Climate variability in east-central California during the past 1000 years reflected by high-resolution geochemical and isotopic records from Owens Lake sediments

Core OL-97A, retrieved from the depocenter of Owens Lake, represents a depo sitional history spanning the past 1000 yr. Among the 17 elements analyzed in the acid-leachable fractions of 315 salt-free samples (at similar to 3 y r/sample), Mg and Li, which come chiefly from authigenic Mg-hydroxy-silicat es, were found to have concentration variations reflecting lake salinity an d climatic changes during the past. A total of 231 isotopic measurements on carbonates from the same samples in the upper 181 cm show that delta(18)O and delta(13)C values range from -5.66 to 0.12 parts per thousand (PDB) and 1.38 to 4.28 parts per thousand (PDB), respectively. The rate of change wi th time in delta(18)O records the rate of change in lake's volume due to cl imate fluctuations, whereas variations in delta(13)C reflect mainly variati ons in biological productivity, nutrient supply, and dissolved carbonate in the lake. Results indicate an effectively dry climate between A.D. 950 and 1220, corresponding to the Medieval Climatic Anomaly (a warm period in nor thern Europe), during which Owens Lake approached playa conditions. Wet cli mates prevailed during A.D. 1220-1480, producing relatively large and deep lakes. Beginning about A.D. 1.550, the regional climate turned colder but h ad frequently oscillating precipitation. Six wet/dry cycles with similar to 50-yr duration occurred between A.D, 1480 and 1760, during the later half of which Owens Lake became a playa. Since similar to A.D. 1880, the lake le vel has steadily dropped from its historic high stand under strong impact o f human activity. (C) 2000 University of Washington.