Sources, Sinks, and Concentrations of Light Hydrocarbons in the

A survey of the concentrations of light hydrocarbons in the Gulf of Mexico has been made aboard the R.V. Alaminos of Texas A&M University. The hydrocarbon analyzer consists of a modified Beckman process gas chromatograph with a flame ionization detector. For surface profiling, gases are ‘stripped’ from seawater taken 3 meters below the sea surface by vacuum extraction with a 12-stage booster pump. These gases are injected periodically into the gas stream of the chromatograph for analysis. The system also has the capability of analyzing discrete seawater samples either by the method of McAullife or by the method of Swinnerton and his co-workers. Coastal waters of the Gulf of Mexico are not in equilibrium with the atmosphere insofar as low molecular weight hydrocarbons are concerned, even though methane in most of the open Gulf of Mexico is in fairly close equilibrium with the atmosphere. The coastal waters of the gulf act both as a source and as a sink for atmospheric methane. The important man-derived sources of methane in the gulf are ports with their associated shipping and industrial activity, offshore petroleum drilling and production operations, and open ocean shipping activity. High light hydrocarbon concentrations have been found in the vicinity of a tanker discharging ‘clean ballast water.’ The important natural sources include seepage from oil and gas reservoirs and anaerobic production of methane. The main sink for atmospheric methane in the Gulf of Mexico is in the Yucatan area, where there is major upwelling of deep water with low hydrocarbon concentrations.