Termination II, Last Glacial Maximum, and Lateglacial chronologies and paleoclimate from Big Cottonwood Canyon, Wasatch Mountains, Utah

Late Pleistocene glaciers and lakes of the Great Basin have been studied extensively due to their excellent utility as paleoclimate proxies; such records are particularly useful where interpreted in combination. The Wasatch Range on the eastern edge of the Great Basin hosted extensive glaciers during the Last Glacial Maximum (LGM), in addition to Lake Bonneville, the region's largest pluvial lake. However, the timing of range-wide glaciation in the Wasatch remains uncertain as compared to the well-established Lake Bonneville chronology. Here we present new cosmogenic exposure ages from the Wasatch Range from low altitude striated bedrock (132.2 +/- 5.9 ka), lateral moraine (20.2 +/- 1.1 ka), nested moraines (15.5 +/- 0.8 ka), and high-altitude bedrock (14.8 +/- 0.7 ka) sites. These ages broadly reveal the local timing of Termination II, LGM, and Lateglacial stadia in the Wasatch, as well as subsequent deglaciation. We then use coupled glacier energy-mass balance and ice-flow models to reconstruct LGM and Lateglacial ice extents in order to determine paleoclimate conditions necessary to produce glacier extents and estimate LGM ice extents in a catchment lacking clear terminus features. Our results provide robust limits on the extents of late Pleistocene glaciers in three drainages of the central Wasatch Mountains and suggest that LGM glaciers reached and abandoned their maxima prior to the Bonneville highstand, while later undergoing rapid deglaciation coeval with the lake's fall from the Provo level. Combining modeled paleoclimate estimates with previously published pluvial lake reconstructions yields LGM temperature depressions ranging from -10 to -8 degrees C (with respect to modern) with 80-150% of modern precipitation, with a best matching Lateglacial temperature depression of -5 degrees C with 200% of modern precipitation. These results support the hypothesis of a relatively cold LGM climate in the Great Basin with little to no increase in precipitation, followed by a period of increased precipitation and warming coincident with Heinrich Stadial 1.