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 i n surface waters, i.e. recycling within or export out of the euphotic zone, were investigated in tie Northeast Water (NEW) Polynya (77-81 de grees N) from 23 May to 17 August 1993. Sampling represented a wide ra nge of ice, hydrographic and nutrient conditions. Phytoplankton and zo oplankton abundances, and phytoplankton production rates were determin ed in the field, whereas potential rates of grazing by copepods, dinof lagellates and appendicularians were calculated from abundances and te mperature, using assumptions from the literature. The potential downwa rd and lateral export of phytoplankton was also calculated by resolvin g a carbon budget for the euphotic zone. The present study suggests th at, in the NEW, different pathways for the cycling of carbon existed i n seasonally ice-free tin the polynya) and continuously ice-covered ar eas (outside the polynya). Outside the polynya, the fate of large-size d phytoplankton could not be assessed because the heterotrophic commun ity presumably grazed on a variety of food items, including ice algae, microzooplankton and large-sized phytoplankton. In the polynya, the f ate of large-sized phytoplankton production was to be mostly recycled at the beginning of sampling and to be mostly exported downward or lat erally as the bloom of large-sized phytoplankton developed. Generally, copepods mostly contributed to recycling, but sometimes dinoflagellat es or appendicularians alone recycled most of the large-sized phytopla nkton production.