EVALUATING SIGNALS OF MOUNTAIN GLACIER AND PALEOLAKE RESPONSE TO HEINRICH EVENT 1, NORTHERN GREAT BASIN, NEVADA

Records of Pleistocene paleolakes in the Great Basin of the southwestern U.S. provide an opportunity to identify the magnitude of temperature and precipitation changes accompanying lake highstands during the last glaciation and deglaciation. Lake Clover and Lake Franklin, located in northeast Nevada, were closed-basin, high elevation lakes that existed to the east of the glaciated Ruby and East Humboldt Mountains (REH). Chronologies of lake shoreline deposits and of moraines indicate that mountain glaciers in the REH were near their maximum length when the lakes had reached their highstands during the late Last Glacial Maximum (ca. 19.0 ka) and during the middle part of Heinrich Stadial 1 (ca. 17.0 ka). To infer climate change during these times in the northeastern Great Basin, results of physically based numerical models of glacier mass balance and ice flow are combined with a hydrologic model of lake water balance. The water balance model is modified from previous applications in the Great Basin; it uses a calibrated evaporation scheme, weekly meteorological inputs, temperature-limited runoff and historical dimensions of modern lakes in the Clover and Franklin valleys to constrain modern hydrology in terms of soil-water storage and runoff. The glacier model computes net annual mass balance of a glacial valley based on monthly meteorological inputs and solar radiation flux. Both models can identify a set of temperature and precipitation solutions accompanying a known Pleistocene glacier or lake extent. Combined results of the two models indicates that synchronous lake highstands and moraine deposition during Heinrich Stadial 1 were accompanied by temperatures as much as 12°C less than modern with near-modern precipitation. This suggests that cooling played a significant role in augmenting effective precipitation during late Pleistocene lake highstands, although additional testing of the two models is needed to more precisely limit temperature and precipitation changes. Model results will be discussed in the context of new records of late Pleistocene temperature change in the Great Basin and hypotheses for the impact of Heinrich Event 1 on climate in the southwestern U.S.