Nutrient dynamics in the western Canadian Arctic. I. New production in spring inferred from nutrient draw-down in the Cape Bathurst Polynya

Ice-retreat from the Cape Bathurst Polynya occurred in late May and early June 2004, and was quickly followed by a decrease in dissolved nutrient concentration at the sea surface. Concentration plots of NO3 versus PO4, and Si(OH)4 versus NO3 showed the ratios of nutrient uptake in the surface layer were in proportions expected for diatom growth (N:P 13.1:1; Si:N 1.8:1) and that water-column NO3 was depleted before PO4 and Si(OH)4. The temporal changes in integrated nitrate, phosphate and silicate concentrations were well described by logistic models that showed maximum consumption rates of 11.8, 0.82, and 17.8 mmol m−2 d−1, respectively, and a total seasonal draw-down of 210 ± 19 mmol NO3 m−2. If we include estimates of NO3 supply by advection, nitrification and freshwater dilution, then the amount of NO3 consumed could be 25−33% higher. Uptake of NO3 above the 1% isolume was balanced by an equivalent (94%) increase in particulate N over a 15 d period beginning at ice break-up. Thus, the amount of particulate spring new production associated with NO3 disappearance was estimated to be 16.1 ± 1.5 g C m−2.