HOLOCENE HYDROCLIMATIC AND VEGETATION RECONSTRUCTION IN THE SIERRA NEVADA USING POLLEN AND STABLE ISOTOPES FROM CONVICT LAKE

The forested environments of the subalpine and upper montane zones of the eastern Sierra Nevada mountains (California) are biodiverse and valuable ecosystems that are sensitive to hydroclimate changes. The history of high-altitude vegetation changes in the eastern Sierra Nevada is underexplored, and this knowledge gap can be addressed using a paleolimnological approach. In this study, we use a long (~9.5 m) sediment core from Convict Lake, a glacial lake situated in the upper montane zone of California’s Sherwin Range, to assess Holocene changes in terrestrial vegetation. The core was dated using radiocarbon, and studied with palynology, elemental analysis, and stable isotope geochemistry applied to bulk organic matter. Pollen assemblages provide evidence of a dry, open woodland in the Convict Creek watershed during the early Holocene, while the data indicate a stable, cool, and relatively wet mid-Holocene with subalpine forests occurring at lower elevations. All datasets point to considerable hydroclimatic variability beginning around 4,500 yr B.P., which may reflect warmer temperatures and more variable winter precipitation. The presence of the subalpine indicator species Tsuga mertensiana coincides with potential late Holocene glacial advances for which scant evidence currently exists. New insights from this study provide crucial baseline data for comparison with climate simulations of the future for the Sierra Nevada, which serve as the most important water source for vast urban and agricultural areas in California and provide millions of dollars in economic revenue annually