Winter production of sea ice algae in the western Weddell Sea

Short- and long-term series of observations were carried out during the US–Russian Ice Station Weddell no. 1 (ISW-1) Expedition, 1992, in the western Weddell Sea. The goal of in situ observations was to assess the winter biological dynamics within the 1-year and newly formed sea ice. It was shown that at the initial stage of ice formation, there is a period of mechanical harvesting of plankton cells from the sea water. In this period, the biomass of ice algae was 10–20 times lower, in terms of chlorophyll a concentration, than that of the underlying phytoplankton. A remarkable increase in chlorophyll a content begins when the ice is 30–40-cm thick and environmental conditions are more favourable for algal growth. As a rule, reproduction of algae in the newly formed ice takes place within the lower layer of ice and close to the skeletal layer, where sea water with high nutrient concentrations is transported to the cells through brine channels during oscillation processes. By contrast, the highest concentrations of chlorophyll a in the 1-year ice were found within the upper layers. It was shown that chlorophyll a concentrations produced by the sea ice algae within both the young and the 1-year sea ice were always remarkably higher than chlorophyll a concentrations in the sea water below the ice. These results also indicate that winter production by ice algae in the extensive Antarctic sea ice zone should be considered an important factor in future biological models of the Southern Ocean.