LAKE SEDIMENT RECORDS OF HOLOCENE ENVIRONMENTAL CHANGE FROM THE NORTH CASCADES, WASHINGTON

The goal of this regional-scale project is to document temperature and moisture balance changes during the Holocene with special attention to high-resolution studies for the last 2000 yr. Sediment cores were collected from six lakes located on a transect across the rain shadow of the North Cascades from glaciated watersheds that receive >200cm/yr in the west to closed basin lakes that receive <30cm/yr in the east. Paleoclimate reconstructions are based on an integrated methodology that combines sedimentary analyses of core transects from shallow to deep water with laboratory analyses of fine-scale sediment features, sediment magnetic characteristics, elemental and isotopic geochemistry, and diatoms. Modern calibration studies are used to supplement our down-core work. Continuous sequences of authigenic carbonate preserved in the sediments of Twin Lakes are being used for oxygen-18 studies (also see Nelson et al., this session). AMS 14C chronologies are supported by tephra analyses and 210Pb profiles. Initial results suggest a warm dry middle Holocene with the onset of colder and possibly wetter conditions after ~4000 yr B.P.