Evidence for an Early Recent Warm Interval in Northwestern Alaska

A warm interval that began at least 10,000 years ago and lasted until at least 8300 years ago is recorded in the coastal tundra covered area of northwestern Alaska by the presence of fossil wood of tree size or tree species, fossil beaver-gnawed wood found beyond the modern range of beaver, evidence of ice-wedge melting, buried soils, and soils that extend below the top of modern permafrost.

Dating of the warm interval is based on eight radiocarbon dates. Although these do not provide tight control for either the beginning or the end, they permit the interpretation that the warm event began at the start of the worldwide, postglacial warming and that it ended at the time of the Anivik Lake glacial readvance in the Brooks Range. If this is correct, the early Recent warm interval and the “postglacial thermal maximum” recognized by Livingstone in the Brooks Range were separated by a period of cooler climate. Deposits 7200 and 3600 years old also record moments when the climate was warmer than at present in coastal northwestern Alaska. Although these may record a continuation of the early Recent warm period, it seems more likely that they represent later and separate brief intervals of warmer climate.

A postglacial thermal maximum between 6000 and 3000 years ago is recorded by pollen profiles in the Brooks Range, but is not clearly recorded in the coastal areas of northwestern Alaska. We suggest that as sea level rose to near its present position, the accompanying maritime climate lowered summer temperatures in this coastal area during the time at which areas farther inland were experiencing the high temperatures of the postglacial thermal maximum.