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HOLOCENE PALEOTEMPERATURES AND PALEOHYDROLOGY OF MARCELLA LAKE, SOUTHWEST YUKON.

PEDERSEN, CY R  University of New Brunswick.
Cwynar, Les C  University of New Brunswick.

Midge (Chironomidae, Chaoboridae, and Ceratopogonidae) distributions are highly sensitive to mean summer surface water temperatures (Walker et al. 1991). In fact, midge analysis is considered to be a key proxy method for inferring past climatic conditions (Battarbee 2000). In this study, midge analysis will be applied to a 5 m sediment record from Marcella Lake, southwest Yukon, to assess the timing and magnitude of temperature changes throughout the past 10,000 years. Marcella Lake was selected after observing the pollen record of the site, which suggests several shifts in regional vegetation. Approximately 6000 calendar years ago, the dominant tree species on the landscape shifted from Picea glauca to Picea mariana, indicating an increase in available moisture within the region (Cwynar 1988). This increase in moisture may have been due to greater precipitation, decreasing temperature (resulting in decreased evaporation), or perhaps both. Combining a historical temperature record with a detailed lake level history (L. Anderson, unpublished) may aid in separating the effects of evaporation from those of precipitation on the local paleohydrology.

Preliminary results indicate that lake levels were low between 6,000 and 4,000 cal. years ago, contradicting inferences made from Marcella’s vegetation history. This discrepancy has stimulated an attempt to develop a new proxy method for qualitatively inferring past lake levels involving the relationship between the abundance of certain midge taxa and lake depth. Forty random surface sediment samples have been collected at various water depths from Marcella Lake. The general distribution of each taxon within the lake basin has been mapped. Mean mental width of the most common taxon, Tanytarsina, has also been measured in order to determine whether it may be useful in documenting changes in lake depth. Should there be a relationship between the distribution of any particular taxa with respect to water depth, or should mental width vary with lake depth, an attempt will be made to reconstruct a qualitative lake level history for Marcella Lake.

Preliminary results suggest that, although most head capsules are distributed uniformly across the lake basin, taxa such as Chaoborus, Sergentia, and Chironomus are more abundant in deep water sediment (7-10 m) whereas head capsules of the tribe Pentaneurini and Cricotopus are concentrated in shallow water sediments (0-4 m). Initial data also demonstrate a trend in deposition with respect to head capsule size. Head capsules isolated from shallow water sediment tend to be larger than those found in deep water sediment.

REFERENCES
Battarbee, R. W., 2000, Paleolimnological approaches to climate change, with special regard to the biological record: Quaternary Science Reviews, v. 19, p. 107-124.

Cwynar, L. C., 1988, Late Quaternary vegetation history of Kettlehole Pond, southwestern Yukon: Canadian Journal of Forestry Research, v. 18, p. 1270-1279.

Walker, I. R., Smol, J. P., Engstrom, D. R., Birks, J. J. B., 1991, An Assessment of Chironomidae as Wuantitative Indicators of Past Climatic Change: Canadian Journal of Fisheries and Aquatic Sciences, v. 48, p. 975-987.


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