The nutrient status in sea ice of the Weddell Sea during winter: effects of sea ice texture and algae

Summary Cores and brine samples from sea ice of the Weddell Sea were analyzed for nutrients (phosphate, nitrate and silicate), salinity and chlorophyll a during winter. Stratigraphic analyses of the cores were also carried out. Bulk nutrient concentrations in the sea ice fluctuated widely and did not correlate with salinity. Nutrient concentrations in cores were normalized to sea-water salinity to facilitate comparison. They varied between zero and two or three times those measured in the water column. Differentiation into young and old sea ice, however, revealed that nutrient concentrations in the young ice in many cases corresponded to those in surface seawater. In older ice, nutrients showed signs of increase as well as depletion or exhaustion relative to the water column. Differentiation of core sections according to ice textural classes and analyses of brine samples clarified some relationships between nutrients, salinity and algal biomass. Most of the changes in the nutrient concentrations are attributed to an increase in biological activity as the seasons progress. Silicate is expected to become the first nutrient likely to limit growth of diatoms in the ice which is ascribed to slower regeneration or dissolution of this nutrient relative to phosphate and nitrate. A consequence of silicate exhaustion may be the succession of different algal assemblages, from a diatom dominated community to one in which autotrophic flagellates form the largest component.