Evaluating the Environmental Influences on D/H Fractionation in Algal Lipids

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A growing interest in using lipid D/H ratios in biogeochemistry and paleoclimatology has resulted in the application of this new tool advancing more rapidly than our understanding of the processes that control D/H fractionation in algae. A quantitative framework in which to evaluate measured D/H values is still lacking. In this project, researchers at the University of Washington will conduct continuous culture experiments with the marine diatom Thalassiosira psuedonana and the coccolithophorid Emiliania huxleyi at a range of nitrate- and light-limited growth rates, temperatures and salinities to determine how these environmental conditions affect D/H fractionation in lipids. Unlike batch cultures, chemostats permit the evaluation of cells at steady state, under controlled laboratory conditions. These results will be validated with natural populations of phytoplankton in three field experiments. In situ incubation experiments will be conducted in the euphotic zone of subpolar and subtropical North Pacific Ocean sites to evaluate the influence of light- and nutrient-limited growth rate on D/H fractionation in lipids from E. huxleyi. The influence of temperature on D/H fractionation in a natural phytoplankton population will be evaluated by monthly sampling of Lake Washington over the course of a year. D/H fractionation will be determined by comparing the isotopic difference between individual lipids and growth water. Both acetogenic (linear) and isoprenoid (branched) lipids will be analyzed in every experiment. Differences in D/H fractionation in lipids from different biosynthetic pathways will provide the means to formulate and test hypotheses of D/H fractionation mechanisms. Broader Impacts: The environmental education of high school students, undergraduates, women and the public will be advanced by this research. Of 10 lab group members working with the principal investigator during the last year, 4 were women and 3 were undergraduates. Two undergraduates joined the principal investigator's expedition to the Marshall Islands and Kosrae in Summer 2009. The lab website has averaged more than 2000 hits per day in recent months.