EAGER: Collaborative Research: A Critical Examination on the Climatic and Environmental Factors Controlling the H isotopic Fractionation Between Plant Leaf Waxes and Precipitation

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Intellectual merit: Precipitation isotopic ratio is arguably the best proxy for quantitative continental paleoclimate reconstructions. Traditional archives, ice cores and speleothems, are spatially restricted. dD values of plant leaf waxes represent a potentially powerful and widely applicable proxy. However, there is major uncertainty in the hydrogen isotopic fractionation between leaf waxes and precipitation (åwax-p) under different climatic and environmental conditions. Several studies have attempted to obtain the mean åwax-p values from lake surface sediments, or even directly from plant leaves, but with only limited success. We propose to determine the dD values of leaf waxes from modern aerosol samples from contrasting ecosystems. Leaf waxes in aerosols integrate current production from higher plants, allowing us to accurately define the åwax-p values throughout the seasonal cycle under specific environmental settings. For the proposed EAGER project, we intend to study two climatically distinct sites (Arizona and Georgia in the US), in order to demonstrate the feasibility of the proposed approach. If successful, we intend to study a global assortment of sites across vegetation and climate gradients. Broader impacts: The proposed work will generate the most accurate values of the apparent hydrogen isotopic fractionation (åwax-p) between modern plant leaf waxes and rainfall in the two highly contrasting climatic and environmental settings, and will pave the way for more comprehensive studies in the future. The results are fundamental for quantitative translation of leaf wax hydrogen isotopic data into paleoclimatic records. This study will promote multidisciplinary collaborations (organic/isotopic geochemistry and atmospheric science), and allow cross-disciplinary training of graduate and undergraduate students. The results have broad impacts in paleoclimatology, stable isotopes in earth science and biology, organic geochemistry.