VERTICAL FLUX OF PHYTOPLANKTON AND PARTICULATE BIOGENIC MATTER IN THEMARGINAL ICE-ZONE OF THE BARENTS SEA IN MAY 1993

Hydrography, nutrients, chlorophyll a (chl a), phaeopigments (phaeo) a nd phytoplankton abundance as well as the vertical flux of particulate organic carbon and nitrogen (POC and PON) and pigments in the upper 2 00 m were investigated at 4 stations along a north-south transect in t he Barents Sea in May 1993. Two stations were located in Arctic water and 2 in Atlantic water. The northernmost station had a well-developed ice edge bloom with high abundance of Fragilariopsis sp., Thalassiosi ra spp. and Chaetoceros spp. The phytoplankton community at the ice ed ge and the northernmost Atlantic station was dominated by Phaeocystis sp. colonies in concert with Chaetoceros spp. and Thalassiosira spp. T he phytoplankton community at the southernmost station was dominated b y large Chaetoceros spp. cells. Vertical flux of biogenic matter in th e upper water column (20-100 m) varied along the transect (2.1-13.3 mg chi a m(-2) d(-1), 0.6-11 mg phaeo m(-2) d(-1) and 409-1090 mg POC m( -2) d(-1)), while vertical flux in the deeper water column (100-200 m) was less variable (0.7-2.9 mg chi a m(-2) d(-1), 1.5-6.5 mg phaeo m(- 2) d(-1) and 200-300 mg POC m(-2) d(-1)). Hydrographic conditions, nut rient status and species specific sinking rates did not have a profoun d influence on the vertical flux of phytoplankton. High daily loss rat es of chi a (4 to 18 % d(-1) of standing stock chi a) and microplankto n at 2 stations (southernmost and northernmost Atlantic) was probably caused by high production of extracellular carbon, increasing the aggr egation potential of the phytoplankton community. Evidence of incomple te dissolution of Phaeocystis sp. colonies was observed to a depth of 200 m. Faecal matter and detritus were the main vehicles for the verti cal export of organic matter to deeper water (below 100 m). Protozoan grazing was more important in retaining organic matter and nutrients i n the upper water than mesozooplankton grazing.