Long term changes in the spatial distribution of seepage suggest offshore oil production may have reduced some seepage due to the reduction in reservoir pressure in the Monterey formation. This can be used as the input source function for problems of oceanographic modeling of seep product dispersal. Most of the seepage occurs in the form of gas bubble plumes which rise through the water column and vent into the atmosphere. We estimate a total gas flux of ca. During gas bubble rise, the hydrocarbons partially dissolve in ambient seawater to form neutrally buoyant dissolved hydrocarbon plumes.
Oil contained in the rising bubbles is left on the sea surface as slicks.
In situ gas chromatograph observations are used to map the dissolved hydrocarbon plume which extends several km down-current from the vents. Oceanographic conditions are determined from high resolution CTD surveys, and moored vector-measuring and acoustic Doppler current meters. We are also establishing a baseline for long-term studies of variations in seep chemistry, intensity, and location.