PHYTOPLANKTON OF THE BARENTS SEA - THE END OF A GROWTH SEASON

Few phytoplankton investigations have been carried out at the end of t he growth season, particularly in the Arctic. In the present study, we monitored the phytoplankton distribution in relation to environmental conditions in the Barents Sea in September 1988 and October 1987. An ice-edge bloom was found in September at 80 degrees N in a stratified meltwater layer, lasting until new ice formation and southward advecti on of the ice cover commenced in the middle of the month. Phytoplankto n populations in the marginal ice zone at this time were not nutrient limited, but biomass was probably reduced due to grazing by small cope pods. Lower chl/C and chl/N ratios in the phytoplankton above the pycn ocline than below in September indicated light-adapted populations. In October the particulate matter was rich in carbon, but had low chloro phyll content, indicating high levels of detritus. The hydrographic co nditions in October differed greatly fi-om those observed in September . The combination of freezing and mixing resulted in higher salinity a nd nutrient concentrations, and caused a homogeneous distribution, as well as reduction, of the phytoplankton stocks in the upper water colu mn. During late October, low incoming radiation, combined with deep ve rtical mixing, resulted in light-limiting conditions for the algae, ev entually stopping photosynthesis and terminating the growth season in the northern Barents Sea.