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Latest Pleistocene advance of alpine glaciers in the southwestern Uinta Mountains, Utah, USA: Evidence for the influence of local moisture sources

Jeffrey S. Munroe^*,1, Benjamin J.C. Laabs^,2, Jeremy D. Shakun³, Brad S. Singer⁴, David M. Mickelson⁴, Kurt A. Refsnider⁴ and Marc W. Caffee⁵

¹ Department of Geology, Middlebury College, Middlebury, Vermont 05753, USA
² Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
³ Department of Geology, Middlebury College, Middlebury, Vermont 05753, USA
⁴ Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton Street, Madison, Wisconsin 53706, USA
⁵ Department of Physics, Purdue University, 1396 Physics Building, West Lafayette, Indiana 47907, USA

Cosmogenic surface-exposure ¹⁰Be dating of Last Glacial Maximum (LGM) moraines indicates that glaciers in the southwestern Uinta Mountains remained at their maximum positions until ca. 16.8 ± 0.7 ka, 2 k.y. after glaciers in the neighboring Wind River Range and Colorado Rockies began to retreat. The timing of the local LGM in the southwestern Uintas overlaps with both the hydrologic maximum of Lake Bonneville and preliminary estimates of the local LGM in the western Wasatch Mountains. This broad synchroneity indicates that Lake Bonneville and glaciers in northern Utah were responding to similar climate forcing. Furthermore, equilibrium line altitudes (ELAs) for reconstructed LGM alpine glaciers increase with distance from the Lake Bonneville shoreline, rising from 2600 m to 3200 m over the 120 km length of the glaciated Uintas. This pronounced ELA gradient suggests that the magnitude of the latest Pleistocene glacial advance in the western Uintas was due, at least in part, to enhanced precipitation derived from Lake Bonneville; thus, the lake acted as a local amplifier of regional climate forcing. This relationship underscores the sensitivity of alpine glaciers to moisture availability during the latest Pleistocene, and further demonstrates the importance of local moisture sources on glacier mass balance.

Key Words: Last Glacial Maximum • alpine glaciers • climate • Rocky Mountains • late Pleistocene