Research papersDimethylsulfide and dimethylsulfoniopropionate production along coastal waters of the northern South China Sea

•DMSP/DMS distribution in northern coasts of SCS in summer is firstly reported.•Bottom DMS increased first then decreased with increasing temperature.•Light intensity had a significant positive effect on particulate DMSP production.

The gross biological dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) production in surface and bottom waters along the coasts of the northern South China Sea (SCS) were investigated during summer of July-August 2000. In surface water, the averaged concentrations of particulate DMSP (DMSPp) and DMS were 42.60±31.94 nM and 2.12±1.38 nM, respectively. In bottom water, the mean DMSPp and DMS contents were 26.37±20.83 nM and 2.09±1.55, respectively. Both DMSPp and DMS contents significantly varied spatially (P<0.05, n=40), but not vertically (P>0.05, n=40). The highest DMSPp concentration (100.62 nM) was recorded on the surface of Shenzhen waters, whereas the lowest (4.33 nM) was on the surface of Zhanjiang waters. DMS fluctuated correspondingly; the highest (6.79 nM) and lowest (0.83 nM) values occurred on the surface of Shenzhen water and bottom water of Nan'ao Island (Shantou), respectively. Correlation analysis further revealed that DMS/DMSPp production was not closely related with salinity and chlorophyll a content (P>0.05, n=40). However, the bottom DMS increased with increasing temperature when it is lower than 28.2 °C (r2=0.52, P<0.01, n=13), whereas it decreased as the temperature further increased (r2=0.86, P<0.01, n=8). Moreover, in surface waters, light intensity showed a significant positive effect on DMSPp production (r2=0.37, P<0.01, n=20), with elevated DMSP concentration under high irradiance. Overall, the sea-to-air fluxes of DMS across the coastal area of the northern SCS in summer were within the range of 0.24-15.07 μmol m−2 d−1, with a mean flux of 2.12±3.20 μmol m−2 d−1.