Thermodynamic evaporation and freshwater mixing models to test salinity proxies for late Pleistocene lake levels, Mono Lake, California

Times of higher paleolake levels in Mono Lake basin correspond to higher abundances of authigenic minerals such as calcite and Mg-smectite in the Wilson Creek Formation, the lake sediments exposed around the modern lake that represent the persistent wetter conditions of the last glacial cycle. It has been suggested that precipitation of these minerals in Mono Lake is controlled by the flux of water (surface and ground), which replenishes Ca2+ and Mg2+ ions in the lake. This water is subsequently depleted due to the high rates of evaporation in the Mono Basin, resulting in precipitation of calcite and Mg-smectite mineral phases. Thermodynamic evaporation models starting with Sierra Nevada spring water can simulate the chemical composition of Mono Lake remarkably well. These models do not, however, consider the mixing of freshwaters in the lake that is hypothesized to result in precipitation of calcite and Mg-smectite. Here, we present the results of our empirical evaporation and mixing (E&M) model using simple thermodynamic approaches. Although this model is highly simplified, it provides a valuable test of the hypothesis.