Collaborative Research: Controls on the Photosynthetic Isotope Effect in the Ocean: The Roles of CO2, Productivity and Species

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WAKEHAM/FREEMAN 9401765/9412739 The relationship between CO2(aq) and the fractionation of carbon isotopes during carbon fixation in the ocean plays a major role in preserving climatically-drive isotopic signatures in sediments. It is known that the fractionation of carbon isotopes during photosynthesis is dependent on a number of factors, including CO2(aq) , nutrient concentrations, temperature, rate of primary production, and species composition. Sedimentation of partculate matter in the ocean then transfers part of this isotopic signal to the sediments, where the isotopic signal may be used as a proxy for inferring past environmental conditions. Factors which determine the photosynthetic isotope fractionation (ep) will be examined in the context of the hypothesis that there is no generally applicable relationship between CO2(aq) and ep. Rather, regional environmental conditions are critical control and different molecular biomarkers may record a variety of ep - CO2(aq) relationships. Three markedly different environments will be used in the study 1) the North Atlantic between the Gulf of Maine and the Sargasso Sea; 2) the equatorial Pacific between 12 degree N and 12 degress S at 140 degree W; and 3) the Peru upwelling area. Isotopic compositions of selected biomarkers will be interpreted using synoptic measurements of temperature, CO2(aq) , segma13C DIC, nutrients and photoplankton species composition. The information will make it possible to reconstruct the paleoenvironmental record in marine sediments and will provide a basis for future assessments of ocean-climate relationships using combined biomarker and isotope techniques.