Title: The role of the ocean in the global atmospheric sulfur cycle
Abstract: The background atmospheric SO 2 concentration above the sea surface has been established at 0.1 × 10 −6 g/m 3 (35 pptv). Several hypotheses to explain the origin of SO 2 above the ocean, far from continental sources, have been discussed. We have shown that one of the mechanisms of SO 2 formation is the biogenic production of reduced organic sulfur compounds in the ocean. Dimethyl sulfide (DMS) has been observed in oceanic areas, with concentrations ranging from 11 to 1150 × 10 −9 g l −1 in surface waters and from 0.2 to 400 × 10 −9 g m −3 (0.07 to 144 pptv) in marine atmosphere. This compound is emitted into the atmosphere and oxidized there by photochemically induced processes. That leads partly to SO 2 formation, and subsequently, to sulfate. This hypothesis is corroborated by a correlation between atmospheric SO 2 concentrations and the relation between atmospheric SO 2 concentrations and biological activity. The flux of sulfur by this process (biological activity → organic sulfides → SO 2 → SO 2 = ) is estimated to range between 27 and 72×10 6 tons of sulfur per year. This biogenic production is comparable to atmospheric sulfur production by sea spray, which is about 44×10 6 T S/yr. Therefore, the oceanic production by these two processes could be estimated as being from 71 to 116×10 6 T S/yr.