NEW INSIGHTS ON LATE PLEISTOCENE-HOLOCENE ENVIRONMENTAL CHANGE AT MONO LAKE (CA) THROUGH OSTRACODE PALEOECOLOGY

The Sierra Nevada Range is a critically important region to California’s water supply, and severe recent droughts have underscored the need to better understand how climate change affects this region. Lacustrine sediment cores, in particular those from endorheic lakes, provide proxy-rich, high-resolution archives of hydroclimatic change. Located in the rain shadow of the eastern Sierra Nevada, Mono Lake (CA) is a hydrologically closed lake that covers ~160 km²and averages ~17 m deep. Mono Lake is known for its well-dated paleoshorelines, which provide quantitative evidence for the lake’s variability in water balance during the last glacial maximum and late Holocene. However, the paleoecological history of Mono Lake during the deglacial transition remains considerably less well understood. One opportunity to address this knowledge gap exists in fossil ostracodes, a group of micro-crustaceans whose calcite carapaces preserve well in lacustrine sediments. We aim to harness the environmental sensitivity of ostracode species assemblages to track paleolimnological changes at Mono Lake from ~16.9-4.2 cal ka BP. This contribution presents a preliminary ostracode analysis from a deep-water sediment core retrieved from the western embayment of Mono Lake. Ostracodes were extracted from sediment samples using a modified freeze-thaw method, and washed through 250 mm, 150 mm, and 63 mm sieves to gain insight into the paleohydraulics impacting the core site during deposition. The three fractions were combined and washed through a 106 mm sieve for counting (n=300/sample) and SEM imaging. Ostracode species encountered in the core include: L. staplini, L. ceriotuberosa, C. patzcuaro, F. caudata, E. meadensis, and Potamocypris sp.. The species assemblages and abundances vary through time. Limnocythere sappaensis was also encountered, but the valves are taphonomically altered and appear to be reworked from older Wilson Creek Formation outcrops exposed near the lake.These results provide some of the first insights into past ecological variability in Mono Lake during the Pleistocene-Holocene transition, and provide important pretext on which to benchmark the climatic changes we are observing today.