DATING FIRST MILLENNIUM AD EXPANSIONS OF ALASKAN COASTAL GLACIERS

Thirty radiocarbon ages and four floating tree-ring chronologies define glacier advances during the first millennium AD (FMA) from 10 forefields of land-terminating glaciers at coastal and near-coastal sites along the Gulf of Alaska. Recognition of these advances has been difficult because subsequent Little Ice Age ice expansions extended farther downvalley than the earlier FMA and in many cases have buried the earlier record. The radiocarbon data primarily derived from wood of buried forests suggest glacial pulses centered on AD 200, 500, 600-650 and 850 with a major peak in activity (10 of 30 ages) during AD 600-650.

Other glacial and nonglacial paleoenvironmental records corroborate this FMA interval as a cold time. Four Alaskan tidewater glaciers were expanding and at least four glaciers from the Coast Range of British Columbia also show expansion during the FMA. Lake records from the Alaska Range show a cold interval centered on AD 600 and from Kodiak, salmon productivity may also have been low during this time. Also from Alaska, the archaeological record shows that the coastal Kachemak Tradition may have been impacted by environmental changes possibly linked to climate variations.

Efforts are underway to precisely tree-ring date the buried forests preserved by these ice expansions. Presently, a tree ring-width series spans from AD 585 through 2003. The more precise calendar dating will help further refine the structure of climate variability during the FMA inferred from the glacial geologic proxy records.