Distribution of biogenic sulphur compounds during and just after the southwest monsoon in the Arabian Sea

The Arabian Sea is characterised by strong seasonal oscillations of biologi cal productivity generated by its monsoonal climate. The southwest monsoon causes reversal in the surface circulation of the Arabian Sea, which genera tes a seasonal upwelling of nutrient-rich waters along the coast of Oman. C oncentrations of biogenic sulphur compounds were measured on a transect fro m the eutrophic waters off the coast of Oman to the oligotrophic waters of the open Arabian Sea, during the UK NERC Arabesque cruise 27 August-4 Octob er 1994. The concentrations of dimethylsulphide (DMS), dimethylsulphoxide ( DMSO) and dimethylsulphoniopropionate (DMSP) were found to be elevated in t he eutrophic area due to enhanced biological production. However, this incr ease in DMS, DMSO and DMSP concentration was not observed until after the s outhwest monsoon had relaxed, and appeared to correspond to increased conce ntrations of hexanoyloxyfucoxanthin, an indicator of prymnesiophytes. DMSO concentrations were correlated with those of DMS and DMSP in the near surfa ce waters of the Arabian Sea. Additionally, DMSO appeared to be ubiquitous throughout the water column, being easily detectable in deep waters, which suggests that DMSO may act as a sink for DMS in the world's oceans. (C) 199 9 Elsevier Science Ltd. All rights reserved.