Temporal variability of dimethylsulfide and dimethylsulfoniopropionate in the Sargasso Sea

Vertical profiles of dimethylsulfide (DMS) and β-dimethylsulfoniopropionate, particulate (pDMSP) and dissolved (dDMSP), were measured biweekly in the upper 140 m of the Sargasso Sea (32°10′N, 64°30′W) during 1992 and 1993. DMS and pDMSP showed strong, but different, seasonal patterns; no distinct intra-annual pattern was observed for dDMSP. During winter, concentrations of DMS were generally less than 1 nmol l-1 at all depths, dDMSP was less than 3 nmol l-1 and pDMSP was less than 8 nmol l-1. In spring, concentrations of both dDMSP and pDMSP rose, on a few occasions up to 20 nmol l-1 in the dissolved pool and up to 27 nmol l-1 in the particulate pool. These increases, due to blooms of DMSP-containing phytoplankton, resulted in only minor increases in DMS concentrations (up to 4 nmol l-1). Throughout the summer, the concentrations of DMS continued to increase, reaching a maximum in August of 12 nmol l-1 (at 30 m depth). There was no concomitant summer increase in dDMSP or pDMSP. The differences among the seasonal patterns of DMS, dDMSP, and pDMSP suggest that the physical and biological processes involved in the cycling of DMS change with the seasons. There is a correlation between the concentration of DMS and temperature in this data set, as required by some of the climate feedback models that have been suggested for DMS. A full understanding of the underlying processes controlling DMS is required to determine if the temperature-DMS pattern is of significance in the context of global climate change.