RUI: Collaborative Research: Glaciation and Climate Change in the Rocky Mountains During the Last Glacial Maximum and the Subsequent Deglaciation

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Mountain glaciers were numerous in the Rocky Mountains of western North America during the last Pleistocene glaciation, and the geologic record of these glaciers provides dramatic evidence of climatic changes during and following the Last Glacial Maximum. This research will build upon and augment the Pleistocene mountain glacial chronologies in the U.S. Rocky Mountain region, and use these chronologies to model past climate changes. The project uses both field and analytical methods to address two broad objectives: (1) to determine the changes from modern climate that would be necessary to sustain Rocky Mountain glaciers at their last Pleistocene maximum extents, along a transect from northern Montana to south-central New Mexico, and (2) to determine the timing and rate of subsequent ice recession, and the magnitudes and rates of climate change necessary to drive that recession. The first objective involves additional glacial mapping and chronology in eight study areas, making use of cosmogenic beryllium-10 surface-exposure dating to constrain the timing and extent of glaciers during Last Glacial Maximum. A numerical model of glacier mass balance and ice flow will allow determination of the character and magnitudes of climatic change sufficient to produce the observed glacial extents. The second objective involves additional surface-exposure dating in four of the eight study areas to constrain the timing and rates of ice recession following its maximum stand, and to allow modeling of the climate changes that caused the recession. The results of this research will include a regional synthesis of glacier-climate reconstructions for the last Pleistocene glaciation and the subsequent deglaciation, an assessment of the climatic significance of the apparent variability in the timing of the Last Glacial Maximum, and an improvement in the chronology of mountain glacier movements.This application of high-resolution glacier modeling and cosmogenic-radionuclide dating methods will provide insight into the history of climate change in the Rocky Mountain region. The time interval of interest is the Last Glacial Maximum (the interval of maximum global ice volume) and the subsequent transition to the present warm period, the latter occurring over approximately 6000 years. This transition was an interval of major global warming, during which substantial changes in atmospheric circulation occurred in the western United States in response to shrinking ice sheets, increased incoming solar radiation, and rising atmospheric carbon dioxide levels. Such changes in airflow undoubtedly brought about changes in regional precipitation patterns, as is suggested by paleoclimate models. The results of this research will assess the accuracy of such models in representing precipitation patterns of the past, and may also provide insight into the accuracy of model predictions of future precipitation changes in the Rocky Mountains region, an area where demand for limited water resources continues to grow.