VARIATION IN PHYTOPLANKTON STANDING STOCK, CHEMICAL-COMPOSITION AND PHYSIOLOGY DURING SEA-ICE FORMATION IN THE SOUTHEASTERN WEDDELL SEA, ANTARCTICA

Changes in physico-chemical conditions, phytoplankton biomass, biochem ical composition and primary productivity were investigated during aut umnal sea-ice formation in the southeastern Weddell Sea, Antarctica. D uring sea-ice growth, brine salinities gradually increased with decrea sing temperatures. Nutrient concentrations in the brine of sea ice old er than 2 weeks were lower than calculated from initial surface seawat er values. The concomittant accumulation of phytoplankton biomass coul d not be explained solely by physical enrichment. We suggest that seve ral microalgal species retained the capacity to assimilate nutrients a nd continued to grow in newly formed sea ice. However, nutrient deplet ions were moderate, and biochemical analyses did not indicate nutrient stress of algal metabolism. Relative abundance of smaller diatom spec ies increased during ice growth, suggesting that pore space available for colonization in conjunction with physiological acclimation capacit y were major factors determining successional patterns in recently for med sea ice. Even though ice algal assemblages apparently sustained th e capacity to acclimate to reduced irradiances brought about by ice gr owth and increasing snow cover, maximum primary production was conside rably lower than values usually reported from spring and summer ice co mmunities. Therefore, autumnal primary production in newly formed sea ice may not add greatly to total annual production, but may provide an important food source for ice-associated grazers during the winter pe riod, when phytoplankton biomass in the water column is extremely low.