Dendritically-Drained Peat Plateaus: A Distinctive Thaw-Sensitive Organic-Rich Permafrost Landsystem in Northwestern Canada

Alexandre Chiasson, Catherine La Farge-England, Jurjen van der Sluijs, Ashley C.A. Rudy, Steven V. Kokelj, Duane G. Froese

Peatlands in northwestern Canada comprise one of the most thaw-sensitive and carbon-rich permafrost landscapes of North America, and undergo rapid thaw due to surface disturbance and climate change. Dendritically-drained peat plateaus (DPPs) are a distinctive permafrost landform assemblage characterized by branching networks of channelized fens and bogs dissecting raised peat plateaus with relatively thin, carbon-rich permafrost underlain by ice-rich till. Using remote sensing, field observations, and geophysical methods, we describe the morphology, permafrost conditions, and developmental history of DPPs and mapped their distribution across the Northwest Territories. These landform assemblages cover ~22,500 km² of the Taiga Plains, forming in the early Holocene (~10,000 cal yr BP) on gently sloping till plains above glacial Lake Mackenzie. In the central Mackenzie Valley, DPPs consist of ~2 m of peat over ice-rich diamict with abundant ground ice. Electrical resistivity tomography surveys indicate that permafrost is typically less than 20 m thick beneath peat plateaus. Taliks underlie channelized fens, promoting advection and lateral heat transfer, which account for thin permafrost and rapid lateral erosion along plateau margins. Variation in assemblages along a latitudinal climate gradient gives rise to contrasting morphologies: southern regions feature larger basins, collapse scars, and wide channelized fens, while northern landscapes have higher densities of narrower fens, smaller collapse scars, and more extensive permafrost plateaus. The long-term interaction between ground ice, geological history, ecology and regional climate drives the development of diverse surface features, allowing us to conceptually define these landform assemblages as a regional permafrost landsystem.