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

Abstract

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 sur- face. Concentration plots of NO3 � versus PO4 3� , 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 3� and Si(OH)4. The temporal changes in integrated nitrate, phosphate and silicate concentrations were well described by logis- tic models that showed maximum consumption rates of 11.8, 0.82, and 17.8 mmol m �2 d �1 , respec- tively, 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 .