Light-stimulated production of dissolved DMSO by a particle-associated process in the Ross Sea, Antarctica

Dimethylsulfoxide (DMSO) is an abundant form of methylated sulfur in marine systems and it is known to be produced from dimethylsulfide (DMS). Using radiolabeled S-35-DMS and gas chromatography techniques, we quantified the dissolved DMSO (DMSOd) produced from photo- and biological oxidation of dissolved DMS and compared the DMSOd production from these pathways with the net change in DMSOd concentrations in unfiltered seawater samples. The net change in DMSOd in light-exposed treatments exceeded DMSOd production from photo- plus biological oxidation of dissolved DMS. This indicated that DMSOd was produced by one or more light-driven processes likely associated with particulate material. Results from in situ incubation arrays showed that the relative importance of DMSOd production processes was dependent on irradiation depth, with the unidentified particle-associated process and dissolved DMS photooxidation the main DMSOd sources close to the surface (0-10 m) and biological oxidation of dissolved DMS the main process at depths at which the light level was low (> 10 m). Deckboard and in situ incubations revealed that DMSOd production from the particle-associated process was stimulated by ultraviolet radiation. Higher particle-associated production of DMSOd in samples more prone to suffer light-induced stress supports the hypothesis that this process was related to phytoplanktonic biosynthesis and release of DMSO because of oxidative stress. Our results suggest that particle-associated DMSOd production is an important source of DMSOd in surface waters of the Ross Sea and also help to explain why DMSOd is periodically the main organosulfur compound detected in the upper water column.