The seawater SO4 -/Na+ ratio is 0.25. However, sulfate enrichments with respect to Na+ have been observed in marine aerosols by several authors. In the northern hemisphere, such an enrichment could be attributed to natural or to anthropogenic continental sources of sulfates. However, far from any continent, for example, in subantarctic areas, we have always observed SO4-/Na+ ratios greater than that of seawater and as large as I. We have shown the existence in the oceanic atmosphere of a relationship between SO2 and primary productivity in seawater. The sulfate excess concentrations are found to be proportional to those of SO2. The sulfate enrichment could be consequently explained by the oxidation of marine SO2. This explanation is consistent with the distribution of SO4-/Na+ ratios on different size particles collected with a high volume cascade impactor. Highest values (>0.5) are always observed in the smallest particles (diameter<0.6 μm); the largest particles have a SO4-/Na+ ratio near 0.25. We conclude that sulfate marine aerosols are produced not only by the atmospheric injection of sea salt, but also by a gas-to-particle conversion process by oxidation of marine SO2. This last source has been estimated to be 84¿106 tons of sulfate per year.