Collaborative Research: Spatial and Temporal Patterns of Drought in Western North America during the Holocene

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This grant produces paleoclimate datasets recording the timing, duration, frequency and magnitude of aridity cycles on a network of paired open and closed micritic basins along the western cordillera of North America from the Pacific NW to the Canadian Arctic. The project employs hydrologic and stable isotope mass balance models to provide quantitative estimates of precipitation and relative humidity changes. The project explores how the temporal-geographic patterns of aridity changed during the Holocene and uses advanced data processing techniques to test hypotheses concerning the periodicities in the paleoclimate archives. These results are used to infer the nature of potential modes of Pacific Ocean variability and to document how they have changed over time. The project tests hypotheses concerning the causes and magnitude of climate variability in the study region during the Holocene. The project also synthesizes data from the literature with ongoing work in Tropical South America to investigate large-scale Pacific Ocean forcing over a range of timescales. Synthesis of these records will result in a better understanding of the Pacific climate system and improved predictability for aridity cycles in western North America. Lake levels along the western cordillera have been relatively stable during the past ~6ka creating high resolution archives during the period of time targeted for most intense study. During the early Holocene megadroughts significantly lowered water levels regionally thereby limiting the resolution to multi-decadal to century scale prior ~6ka. Geochronology is provided by 137Cs, 210Pb, 14C, tephra chronology and geomagnetic correlation. The same methods are applied at all study sites to simplify data interpretation and increase robustness of findings. Multiproxy studies will include stable isotopes, grayscale, diffuse spectral reflectance, XRF, magnetic measurements, and organic and inorganic carbon by loss on ignition. The group collaborates with the University of British Columbia, who use chironomid assemblages to reconstruct paleotemperatures. The multi-millennial hydrologic record with sub-decadal resolution is then compared with high resolution coupled ocean atmosphere GCM simulations currently being conducted by a collaborator at Purdue University.The work is relevant to western North America where populations are rapidly expanding and water resources are stressed. The relatively sparse preinstrumental climate records for this region indicate that it is highly sensitive to Pacific Ocean variability and to the interaction between the PDO and AMO. A deeper understanding of the past behavior of these modes of variability is needed to improve predictive capabilities. The goal is to investigate climatic change at a time-resolution relevant to human society, and answer questions such as: How have the intensity and periodicity of droughts and pluvials changed during the Holocene? What is the spatial pattern of aridity cycles in western North America during this period? What boundary conditions and forcing factors are related to extreme droughts and pluvials?