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MEPS 484:47-62 (2013)  -  DOI: https://doi.org/10.3354/meps10298

Nutrient dynamics in the western Canadian Arctic. II. Estimates of new and regenerated production over the Mackenzie Shelf and Cape Bathurst Polynya

Kyle G. Simpson1,3,*, Jean-Éric Tremblay1,4, Sonia Brugel2, Neil M. Price

1Department of Biology, 1205 Ave. Dr. Penfield, McGill University, Montréal, Québec H3A 1B1, Canada
2Institut des Sciences de la mer de Rimouski, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada
3Present address: Institute of Ocean Sciences, Fisheries & Oceans Canada, PO Box 6000, 9860 West Saanich Road, Sidney, British Columbia V8L 4B2, Canada
4Present address: Département de Biologie, Université Laval, Québec, Québec G1K 7P4, Canada

ABSTRACT: Uptake of 15N-labelled nitrate, ammonium, and urea was measured over a quasi-annual cycle in the Cape Bathurst Polynya in the Amundsen Gulf and on the Mackenzie Shelf, during the Canadian Arctic Shelf Exchange Study (CASES) in 2003 and 2004. Before the phytoplankton bloom and in autumn, nitrogen uptake was slow, representing less than 5% of annual consumption. Uptake rates increased exponentially after ice retreat and within 3 wk reached a maximum of 38.6 mmol N m-2 d-1. During spring, NO3- uptake supported new production of 166 mmol N m-2 and f-ratios rose from 0.1-0.2 to 0.6-0.9. Filter fractionation showed that GF/F filters retained 93.1 ± 1.3% of the 15N incorporated into particulate matter, suggesting that phytoplankton were responsible for the majority of the N uptake. Although free-living bacteria took up relatively more 15N in autumn and in the lower part of the euphotic zone than phytoplankton, their assimilation of inorganic N had little effect on water column integrated f-ratios or new production. Urea supplied almost half the N assimilated by phytoplankton annually and about 80% of the regenerated production during the spring bloom. Total new production, estimated from water column integrated 15N-nitrogen uptake rates and linear models that interpolated rates over unsampled periods, was 342-415 mmol N m-2 yr-1. Total annual N production for the region was 1.24-1.48 mol N m-2 yr-1.


KEY WORDS: Nitrogen uptake 15N isotopes · 15N uptake · Phytoplankton · Bacteria · Amundsen Gulf · Arctic Ocean · New production · Primary production · Polynya


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Cite this article as: Simpson KG, Tremblay JÉ, Brugel S, Price NM (2013) Nutrient dynamics in the western Canadian Arctic. II. Estimates of new and regenerated production over the Mackenzie Shelf and Cape Bathurst Polynya. Mar Ecol Prog Ser 484:47-62. https://doi.org/10.3354/meps10298

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