Pathways of carbon cycling in the euphotic zone: The fate of large-sized phytoplankton in the Northeast Water Polynya

The fate of large-sized phytoplankton and pathways of carbon cycling in surface waters, i.e. recycling within or export out of the euphotic zone, were investigated in the Northeast Water (NEW) Polynya (77-81°N) from 23 May to 17 August 1993. Sampling represented a wide range of ice, hydrographic and nutrient conditions. Phytoplankton and zooplankton abundances, and phytoplankton production rates were determined in the field, whereas potential rates of grazing by copepods, dinoflagellates and appendicularians were calculated from abundances and temperature, using assumptions from the literature. The potential downward and lateral export of phytoplankton was also calculated by resolving a carbon budget for the euphotic zone. The present study suggests that, in the NEW, different pathways for the cycling of carbon existed in seasonally ice-free (in the polynya) and continuously ice-covered areas (outside the polynya). Outside the polynya, the fate of large-sized phytoplankton could not be assessed because the heterotrophic community presumably grazed on a variety of food items, including ice algae, microzooplankton and large-sized phytoplankton. In the polynya, the fate of large-sized phytoplankton production was to be mostly recycled at the beginning of sampling and to be mostly exported downward or laterally as the bloom of large-sized phytoplankton developed. Generally, copepods mostly contributed to recycling, but sometimes dinoflagellates or appendicularians alone recycled most of the large-sized phytoplankton production.