A PRELIMINARY HIGH-RESOLUTION LATE HOLOCENE DIATOM STRATIGRAPHY AND HYDROCLIMATIC RECONSTRUCTION FROM JUNE LAKE (EASTERN SIERRA NEVADA)

We investigated June Lake (Mono County, CA) as a geological archive of Holocene environmental change. Situated in the eastern Sierra Nevada, a key area for California’s water supply, June Lake may hold clues to ancient climatic changes in the region. We analyzed continuous samples from an ~1.7-meter core collected from deep water in the northeastern sub-basin of June Lake for changes in fossil diatom assemblages and sediment grain size. Our objective is to reconstruct limnological and environmental changes over the past ~2,000-3,000 yrs. The core consists of laminated diatom ooze with variable siliciclastic detritus content, tephra layers, and occasional banded calcareous intervals. The ages and rates of sediment accumulation in the core are constrained by radiocarbon dating. Initial results of the microfossil analysis suggest that the dominant diatom species throughout most of the core is Stephanodiscus klamathensis, previously only observed in Pliocene-aged diatomite sequences in the western US. Stephanodiscus klamathensis constitutes ~95% of the diatom assemblage towards the bottom of the core, ~3,000 yrs. ago, and decreases to ~20% at the top. Other commonly occurring species include Lindavia ocellata, Fragilaria crotonensis, and Nitzschia dissipata. Lake-level change will be estimated using the ratio of planktonic to benthic diatoms refined by a 3D model of the lake basin, with increased benthic diatoms signaling a shallower lake and lower effective moisture. The results will be integrated with regional paleoenvironmental data to expand current understanding of hydroclimate in the eastern Sierra Nevada in the late Holocene.