QUANTIFYING THE PRECIPITATION FORCING DRIVING PLUVIAL LAKE HIGHSTANDS IN THE NORTHERN GREAT BASIN (Invited Presentation)

In western North America the presence or absence of lakes in terminal basins provides a measure of wetness driven by changes in precipitation and/or evapotranspiration, hydroclimate metrics that can readily be compared to paleoclimate model output. The northern Great Basin during the last deglaciation contains the deepest and largest pluvial lakes in western North America with wetter conditions being recorded by shoreline datasets whose highstand ages show an asynchronous temporal response across the northern Great Basin. In this contribution we demonstrate how the size distribution of terminal lakes in combination with hydrologic scaling relationships can be used to determine the hydroclimate drivers of past wet conditions. Further, when co-located spatially, the differing hydroclimate sensitivity of lakes and analogous glacier mass balance constraints provides a quantitative estimate of temperature and precipitation change in the past that agrees well with independent macrofossil-based estimates and qualitative measures of wetness from compilations of hydroclimate proxies.

Two key findings emerge from our analysis of the northern Great Basin pluvial lakes. First, Pleistocene lakes during the Last Glacial Maximum (LGM) in the northern Great Basin do not require substantial precipitation increases to explain many lake shoreline extents and sit in a no-change ‘transition zone’ between a wet-dry dipole indicated by both proxies and climate models. As such, we infer that reduced evaporation was an important driver of wet conditions during the LGM. Second, lake highstands in the northern Great Basin achieved asynchronously during Heinrich Stadial 1 likely do require substantial (>40%) increases in precipitation as evidenced by: rapid increases in lake levels recorded in robust chronologies in several of the smaller lake basins; minimal changes in temperature during HS1 vs. the LGM; and post-LGM highstand lake areas increasing by ~50-70% across the northern Great Basin.