Developing a Network of n-Alkane Hydrogen Isotope Records to Identify Drivers and Impacts of Holocene Droughts

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This project will address patterns and drivers of past droughts and their effects on humans and the biosphere. The researchers will analyze lake-sediment cores to develop records of precipitation variability associated with past shifts in major drivers of atmospheric circulation that influenced the broader circum-Caribbean region, including the U.S. Gulf Coast. The precipitation records will be compared to evidence of past human activity and biomass burning in lake watersheds, to explore local consequences of regional shifts in atmospheric drivers. The work will form the foundation for an expanded network of precipitation reconstructions across the region that will allow examination of processes at a larger spatial scale and of additional drivers. The project will provide experience in multi-laboratory collaborative research to four faculty and ten or more graduate and undergraduate students. Results from project activities will be broadly disseminated in publications and presentations. The researchers will share scientific knowledge of past environmental change with K-12 students and teachers in Tennessee and North Carolina through outreach projects that will include hands-on activities and authentic research. The researchers will develop precipitation records using compound-specific hydrogen isotope analyses of n-alkanes in lipids in sediment cores from five lakes along two transects that cross climate and ecosystem regions. Hydrogen isotope analysis of lipids in sediment cores is an alternative to oxygen isotope analysis of biogenic carbonates that can be applied in a wide variety of lakes, making possible the development of a network of sites using the same precipitation proxy. The hydrogen isotope records will be produced from existing cores from lakes in Costa Rica, and will serve as the western anchor in a larger network of precipitation records that the researchers plan to develop through the broader circum-Caribbean region, including the U.S. Gulf Coastal Plain. The hydrogen isotope analyses will document the geography of multi-decadal drought during the Terminal Classic Drought (~1200-850 cal yr BP), the Little Ice Age (~500-100 cal yr BP), and at other times, and reveal whether these were exceptional or outlier droughts for the Holocene as a whole. Comparison with local paleoenvironmental and archaeological evidence will show how past droughts affected vegetation, fire regimes, and prehistoric agriculture.