Distribution, Occurrence, and Fate of Biogenic Dimethylated Sulfur Compounds in the Yellow Sea and Bohai Sea During Spring

The spatial distributions of biogenic dimethylated sulfur compounds (BDSCs), including dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide, were determined in the Yellow Sea and Bohai Sea during a survey in April-May 2014 and the occurrence and fate of BDSCs in the surface seawater were investigated. The concentrations of DMS and DMSP were significantly correlated with the stocks of chlorophyll a and a decreasing trend was observed from the inshore to the offshore areas. In situ incubation experiments indicated that more than half of the degraded dissolved DMSP (DMSPd) was transformed into DMS. Irradiation experiments showed that the photooxidation of DMS under ultraviolet B, ultraviolet A, and visible light accounted for 23.9%, 71.8%, and 4.3% of the total photooxidation of DMS, respectively. The sea-to-air fluxes of DMS ranged from 0.24 to 34.11 mu mol m(-2) day(-1) with a mean of 8.84 mu mol m(-2) day(-1). A comparison of the DMS production rate and main removal rates indicated that bioproduction cannot completely maintain the removal of DMS and might not be the only but the primary source of DMS in the surface seawater. Additionally, the average turnover times of microbial consumption, photooxidation, and sea-to-air exchange of DMS were 1.53, 1.16, and 4.28 day and the contributions of the three removal pathways were 40.0%, 41.2%, and 18.8% respectively; this indicated that microbial consumption and photooxidation played dominant roles in controlling the removal of DMS from the surface seawater. Plain Language Summary Dimethylsulfide (DMS) in the atmosphere can alter the environment and climate by its certain oxidation products. DMS emission from the ocean to the atmosphere is the most important source of atmospheric DMS. Therefore, it is of great importance to investigate the distribution, occurrence, and fate of marine DMS. In our study, the concentrations of DMS, dimethylsulfoniopropionate (DMSP, the precursor of DMS), and dimethylsulfoxide (the photooxidation or microbial oxidation product of DMS) in the marine boundary layer of the Yellow Sea and Bohai Sea were determined, and in situ deck incubation and irradiation experiments were conducted to research the cycle processes of the dimethylated sulfur compounds. We found that the concentrations of DMS and DMSP were mainly influenced by the freshwater input in the study area. The concentrations of DMS and DMSP were significantly correlated with the stocks of chlorophyll a. DMS in the surface water was primarily removed by microbial metabolism and photooxidation. In addition, the flux of DMS from the study area to the atmosphere was also estimated, suggesting it is an important net source of atmospheric DMS.