Doctoral Dissertation Research: High-Resolution, Late Quaternary Climate and Vegetation Record for the American Midwest: Isotope and Pollen Evidence from Stalagmites and Flowstone

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Climate proxies from ice sheets and ocean cores have revealed major global climate changes during the past 150,000 years and beyond. Much less is known about the effects of these global changes at the regional to local level, however. This doctoral dissertation research project will create a southern Indiana paleoenvironmental record for periods of the past 150,000 years using cave-based proxies from three sites. This record will be used to examine the substantial regional climate fluctuations that occurred due to ice sheet proximity during glacial advances and retreats. Because a firm understanding of the causal mechanisms of regional- to local-scale climate variations is crucial to improving and checking the accuracy of global climate models, this focused study will help contribute to a much broader range of inquiry into long-term climate dynamics. This research also will have positive implications for research on climate dynamics in the Midwestern U.S., a region whose economy is strongly influenced by climate, because current global climate models for the region struggle to replicate some past aspects of climate, such as late glacial wind fields and non-analog climates indicated by pollen records. Because the caves to be studies in southern Indiana are close to locations where the Laurentide Ice Sheet reached its southernmost limit in central Indiana during glacial maxima, climate gradients that were very abrupt immediately south of the ice margin and associated climate changes should be readily recorded in climate proxies, thereby contributing to basic understanding about the localized climatic dynamics near ice sheets. This project will provide much-needed high-resolution paleoclimate data and modern precipitation isotope records that currently are lacking for this part of the Midwest, thereby helping to develop a more complete understanding of the natural variations of Indiana's climate to aid scientists, policy makers, and the public in dealing with issues associated with climatic variation and change. Data will be made freely accessible to researchers through the NOAA Paleoclimatology database, while results will be shared with cave owners, schools, and state organizations for dissemination to residents to improve scientific awareness and teach the value of preserving fragile cave environments. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.Cave speleothems (mineral deposits like stalagmites, stalactites, and flowstones) can preserve a record of environmental changes in the area above the cave and are particularly valuable because they offer very accurate uranium-series ages up to 450,000 years. Through the conduct of this project, the doctoral students whose dissertation research will be supported by this award will determine the processes controlling modern precipitation isotope (delta-O-18, delta-H-2, and d-excess) values for the Midwestern U.S. and the relative effect of each process. He will create a paleoclimate record by analyzing stalagmites from three caves, develop a vegetation record from pollen trapped in flowstones that extends existing regional pollen records, and integrate the stalagmite and vegetation data to produce a single regional paleoclimate record. Variations in the oxygen isotope characteristics of speleothem carbonate will offer clues to changes in rainfall source, amount, and seasonality, while analysis of modern day precipitation isotope signatures will provide insight into what caused these changes. Analyses of carbon isotopes and ultraviolet-stimulated speleothem luminescence will reflect variations in soil productivity, while pollen trapped in speleothems will provide evidence of local vegetation at the time of deposition. The analyses of stalagmites from three southern Indiana caves therefore will produce overlapping paleoclimate records that will be combined to determine regional climate patterns and history. The combined speleothem records will produce a robust environmental record from multiple proxies with strength drawn from integrating spatially distinct samples.