A 3,000 YEAR RECORD OF HYDROCLIMATE IN THE EASTERN SIERRA NEVADA, CALIFORNIA'S HEADWATERS, USING DIATOM PALEOECOLOGY

California is the US state with the highest population and agricultural output, and much of its water supply is dependent on snowmelt from the eastern Sierra Nevada mountains. Recent years have witnessed changes in the availability of water from this snowmelt, and future climate change is likely to impact this resource even more. June Lake (Mono County) is perfectly situated near the eastern Sierra and Basin and Range boundary to record past hydrologic changes in its sediments. We collected a ~1.7 m sediment core from June Lake that covers the past ~3,000 yrs and analyzed it for changes in diatom assemblages. The core is composed of diatomaceous ooze, calcareous mud, tephra layers, and sapropel. The core was radiocarbon dated and sedimentation rates were determined using charcoal and terrestrial plant macrofossils. Shifts in the dominant diatom genera, Stephanodiscus and Lindavia, reflect changes in lake stratification. These changes are most likely controlled by variability in seasonality and precipitation; longer winters with heavy snowfall lead to a well-mixed water column and shorter winters where the lake can absorb solar heat for more of the year lead to stratification. The diatoms suggest the possibility for longer winters during three periods: (a) 3,000-2,680 yrs BP, (b) 2,310-1,730 yrs BP, and (c) 560-100 yrs BP. Changes in lake level were estimated using the ratio of planktonic to benthic diatoms and patterns of carbonate accumulation. These data suggest that the modern June Lake may be an extreme lowstand in comparison to the water level history of the preceding ~3,000 yrs. These results help expand our knowledge of hydroclimate in the eastern Sierra Nevada in the late Holocene.