Temporal and spatial variations of three dimethylated sulfur compounds in the Changjiang Estuary and its adjacent area during summer and winter

Environmental context Dimethylsulfide is a biogeochemically important sulfur gas emitted from the oceans that can lead to aerosol formation, thereby affecting earth albedo and climate. Studies on the biogeochemistry of dimethylsulfide and its precursors and oxidation products in coastal waters can link the atmospheric chemistry of dimethylsulfide with the bioavailable organic sulfur pool in the oceans. The ensuing information is essential for understanding the biogeochemical dynamics of sulfur and its global cycles. Abstract The spatiotemporal distribution patterns of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO) and chlorophyll a (Chl-a), as well as the oceanographic parameters influencing the concentrations of DMS, DMSP and DMSO, were measured in the Changjiang Estuary and its adjacent area during two cruises from 21 February to 10 March 2014 and from 10 to 22 July 2014. The concentrations of DMS and DMSP showed significant seasonal variation, i.e. higher values in summer than in winter. This result corresponded well with the seasonal change in Chl-a in the study area. The distribution of dissolved DMSO (DMSOd) decreased significantly with distance from shore, suggesting a primary source of terrestrial and riverine inputs. The seasonal variations of both DMSOd and particulate DMSO (DMSOp) were weaker than other sulfur compounds. Significant relationships were observed between DMS, particulate DMSP (DMSPp), DMSOp and Chl-a, suggesting that phytoplankton biomass plays an important role in controlling the distributions of DMS, DMSP and DMSO in the study area. The positive relationship between DMSPp and DMSOp suggested similar sources and cellular functions in algae, whereas the oxidation of DMS to DMSOd appeared to be a predominant source of DMSOd in winter in the area adjacent to the river mouth. The average sea-to-air fluxes of DMS in the Changjiang Estuary and its adjacent area were 0.37 and 1.70 µmol m–2 day–1 in winter and summer respectively; these values are much lower than those in other continental shelf seas.