| Summary: | Available data concerning the sinking rates of ice algae are highly divergent, while the characteristics of particles formed from other large organic pools in sea ice have received little study. As an initial step to remedy this situation, funds are provided to study the role of exopolymeric substances (EPS), produced by ice algae, in particle formation. The importance of EPS to particle coagulation and sinking rate is well established for temperate water columns. In sea ice, EPS comprise 20-70% of total particulate organic carbon, but their role in the sinking rate and composition of particles exported from sea ice is poorly understood. Based on previous studies, the PIs predict both positive and negative effects of EPS on particle sinking rate depending on EPS quantity. EPS also is predicted to increase the ratio of carbon to nitrogen (C:N) in the organic matter, which serves as a nutritional indicator. Based on documented trends in the EPS content of first-year Arctic sea ice, the PIs specifically predict slower sinking rates and higher C:N in particles produced after the export of ice algae, and from the upper levels of the ice column. They also predict slower sinking rates and higher C:N where snow cover is thicker. They will measure the sinking rates of particles released from melted sea-ice cores and test their hypotheses by relating the observed sinking rates to variables such as EPS concentration in the ice. Changes in the contribution of the sea-ice community to different flux periods will be investigated using microscopy and DNA-based molecular techniques. Finally, to help explain the spatial variability in the EPS content of sea ice, they will quantify EPS production rates of cultured ice algae as a function of light level. This work is designed to provide a conceptual framework for understanding and predicting spatial and temporal variability in the sinking rates and nutritional quality of particles released from Arctic sea ice in relation to variables measured in the ice such as: snow depth, chlorophyll, particulate organic carbon, and EPS. The knowledge resulting from this study will contribute to our understanding of the Arctic Ocean carbon cycle and how it may be modified in response to climate variability.
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