LATEST PLEISTOCENE AND HOLOCENE CLIMATE AND ENVIRONMENTAL CHANGE FROM ALPINE LAKE SEDIMENTS AT GRAND TETON NATIONAL PARK, WY

Paleoclimate reconstructions from alpine regions in the western U.S. are important for placing observed recent changes to these sensitive environments in a longer-term context, and for improving our ability to accurately predict and model future changes. This research is designed to use lake sediments to reconstruct the timing and magnitude of postglacial climate variability and associated environmental impacts in the Teton Mountain Range, Grand Teton National Park (GRTE), WY. Most alpine lakes in GRTE formed following regional deglaciation roughly 15 ka. Lake sediment fill marks the timing of glacier retreat from individual basins and contains a continuous and datable record of subsequent upstream glacier activity and environmental conditions. Multiple sediment cores from Taggart (43°42'15N N, 110°45'20"W), Bradley (43°42'51"N, 110°45'20"W), and Jenny (43°45'50"N, 110°43'46"W) Lakes were retrieved from a lake ice platform using a percussion-driven piston coring system. At least one core from each lake contains well-laminated, clay-rich basal sediments. These sediments are interpreted to have been deposited during early phases glacier recession (lake inception) and confirm complete recovery of the postglacial sediment package. The depth to this clay layer in Jenny Lake corresponds to a distinct acoustic reflector visible in sub-bottom profiles. Geochronologic control of the cores and correlation between core sites is aided by the presence of two prominent tephra deposits at ~100 cm and ~190 cm depths. Based on their stratigraphic positions, physical characteristics, and major element geochemistry, these horizons are tentatively identified as the Mazama (~7.5 ka) and Glacier Peak (~13.5 ka) tephra beds, respectively. Multiple physical and geochemical proxies, including sediment density (gamma ray and dry bulk), magnetic susceptibility, color spectrophotometry, loss on ignition and biogenic silica are evaluated at multi-decadal resolution and reveal variable latest Pleistocene and Holocene environmental conditions at GRTE.