Role of exopolymers in the cycling of carbon in arctic seas

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Sea-ice harbors various ecological roles, which range from its influence on the Earth's climate and the freshwater balance of the Arctic Ocean, to its significance for the marine food chain. Seasonal sea-ice constitute about 50% of the total ice surface in the Arctic Ocean. During the past two decades, rapid warming of the Arctic and an associated decrease in ice cover have been observed. Current models suggest that this trend will continue. Sea-ice supports a diverse community of organisms, from viruses and bacteria, flagellates, ciliates, crustaceans, and other meiofauna. Primary production in the sea-ice is usually dominated by diatoms, which can reach very high biomasses in the spring.  Diatoms are also responsible for intense phytoplankton blooms taking place in open waters during the summer. Diatoms are main producers of exopolymeric substances (EPS), gel-like substances that can contribute a large fraction of the organic carbon in the sea-ice in the spring. Because EPS are sticky gels, they can favor aggregation and rapid sinking of algal biomass at the termination of blooms. Very little is known on the role of EPS, and the factors that regulate their production, in the Arctic. This research will investigate the dynamics of EPS in seasonal sea-ice and in the water column at the end of diatom blooms in seasonally ice-covered Arctic seas. The general objectives of this study are: 1) to evaluate the influence of biotic and abiotic factors on EPS concentrations and production in the sea-ice and open water in seasonally ice-covered Arctic seas, and 2) to assess the role of EPS in the cycling and sinking of algal blooms under contrasting biochemical environments in the Arctic. This research will contribute to our understanding of the carbon cycle in the Arctic and will provide key knowledge for predictive models in view of on-going changes taking place in the Arctic.