9709502 Rhode The Bonneville Basin of western Utah and eastern Nevada has one of the best known late Pleistocene paleoenvironmental records in the world, but our understanding of the history of terrestrial biota in the region lags behind our understanding of lake levels or regional paleoclimates. Recently a large number of ancient packrat middens have been collected from the mountains surrounding the Great Salt Lake Desert, providing a rich source of fossil plant and animal remains dating through the last 50,000 years. Under this proposal, a series of analyses of these midden samples will be undertaken. Samples from these middens will be radiocarbon dated to derive a long term chronology of midden strata. Plant macrofossils, pollen, insect remains, and vertebrate faunal elements will be identified, to reconstruct biotic distributions through time. Stomatal density and concentrations of stable isotopes of hydrogen and carbon will be examined to determine changes in water use efficiency of certain plant taxa (limber pine) in response to changes in climate and atmospheric chemistry during the glacial-interglacial cycle. Postulated changes in body size of the bushy-tailed woodrat in response to climate change during this same time period will be evaluated using fecal pellets as a proxy measure. When these data sets are integrated together, this midden record will be used to identify and date major shifts in vegetation associations, the distribution of insect and vertebrate taxa, and changes in physiology and morphology of plant and animal taxa in response to dramatic changes in climate and atmospheric CO2 concentration, within a single regional ecosystem during the last 50,000 years. These data will provide the basis for paleoclimatic estimates in the region to complement and cross-check other paleoclimatic proxy data and climate model results from the Bonneville Basin, contributing to one of the most detailed and well dated long-term terrestrial records of climate change and responses b y geological and biological systems available.
