PRELIMINARY INSIGHTS ON THE ECOLOGICAL CONSEQUENCES OF LATE QUATERNARY ENVIRONMENTAL CHANGES ON MONO LAKE (CALIFORNIA)

The Sierra Nevada serves as California’s headwaters, providing freshwater from melting snowpack that sustains one of America’s largest populations and economies. The influence of climate change on the Sierra Nevada is therefore an issue of immense interest to water and ecosystem managers in California. Historical records of precipitation, temperature, and evaporation from these mountains are relatively short or discontinuous, creating many knowledge gaps that have the potential to be addressed by proxies contained within lake sediments. Yet accurate dating of lake deposits from the Sierra Nevada has been a major challenge, and as a consequence a coherent regional picture of surface water response to late Quaternary environmental changes has proven elusive. Our team has studied two partially laminated sediment cores from Mono Lake, the largest lake on the eastern side of the Sierra Nevada crest in Mono County (California). One of the oldest lakes in the American West, Mono Lake has the benefit of long-term hydrological closure, a robust paleoshoreline record, and extensive ash beds that serve as chronological markers. To overcome hurdles associated with core chronology, we employed radiocarbon dating of high-quality terrestrial organic materials (plant macrofossils, charcoal, and sorted pollen extracts) and correlations to well-understood tephras in order to develop precise age-depth models that span much of the last deglaciation and Holocene. Ostracod and diatom archives reveal variability in benthic and planktic life, with assemblage changes responding to lake level, water temperature, water chemistry, and substrate characteristics. Pollen, charcoal, and dung fungus data track variability in the terrestrial ecosystem surrounding Mono Lake, which has been sensitive to temperature, fire regime, and megaherbivores. In aggregate, the available paleoecological data suggest linkages between high latitude processes and the hydroclimate of California. Ongoing research on sediment chemistry, paired with thin section analysis of laminations, promises to reveal additional insights on the environmental history of the Mono Basin.