Model structure and analysis of dimethylsulphide (DMS) production in the southern North Sea, considering phytoplankton dimethylsulphoniopropionate- (DMSP) lyase and eutrophication effects

A model for dimethylsulphide IDMS) production in the southern North Sea is presented. This model is coupled to the phytoplankton model FYFY, which calculates the biomass of different phytoplankton groups with their specific contents of dimethylsulphoniopropionate (DMSP), the precursor of DMS. The combined models provide a synoptic view of the seasonal distribution of DMS and its sea-to-air exchange rates. Results are in close agreement with field data, showing a spring peak and high concentrations in the coastal area off continental Europe. Model analysis shows high sensitivity to phytoplankton DMSP-lyase, particularly in the description of the spring peak of DMS. Omission of this pathway for DMS production leads to an underestimation of the annual sea-to-air flux of up to 25%. Model output also suggests that anthropogenic eutrophication of the southern North Sea may have caused a 2.5-fold increase between the beginning of this century and the 1980s in the mean annual emission of DMS to the atmosphere.