Olympia Interstadial; vegetation, landscape history, and paleoclimatic implications of a mid-Wisconsinan (MIS (sub 3) ) nonglacial sequence from southwest British Columbia, Canada

Lithostratigraphic, (super 14) C, and palynologic analyses of peat and silty peat at three nearby sites reveal a 25 000 year vegetation and climate history of the Olympia Interstade for the Fraser Lowland, British Columbia, 300 km within the southern limit of the Cordilleran Ice Sheet. At Lynn Valley, Polypodiaceae fern spores and nonarboreal pollen dominate >47.8 (super 14) C ka BP, reflecting unstable and cold landscapes. A Pinus-Poaceae Zone follows, representing pine parkland and cool dry climate. Fluctuating values of Picea and Tsuga mertensiana pollen at Lynn and Seymour Valleys and Port Moody characterize most of the Olympia Interstade during local peat deposition in Cyperaceae and Myrica wetlands until about 26.7 (super 14) C ka BP under a cool and moist climate. A brief Pinus-Tsuga heterophylla zone at Lynn Valley 44-39 (super 14) C ka BP suggests a climatic optimum. A Poaceae-rtemisia assemblage and deposition of silty sand after 26.7 (super 14) C ka BP reflect cooling and drying after which a unique Lycopodium assemblage at Lynn Valley suggests cold arid climate and Fraser Glaciation onset. These sequences have no progression to vegetation typical of warm, interglacial, Holocene-like climates, indicating an interstadial not an interglacial interval. Correlation with vegetation changes elsewhere in western North America suggests that the Olympia Interstade started about approximately 52 (super 14) C ka BP ( approximately 57 cal ka BP) and ended about 26 (super 14) C ka BP (30 cal ka BP).