Distributions of dimethylsulfide and its related compounds in the Yangtze (Changjiang) River Estuary and its adjacent waters in early summer

Dimethylsulfide (DMS) is an important and dominant sulfur compound that is transferred from the ocean to the atmosphere. In this study, the spatiotemporal variations in DMS concentrations and its two closely related compounds, namely, dimethylsulfoniopropionate (DMSP) and acrylic acid (AA), were investigated in the Yangtze (Changjiang) River Estuary and its adjacent waters, where the salinity changed dramatically in June 2014. The concentration ranges (average values) of DMS, DMSP, and AA were 1.10-27.5 (8.53), 5.93-195 (40.1), and 4.2-122.6 (17.9) nmol L−1 in the surface waters, respectively. The DMS and DMSP concentrations were higher in the study area than in its neighboring regions because of the high levels of nutrients originating in the Yangtze and Qiantang Rivers. However, the AA concentration was lower in the study area. Although no significant correlations were found between DMS, DMSP, or AA and salinity, high concentrations of DMS, AA, and DMSP were recorded between the salinity levels of 26‰ and 31‰. DMS and AA concentrations were positively correlated with chlorophyll a. The average AA/(DMSP+AA) and DMS/(DMSP+AA) ratios were 36.9% and 17.1%, respectively. The vertical profiles of DMSP and DMS presented similar variation patterns, and high concentrations of both compounds were mostly detected in the surface waters. By contrast, AA showed a different variation pattern compared with those of DMSP and DMS because AA could have other potential sources. The low average sea-to-air flux of DMS (that is, 6.55 μmol m−2 d−1) was mainly attributed to the low wind speed in early summer.