Decrease in natural marine hydrocarbon seepage near Coal Oil Point, California, associated with offshore oil production

Prolific natural hydrocarbon seepage occurs offshore of Coal Oil Point in t he Santa Barbara Channel, California. Within the water column above submari ne vents, plumes of hydrocarbon gas bubbles act as acoustic scattering targ ets, Using 3.5 kHz sonar data, seep distribution offshore of Coal Oil Point was mapped for August 1996, July 1995, and July 1973. Comparison of the se ep distributions over time reveals more than 50% decrease in the areal exte nt of seepage, accompanied by declines in seep emission volume, in a 13 km( 2) area above a producing oil reservoir. Declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are t he mechanisms inferred to explain the declines in seep area and emission vo lume.