A Two-Year Water-Column Time Series of Geochemical Data During a Limnological Shift in Mono Lake, California, 2017-2018

Mono Lake is a hypersaline (approximately 85 ppt), alkaline (pH 9.8), closed-basin lake located in the eastern Sierra Nevada Mountains of California, USA (38 degrees N, 119 degrees W). Water enters the lake primarily from snowmelt and exits by evaporation (approximately 1 m/yr). This hydrological condition, plus weathering reactions in the lake's tributaries, produce the uniquely high salinity and pH characteristic of Mono Lake (Garrels and MacKenzie, 1967). These properties also tightly tie lake levels and water chemistry to climate, with modern and Pleistocene high stands correlated with wet Sierra Nevada conditions (Benson et al. 1998). Mono Lake is typically monomictic, with thermal-driven summer stratification that is disrupted by winter, wind-driven overturn. However, in years with very high summer freshwater inputs, a buoyant layer with approximately 10 ppt lower salinity can form at the surface of the lake that withstands winter mixing. This typically leads to protracted stratification that can continue for five or more years. During this time, the hypolimnion becomes euxinic, with sulfide concentrations reaching hundreds of micromolar (Miller et al. 1993). For example, following the high precipitation associated with the 1982 El Nino-Southern Oscillation (ENSO) event, snow melt brought a 2.6 m lake level rise that triggered persistent tratification from 1983 through 1989 (Melack et al. 2017). Mono Lake was again meromictic from 1996 to 2004, from 2006 to 2008, and briefly in 2010. It has since remained monomictic until the exceptional snow melt in 2017 when our study began. This data release contains two tables in *.csv format: water samples taken for various nutrient levels in Discrete_Water_Samples_2017-2018.csv and water conditions collected over a depth profile in Mono_Lake_CTD_2017-2018.csv.