DINOTROPHY: Deuterium in Organic Biomarkers: A new tool to investigate the role of Marine Mixotrophy in the Global Carbon Cycle

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New conceptual understanding sees the traditional dichotomy between producers and consumers in the marine food web replaced by one that recognises that mixotrophy is widespread. Many "phytoplankton" eat, while 50% of "microzooplankton" perform photosynthesis. This mixotrophic behaviour enhances primary production, biomass transfer to higher trophic levels, and affects the sequestration of atmospheric CO2. Science requires a tool to measure the contributions of phototrophy & heterotrophy in plankton to aid in climate change modelling. We have shown that hydrogen (H) isotopic signature of lipids is uniquely sensitive to the expression of heterotrophy relative to photosynthesis. This project will investigate the H isotope fractionation mechanisms (at molecular level, i.e. "site-specific") during biosynthesis of organic compounds in mixotrophic protists. It will establish the H isotope signature of lipid biomarkers as a novel tool to investigate the metabolic changes in these oceanic protists and thus provide a tool to determine the impact of mixotrophy on the global carbon cycle. This project will develop a numerical biochemical model based on a combination of chemostat experiments and cutting-edge mass spectrometry (MS) and nuclear magnetic resonance (NMR) isotopic ratio (ir) measurements. This include using irMS coupled to Gas Chromatography to measure the isotopic composition of lipids and to a high Temperature Conversion Elemental Analyzer after isotope equilibrations for measurement of non-exchangeable H in carbohydrates. NMR spectrometry adapted for the emerging technique of irm-NMR (ir measured by NMR) that can perform position-specific isotope analysis will elucidate the non-statistical distribution of 2H in different sites of a given molecule. The project will foster a new cross-disciplinary group uniquely skilled in isotope biogeochemistry and dedicated to extend our knowledge of the Plankton Physiological Ecology as well as its role on the Earth System.