EVIDENCE FOR YOUNGER DRYAS-AGE COOLING ON THE NORTH PACIFIC COAST OF AMERICA

A review of the Palynological evidence from the Olympic Peninsula of W ashington State north to the Alaska Panhandle strongly supports the ex istence of a climatic oscillation similar in timing and effect to the Younger Dryas cooling (11-10 ka BP) of Europe and eastern North Americ a. The evidence includes many late-glacial pollen peaks of mountain he mlock (Tsuga mertensiana), an indicator of cool and moist climate, rev ersals from forest to non-aboreal vegetation, and paleoclimate analysi s using pollen-climate transfer functions on the Queen Charlotte Islan ds. Evidence of cooler ocean waters, based on fossil foraminifera in c ores from the continental shelf, also supports an interpretation of a Younger Dryas-age climatic reversal. On the other hand, geological evi dence of glacier readvances during the Younger Dryas chronozone is wea k and poorly dated. Although more and better-constrained (AMS) dates a re needed to confirm the timing of the Pacific Northwest cold oscillat ion, results so far point to maximum cooling and increased moisture be tween ca. 10.7-10 ka BP, followed by rapid warming in the early Holoce ne. Additional late-glacial sites need to be investigated in detail to confirm the geographical pattern of vegetation and climate change dur ing this interval, which is best expressed in hypermaritime and mariti me climate regions, similar to the Younger Dryas event around the Nort h Atlantic. These results suggest that the search for causal mechanism s to drive the Younger Dryas cooling cannot be limited to events in th e North Atlantic region, but should focus on possible hemispheric or g lobal processes.