Methane concentrations have been measured in the surface waters and at depth for several different marine environments. Measurements have also been made in rain water collected in Washington, D.C., over the Pacific Ocean, and in Hawaii. In tropical open ocean areas, surface water concentrations average 4.5 × 10−5 ml/l and decrease to values approaching 0.6 × 10−5 ml/l at a depth of 5000 meters. In natural anoxic conditions (i.e., Cariaco Trench, Black Sea, Lake Nitinat) concentrations can increase as much as four orders of magnitude. In the case of Lake Nitinat, 1.6 ml/l is found at a depth of 200 meters. Nearshore and bay concentrations can be 2–3 orders of magnitude higher than open ocean surface values. Open ocean surface waters are slightly supersaturated with methane, whereas estuary systems are highly supersaturated. Open ocean surface values remain fairly constant, whereas bay and river systems vary considerably, depending on the time of year, addition of pollutants, and tidal mixing. Rain water analyses yielded an average concentration of 5.0 × 10−5 ml/l for the Hawaiian and Pacific samples, and an average concentration of 8.8 × 10−5 ml/l was found for the Washington, D.C., area. Atmospheric methane concentrations over the open ocean remain fairly constant at 1.4 ppm. Atmospheric values in Washington, D.C., at NRL averaged 1.7 ppm.

Carbon monoxide, ethylene, and propylene were produced in illuminated, cell-free distilled water or natural seawater systems to which dissolved organic matter produced by phytoplankton had been added. Methane and the higher saturated gaseous hydrocarbons were not produced. In the dark, little or no carbon monoxide and no hydrocarbons were produced in the distilled water systems; only carbon monoxide was produced in natural seawater, but less was produced than in the light.

The surface waters of the western Atlantic are supersaturated with respect to the partial pressure of carbon monoxide in the atmosphere. Under these conditions, the net transport of carbon monoxide across the air-sea interface must be from the sea into the atmosphere. Thus, the ocean appears to act as a source of carbon monoxide. The ocean may be the largest known natural source of this gas, contributing possibly as much as 5 percent of the amount generated by burning of fuels by man.

Low molecular weight hydrocarbons in the surface waters of the North and South Pacific have been measured. Methane concentrations average 4.2 x Inl/l, while the Cz-C, hydrocarbons averaged 1-5 x 10-6 ml/l. A large broad peak was found between 10" N and 10" S for the unsaturated hydrocarbons. Large concentrations of the C,-C, hydrocarbons were found in the different types of Antarctic sea ice. Atmospheric methane concentrations averaged 1.44 0.04 ppm and decreased t o 1.36 kO.04 pprn at the Intertropical Convergence Zone (ITC).

Since our data indicate that normal paraffins are less soluble in seawater than in distilled water, it is possible to speculate upon the geochemical fate of dissolved normal paraffins entering the ocean from rivers. If the fresh river water is saturated or near saturated with respect to normal paraffins (because of pollution, for example), salting out will occur in the estuary. The salted out molecules might either adsorb on suspended minerals, on particulate organic matter, or rise to the surface to exist as surface slicks. In either event they will have a different biogeochemical pathway from that which they would have if they were dissolved.The salting out of dissolved organic molecules in estuaries applies not only to normal paraffins but to all natural or pollutant organic molecules whose solubilities are decreased by addition of electrolytes. It is thus possible that regardless of the levels of dissolved organic pollutants in river water, only given amounts will enter the ocean in dissolved form owing to salting out effects of estuaries. Estuaries may act to limit the amount of dissolved organic carbon entering the ocean, but may increase the amount of particulate organic carbon entering the marine environ-