Holocene Evolution of Lakes in the Bluefish Basin, Northern Yukon, Canada

Abstract

This 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 14 C 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 14 C 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. a comparison 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. key words: thaw lakes, lake levels, Holocene, lake sediments, plant macrofossils, radiocarbon dating, Bluefish Basin, northern Yukon rÉsuMÉ. La présente étude retrace l'évolution des lacs de l'Holocène situés dans le bassin Bluefish, dans le nord du Yukon. Elle s'appuie sur la lithologie des lacs, la répartition des macrofossiles de plantes et la datation par le radiocarbone des matières organiques de base se trouvant dans les carottes de sédiments provenant d'anciens bassins lacustres. La datation par le radiocarbone de la matière organique de base d'anciens bassins lacustres fait remonter cette matière à l'Holocène supérieur (< 3 770 ans avant le présent), tandis que la datation par le radiocarbone des plateaux de tourbe polygonaux (~2 m d'épaisseur) qui entourent la plus grande partie du groupement d'anciens bassins lacustres remonte à l'Holocène inférieur (entre 11 435 et 8 200 ans avant le présent). La répartition des macrofossiles de plantes dans quatre des cinq carottes provenant des anciens bassins lacustres laisse voir une transition allant d'une végétation aquatique émergente à une végétation de zone humide et de type terrestre, ce qui attesterait du déclin graduel des niveaux d'eau. dans la cinquième carotte, les macrofossiles présentaient des preuves d'un assèchement lacustre soudain. L'absence de datation par le radiocarbone de l'Holocène moyen (de 7 000 à 4 000 a...

Contemporary (1951–2001) Evolution of Lakes in the Old Crow Basin, Northern Yukon, Canada: Remote Sensing, Numerical Modeling, and Stable Isotope Analysis

“…these strong relations are not surprising, considering that the precipitation record comprises half of the P-E index, but they do suggest that atmospheric and pressure systems can affect the spatiotemporal variation of lakes in the region. Such a relation was also observed in the late Pleistocene-Holocene variations of lake water levels: the melting of the Laurentide ice sheet and subsequent rise in sea level reconfigured the regional atmospheric circulation patterns (Lauriol et al, 2009). A comparison of the P-E index and lake surface area variations with atmospheric oscillations affecting the northern Yukon can help to determine whether the observed spatio-temporal variations are affected by these natural oscillations.…”

“…Field observations of the presence of drained lake basins and abandoned shorelines around some lakes in the Old Crow Basin suggest that lake drainage or a reduction in lake surface area is ongoing in the region. In fact, a paleoecological study by Lauriol et al (2009) shows that water levels in lakes of the nearby Bluefish Basin began to decrease gradually around 3700 yr. BP, which coincided with the arrival of a cold and dry climate. (One lake, however, showed evidence of sudden drainage.…”

Vegetation-Permafrost Relations within the Forest-Tundra Ecotone near Old Crow, Northern Yukon, Canada

“…Glacial Lake Old Crow drained catastrophically by incision of a spillway near the Yukon‐Alaska border, connecting the Porcupine River with the Yukon River basin (Lauriol et al , ). Permafrost developed in the sediments freshly exposed by lake drainage.…”

“…Permafrost developed in the sediments freshly exposed by lake drainage. These deposits underlie Old Crow Flats, a 5600 km 2 peatland with thousands of shallow lakes that cover approximately 35 per cent of its surface (Figure ) (Lauriol et al , ; Roy‐Léveillée and Burn, ). Old Crow Flats is recognised through the Ramsar convention as a wetland of international significance (The Secretariat of the Convention on Wetlands, 2014).…”

A modified landform development model for the topography of drained thermokarst lake basins in fine‐grained sediments

“…Glacial Lake Old Crow drained catastrophically by incision of a spillway near the Yukon–Alaska border (Lauriol et al . ). Surface conditions in the lake basin sediments have evolved from marshes through fens, to sphagnum bogs (Ovenden, ).…”