PRELIMINARY INSIGHTS ON LATE QUATERNARY PALEOPRODUCTIVITY IN MONO LAKE, (CA) FROM ELEMENTAL AND STABLE ISOTOPE GEOCHEMISTRY

Mono Lake (California, USA) is a hydrologically closed basin that presently covers ~160km² and averages ~17m deep. The lake is located in the rain shadow of the Eastern Sierra Nevada, directly north of the Mono and Inyo Volcanic chains, whose tephras provide important chronological markers for the region. Hydrologically closed lakes are particularly sensitive to changes in water balance, and their sediments often contain high resolution archives of climatic and limnological processes. Mono Lake is famous for its well-dated paleoshorelines, which provide quantitative evidence for water levels in the late Pleistocene and latest Holocene, but much less is known about the aquatic environmental history of the deglacial and early Holocene. However, long sediment cores from Mono Lake can potentially address this knowledge deficit. Our objective is to document variability in relative primary production using an ~11m sediment core and multiple indicators (total carbon, total inorganic carbon, biogenic silica, C:N, δ¹³C_org, δ¹⁵N_org, and magnetic susceptibility). Radiocarbon dating is presently underway and correlations to shallow water cores and paleoshorelines will help contextualize interpretations of paleoproductivity with respect to hydroclimate and lake levels. Preliminary core analysis has identified seven different facies types, which are compositionally variable and range from finely laminated muds to massive pumice tephra. These facies stack vertically into five different units, based on physical properties and geochemical trends. Several units are rich in organic matter, with total organic carbon (TOC) values exceeding 2.0 wt.%. This suggests limnological conditions that were conducive to the production and preservation of organic matter. Other units show low TOC but high magnetic susceptibility and C:N, which likely reflects dilution with terrigenous material. The total inorganic carbon chemostratigraphy shows some of the most abrupt changes across unit boundaries in the data set. These geochemical shifts provide the foundation for understanding how limnological processes have changed since the last glacial period at Mono Lake.