Biomarker-based limnology of Great Salt Lake over the last two glacial cycles

Great Salt Lake (GSL), Utah, USA, is a large hypersaline lake currently experiencing desiccation due to water use and evaporation exceeding recharge. At times in the past it has been an expansive freshwater lake, the remnants of which are still visible on the landscape as the Bonneville Salt Flats. The long-term history of the lake beyond the present and highstand shorelines can be further explored with sediment cores drilled by the Global Lakes Drilling (GLAD) project in 2000 recovering sediment down to 120 m below lake floor. We update the age model with new uranium-series measurements on aragonite-rich sediment layers and halite deposits. The new dating helps constrain the timing of events around glacial terminations and in the lower half of the core as well as provide a new bottom core age of 236.3 ka (2σ = 6.7 kyr), capturing the penultimate interglacial period rarely recorded in continental archives. We measure the abundances of microbial membrane lipids (glycerol dialkyl glycerol tetraethers; GDGTs) and n -alkanoic acids to reconstruct aspects of aquatic productivity, ecology, and limnology at GSL over the last two glacial cycles. While the extreme hypersalinity of GSL impedes interpretations of GDGTs as a proxy for temperature, there are many other indicators of lake salinity, stratification, and productivity that can be investigated using this compound class. We detect lake freshening corresponding to the expanded lake phases named “Bonneville” (last glacial) and “Little Valley” (penultimate glacial), with new U-series ages constraining them to ~25 ka (2σ = 3 kyr) and ~138 ka (2σ = 5.6 kyr), respectively. For the penultimate interglacial, we find limnological conditions at GSL are similar to those outside of the expanded lake phases. Coincident with freshening, GDGTs and n -alkanoic acids show increases in aquatic productivity and more vigorous lake overturning. The times of expanded lakes at GSL coincide with periods of increased moisture recorded in other regional archives, specifically lake highstands and higher water table elevation, in turn driven by climate forcing.