The influence of ocean acidification on surface seawater DMS, DMSP and DMSO concentrations

Dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) cycling in the surface ocean has an important impact on the biogenic sulfur loading of the atmosphere. Calcifying phytoplankton, such as the ubiquist coccolithophorids, are import producers of the DMS precursor DMSP. Thus, the effect of increasing pCO2 and consequential acidification of the ocean might impact the sulfur cycle in the future both in the ocean and in the atmosphere. Several studies were performed to investigate the elevated pCO2 effect on DMS and DMSP. However, the results have not built consensus, in fact many are contradictory. During SOPRAN II, DMS, DMSP and DMSO concentrations were measured in a mesocosm study in Bergen (Norway) which investigated the consequences of ocean acidification. With increasing pCO2 the DMS and DMSP concentrations decreased up to four times and up to a factor of 1.3, respectively. The DMSO concentrations also decreased; however, the effect was small. Emiliania huxleyi, a coccolithophorid alga, declined in their cell abundance and this might be the reason for low DMSP and DMS concentrations. However, other algae species, zooplankton and bacteria, which are also more or less affected by ocean acidification, might likewise influence the concentrations of the sulfur compounds. This needs to be clarified by further data analysis.