Pergamon Quaternary Science Reviews, Vol. 14, pp. 449-47 1, 1995. Copyright0 1995Elsevier Science Ltd. Printed in Great Britain. All rights reserved. 0277-3791l95 $29.00 0277-3791(9S)ooo&X LATE PLEISTOCENE AND HOLOCENE PALEOENVIRONMENTS OF THE NORTH PACIFIC COAST DANIEL H. MANN* and THOMAS D. HAMILTON? *Alaska Quaternary Center; University of Alaska Museum, 907 Yukon Drive, Fairbanks, AK 99775, U.S.A. I-US. Geological Sur v ey , 4200 University Drive, Anchorage, AK 99508, U.S.A. Abstract - Unlike the North Atlantic, the North Pacific Ocean probably remained free of sea ice during the last glacial maximum (LGM), 22,000 to 17,000 BP. Following a eustatic low in sea level of ca. -120 m at 19,000 BP, a marine transgression had flooded the Bering and Chukchi shelves by 10,000 BP. Post-glacial sea-level history varied widely in other parts of the North QSR Pacific coastline according to the magnitude and timing of local tectonism and glacio-isostatic rebound. Glaciers covered much of the continental shelf between the Alaska Peninsula and British Columbia during the LGM. Maximum glacier extent during the LGM was out of phase between southern Alaska and southern British Columbia with northern glaciers reaching their outer limits earlier, between 23,000 and 16,000 BP, compared to 15,00&14,000 BP in the south. Glacier retreat was also time-transgressive, with glaciers retreating from the continental shelf of southern Alaska before 16,000 BP but not until 14,000-13,000 BP in southwestern British Columbia. Major climat- ic transitions occurred in the North Pacific at 24,000-22,000, 15,000-13,000 and 11 ,OOO-9000 BP. Rapid climate changes occurred within these intervals, including a possible Younger Dryas episode. An interval of climate warmer and drier than today occurred in the early Holocene. Cooler and wetter conditions accompanied widespreadNeoglaciation,beginning in some mountain ranges as early as the middle Holocene, but reaching full development after 3000 BP. INTRODUCTION The North Pacific Ocean borders the Asian and North American continents along an intricate coastline arcing between Japan and California (Fig. 1). Unlike the Atlantic Ocean, the North Pacific is virtually barred from the Arctic Ocean, being connected only through the shallow and narrow Bering Strait. Across this strait and surrounding parts of the Bering Platform, the fauna and flora of Asia and North America have mingled. By this route, humans probably first entered the New World (Meltzer, 1993). Biotic interchange between continents is one reason why the paleoclimates and paleogeography of the North Pacific coastline are of special interest. Another reason is that, like the North Atlantic, the North Pacific greatly affects the climate and weather over the surrounding landmasses, especially downwind in North America (e.g. Charles et al., 1994). Past and future climatic changes are intimately tied to oceanographic and climatic processes in the Pacific Ocean. Although the largest of the three major oceans, the Pacific is poorly understood in terms of its late Pleistocene history. This lack of information is especially notable in the Russian sectors of the coast. Paleoceanographic research has lagged in the North Pacific because the carbonate-compensation depth, the water depth where calcareous microfossils dissolve, is above the bottom over large reaches of this deep ocean (Archer and Maier-Reimer, 1994). In other oceans, most notably in the North Atlantic, our reconstructions of pale- oceanography and paleotemperature are largely based on calcareous microfossils such as foraminifera contained in deep sea cores. We review here the late Pleistocene (25,000-10,000 BP) and Holocene (10,000-O BP) paleoclimate and paleogeography of the coastal regions bordering the North Pacific from northern Japan, through Alaska, and down the northwest coast of North America through British Columbia into Washington state. Emphasis is placed on coastal areas of Alaska, the areas we know best. All ages are expressed as uncalibrated radiocarbon years before present. The reader is cautioned that the wide geographical separation of data sites introduces assumptions about spa- tial scales into the paleogeographic reconstructions we present. As the distance between data sites increases, so does the uncertainty in the reconstructed image of the paleolandscape. The patch size relevant to an organism, whether human or spruce tree, can be far smaller than the resolution of our reconstructions. Scale problems also derive from the available temporal control since most studies rely on radiocarbon chronologies whose resolu- tions range from hundreds to thousands of years. Rates of climatic or geographic changes, which may have been critical in determining species survival or extinction, generally are inadequately known at present. THE NORTHWEST PACIFIC OCEAN The northwest Pacific Ocean stretches from Hokkaido to the Commander Islands and includes the Sea of Okhotsk and the Sea of Japan (Fig. 1). Today this sector 449