NEW RECORDS OF DE-GLACIAL AND HOLOCENE HYDROCLIMATE AND ENVIRONMENTAL CHANGE FROM THE MATANUSKA-SUSITNA REGION OF SOUTH-CENTRAL ALASKA

Alaska’s large geographic area, topographic relief, and varying influences by Arctic and Pacific ocean-atmosphere processes lead to persistent regional differences in climatology, hydrology and ecology that require detailed spatial observations to be recognized. Therefore, a similarly comprehensive spatial representation is also needed to better understand the de-glacial and Holocene climatic and environmental history of Alaska on regional scales. Newly recovered marl lake sediment records from the Matanuska-Susitna region of Knik Arm on Cook Inlet near Wasilla, ~50 km north of the city of Anchorage, AK provide new details on paleoclimatic change for near coastal elevations in the south-central region. Complete sediment records containing de-glaciation were obtained from three lakes with varying rates of groundwater through-flow and corresponding differences in evaporative effects on lake water oxygen and hydrogen isotopes. Geochronology is being developed through identification of known Holocene tephras and AMS radiocarbon dating of abundant terrestrial macrofossils. Modern and historic sediments are dated by ²¹⁰Pb. The hydrologically-open site, unaffected by evaporation and with exceptionally high rates of marl sedimentation, provides clearly defined oxygen isotope excursions in the late 1970s and early 1940s when Pacific forcing is known to have undergone shifts. A hydrologically-closed site with overriding evaporative effects provides a corresponding record of effective moisture. Our preliminary data indicate strong correspondence between these independent records of changes in atmospheric circulation and moisture balance.