Dynamics of the vernal bloom in the marginal ice zone of the Barents Sea: Dimethyl sulfide and dimethylsulfoniopropionate budgets

Phytoplankton is known to be a I;ey element in the production and eventual oceanic efflux of dimethyl sulfide (DMS) to the atmosphere. We hypothesized that the alternation of Phaeocystis pouchetii and diatoms, the two major algal components of the spring bloom, would modulate the input of particulate organic sulfur (POS), dimethylsulfoniopropionate (DMSP), and DMS into the mixed layer of the marginal ice zone. A bloom of diatoms is expected to present similar pathways but to have very different rates of POS/DMSP/DMS production and POS/DMSP sinking and no or low DMS flux to the atmosphere as contrasted to the cycling occurring during the P. pouchetii phase of the bloom. Our initial hypothesis cannot be accepted based on our observations in the Barents Sea during the spring of 1993. The contribution of diatoms to the water column budgets of DMSP and DMS was significant and cannot be overlooked. We suggest that the physiological stage of the bloom is perhaps more important to biogeochemical cycling than its phytoplankton species composition in controlling DMSP and DMS fluxes in Arctic waters. Loss of particulate DMSP in the mixed layer was mainly by release into the dissolved pool and by sedimentation rather than by grazing, except in ice-free waters. Cycling of DMS in the mixed layer was predominantly biological in ice-free waters, while in Polar Front waters, ventilation was proportionally more important due to depressed microbiology.