Development of thermokarst lakes during the holocene at sites near Mayo, Yukon territory

The origin and growth of numerous thermokarst lakes near Mayo, central Yukon, has been examined, using ground surveys, aerial photographs and dendrochronology. Many of the lakes are currently expanding, at rates of axial increment up to 1.2 m/yr. Three lakes, whose axes are currently enlarging at about 1.0 m/yr, were studied in particular detail: tree-ring analysis indicates that these lakes formed by the middle to the late part of the last century. The talik profile was determined beneath one lake, and is consistent with the Stefan solution for thawing of ice-rich soil with such an initiation date and rate of expansion. Organic-rich horizons containing logs, vegetative detritus and fresh-water ostracods have been exposed in two retrogressive thaw slumps near the lakes. These horizons have been interpreted as the bottoms of former thermokarst lakes. Radiocarbon dates of approximately 8500 BP, 3900 BP and 2300 BP have been obtained, indicating several periods of thermokarst activity during the Holocene. The results suggest that thermokarst lake development is not solely associated with changing climatic conditions in this region, since the current lakes and those that formed around 2300 BP do not appear to be directly linked to climatic warming. It is suggested that the most recent initiation of thermokarst activity is related to the effects of forest fires.

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