Distribution and metabolism of dimethylsulfoniopropionate (DMSP) and phylogenetic affiliation of DMSP‐assimilating bacteria in northern Baffin Bay/Lancaster Sound

We determined the distribution and bacterial metabolism of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the two dominant surface water masses in northern Baffin Bay/Lancaster Sound during September 2008. Concentrations of particulate DMSP (DMSPp; 5–70 nmol L −1 ) and the DMSPp:Chl a ratios (15–229 nmol μ g −1 ) were relatively high, suggesting the presence of DMSP‐rich phytoplankton taxa. Photosynthetic picoeukaryotes and total prokaryotes were tenfold and threefold more abundant in Baffin Bay surface water (BBS) than in Arctic surface water (AS), respectively. Heterotrophic bacterial production (0.07–2.5 μ C L −1 d −1 ) and bacterial turnover rate constants for dissolved DMSP (DMSPd) were low (0.03–0.11 h −1 ) compared with the values previously reported in warmer and more productive environments. Nonetheless, a relatively large proportion (12%–31%) of the DMSP metabolized by the bacteria was converted into DMS. Additionally, between 40% and 65% of the total bacterial cells incorporated sulfur from DMSPd, with Gammaproteobacteria and non‐ Roseobacter Alphaproteobacteria (Alf R‐ ) contributing proportionally more to total DMSP‐incorporating cells. The contribution of Alf R‐ to the total prokaryotic community was 50% higher in BBS than in AS, while the bacterial rate constants for DMSPd turnover were 78% higher in BBS than in AS. These results show that the two different Arctic water masses host specific microbial assemblages that result in distinct affinity for DMSP.