Dimethylsulfide (DMS) and dissolved and particulate dimethylsulfoniopropionate (DMSPd, DMSPp) were measured in sea surface layer along the Mauritanian coast, Northwest Africa, during the upwelling season in February 2008. DMS, DMSPd and DMSPp surface concentrations of up to 10 nmol L−1, 15 nmol L−1 and 990 nmol L−1, respectively, were measured. The maximum DMSPp concentration is the highest reported from upwelling regions so far and indicates that the Mauritanian upwelling is a hot spot of DMSP and, thus, DMS production. Dinoflagellates were responsible for the DMS production. Other phytoplankton groups seemed to have only a minor or no influence on the DMS and DMSP production. Decreasing nitrogen (i.e. increasing nitrogen limitation) most likely triggered a switch from high DMSP production to high DMS production. It seems that both nitrogen limitation and the intensive solar radiation in the tropics induced stress in DMSP producing algae and activated their antioxidant system. Our results underline the importance of coastal upwelling regions as ecosystems with a pronounced temporal and spatial variability which result in high DMSP and DMS production.