High Resolution Time-Series of California Climate Over the Last 12,000 Years: Testing the North Atlantic and North Pacific Linkage

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Numerous episodes of severe annual and multi-annual drought have been recorded in instrumental climate data and historical records from California. Such records extend back only 200 years or less. Paleoenvironmental reconstructions of prehistoric climate indicate that even more severe and longer multi-decadal droughts have occurred in the prehistoric period. Unfortunately, these paleo records are often fragmentary and are not sufficient to provide a clear and continuous record of drought intensity, duration and frequency over the past 12,000 years. Using a calibration-set approach, the proposed research will statistically assess how current differences in air temperature and precipitation, lake water temperature, salinity, and depth are reflected in the contemporary elemental chemistry and carbon and oxygen isotopic composition of lake waters, and the chironomids (midge fly larva), cladocera (crustacean), diatoms (unicellular algae), pollen and stomates found in lake sediments. Surficial sediment and water samples from at least 50 small lakes in the Sierra Nevada will be collected and analyzed. The lakes will be chosen to provide a network of sites at different elevations displaying differences in air and water temperatures, depth, salinity and evaporative balance. If statistically significant relationships are found between climate and lake conditions and the geochemical and biological proxies, the relations will be quantified in the form of mathematical transfer functions. The newly developed transfer functions will then be available for application to geochemical records and fossil biological assemblages contained within the sediments of lake cores that span the last 12,000 years. The changes in climate, lake temperature, depth and salinity from such lake cores can provide long and continuous records of major droughts in this sensitive region. Due to its large population, massive agricultural base and generally semi-arid climate with strongly seasonal precipitation, California is extremely sensitive to the impact of droughts. Although annual and multi-year droughts of the 20th Century have caused significant economic problems, the more severe multi-decadal droughts evident in some fossil records from the past 2000 years would have a catastrophic impact upon natural ecosystems, agriculture and society in the state. Appropriate continuous records of past climate do not yet exist to appraise the absolute magnitude, exact duration and potential frequency of such droughts over long time scales. Without such information it is difficult to determine the causes of such large scale episodes of aridity and assess the probability of such an event in the future. The proposed research will assess if the geochemistry, microscopic flora and microscopic fauna of small lakes in the Sierra Nevada are sensitive to differences in temperature, salinity and lake depth, and if the geochemical content and remains of such organisms from lake sediments can be used to reconstruct long histories of climate and drought in California. The results of the proposed research will be of importance to climatologists, hydrologists, paleontologists, biologists, biogeographers and water resource managers.