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 from the 18 km2 marine seep field offshore from Coal Oil Point, Santa Barbara, California. The hydrocarbon gas emission rate is 1.7 ± 0.3 × 105 m3 d−1 (including gas captured by a subsea seep containment device) and the associated oil emission rate is 1.6 ± 0.2 × 104 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. Our 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 Oil Point seeps (80±12 td−1) is 4 times higher than previous estimates. The most intense areas of seepage correspond to structural culminations along anticlinal axes. Seep locations are mostly unchanged from those documented in 1946, 1953, and 1973. An exception is the seepage field that once existed near offshore oil platform Holly. A reduction in seepage within a 1 km radius around this offshore platform is correlated with reduced reservoir pressure beneath the natural seeps due to oil production. Our findings suggest that global emissions of methane from natural marine seepage have been underestimated and may be decreasing because of oil production.

[1]  Walter K. Link,et al.  Significance of Oil and Gas Seeps in World Oil Exploration , 1952 .

[2]  D. Hammond,et al.  The use of carbon and sulfur isotopes as correlation parameters for the source identification of beach tar in the southern California borderland , 1981 .

[3]  M. Hovland,et al.  Environmental effects of submarine seeping natural gas , 1992 .

[4]  M. Hovland,et al.  The global flux of methane from shallow submarine sediments , 1993 .

[5]  H. Medwin,et al.  Counting bubbles acoustically: a review , 1977 .

[6]  A. Yayanos,et al.  The Distribution of Methane in the Upper Waters of the Southern California Bight , 1992 .

[7]  A. Lacroix.  Unaccounted-for sources of fossil and isotopically-enriched methane and their contribution to the emissions inventory: A review and synthesis , 1993 .

[8]  I. R. Kaplan,et al.  The chemistry of marine petroleum seeps , 1977 .

[9]  M. Hovland,et al.  The global production of methane from shallow submarine sources , 1992 .

[10]  L. Horvitz,et al.  Vegetation and Geochemical Prospecting for Petroleum , 1972 .

[11]  Steven G. Ackleson,et al.  Natural Oil Slicks in the Gulf of Mexico Visible From Space , 1993 .

[12]  W. Sweet.  Marine Acoustical Hydrocarbon Detection , 1973 .

[13]  R. Spies,et al.  Infaunal benthos of a natural petroleum seep: Study of community structure , 1980 .

[14]  R. Spies,et al.  The infaunal benthos of a natural oil seep in the Santa Barbara channel , 1979 .

[15]  K. Landes.  Mother Nature as an Oil Polluter , 1973 .

[16]  Graham B. Wallis,et al.  The terminal speed of single drops or bubbles in an infinite medium , 1974 .

[17]  Alan Judd,et al.  The evidence of shallow gas in marine sediments , 1992 .

[18]  Paul J. Crutzen,et al.  Methane's sinks and sources , 1991, Nature.

[19]  R. D. Wilson,et al.  Natural Marine Oil Seepage , 1974, Science.

[20]  J. Southon,et al.  Radiocarbon evidence of fossil-carbon cycling in sediments of a nearshore hydrocarbon seep , 1990, Nature.

[21]  David M. Farmer,et al.  The Measurement of Bubble-Size Distributions by Acoustical Backscatter , 1992 .

[22]  P. Mikolaj,et al.  Natural Oil Seepage at Coal Oil Point, Santa Barbara, California , 1970, Science.

[23]  R. Crippen,et al.  Natural oil seep detection in the Santa Barbara Channel, California, with Shuttle Imaging Radar , 1985 .

[24]  D. desmarais,et al.  Natural isotope study of trophic enrichment of marine benthic communities by petroleum seepage , 1983 .