The midcontinental United States (US) is one of the world's largest agricultural centers and home to more than 70 million Americans. In recent decades, hydro-climate events in this region have intensified, with generally more frequent and prolonged flooding in the eastern midcontinental US and more severe and sustained droughts in the west. This east-west pattern of hydro-climate variability may be persistent and long-standing, resulting from natural large-scale ocean-atmosphere circulation regimes, or it may be a more recent manifestation of anthropogenic climate change. Given that instrumental meteorological records typically span no more than ~150 years, investigation of the causes of hydroclimate changes in the Midwest on timescales of hundreds to thousands of years requires analysis of high-resolution paleoclimate records, the development of which is the primary objective of this research. Through geochemical analysis of lake sediment, the researchers will produce a series of records of lake-level and precipitation changes that will span the past 2000 years in order to determine the spatiotemporal patterns and underlying drivers of midcontinental hydro-climate variability. This research will 1) produce a long timescale perspective on hydroclimate that will inform water resource management strategies, and 2) elucidate regional-scale responses of hydro-climate to increasing global temperatures. As part of this project, the investigators will be working with local, state, and federal agencies, including the United States Geological Survey, to incorporate the results of this research into flood model development efforts and fluvial erosion hazard mitigation. The data from this project will additionally inform and benefit research into climate-society interactions, including the impact of abrupt and long-term climate changes on Native American societies that once populated the midcontinental US, but abruptly abandoned much of the region ~600 years ago.
Methodologically, there are three specific objectives of this research. 1) The researchers will reconstruct changes in atmospheric circulation and precipitation seasonality in the midcontinental US during the last 2000 years using oxygen isotope (d18O) measurements of carbonate minerals in sediment from two hydrologically open lakes. 2) The researchers will produce records of local hydroclimate conditions (precipitation:evaporation ratios and lake-level variability) using d18O, grain size, carbon:nitrogen, and diatom analysis of sediment from four hydrologically closed lakes. 3) The researchers will statistically evaluate the open and closed lake hydro-climate records in the context of atmosphere-ocean variability known from empirical paleoclimate records and model simulations. Using these approaches, the researchers will quantify the respective influences of atmospheric circulation and precipitation seasonality on regional midcontinental hydro-climate and determine the underlying role(s) of ocean-atmosphere processes. Specifically, the investigators will test three hypotheses. 1) Multi-decadal to centennial hydroclimate variability in the midcontinental US during the last 2000 years was characterized by an east-west hydroclimate dipole with its hinge line located between the Great Plains and Midwest at ~96oW. 2) Hydroclimate dipole variability was driven by atmospheric circulation resembling the Pacific North American mode that altered seasonal precipitation patterns. 3) Midcontinental hydroclimate and atmospheric circulation anomalies were predominantly controlled by Pacific basin atmosphere-ocean processes. A critical component of this research is the education and training of undergraduate and graduate students while actively working to increase diversity in STEM fields by recruiting and supporting women and underrepresented minorities in science. One PhD, 2 MSc, and 4 undergraduate students will be directly supported by this project, while several others supported by other sources will also contribute. Because translation of science to the public is a critical component of any effective research project, the researchers and their institutions will engage in outreach activities including the development of an educational module for 4th to 9th grade students focused on 1) Midwest climate, both paleo and modern, 2) paleoclimate reconstruction techniques, and 3) water resource variability. This module will be developed and implemented by IUPUI's Center for Earth and Environmental Sciences and made publicly available for other educators to use. The researchers will work with the Indiana State Museum to incorporate the projects results into an interactive exhibit on midcontinental Native Americans.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
