Sea ice biological communities and nutrient dynamics in the Canada Basin of the Arctic Ocean

Abstract

Salinity, concentrations of silicate (Si), phosphate (P), and chlorophyll a (chl a), and the species composition of floral and faunal communities were assessed in multi-year (MY) and first-year (FY) ice, and at the water–ice interface, during the SHEBA ice camp drift in the Canadian Basin of the Arctic Ocean, October 1997–October 1998. Mean integrated salinity values varied from 0.1±0.8‰ within the snow–ice boundary to 3.2±1.46‰ at the water–ice interface in the MY ice. Salinity of FY ice increased with increasing ice thickness, from 0.41±0.19‰ in October to 3.39±1.75‰ in March. We found very low concentrations of both Si and P in MY and FY ice in late fall (<0.01 μM), after the summer season of 1997. Mean integrated concentration of nutrients increased with the freeze-up of ice, reaching maximum values in the summer of 1998. Ice algal biomass was dominated by diatoms in the MY and FY ice, with more pennate than centric species. Species of dinoflagellates and green algae were subdominant. Green algae, typically confined to the upper part of the ice, were distributed throughout the ice thickness. During summer, the brackish-water green alga Ulothrix implexa formed long rope-like tufts attached to the hull of the icebreaker; development of this species has not previously been observed in the central Arctic Ocean. Biomass, cell abundance and chl a concentrations were high in the bottom sections of both MY and FY ice during the pre-freezing period, then decreased in winter and reached maximum values in spring and summer. The total algal biomass showed a pattern similar to chl a dynamics, decreasing from 1.7 μg C l −1 in October to values <0.1 μg C l −1 in winter. Algal carbon biomass and chl a concentration co-varied significantly in the FY ice ( r 2=0.79), but less so in the MY ice ( r 2=0.49). An unexpected feature with respect to sea ice invertebrates was the absolute absence of living interstitial fauna within the interior of MY and FY sea ice. In addition, the under-ice fauna was species-poor. Comparisons of SHEBA results with historical data showed that the physical–chemical characteristics of sea ice and the biological structure of ice communities found in this study were very different from conditions during the 1970s. It is likely that the changes resulted from increased melting of the arctic ice pack over the last two decades.