MODELLING CLIMATE CONSTRAINTS ON THE FORMATION OF PLUVIAL LAKE BONNEVILLE IN THE GREAT BASIN, UNITED STATES

Lake Bonneville was the forefather of the modern Great Salt Lake, expanding its footprint to cover roughly 50,000 km², nearly 1/4 the size of Utah. Its immense size has long raised the question of what climatic conditions were required sustain such a large lake, and whether its high stand shorelines record a fundamentally wetter climate than today. This study addresses this question using a hydrologic balance model to estimate the range of precipitation and temperature (P‐T) conditions required to maintain Lake Bonneville at two lake levels during the late Pleistocene. By intersecting lake-derived P-T curves with P-T curves determined from glacial modelling in the Wasatch Mountains we are able to place tighter climatic constraints, which suggest gradually increasing wetness from ~21 to 15 ka. We propose that Lake Bonneville approached its highest level from ~21–20 ka under conditions roughly 9.5°C colder but only 7% wetter than modern. As the lake neared its pre-flood Bonneville level (~18.2–17.5 ka), we estimate that climate conditions were roughly 16% wetter and ~9°C colder than modern. Lake Bonneville ultimately abandoned the overflowing Provo level at ca. 15–14.8 ka, under conditions that were roughly 21% wetter and ~7°C cooler. These results suggest that regional LGM high stands were caused by a climatic optimum in which moderately wetter conditions combined with depressed temperatures to create a positive hydrologic budget. Later high stands of Lake Bonneville and nearby pluvial lakes were likely achieved under larger increases in precipitation, prior to a transition to drier conditions after ~15 ka.