GRGC: High Resolution (Century to Dacadal) Isotopic (18O and 13C) Record Preserved in Speleothem Calcite: Holocene Vegetation and Climate Change in the Midwest

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9316875 Gonzalez The eastern portion of Iowa and surrounding states, Minnesota, Wisconsin, Illinois, and Missouri are characterized by the presence of a well developed karst in which cave development is extensive. We propose to study the stalagmite age and isotopic record in three to four different "basins" in a region encompassing the karsted southern edge of the Prairie Peninsula where the Holocene history of the peninsula is virtually unknown. This research compliments current and proposed research by R. G. Baker and others that study the palynological, plant macrofossil and soil record and attempts to fill information gaps in the Holocene vegetation and climatic history. We propose to use the picomole to subpicomole resolution of combined isotope dilution and mass spectrometry U-Th methods to accurately date speleothems (stalagmites) and the carbon and oxygen isotopic composition of calcite to extract a record reflecting climatic change. The goals of these research are; 1) Better define the extent of the climate-induced vegetation change in the upper Midwest utilizing delta 13C shifts and U-series dates; 2) Provide a more precise and accurate timing of climate-induced vegetation change in the region; 3) Attempt to generate a quantitative record of temperature change at the decadal scale for the Midwest; 4) Attempt to define rates of vegetation change and biomass turnover over the cave areas using changes in the delta 13C; 5) Attempt to resolve annual and possibly semi-annual changes in speleothem calcite; 6) Provide a well dated history of changes in the southern edge of the Prairie Peninsula; 7) Attempt to estimate precipitation from growth rate changes. Multiple speleothems will be analyzed within individual basins and caves to replicate and validate timing and magnitude of isotopic shifts, growth rate changes, or the presence of basin wide desiccation events. Careful attention will be given to cave selection with special emphasis in the identificati on of evidence of desiccation and flooding events which will diminish and validity and utility of isotopic analysis for climatic inferences. Attempt will be made to find study sites in close proximity to those being studies by Baker and others so that precise timing for vegetation changes can be provided.