SUMMARY

Pollen records from the northern California and southern Oregon margin of the northeast Pacific Ocean (Sites 1019 and 1020 and piston Core EW9504-17) capture vegetational-environmental changes on the North American northwest coast. Glacial vegetation is dominated by montane conifer types accompanied by a significant amount of herbs. Major climatic thresholds such as glacial-interglacial transitions are marked by high-amplitude peaks of the pioneer alder that precede the expansion of interglacial lowland oak woodlands and coastal redwood forests. The similarity in the structure of oak- and redwood-based pollen ratios, insolation, and ¹⁸O curves implies that environmental fluctuations on the Pacific Northwest coast reflect large-scale variations in global climate over the last ~150 k.y. Comparison of preliminary pollen and oxygen isotope data from Sites 1019 and 1020 indicates that similar relationships prevailed over the last 500 k.y. We suggest that differences in the development of lowland oak- and redwood-dominated vegetation on the northwest coast of North America reflect fluctuations in large-scale climate controls and fluctuations in regional maritime conditions offshore.