Phytoplankton production in the North Water Polynya: size-fractions and carbon fluxes, April to July 1998

摘要

In order to understand the mechanisms responsible for the high productivity and bio-geochemical cycling of carbon in the North Water Polynya (NOW), we determined physical properties and nutrient concentrations of the upper water column, and phytoplankton production, during spring/summer (April to July) 1998. Phytoplankton production of total organic carbon (P_(TOC)) was partitioned into production of dissolved and particulate organic carbon (Pnoc and Ppoo respectively), the latter being further partitioned into production of large and small phytoplankton (P_L and P_S, respectively) using 5 m as threshold. The highest P_(TOC) was 6 g C m~(-2) d~(-1) at peak bloom. The fraction of P_(DOC) in P_(TOC) was lower in periods of high P_(TOC) than those of low P_(TOC) Averaged over the whole polynya for the sampling period, P_(DOC) and P_(POC) accounted for 34 and 66 % of the fixed carbon, respectively, and 81 and 19% of P_(POC) were in the P_L and P_S fractions, respectively. Variations in the integrated assimilation numbers of large and small phytoplankton were mostly explained by nutrients and irradiance. Even though P_(POC) was dominated by large phytoplankton, the sinking rates of the phytoplankton cells were relatively low (0 to 0.7 m d~(-1)), hence low export of P_(POC) to depth (17%), and relatively high potential transfer to large pelagic organisms through the herbivorous food web. This explains why the NOW is a major feeding and spawning area for fish, mammals and birds.