AN UPDATED CHRONOLOGY FOR THE UPPER FREMONT GLACIER ICE CORES: CLIMATE AND ENVIRONMENTAL IMPLICATIONS

The Upper Fremont Glacier (UFG), located in the Wind River Range of Wyoming, has been studied extensively to examine interior continental pollution and climate over the past 250 years. Here we present a new chronology for two ice cores recovered from UFG in the 1990s. The new depth-age scale is consistent with the few unambiguous age control points from the original UFG chronologies, but refinement by synchronizing the ice core water isotopes to a nearby tree-ring width index suggests changes of up to 80 years from the original chronology. The significant changes in the dating of these ice cores fundamentally alters previous interpretations of climate and pollution records preserved in the cores. On the new chronology, industrial pollutants parallel trends observed in Arctic ice cores, and mercury increases previously attributed to the mid-19^th century Gold Rush are now shifted into the early-20^th century, consistent with records from other North American ice and lake sediment cores. Preliminary ice flow modeling indicates glacier and basin geometry are the main controls on the depth-age scale at UFG and that accumulation at UFG has been relatively constant over the past 250 years. Comparisons of the UFG ice core water isotopes to new measurements of cellulose oxygen isotopes from nearby trees will provide a multi-proxy understanding of climate in this region.