The southwestern U.S. is currently experiencing profound water stress and is predicted to face declining water availability in the coming century. Past variations in the abundance of water in this region can be documented from study of ancient lake basins there. This project will produce a reconstruction of water availability, vegetation, and moisture sources in the Searles and Death Valley basins of the southwestern U.S. spanning the last 150,000 years. The researchers will use shoreline deposits from each basin to constrain ancient lake levels. Sediment core records from the centers of each basin will provide paleoclimate information that spans both wet and dry periods. Plant wax preserved in the cores will provide insight into past vegetation changes that reflect variations in moisture sources. Radiometric dating of sediments will give precise ages of environmental changes in the ancient lakes. Lake shoreline ages will be used to interpret past lake volumes in the Searles and Death Valley basins. Collectively, this information will be used to model past river flow and water budgets. This work will also lay the foundation for future development of a continuous 3.2 million-year sediment record from the Searles basin, including past warm periods. This project will train graduate and undergraduate students at 5 institutions. Binghamton University participants will lead field tours to visitors to Death Valley National Park through a partnership with the Death Valley Natural History Association. Outreach at the University of Southern California will involve collaboration with the La Brea Tar Pits Museum and will focus on teaching 4th grade visitors how Pleistocene lakes relate to the museum fossil fauna of the same age. The MIT group will incorporate project findings into climate-themed outreach at the Cambridge Science Festival, Girls' Day at the MIT Museum, and at the New England Aquarium. Researchers from SUNY College at Oswego and Keystone College will incorporate research outcomes into paleoclimate and sustainability courses that reach hundreds of students per year.

The southwestern U.S. is a water-stressed region that is projected to experience declining water availability over the coming century. Model projections show substantial disagreement in the regional circulation responses to projected emissions scenarios, with divergent predictions of the magnitude and spatial fingerprint of future drying. Lake records have the potential to offer detailed reconstructions of the hydrological, atmospheric, and vegetation responses to a wide range of forcings and to provide future opportunities to benchmark model performance. Lake records from the Searles and Death Valley basins in southern California show dramatic lake level and vegetation changes over the last 150 kyr, reflecting in part large changes in river flow from the societally-important Owens River system. These records require new analyses to improve imprecise chronologies and refine lake level reconstructions and correlations from these neighboring basins. This project is a multi-faceted reconstruction of past hydrologic and vegetation changes spanning the last 150 kyr in the Searles and Death Valley basins. The researchers will use tufa and other nearshore deposits to constrain lake levels in both basins, and existing and new measurements from a recently collected core, SLAPP-SRLS17 from Searles basin, and core DV93-1, Death Valley, to provide continuous multi-proxy records. Sedimentary structures and textures, evaporite mineralogy and facies, siliciclastic grain size changes, and rock magnetic variations in cores will be used with shoreline constraints to model past hydrologic and lake chemistry changes in Searles basin, providing quantitative constraints on past river inflows and precipitation-evaporation balance. Plant wax delta13C and pollen will provide insight into past vegetation changes, and plant wax deltaD will be used to track changes in moisture source and water vapor history. In both basins, U/Th dating will be used to provide precise age models, with support from 14C and paleomagnetic measurements in Searles Lake deposits. Paleointensity variability and evidence for magnetic field excursions will provide an independent method for dating the SLAPP-SRLS17 core. Together, the two basins will provide replicated, well-dated hydrological and vegetation records using independent approaches to test interpretations of the cave oxygen isotope records from nearby Devils Hole and Leviathan Caves to the northeast. These records will provide a quantitative estimate of the volumetric changes in water storage and the magnitude of precipitation isotopic shifts to better determine atmospheric circulation changes and the resulting hydrologic implications.

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.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Justin Lawrence
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University of Southern California
Los Angeles
United States
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