LACUSTRINE RECORDS OF ENVIRONMENTAL CHANGE FROM THE EASTERN SIERRA NEVADA: AN UPDATE ON LAMINATED SEDIMENT CORES FROM THE MONO BASIN (CALIFORNIA, USA) (Invited Presentation)

Lakes in the Mono Basin (Mono County, California) provide a remarkable opportunity to evaluate sedimentary signals of Quaternary environmental change in a region that is critically important to water resources in the western United States. Situated to the east of the Sierra Nevada crest on the margin of the Great Basin, lakes in the Mono Basin are influenced by many of the same climatic processes that control freshwater availability in the Sacramento-San Joaquin Delta. This includes a profound reliance on seasonal snowmelt from the Sierra Nevada winter snowpack to recharge streamflow and restore water levels. Therefore, accurately reading proxy records from the Mono Basin can reveal much about the hydroclimate history of California, as well as the ecological consequences of climate change for aquatic and terrestrial flora and fauna. We have pursued research using long sediment cores from Mono Lake and June Lake. Both lake basins are hydrologically closed at the surface but their origins and characteristics vary widely. Mono Lake is tectonic in origin, and its proximity to the Mono-Inyo Craters, as well as its hydrothermal plumbing system, have created one of the most unique and ancient lentic ecosystems in the United States. On the other hand, June Lake is considerably smaller and formed from glacial erosion more recently; it is less directly impacted by volcanic processes and lacks the spectacular paleoshorelines and tufas that have made Mono Lake famous. Nevertheless, both lakes have accumulated laminated sediments in their profundal environments; establishing the timeline of deposition at each site has focused on (a) detailed stratigraphic observations, (b) radiocarbon dating of plant macrofossils, pollen purified by flow cytometry, and charcoal, and (c) chemical identification of tephras of known age. Organic geochemistry, ostracodes, diatoms, pollen and charcoal have revealed the sensitivity of Mono Lake and June Lake to changes in temperature, precipitation, and water chemistry during the latest Pleistocene and Holocene, and by anthropogenic activity starting around the Industrial Revolution. Ongoing research at the scale of individual laminae using thin sections and scanning x-ray fluorescence is showing promise for characterizing event sedimentation to further refine environmental interpretations, particularly in the Early Holocene.