HOLOCENE DUST DEPOSITION IN ALPINE LAKES OF THE WESTERN U.S.-- RESOLVING REGIONAL AND REMOTE SOURCES IN SEDIMENTARY ARCHIVES

Sedimentary deposits in a number of high alpine lakes in the western United States have been recently demonstrated to be dominated by mineral dust accumulation, and to provide important archives for reconstructing environmental, climatologic and anthropogenic variability in the region. For example, episodes of increased mineral dust flux to these lakes are hypothesized to signify increased wind erosion in the region during arid intervals over the past several thousand years, providing paleo-drought records against which current conditions can be evaluated. Perhaps less appreciated, however, is that the accumulation of dust from remote sources such as Asia may be a proxy for wetter rather than drier conditions. Models and observation-based studies indicate that this typically fine material travels high in the atmosphere, where it can ‘seed’ clouds and induce precipitation. Trends in the content of regionally vs. remotely derived dust in lake sediments thus can provide quite different paleoclimate information.

Here we present the preliminary results of a study aimed at developing techniques to resolve contributions of regionally vs. remotely sourced dust in lacustrine sediments. Late Holocene sedimentary deposits from three well-studied alpine lakes, including Pear Lake, CA, Senator Beck Lake, CO, and North Lake, WY, were analyzed. Particle size analyses from various horizons in cores recovered from each of the lakes were used to identify changes in contributions of end-member populations over roughly the past 1500 years. Major, minor, and trace elements were used to evaluate the provenance of silt and clay-sized isolates from these horizons. We evaluate the potential utility of our methods for differentiating the signals of regional vs remotely sourced dust, and thereby for obtaining more complete reconstructions of past precipitation patterns.