Holocene geologic and climatic history around the Gulf of Alaska

Though not as dramatic as during the last Ice Age, pronounced climatic chan ges occurred in the northeastern Pacific over the last 10,000 years. Summer s warmer and drier than today's accompanied a Hypsithermal interval between 9 and 6 ka. Subsequent Neoglaciation was marked by glacier expansion after 5-6 ka and the assembly of modern-type plant communities by 3-4 ka. The Ne oglacial interval contained alternating cold and warm intervals, each lasti ng several hundred years to one millennium, and including both the Medieval Warm Period (ca. AD 900-1350) and the Little Ice Age (ca. AD 1350-1900). S almon abundance fluctuated during the Little Ice Age in response to local g laciation and probably also to changes in the intensity of the Aleutian Low . Although poorly understood at present, climate fluctuations at all time s cales were intimately connected with oceanographic changes in the North Pac ific Ocean. The Gulf of Alaska region is tectonically highly active, result ing in a history of frequent geological catastrophes during the Holocene. T welve to 14 major volcanic eruptions occurred since 12 ka. At intervals of 20-100 years, large earthquakes have raised and lowered sea level instantan eously by meters and generated destructive tsunamis. Sea level has often va ried markedly between sites only 50-100 km apart due to tectonism and the i sostatic effects of glacier fluctuations.