A paleolimnological investigation of climatic and hydrological conditions during the late Pleistocene and Holocene in the Sierra Nevada, California, United States

Modern physical, limnological, and biological data were collected from 57 small lakes in the Sierra Nevada, California, USA. The lakes cover an altitudinal range of 1,360 m (2,115 - 3,475 m a.s.l.), therefore spanning steep air temperature and effective moisture (precipitation minus evaporation) gradients. Diatoms were enumerated from the modern (0 - 1 cm) sediment samples from the 57 lakes. Weighted-averaging calibration and regression were used to develop robust diatom-inference models for surface-water temperature, salinity, and lake depth.; High-resolution (subcentennial to centennial) fossil diatom analysis was undertaken from sediments spanning the Pleistocene-Holocene transition from three central Sierra Nevada lakes. Five distinct, rapid changes in diatom community composition occurred concurrently at all lakes. Fossil diatoms indicate that from ∼14,500 - ∼13,700 cal yr B.P. conditions were cold, then became warmer and wetter from ∼13,700 - ∼13,000 cal yr B. P. A return to cooler conditions occurred from ∼13,000 - ∼11,500 cal yr B.P., coincident with the Younger Dryas (YD) chronozone. A notable wet-dry oscillation occurred within the YD. Following the YD, climate warmed rapidly. Although each lake responded to climate change, canonical correspondence analysis (CCA) showed that the trajectory of change for each lake was unique, due to differences in elevation, geology, and vegetation.; A second, high-resolution, paleohydrological record was reconstructed from Holocene sediments from Kirman Lake in the eastern Sierra Nevada. Diatom-based reconstructions were verified using sediment lithology, organic content, and carbon to nitrogen ratios (C:N). Collectively the data suggest conditions were wetter than present from ∼9,500 - ∼7,500 cal yr, then became drier from ∼7,500 to ∼2,900 cal yr B.P. At ∼2,900 cal yr B.P., climate shifted to being wetter, but variable, with three distinct multicentennial droughts. These results indicate that droughts that are longer and more intense than those recorded in historical measurements are common during the Holocene.; Data from this study show that conditions in the Sierra Nevada have varied dramatically over the last{09}∼14,500 years and that rapid climate changes are common. This information is beneficial for climate models and water resource managers as they try to predict and plan for future climate regimes in California.