Production and release of dimethylsulphide from an estuary in Portugal

The distribution of dimethylsuphide (DMS) and its precursor dimethylsulphoniopropionate, in both particulate (DMSP_p) and dissolved fractions (DMSP_d) was surveyed along estuarine water profiles of Canal de Mira (Ria de Aveiro, Portugal), on 45 occasions during one year. The field campaigns revealed pronounced gradients, which were to some extent interpreted with reference to supporting hydrographic parameters like salinity, temperature and chlorophyll a. Surface water concentrations showed a clear seasonal variation with peak values during the warmer months. Mean summer concentrations for DMS, DMSP_p and DMSP_d, were, respectively, a factor of 1.8, 1.9 and 2.9 times higher than winter concentrations. Surface water concentration was the main factor controlling DMS emissions into the atmosphere, which were estimated to be, as a mean, 5.4 and 27.3 nmol m^-2 h^-1 for winter and summer, respectively. In addition, DMS fluxes from two intertidal mud flat sites in Canal de Mira were examined monthly over a year. Average emission rates were a factor of 2–5 times higher than those estimated for estuarine waters and revealed strong seasonal variations, with summer peaks apparently related to ambient temperature. The relative contribution of estuarine waters and mud flats for local DMS budget is discussed in terms of tidal cycles and exposed surface area.