Paper No. 7
Presentation Time: 10:10 AM


PUTNAM, Aaron E., Lamont-Doherty Earth Observatory, Columbia University, 217 Comer, 61 Route 9W - PO Box 1000, Palisades, NY 10964, BIRKEL, Sean, Department of Earth Sciences, University of Maine, 5790 Bryand Global Sciences Center, Orono, ME 04469-5790, SCHAEFER, Joerg M., Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, DENTON, George H., School of Earth & Climate Sciences / Climate Change Institute, University of Maine, 5790 Bryand Global Sciences Center, Orono, ME 04469, BROECKER, Wallace, Columbia University, Lamont-Doherty Earth Observatory, New York, NY 10027, PUTNAM, David E., Environmental Science and Sustainability, University of Maine at Presque Isle, 181 Main Street, Presque Isle, ME 04769, EVENSON, Edward B., Earth and Environmental Sciences, Lehigh University, 1 W. Packer Ave, Bethlehem, PA 18015, FINKEL, Robert C., Department of Earth and Planetary Science, University of California, Berkeley, 371 McCone Hall, Berkeley, CA 94720, ROOD, Dylan H., AMS Laboratory, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF, United Kingdom and SCHWARTZ, Roseanne, Geochemistry, LDEO, Columbia University, Palisades, NY 10964,

Accurate knowledge of the timing and magnitude of mountain snowline depression during glacial maxima and subsequent terminations at boreal middle latitudes can aid in deciphering the relative roles of orbital insolation, ice-sheet feedbacks, atmospheric circulation, and greenhouse gases in driving Northern Hemisphere ice ages. Here, we present reconstructions of mountain glacier activity in the Rocky Mountains of Wyoming and the Sierra Nevada of California. Our reconstructions are based on glacial geomorphologic maps, glaciological modeling, and 10Be surface-exposure chronologies targeting exceptionally well-preserved moraine sets deposited at the culminations of the past two ice ages. Our field sites straddle the Great Basin, which harbored extensive pluvial lakes during the Last Glacial Maximum (LGM) and Heinrich Stadial 1. More than 180 10Be dates indicate coeval signatures of mountain glacier activity during the LGM and the last deglaciation in the Wind River Range and Sierra Nevada. These western cordilleran mountain glacier systems achieved maximum configurations concomitant with northern ice sheets. However, during the last deglaciation, snowline rise and mountain glacier recession from LGM to Holocene values led the disappearance of northern ice sheets by several millennia. Altogether, these results support a continent-wide climatic driver of glaciation in the western cordillera of the United States at the culmination of the last two ice ages, and provide insight into controls on ice age climate in western North America.