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A CHIRONOMID BASED PALAEOENVIRONMENTAL RECONSTRUCTION OF ANTIFREEZE POND IN YUKON, CANADA
Barley, Erin M. Simon Fraser University.
WALKER, IAN R. Okanagan University College.
In Eastern Beringia (Yukon and Alaska), the transition from the full glacial (26,000 to 14,000 14C yr BP) to the Holocene (10,000 14C yr BP to present) was marked by increasing moisture and temperatures. However little quantitative paleoclimatic data exists to document the extent of full glacial conditions, or the timing and rate of climatic amelioration. Chironomid (non-biting midge) assemblages show strong correlation with their environments, and are a useful proxy for reconstructing past temperatures. A training set of 121 lakes in Alaska, Yukon, Northwest Territories, and British Columbia was used to develop a transfer function relating mean July air temperatures to chironomid assemblages. The strongest model was produced by WA-PLS (2 components) with a bootstrapped error of 1.35˚C and an r2(boot) of 0.51.
The model was applied to the chironomid record of Antifreeze Pond in southwestern Yukon. The lowest zone (pre-Late glacial; AMS basal dates submitted) revealed mean July air temperatures 2.5˚C colder than present, though comparable assemblages in the high arctic suggest even colder conditions. A sharp rise to near present temperatures is followed by a hiatus in the chironomid record suggesting Antifreeze Pond (currently 120 cm deep) dried up. At 12,400 14C yr BP chironomids re-appear and indicate temperatures near present; the appearance of semi-terrestrial taxa (Limnophyes, Parametriocnemus/Paraphaenocladius, and Doithrix/Pseudorthocladius) suggests fluctuating water levels. Holocene temperatures are not significantly different from present, and peaks of semi-terrestrials again suggest fluctuating pond levels.
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