ENVIRONMENTAL-CONTROL AND POTENTIAL FATE OF SIZE-FRACTIONATED PHYTOPLANKTON PRODUCTION IN THE GREENLAND SEA (75-DEGREES-N)

Environmental control and potential fate of phytoplankton production w ere investigated in the Greenland Sea (75-degrees-N) in June 1989. Phy toplankton biomass, taxonomic composition and production were size fra ctionated. Total primary production was generally high (Up to > 0.9 g CM-2 d-1), especially in the Arctic Front. The production per unit bio mass P(B)(z) was a nonlinear function of the vertical distribution of irradiance E(z), especially for the >5 mum fraction where E(z) account ed for 60 to 97 % of the variance of P(B)(z). Much of the subsurface c hlorophyll was probably not photosynthetically active due to limitatio n by irradiance. There was a marked transition in several variables at the Arctic Front. To the west (Arctic Domain), waters were cooler and slightly less saline than to the east (Atlantic Domain), concentratio ns of silicate were lower, and total primary production was generally lower. The structure of phytoplankton assemblages (diatoms and dinofla gellates) changed at the front. Results confirmed the previously repor ted trend of a progressive decrease of phycoerythrin-containing cyanob acteria with increasing latitude. In the Arctic Domain, primary produc tion was generally dominated by cells >5 mum, but this was not proport ionally reflected in the standing stock which was dominated by the <5 mum fraction. This difference between production and standing stock wa s potentially due to strong grazing on the large cells. In the Arctic Front, production was equally shared by large and small cells, but the standing stock was still dominated by cells <5 mum. Potential rates ( i.e. calculated, not measured) of grazing and sedimentation of large v ersus small cells in the Arctic Front were lower than in the Arctic Do main. In the Atlantic Domain, both primary production and standing sto ck were largely dominated by cells < 5 mum.