Synthesis of particulate and extracellular carbon by phytoplankton at the marginal ice zone in the Barents Sea

Abstract

Large phytoplankton biomass accumulates during ice‐edge blooms in Arctic waters, where taxa such as diatoms or the prymnesiophyte Phaeocystis pouchetii usually dominate. Based on characteristics from temperate phytoplankton, we hypothesized that in Barents Sea waters, a larger fraction of primary production would be extracellular (for synthesis of colonial mucilage) during periods of dominance by P. pouchetii as opposed to periods when diatoms dominated. This alternation of P. pouchetii and diatoms would affect the relationship between the particulate and dissolved carbon pools in the upper water column of the marginal ice zone (MIZ). Results presented in this paper do not support this hypothesis. Although P. pouchetii contributed strongly to the extracellular carbon pool (mucilage and dissolved organic carbon, DOC) during an ice‐edge bloom in May 1993, arctic diatoms contributed an equal amount of exuded carbon. Three process stations visited along a north‐south transect in the MIZ in the Barents Sea, presented between 36% and 55% of the primary production as extracellular carbon, defined as labeled organic matter which passes through a Whatman GF/C filter. No difference in the carbon allocation between diatom‐ and P. pouchetii‐rich phytoplankton was observed in these stations. In contrast, the station located in ice‐free waters had 18% of primary production in the extracellular fraction. These results (1) highlight similar carbon allocation for diatom‐ and P. pouchetii‐dominated phytoplankton in surface waters of the Barents Sea during the spring and/or ice‐edge bloom at the MIZ and (2) suggest that polar phytoplankton may be stronger producers of extracellular carbon, and possibly DOC, than previously thought.