MEPS 255:235-248 (2003)  -  doi:10.3354/meps255235

ABSTRACT: 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 DMSO_d concentrations in addition to those of DMS and DMSP_d. This study is the first to demonstrate this effect for DMSO_d. Weight-specific production rates for DMSO_d due to the presence of copepods in incubation experiments were 0.14 to 23 nmol mg^-1 dry wt (DW) d^-1 (median = 1.02 nmol mg^-1 DW d^-1) and were occasionally higher than rates for the production of DMSP_d. Weight-specific production rates for dimethylsulfide were 0.011 to 2 nmol mg^-1 DW d^-1 (median = 0.23 nmol mg^-1 DW d^-1) and for DMSP_d 0.005 to 6.86 nmol mg^-1 DW d^-1 (median = 0.71 nmol mg^-1 DW d^-1). In comparison, the volumetric and individual-normalized production rates for DMS and DMSP_d, 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 DMSP_d was statistically significant in more than 85% of the incubation experiments conducted, but in fewer than 50% of the incubations for DMSO_d. 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 on in situ level of DMS, DMSP_d and DMSO_d in the North Water. Weight-specific production rates were used to calculate in situ production rates, which ranged from 0.002 to 21.7 nmol m^-3 d^-1 for DMS, from 0.001 to 85.8 nmol m^-3 d^-1 for DMSP_d, and from 0.003 to 184 nmol m^-3 d^-1 for DMSO_d. Comparison of these results with the average concentrations of DMS, DMSP_d and DMSO_d in the water column of the polynya indicates that copepod grazing was a minor mechanism in the release of these compounds in the North Water.

KEY WORDS: Arctic · Biogeochemical cycles · Copepods · Dimethylsulfide · Dimethylsulfoniopropionate · Dimethylsulfoxide · Grazing · Polynya