offshore platform is correlated with reduced reservoi r pressure beneath the natural seeps due to oil production. Our findings su ggest that global emissions of methane fi om natural marine seepage have be en underestimated and may be decreasing because of oil production.