CONSTRAINING LATE PLEISTOCENE CLIMATE OF THE NORTHEASTERN GREAT BASIN USING MASS BALANCE MODELING OF PALEOLAKES AND GLACIERS

Records of pluvial lakes and mountain glaciers provide a valuable opportunity to understand temperature and precipitation changes during the late Pleistocene. Improved cosmogenic ¹⁰Be chronologies of glacial deposits in the Ruby and East Humboldt Mountains and ¹⁴C dating of pluvial lacustrine deposits in the neighboring Lake Franklin valleys reveal multiple intervals between 19-15 ka when glacier maxima and lake highstands coincided. It is therefore possible to infer climate conditions, chiefly precipitation and temperature, during this time interval using numerical modeling of large paleolakes and mountain glaciers. Mass balance modeling that accounts for differing temperature sensitivities of glaciers and lakes to temperature and precipitation narrows the range of paleotemperature and precipitation conditions during glacier maxima and lake highstands. Models use physically based expressions for monthly melting, regionally calibrated evaporation, and sublimation in lake watersheds, including a temperature-controlled timing of runoff. Modeled snowpack sublimation values ranged from 20-70% of monthly accumulation season precipitation within the watershed. The combined glacier and lake model results indicate that, with no mass loss by sublimation in the Lake Franklin basin, paleotemperature was 8.8-10.4 °C less than modern with precipitation at 1.9-1.1x modern. At 20% mass reduction by sublimation, model results indicate a paleotemperature 8.0-11.6 °C less than modern and precipitation range of 2.1-1.4x modern. At 40% mass reduction by sublimation, results indicate a temperature depression of 7.6-8.2 °C and this results in precipitation at 2.4-2.3x modern. These model results highlight the importance of accounting for winter snowpack processes in modeling glacier and lake mass balance, and are consistent with previous suggestions that both cooling and greater-than-modern precipitation accompanied glacier and lake maxima during the late Pleistocene.