Reconstruction of Quaternary Climates Using Stable Isotopic Analyses of Packrat Middens

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SBR-9631420 Valery J. Terwilliger U. Kansas This award funds a project to study the climate variations at a regional scale by measuring the stable oxygen, hydrogen and carbon isotopic ratios of plant remains in packrat middens found in two mountain ranges in the western U.S. To constrain the variables that affect the isotopic compositions in plant materials, the PI also propose to grow plants in a greenhouse under controlled conditions. From a climatic study point of view, the 40,000 year-old long plant remains in packrat middens are very valuable samples for stable isotope work. The possibility of comparing leaves and stems provides further advantage to examine the isotopic variations due to a change in source water versus a change in the atmospheric conditions (e.g. humidity). Such isotopic analyses of plant remains are widely used to interpret climate. This project pushes interpretations to address more directed questions about climate at a finer scale than has previously been attempted. To interpret the isotopic records, it is important that the contemporary leaves and stems be studied and compared between the two species and two locations. The controlled experiments proposed are useful for understanding the physiological pathways of oxygen, hydrogen and carbon isotopes. Climatic processes that operate within regional scales are poorly understood. This limited knowledge is the primary reason that predictive models of climatically induced environmental change are least rigorous for small areas. Reconstruction of environmental developments in the climatically changeable Quaternary period is considered to be the most promising source of information for improving the sophistication of these models. This requires not only efforts to answer more directed questions about past environments but also efforts to improve the resolution of climatic inferences that can be made from proxies. This project should contribute to these wider needs for knowledge about environmental development s within small areas.