A 6,000-YEAR RECORD OF DROUGHT IN NORTH-CENTRAL WASHINGTON FROM LAMINATED LAKE SEDIMENTS
In light of extended ~5-year drought conditions that currently affect much of western North America, substantial effort has been focused on understanding the natural cyclicity and magnitude of such events from the paleoclimate record. Here we present a ~6,000-year record of drought variability with ~5-year resolution based on a multiproxy study including oxygen/carbon isotopes and sediment grayscale analyses from Castor Lake in north-central Washington State. The grayscale record correlates well with the ~1500-year Palmer Drought Severity Index (PDSI) reconstructed from tree-ring data across the west. This serves to validate the legitimacy of both methodologies and allows for confident interpretation of the period for which only lake data are available. Spectral analyses of the ~6,000-year record from Castor Lake reveals a strong and dominant periodicity centered on ~50-years. Such timescales are coincident with those observed in Pacific Ocean variability, and suggest that the PDO may have exerted an influence on regional drought patterns for at least the past ~6,000 years.