Influence of copepod grazing on concentrations of dissolved dimethylsulfoxide and related sulfur compounds in the North Water, northern Baffin Bay

The impact of copepod grazing on the biogeochemical cycling of dimethylated-sulfur compounds was investigated in the North Water polynya, northern Baffin Bay, during the period 21 April to 24 June 1998. The results show that zooplankton grazing can influence DMSOdconcentrations in addition to those of DMS and DMSPd. This study is the first to demonstrate this effect for DMSOd. Weight-specific production rates for DMSOddue to the presence of copepods in incubation experiments were 0.14 to 23 nmol mg–1dry wt (DW) d–1(median = 1.02 nmol mg–1DW d–1) and were occasionally higher than rates for the production of DMSPd. Weight-specific production rates for dimethylsulfide were 0.011 to 2 nmol mg–1DW d–1(median = 0.23 nmol mg–1DW d–1) and for DMSPd0.005 to 6.86 nmol mg–1DW d–1(median = 0.71 nmol mg–1DW d–1). In comparison, the volumetric and individual-normalized production rates for DMS and DMSPd, which were used to derive weight-specific production rates for these compounds, were similar to published results. The influence of copepod grazing on the production rates of DMS and DMSPdwas statistically significant in more than 85% of the incubation experiments conducted, but in fewer than 50% of the incubations for DMSOd. These results suggest that the impact of copepod grazing might be less important for the biogeochemical cycling of DMSO than that of DMS and DMSP. Analysis of the data indicates that grazing may influence the release of DMSO and DMSP in different ways. A secondary objective of the study was to assess the potential role of copepod grazing onin situlevel of DMS, DMSPdand DMSOdin the North Water. Weight-specific production rates were used to calculatein situproduction rates, which ranged from 0.002 to 21.7 nmol m–3d–1for DMS, from 0.001 to 85.8 nmol m–3d–1for DMSPd, and from 0.003 to 184 nmol m–3d–1for DMSOd. Comparison of these results with the average concentrations of DMS, DMSPdand DMSOdin the water column of the polynya indicates that copepod grazing was a minor mechanism in the release of these compounds in the North Water.