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Paleoecology of the Scottie Creek District,
Beaver Creek, Yukon

by Gordon D. MacIntosh, Department of Geology and Geophysics

During the realignment of the Alaska Highway, several archaeological sites were discovered that date as early as 10,130 years BP. The partially articulated remains of a horse from these sediments were dated to the full glacial period at 20,660 - 100 BP.

The discovery of these early archaeological and paleontological sites raised several paleoecological questions about the region. The initial opportunity to study this area inspired the multidisciplinary investigation that was the basis of my Master's thesis. Previously, little was known of the paleoecology of the region other than the work done by Rampton at Antifreeze Pond in 1971.

The study area lies in what was once the extreme southeastern portion of Beringia. During the Late Wisconsin (35,000 to 10,000 years BP), this area was in close contact with the ice front of the Macauley-Kluane glaciation. The close proximity of this large body of ice should have had a direct effect on the local climate, making it colder and possibly moister. The purpose of this research was to discover the effect of the glacial and postglacial environment on the local climate and vegetation as the ice receded, as well as its implications for early man.

The paleoenvironmental reconstruction is primarily based on the pollen and macrofossil analysis of a core taken from Daylight Coming Out Lake, which is located only 10 km from the position of the Late Wisconsin Macauley-Kluane ice front. The lake was selected primarily for its location away from low-lying valleys, which would have been disturbed by outwash from the Macauley-Kluane Glaciers. The core taken from Daylight Coming Out Lake covers almost 12,000 years from the Late Wisconsin to present.

To supplement the pollen record of Daylight Coming Out Lake, especially a Late Holocene segment of peaty sediments with poor pollen recovery, a second pollen core was taken from Island Lake. This lake was formed by thermokarst processes 5,000 years BP.

The pollen and macrofossil records from Daylight Coming Out Lake and Island Lake, when combined with the pollen record at Antifreeze Pond, provide us with a clearer view of changes in both the regional and local vegetation and climate from the Late Wisconsin to the present.

The vegetational and climatic history of the Scottie Creek district can be differentiated into four major climatic periods based on pollen and macrofossil evidence. These intervals are similar to those found in other sites in central Alaska and Yukon.

The oldest period is the herb interval, which dates from the late glacial to 11,000 years BP. In this interval, the vegetation is a herbaceous tundra with grasses, sedges, and sage that is interpreted to represent very cold, dry conditions. The pollen evidence also tends to support two separate habitats: a dry upland habitat dominated by grasses and Artemisia, and a wetter lowland habitat dominated by sedge, grasses, and willow. Temperatures increased slowly from a July mean of 3C to 5C during the glacial advance around 18,000 years BP to around 6C at the start of deglaciation around 13,500 years BP.

The next period, from 11,000 to 8,000 years BP, is represented by the birch zone. This interval shows a large increase in the number of dwarf and shrub birch, indicating a change to warmer and possibly moister conditions. Mean July temperatures at the start of this zone were probably around 9C, and they may have continued to increase as summer insolation reached its maximum. Wind velocity and loess deposition also reached their peak levels during this period. The birch rise was approximately 1,000 years later than other regions in the interior due to the cooling effects of the large piedmont glacier in the Wesley Basin. It is during this period of climatic amelioration and retreat of the glaciers that the first people arrived in the Scottie Creek district.

The start of the spruce interval, around 8,000 years BP, is marked by the arrival of Picea into the area from refugia south of the continental ice sheet under climatic conditions that were slightly warmer than present. The late arrival of spruce into this area is due to its long, circuitous migration route through northern Yukon and central Alaska. Populus also appears during this interval, which is also considerably later than most sites in central Alaska.

The alder interval notes the arrival of Alnus around 5,500 years BP in slightly cooler and wetter conditions than those of the spruce interval. Treeline fluctuations suggest that mean July temperatures during this period range from 12C to 13.5C. The wetter conditions during this period may be responsible for the extensive paludification of the landscape and formation of many of the thermokarst lakes in the area. During the last 5,000 years, the boreal forest has changed little and the deposition of the White River Ash at 1,850 years BP had no effect on the terrestrial vegetation of the region.

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