HIGH-LATITUDE TERRESTRIAL PROXIES OF INCREASED PRECIPITATION IN WESTERN NORTH AMERICA DURING THE MEDIEVAL CLIMATE ANOMALY: CONNECTIONS WITH LOW LATITUDE MOISTURE RECORDS

Lake level and tree-ring records from southwestern North America indicate extreme drought conditions during about AD 900-1100 and again from 1200-1350. The earlier interval is coincident with the Medieval Climate Anomaly when many high latitude Northern Hemisphere sites experienced warming. Recent tree-ring dating of buried forests at major tidewater glaciers from the Gulf of Alaska show strong advance about AD 1050, possibly forced by increased winter precipitation. In addition to glacier expansions, a new ring-width record from the Gulf of Alaska that now spans the interval of the Medieval Climate Anomaly also suggests elevated precipitation levels centered on AD 1050 and again in AD 1300. This inferred increase in precipitation persisted for several decades during each interval. Together with the low latitude records of dryness, these terrestrial proxies support a “dry-winter-in-California, wet-winter-in-Alaska” model. The relative changes in moisture flow across North America during Medieval times is consistent with a contraction of the circumpolar vortex.