Pronounced climatic variations in Alaska during the last two millennia

Paired oxygen-isotopic analyses of abiotic carbonate and benthic-ostracode shells from lake sediments provide a continuous quantitative record of grow ing-season temperature for the past 2000 years in the northwestern foothill s of the Alaska Range. This record reveals three time intervals of comparab le warmth: anno Domini (A.D.) 0-300, 850-1200, and post-1800, the latter tw o of which correspond to the Medieval Climatic Anomaly and climatic amelior ation after the end of the Little Ice Age. The Little Ice Age culminated at A.D. 1700, when the climate was approximate to1.7 degreesC colder than at present. A marked climatic cooling also occurred around A.D. 600, coincidin g with extensive glacial advances in Alaska. Comparisons of this temperatur e record with ostracode trace-element ratios (Mg/Ca, Sr/Ca) further suggest that colder periods were wetter and vice versa during the past 2000 years.