EXPANSION OF ALPINE GLACIERS IN PACIFIC NORTH AMERICA IN THE FIRST MILLENNIUM A.D

Abstract

Radiocarbon ages and lichen-dated moraines from 17 glaciers in coastal and near-coastal British Columbia and Alaska document a widespread glacier advance during the first millennium A.D. Glaciers at several sites began advancing ca. A.D. 200-300 based on radiocarbon-dated overridden forests. The advance is centered on A.D. 400-700, when glaciers along an ~2000 km transect of the Pacific North American cordillera overrode forests, impounded lakes, and deposited moraines. The synchroneity of this glacier advance and inferred cooling over a large area suggest a regional climate forcing and, together with other proxy evidence for late Holocene environmental change during the Medieval Warm Period and Little Ice Age, provide support for milleannial-scale climate variability in the North Pacific region. © 2006 Geological Society of America.