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 (Ã¥wax-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.
Climate change is one of the most pressing concerns for humans on earth today. There is an urgent need to obtain quantitative understanding of the past and future change. The reconstructed paleoclimate records along with the observations of modern climate are useful for the climate models which can infer past and predict future climate. Proxies from diatoms, forams and coral are commonly used for paleoclimate study. These traditional records, though useful, are spatially restricted. Thus, isotopic ratio in precipitation is proposed to be the best proxy for reconstructing paleoclimate in the continent. However, there is major uncertainty in the apparent hydrogen isotopic fractionation (εwax-p) between modern plant leaf waxes and precipitation, which may vary greatly under different climatic and environmental conditions. This study aims to determine the dD values of leaf waxes in aerosol samples, suspended fine particles in the atmosphere, and in its precipitation samples from two areas with clear contrasting climate (Arizona and Georgia) in order to assess if the εwax-p value changes with climatic and environmental conditions. More than 60 high quality aerosol samples and 20 precipitation samples from the above two sites were successfully collected for the analysis of lipid compositions and hydrogen isotopic ratios. A new way is proposed in this study to examine how the apparent hydrogen fractionation ratios between plant leaf wax and precipitation change with climatic conditions through the direct measurements of hydrogen isotopic ratio in leaf wax in particles suspsended in the air and in precipitation. The results of this study will help to establish a more accurate quantitative precipitation proxy for paleoclimate reconstruction. This study also stimulates multidisciplinary collaboration especially linking modern atmospheric science to paleoclimatology. Such collaboration allows graduate and undergraduate students to receive broader training in environmental science.
