Distribution and air–sea exchange of reduced sulphur gases in European coastal waters

Recent research work provided the basis for a much improved understanding of the open ocean sources of dimethylsulphide (DMS), carbonyl sulphide (COS), and carbon disulphide (CS2) to the atmosphere. Coastal ocean emissions remained less well constrained, arguably because of the inherently high variability of coastal and estuarine systems. This article presents a review of the spatial and seasonal distributions of DMS, COS and CS2 together with a preliminary assessment of their respective emissions from European coastal waters. Our data compilation considers winter/summer scenarios and explicitly distinguishes shelf waters and estuarine systems. For DMS, our findings indicate similar emission rates for shelf waters and estuarine systems and an annual DMS source of approximately 16 Gmol a−1. Our annual emission estimates for COS and CS2 are 0.26 Gmol a−1 and 0.16 Gmol a−1, respectively, and suggest significant contributions from estuarine systems to total shelf emissions in both cases (COS: 27%; CS2: 19%). On this basis we recommend that estuarine COS and CS2 emissions should be considered in future global emission estimates. Comparisons of our emission estimates to previous estimates of global marine sulphur gas emissions indicate disproportionally high contributions from European coastal waters. Given that emission rates from European shelves may be similar to those of other coastal shelf areas, our findings suggest that the coastal marine sources of DMS, COS and CS2 may have been underestimated in previous work.