RECONSTRUCTION OF LATE PLEISTOCENE MOUNTAIN GLACIATION AND CLIMATE IN THE NORTHEASTERN GREAT BASIN, WESTERN USA

Late Pleistocene glaciation in the Great Basin spanned dozens of mountain ranges, many of which were bordered by pluvial lakes. The region therefore offers a unique geographic setting for reconstructing climatic change through the last glaciation, including the last-glacial interglacial transition. Here, we reconstruct the extent of Late Pleistocene glaciers in the northeast Great Basin, focusing on glaciated mountains neighboring the geographic extent of Lake Bonneville where the history of glacier change is limited by cosmogenic chronologies of deposits and landforms. Reconstructions use a set of established geospatial tools that compute ice thickness and areal extent from valley topography and inferred basal shear stress along flow paths upstream of known ice margins. Paleoglacier equilibrium lines are estimated from reconstructed glacier surfaces to infer climate from the time of glacier maxima through the time of ice retreat. The resulting pattern of mountain glaciation displays a range of paleo-glacier equilibrium-line altitudes (ELAs) of 2480-3450 m asl during the regional glacial maximum (22-19 ka), with a strong latitudinal trend in the area west of Lake Bonneville. East of Lake Bonneville, ELAs rise by more than 700 m from east to west, a pattern consistent with previous reconstructions and suggesting significant differences in moisture availability across the region. During the subsequent interval 18-16 ka, glaciers throughout the region remained (or readvanced to) near their maximum length, thereby displaying a similar overall pattern in regional glaciation with only slightly higher ELAs. Climate inferred from the reconstructed ELA pattern for the intervals 22-19 ka and 18-16 ka suggests the greatest temperature depressions in the Wasatch Range and in glaciated mountains west of Lake Bonneville, and lesser temperature depressions in the Uinta Mountains. The magnitude of regionwide ELA-based temperature depression is consistent with numerical models of paleoglaciers and Lake Bonneville and paleoclimate proxies from Lake Bonneville, suggesting a temperature depression of 8-12° C prior to the onset of ice retreat.