Comparison of summer and winter inorganic carbon, oxygen and nutrient concentrations in Antarctic sea ice brine

During summer (January 1991) and winter (April 1992) cruises to the southern Weddell Sea (Antarctica), brine samples were collected from first year sea ice and analysed for salinity, temperature, dissolved oxygen and major nutrient concentrations. Additionally, the carbonate system was determined from measurements of pH and total alkalinity. During winter, brine chemical composition was largely determined by seawater concentration in the course of freezing. Brine temperatures ranged from- 1.9 to- 6.7”C. Precipitation of calcium carbonate was not observed at the corresponding salinity range of 34 to 108. Removal of carbon from the total inorganic carbon pool (up to 500 pmol C, kg-‘) was related to reduced nutrient concentrations, indicating the presence of photosynthetically active ice algal assemblages in the winter sea ice. However, nutrient and inorganic carbon concentrations did generally not reach growth limiting levels for phytoplankton. The combined effect of photosynthesis and physical concentration resulted in 0, concentrations of up to 650 pmol kg-‘. During summer, brine salinities ranged from 21 to 41 with most values> 28, showing that the net effect of freezing and melting on brine chemical composition was generally slight. Opposite to the winter situation, brine chemical composition was strongly influenced by biological activity. Photosynthetic carbon assimilation resulted in a C, depletion of up to 1200 pmol kg-‘, which was associated with CO, (aq) exhaustion and 0, concentrations as high as 933 pmol kg- ’. The concurrent depletion of major nutrients generally corresponded to uptake ratios predicted from phytoplankto