Contents of total organic sulfur and dimethylsulfoniopropionate in five marine phytoplankton groups

Abstract

Ocean emit variety of volatile sulfur compounds to the atmosphere through air-sea gas exchange including dimethylsulfide (DMS), carbon disulfide (CS2), methanetiol (MeSH), dimethyldisulfide (DMDS), hydrogen sulfide (H2S), and carbonyl sulfide (COS). DMS is the most abundant form of sulfur released from the ocean (Kettle et al., 1999). Biological production of DMS is a major source of tropospheric sulfur and can affect the Earth's radiation balance. DMS, which plays such a role in the global environment, is mostly caused by decomposition of dimethylsulfo niopropionate (DMSP), a precursor of oceanic marine organisms. Thus, the role of marine phytoplankton in relation to the circulation of sulfur in the ocean is very important. Phytoplankton not only has DMSP, a precursor of DMS, but also possesses DMSP lyase, and has a great influence on DMS production through various actions in the ocean. The content of organic sulfur (especially DMSP) in marine phytoplankton varies considerably between taxa and even within the same species because there is considerable variability depending on environmental conditions (temperature, pH, CO2 concentration, nutrient status and irradiation). In this study, the contents of major sulfur contents in each species of phytoplankton were analyzed and quantified. Although in some phytoplankton groups, most of the sulfur is found in the protein fraction (Cuhel et al., 1982, Giovanelli et al., 1980), other sulfur such as DMSP compounds may represent equally significant percentages or the majority of the sulfur in other phytoplankton. The species studied in this study were divided into five classes. Species belonging to all taxa maintain organic sulfur, carbon and nitrogen at similar rates. Since organic sulfur, organic carbon and organic nitrogen are essential elements for the growth of organisms, they are maintained in a constant ratio. On the other hand, the ratio of DMSP to the total POS of these phytoplanktones is very high in the ratio of dinoflagellates and prymnesiophytes. Most of the species belonging to this class have high levels of organic sulfur in DMSP form. These results indicate that species belonging to dinoflagellates or prymnesiophytes, which have a large amount of DMSP, are more influential on the production of DMS gas emitted from the ocean.