Biogeochemistry of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the surface microlayer of the western North Pacific

Twenty-eight sea-surface microlayer samples as well as the bulk surface water samples were collected at seven stations in the western North Pacific in early June 2001 for studying the behavior of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the surface water. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were, respectively, 2.8 (0.5-12.2), 13.9 (7.3-39) and 23.4 (6.6-100.5) nM in the surface microlayer, and those in the bulk surface water were 2.6 (0.8-6.9), 11.2 (5.2-23.4) and 19.1 (6.2-72.8) nM. In the bulk surface water, the concentrations of DMS were positively well correlated with the concentrations of chlorophyll a. The enrichment factors (EF) of DMS in the surface microlayer ranged from 0.38 to 2.94 with a mean of 1.10, and those of chlorophyll a ranged from 0.72 to 2.61 with a mean of 1.28. The mean EFs of DMSPd and DMSPp in the microlayer were 1.24 and 1.14, respectively. A striking finding in this study is that the concentrations of DMS, DMSPd and DMSPp in the microlayer were closely correlated with them in the corresponding bulk surface water, suggesting that the microlayer DMS, DMSPd and DMSPp are directly controlled by the bulk surface water below. It is noted that the production and consumption rates of DMS in the microlayer were generally higher than those in the bulk surface water and the production rates of DMS were significantly well correlated with the concentrations of DMSPd. In addition, our study showed that the major sink of DMS in the microlayer was escape into the atmosphere, which greatly exceeded its bacterial consumption.