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

学术价值：降水同位素比可以说是定量大陆古气候重建的最佳代理。传统的档案，冰芯和洞穴沉积物，在空间上受到限制。植物叶蜡的dD值代表了潜在的强大的和广泛适用的代理。然而，在不同的气候和环境条件下，叶蜡和降水之间的氢同位素分馏存在很大的不确定性。有几项研究试图从湖泊表层沉积物，甚至直接从植物叶片中获得平均磷含量，但成功有限。我们建议确定从对比生态系统的现代气溶胶样品的dD值的叶蜡。气溶胶中的叶蜡整合了高等植物目前的生产，使我们能够在特定的环境设置下准确地定义整个季节周期中的awax-p值。对于拟议的EAGER项目，我们打算研究两个气候不同的网站（亚利桑那州和格鲁吉亚在美国），以证明拟议的方法的可行性。如果成功，我们打算研究全球各地的植被和气候梯度。更广泛的影响：拟议的工作将在两种高度对比的气候和环境背景下产生现代植物叶蜡和降雨之间的表观氢同位素分馏（Δ wax-p）的最准确值，并将为未来更全面的研究铺平道路。研究结果为将叶蜡氢同位素数据定量转化为古气候记录奠定了基础。这项研究将促进多学科合作（有机/同位素地球化学和大气科学），并允许研究生和本科生的跨学科培训。这一成果在古气候学、地球科学和生物学中的稳定同位素、有机地球化学等方面具有广泛的影响。

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.