Late Pleistocene Glacial and Environmental Change, Eastern Glacier National Park, Montana

Few records in the alpine landscape of western North America document the geomorphic and glaciologic response to climate change during the Pleistocene-Holocene transition. While glacial moraines can provide snapshots of glacier extent in the northern U.S. Rocky Mountains, high-resolution records of environmental change spanning glacial retreat at the end of the Last Glacial Maximum, the Younger Dryas (YD) cooling, and subsequent warming into the stable Holocene are rare. We describe the transition from the late Pleistocene to the early Holocene using a ~17 ka sediment core from Swiftcurrent Lake in eastern Glacier National Park, MT, with a focus on ~17-11 ka. Total organic carbon (%TOC), total inorganic carbon (%TIC), grain size, and carbon/nitrogen (C/N) values provide evidence for warming climate from the late Pleistocene into the Holocene, with the exception of a well-constrained interval of rapid cooling during the YD between 12.5 and 11.5 ka. The variable concentration of detrital dolomite, derived from glacial erosion of bedrock near the valley headwall and cirque basin, provides a high-resolution record of Grinnell Glacier advance and retreat. Dolomite concentrations decrease during glacial retreat and increase during periods of advancing ice, corroborated by sedimentological and geochemical data. We interpret increased dolomite concentration in Swiftcurrent Lake as reflecting enhanced glacial erosion and sediment transport, likely a result of more proximal ice terminus position, possibly increased hydrologic energy, and a reduction in the number of alpine lakes acting as sediment sinks in the valley