Dimethylsulfide (DMS) production by size-fractionated particles in the Labrador Sea

We measured the production of dimethylsulfide (DMS) by size-fractionated pa rticles during a cruise in the Labrador Sea in May-June 1997. The experimen ts were conducted at 2 stations characterised by low levels of nitrate and high levels of phytoplankton biomass and particulate dimethylsulfoniopropio nate (DMSPp). Samples were size fractionated to assess the size distributio n of DMSPp and the potential DMS production associated with the different s ize fractions. The potential for DMS production was estimated by incubating the filters in pre-filtered and boiled seawater amended with 500 nM of dis solved DMSP (DMSPd). At both stations, the highest DMSPp concentrations wer e measured in the 2 to 11 and >20 mu m size fractions. Elevated potential n et DMS production rates were also associated with these 2 size fractions, w hich were responsible for 40 to 53 % and 23 to 31% of the cumulative produc tion, respectively. Only 4% of the potential net DMS production was measure d in the 0.7 to 2 mu m fraction, which presumably contained many of the fre e-living bacteria. The potential net DMS production rates of the different size fractions were linearly related (Spearman correlation coefficient = 0. 86) to the concentrations of DMSPp in the fractions. These results suggest that DMSP-cleaving activity was spatially associated with DMSP-producing al gae or DMSP-rich detritus (e.g. faecal pellets, marine snow).