MEPS 256:13-27 (2003)  -  doi:10.3354/meps256013

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

Zhi-Ping Mei1,6,*, Louis Legendre1,2, Yves Gratton3, Jean-Éric Tremblay4, Bernard LeBlanc1, Bert Klein1, Michel Gosselin5

1GIROQ, Department of Biology, Laval University, Sainte-Foy, Québec G1K 7P4, Canada
2Laboratoire d¹Océanographie de Villefranche (LOV), BP 28, 06234 Villefranche-sur-Mer Cedex, France
3INRS-Eau, 2800 rue Einstein, Sainte-Foy, Québec G1K 4C7, Canada
4McGill University, Department of Biology, 1205 Dr. Penfield, Montreal, Québec H3A 1B1, Canada
5Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada
6Present address: Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada

ABSTRACT: In order to understand the mechanisms responsible for the high productivity and biogeochemical 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 (PTOC) was partitioned into production of dissolved and particulate organic carbon (PDOC and PPOC, respectively), the latter being further partitioned into production of large and small phytoplankton (PL and PS, respectively) using 5 µm as threshold. The highest PTOC was 6 gC m-2 d-1 at peak bloom. The fraction of PDOC in PTOC was lower in periods of high PTOC than those of low PTOC. Averaged over the whole polynya for the sampling period, PDOC and PPOC accounted for 34 and 66% of the fixed carbon, respectively, and 81 and 19% of PPOC were in the PL and PS fractions, respectively. Variations in the integrated assimilation numbers of large and small phytoplankton were mostly explained by nutrients and irradiance. Even though PPOC 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 PPOC 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.

KEY WORDS: Primary production · Phytoplankton biomass · Dissolved organic carbon · Particulate organic carbon · PBopt · Export · Biogeochemical cycling · North Water (NOW) Polynya

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