Collaborative Research: EAGER--Evaluating Fluid Inclusion Geochemistry of U-Th Dated Speleothems as a Tool for Resolving Paleoclimate Controversies in the American Southwest

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Global hydrologic reorganization throughout the Northern Hemisphere occurred synchronously with repeated large, sub-millennial-scale climate changes in the northern North Atlantic region during the last deglaciation. However, how this reorganization affected the continental hydroclimate in the drought-prone American Southwest remains poorly resolved. Continental-based paleoclimate reconstructions for this region are contradictory in large part due to two sources of discrepancy: (1) uncertainty in age constraints, and (2) fundamental ambiguity in speleothem-based proxy records.This project-- a collaborative effort between scientists from the University of California at Davis and Harvard University-- seeks to resolve the apparent contradictions in the inferred glacial-interglacial climate reconstructions for the American Southwest using cave deposits from the Sierra Nevada in California. The researchers will employ novel techniques to generate both a robust chronologic framework (using U-Th dating via laser ablation MC-ICPMS) and a record of precipitation (using temperature-dependent noble gas concentrations in fluid inclusions as a temperature proxy independent of other climate processes and stable isotopic composition of inclusion fluids as a more direct proxy of precipitation composition and source region) over the past ~20,000 years at the study site. Successful proof-of-concept of these innovative approaches would open the door for applications to a wide variety of questions in paleoclimate.The outcomes of this work should lead to better understanding of how climate change impacts the hydroclimate of the American Southwest, an area that is vulnerable to water resource limitation. Additional broader impacts include development of a new facility for routine high-precision U-series dating (of which there are only a handful in the US), development of the noble gas proxy in carbonates, and training of graduate students at two institutions.