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Great Slave Lowland: The Legacy of Glacial Lake McConnell

2016; Springer Nature (Netherlands); Linguagem: Inglês

10.1007/978-3-319-44595-3_5

2213-2104

S A Wolfe, P D Morse, Steve V. Kokelj, Adrian J. Gaanderse,

Geology and Paleoclimatology Research

The Great Slave Lowland of the Taiga Shield is an 11,000 km2 low-elevation granitic bedrock plain along the north shore of Great Slave Lake, Northwest Territories. It is characterized by a mosaic of coniferous and deciduous forest cover, wetlands, sparsely vegetated bedrock outcrops, and peatlands. The region was glaciated until about 13,000 years ago and then inundated by Glacial Lake McConnell and by ancestral Great Slave Lake, which gradually declined towards the present lake elevation. Consequently, fine-grained glacilacustrine and nearshore lacustrine sediments are broadly distributed across the region. Permafrost is widespread within forest-covered sediments and peatlands, but is not sustained beneath bedrock outcrops, leading to an extensive, but discontinuous, permafrost distribution. Lithalsas, which are permafrost mounds up to 8 m in height and several hundred metres in length, are also abundant. These form by ice segregation within mineral soil, as permafrost aggrades into the fine-grained sediments following lake level recession. Lithalsas are most common within the first few tens of metres above the present level of Great Slave Lake, indicating that many are late Holocene in age and some <1000 years. These elevated surfaces favour the establishment of deciduous forests with thin organic ground cover and with mean annual ground temperatures typically between −0.5 and −1.5 °C. With annual mean air temperatures consistently warming since the 1940s, this terrain is vulnerable to thawing and subsidence, with impacts on the ecology, hydrology, and population of the region.