Nutrient limitation of the bottom‐ice microalgal biomass (southeastern Hudson Bay, Canadian Arctic)1

Abstract

In April 1983, differential‐enrichment bioassays were conducted on natural sea‐ice microalgae from Hudson Bay, Canadian Arctic. Incubations were done both in the laboratory (at about 4°– 5°C), and in situ at the ice‐water interface (−1.5°C). Actual growth of the cultures was nutrient limited. On the basis of our observations and using recalculated data from the literature, we tentatively set the mean generation time of Arctic‐ice microalgae between 8 and 17 days. Nitrogen was demonstrated to govern the algal yield when illumination and grazing allowed the algae to grow. The low (NO3− + NO2− + NH4+):PO43− mean ratio (5.9) in the water at the ice interface leads to the same conclusion. In situ dissolved inorganic nitrogen and phosphorus progressively decreased during the course of sampling, but were never exhausted. We hypothesize that the Ks of epontic as well as of other benthic microalgae is higher than that of phytoplankton, so that they cannot deplete the natural nutrient reservoir. We conclude that the bottom‐ice dynamics is controlled not only from above, by the seasonal (climatic) changes in light intensity as generally assumed, but also from below, by the shorter term (hydrodynamic) events of vertical mixing that replenish the ice‐water interface with nutrients.