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32nd Annual Arctic Workshop Abstracts
March 14-16, 2002
INSTAAR, University of Colorado at Boulder

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MERCIER, GENEVI»VE . Department of Geography, University of Ottawa, Ottawa, ON, Canada..
Lacelle, Denis . Department of Geography, University of Ottawa, Ottawa, ON, Canada..
Lauriol, Bernard . Department of Geography, University of Ottawa, Ottawa, ON, Canada..
Duguay, Claude . Centre dÓ┼tudes nordiques et d┼partement de g┼ographie, Universit┼ Laval Sainte-Foy, Qu┼bec, Canada..

Multi-proxy analyses were carried out on cores taken from peatland surfaces developed in thermokarst depressions to determine the vegetation succession and climatic conditions prevailing during the Holocene. 12 cores were taken from the Bluefish Basin (Yukon Territory) which is located in the continuous permafrost zone. Both macrofossils and stable isotopes analyses (d18O and dD) were carried out on the cores. A 1.5 m core was recovered from the center of a plateau, which overlies a late Wisconsin lakebed (gyttja). The results indicate a succession from 9,950 BP from an open water surface (Zone 1) to a nutrient-rich eutrophic shallow pond (Zone 2). A decrease in aquatics and shallow water species is observed around 8,200 BP (Zone 3). Zone 4 consists of herbaceous fragments and charred particles. Eleven conventional radiocarbon dates were obtained at the contact between the lakebed sediment and organic matter. The dates indicate a transition from open water surfaces to an important period of mosses, Sphagnum sp. and herbaceous sp. accumulation between 3,500 BP and 1,500 BP. The 18O and D data of the peat pore water provides some information about the hydrological history of the sites. The d18O and dD indicate that the majority of the ground ice (water) is derived from meteoric rainfall and snow meltwater. In the case of ground ice extracted from the lakebed sediment (gyttja), evaporation influences the isotopic composition of the water, enriching the water in 18O and D.


Figure 1. Macrofossils concentrations per 150 cc of sediment from Bluefish-1.


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