Dissolved methane distributions and air‐sea flux in the plume of a massive seep field, Coal Oil Point, California

Large quantities of natural gas are emitted from the seafloor into the stratified coastal ocean near Coal Oil Point, Santa Barbara Channel, California. Methane was quantified in the down current surface water at 79 stations in a 280 km 2 study area. The methane plume spread over an area of ∼70 km 2 and emitted on the order of 5 × 10 4 mol d −1 to the atmosphere. A monthly time series at 14 stations showed variable methane concentrations which were correlated with changing sub‐mesoscale surface currents. Air‐sea fluxes estimated from the time series indicate that the air‐sea flux derived for the 280 km 2 area is representative of the daily mean flux from this area. Only 1% of the dissolved methane originating from Coal Oil Point enters the atmosphere within the study area. Most of it appears to be transported below the surface and oxidized by microbial activity.