Holocene Evolution of Lakes in the Bluefish Basin, Northern Yukon, Canada
Keywords:thaw lakes, lake levels, Holocene, lake sediments, plant macrofossils, radiocarbon dating, Bluefish Basin, northern Yukon
AbstractThis study documents the Holocene evolution of lakes located in the Bluefish Basin, northern Yukon, on the basis of lake lithology, distribution of plant macrofossils, and radiocarbon dating of the basal organic material in sediment cores obtained from former lake basins. Basal organic matter from former lake basins is radiocarbon-dated to the late Holocene (< 3770 yr. BP), whereas the 14C ages from the polygonal peat plateaus (~2 m thick) that surround most of the former lake basins cluster in the early Holocene (between 11 435 and 8200 yr. BP). Plant macrofossil distribution in four out of five cores obtained in former lake basins indicates a transition from emergent aquatic vegetation to wetland and terrestrial-type vegetation, suggesting a gradual decline in water levels. The fifth core analyzed for macrofossils showed evidence of sudden lake drainage. The absence of 14C ages from the middle Holocene (7000 to 4000 yr. BP) suggests that the lakes had a greater spatial coverage and water levels during that period, a conclusion supported by the greater surface area occupied by the former lake basins relative to modern lakes and by the fact that the middle Holocene was a wet period in northern Yukon. The gradual decrease in water levels during the late Holocene could be attributed to partial drainage of lakes, increased evaporation under a drier climate, or a combination of both. Acomparison with other regional climate records indicates a change toward drier climate conditions around 4500 yr. BP as a result of a reconfiguration in large-scale atmospheric circulation patterns, suggesting a climate-driven change in hydrological conditions.