GSA QUATERNARY GEOLOGY AND GEOMORPHOLOGY DIVISION DISTINGUISHED CAREER AWARD: CLIMATE OF THE WESTERN OLYMPIC PENINSULA, NW U.S.A., DURING THE LATTER PART OF MIS 2 (LAST GLACIAL MAXIMUM)

Glaciers advanced down each major valley of the western Olympic Peninsula (OP) during MIS 2, extending to the coastal lowlands but terminating within the ice limits of MIS 3 and older glaciations. The factors influencing MIS 2 mountain glaciation are poorly understood. To contribute to a better understanding, we analyzed the climate from 25.7- 18.7 cal BP, (c. the last glacial maximum - LGM), based on a reexamination of pollen data supplemented with new data from fossil beetles. Pollen and plant macrofossils provide evidence that the LGM vegetation of the western OP was a Sitka spruce-mountain hemlock parkland. Both dominant tree types occur on the OP today but not at the same elevation. Forest patches in which these species co-occur today are in SE Alaska where the mean summer temperature (MST) is 4°C cooler and snow cover persists throughout winters. LGM fossil beetle assemblages from near Kalaloch on the coast, and from a high cut bank on the South Fork of the Hoh River, contain species that currently inhabit riparian and lacustrine habitats in the boreal zone of Canada and Alaska, and in higher elevations in the Cascades and Rocky Mountains. Olophrum species, which today are unknown from the OP, are represented by fossils of O. rotundicolle, O. boreale and O. consimile. O. consimile is especially well represented and today does not occur below c. 1000m in the northern Cascades of Washington. Using adiabatic lapse rate, it is estimated that MST would have been at least 4°C cooler than today. The absence of wood-boring beetles, in contrast to fossil beetle assemblages from MIS 3 deposits at Kalaloch, indicates an open landscape, which is consistent with a parkland vegetation. Estimates of the amount of lowering of MST for both pollen and fossil beetles are similar even though the methods used were different. Both proxies provide evidence that the LGM climate was at least as wet as the western OP today but not as dry as the Puget lowland during the LGM. The amount of climatic cooling on the OP during the LGM was considerably less than at similar latitudes in mid-continental or eastern North America, indicating a strong modulation of climate by the Pacific Ocean. A cool and wet summer climate during the LGM on the OP is consistent with glaciers advancing to the lowlands, but leaves open the question of why glaciation was less extensive than during MIS 3.