Significance of sedimentation and grazing by ice micro- and meiofauna for carbon cycling in annual sea ice (northern Baffin Bay)

The fate of first-year ice algae production was assessed from April to June 1998, in the North Water Polynya. A landfast ice station was regularly visited and sampled for biomass, composition, and production of bottom ice algae, composition and grazing of the bottom ice meiofauna, and under-ice sedimentation. The latter was assessed using particle interceptor traps, which were installed at 1 m underneath the ice. The composition, carbon biomass and grazing of the bottom ice microfauna were also assessed at various stations within the polynya. A carbon budget for ice production and export, including meio-and microfauna grazing and sedimentation, was calculated based on 2 independent estimates. At the landfast ice station, the ice algae community was strongly dominated by pennate diatoms, with Nitzschia frigida averaging 85% of total cell numbers. The biomass of microheterotrophs and microautotrophs was less than 1% of total bottom ice carbon at the stations visited. Heterotrophic dinoflagellates and ciliates dominated the bottom ice microfauna community. Size-frequency distributions for the dominant ciliates (Strombidium spp. and hypotrichs) and dinoflagellates suggest that only the latter were able to utilise ice diatoms as a food resource. There was good agreement between carbon budget estimates and results showed that very little ice algal production was channelled through the meio-and microfauna within the ice. The bulk of the bottom ice carbon biomass was readily exported to the water column through direct sinking (75% of ice export). These results stress that the main flow of organic carbon at the ice-water interface was through sedimentation of ice algae and suggest that food-web interactions within the ice do not influence the availability of ice algae to pelagic grazers, in seasonally ice covered areas.