NUMERICAL MODELING OF LATEST PLEISTOCENE GLACIER MASS BALANCE AND ICE FLOW IN THE WESTERN RUBY MOUNTAINS, NEVADA, U.S.A

Seitz Canyon features one of the best preserved sequences of dated Pleistocene terminal and recessional moraines in the Great Basin. The sequence provides an opportunity to limit changes in climate during an interval of nearly continuous moraine deposition spanning ~21-15 ka, which represents the latter part of the last glaciation and overlaps with highstands of several pluvial lakes in the northeastern Great Basin. Numerical models of steady-state glacier mass balance and ice flow, developed by Plummer and Philips (2003), were applied to Seitz Canyon and the adjacent Hennen Canyon to simulate maximum and recessional ice extents. The goal of this modeling was to limit the range of temperature and precipitation combinations that accompanied the interval of moraine deposition. Model experiments indicate that, if precipitation was less than or near modern, then temperature was ~13-11º C less than modern while the glaciers in Seitz and Hennen Canyons were at their maximum extent at 21-20 ka. This result is consistent with modeling of mountain glaciers elsewhere in the Great Basin, including glaciers that were immediately downwind of Pluvial Lake Bonneville. Deposition of recessional moraines in Seitz Canyon at 17-15 ka was coeval with highstands of several pluvial lakes in the Great Basin; we consider a range of possible climate scenarios for this time interval. For less than or near modern precipitation, model experiments indicate a temperature depression of ~9.5-10.5º C. For precipitation rates 50-100% greater than modern, temperature depression was ~7.5-8.5º C. Overall, these results are consistent with several independent estimates of temperature depressions in the Great Basin during the last glaciation, and provide new limits on temperature and precipitation responses to changing atmospheric circulation in the western U.S. during the last glaciation.