Evaluating sedimentary geochemical lake-level tracers in Walker Lake, Nevada, over the last 200 years

Walker Lake, a hydrologically closed, saline, alkaline lake located along the western margin of the Great Basin of western United States, has experienced a 77% reduction in volume and commitment drop in lake level as a result of anthropogenic perturbations and climatic fluctuations over the last century. The history of lake-level change in Walker Lake has been recorded instrumentally since 1860. A high-resolution multi-proxy sediment core record from Walker Lake has been generated through analysis of total inorganic carbon (TIC), total organic carbon (TOC), and oxygen and carbon isotope ratios (dO and dC) of both downcore bulk TIC and ostracods over the last 200 yr. This allows us to examine how these sediment indices respond to actual changes in this lake’s hydrologic balance at interannual to decadal timescales. In Walker Lake sediments, changes in %TIC, %TOC, and dC and dO of TIC and ostracods are all associated to varying degrees with changes in the lake’s hydrologic balance, with dO of the TIC fraction (dOTIC) being the most highly correlated and the most effective hydrologic indicator in this closed-basin lake. The dOTIC record from Walker Lake nearly parallels the instrumental lake-level record back to 1860. However, comparison with sporadic lake-water dO and dissolved inorganic carbon dC (dCDIC) results spanning the last several decades suggests that the isotopic values of downcore carbonate sediments may not be readily translated into absolute or even relative values of corresponding lake-water dO and dCDIC. Changes in the lake’s hydrologic balance usually lead to changes in isotopic composition of lake waters and downcore sediments, but not all the variations in downcore isotopic composition are necessarily caused by hydrologic changes.