ABSTRACT: Holocene paleoenvironments inferred from a lake at treeline, southwest Yukon Territory, Canada.

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Abstract

A sediment core from Upper Fly Lake (61.04°N, 138.09°W, 1326 m.a.s.l.) has been analyzed for pollen, chironomids, magnetic susceptibility, sediment organic content, and sediment carbonate content. The pollen spectra indicate the lake was surrounded by a herb-tundra environment dominated by Salix, Artemisia, and Cyperaceae from 13,000 to 11,000 cal yr BP, followed by Betula dominated shrub-tundra to 10,000 cal yr BP. Picea migrated into the region around 10,000 cal yr BP, and although this pollen has dominated the assemblages up to the present time, today there are only a few trees in the immediate watershed suggesting that most of the Picea pollen is transported from lower elevation forests. Heterotrissocladius then Psectrocladius were dominant in the oldest sediments, and between 12,000 and 10,000 cal yr BP the chironomid assemblages were mainly comprised of Micropsectra. Between 10,000 and 5,000 cal yr BP Chironomus, individuals of the subtribe Tanytarsina, and Corynocera oliveri were the dominant taxa. Following a brief period (5,000-1,000 cal yr BP) dominated by Cricotopus/Orthocladius, Sergentia increased in abundance. Around 100 cal yr BP, the assemblage again shifts to one dominated by Corynocera oliveri, Chironomus, and individuals of the subtribe Tanytarsina. Air temperature estimates based on new chironomid calibration dataset reconstructions will be presented, and compared with pollen-inferred air temperature reconstructions. Independent oxygen isotope records inferring changes in precipitation over the past 7,500 cal yr BP (Anderson et al. 2005 Quat. Res. 64:21) will be combined with the estimated air temperature reconstructions to interpret postglacial climate variations in the southwest Yukon.

Bibliography of Canadian Geomorphology