Significant underestimation of peatland permafrost along the Labrador Sea coastline in northern Canada

Abstract

Abstract. Northern peatlands cover approximately four million km2, and about half of these peatlands are estimated to contain permafrost and periglacial landforms, like palsas and peat plateaus. In northeastern Canada, peatland permafrost is predicted to be concentrated in the western interior of Labrador but is assumed to be largely absent along the Labrador Sea coastline. However, the paucity of observations of peatland permafrost in the interior, coupled with traditional and ongoing use of perennially frozen peatlands along the coast by Labrador Inuit and Innu, suggests a need for re-evaluation of the reliability of existing peatland permafrost distribution estimates for the region. In this study, we develop a multi-stage consensus-based point inventory of peatland permafrost complexes in coastal Labrador and adjacent parts of Quebec using high-resolution satellite imagery, and we validate it with extensive field visits and low-altitude aerial photography and videography. A subset of 2092 wetland complexes that potentially contained peatland permafrost were inventoried, of which 1119 were classified as likely containing peatland permafrost. Likely peatland permafrost complexes were mostly found in lowlands within 22 km of the coastline, where mean annual air temperatures often exceed +1 ∘C. A clear gradient in peatland permafrost distribution exists from the outer coasts, where peatland permafrost is more abundant, to inland peatlands, where permafrost is generally absent. This coastal gradient may be attributed to a combination of climatic and geomorphological influences which lead to lower insolation, thinner snowpacks, and poorly drained, frost-susceptible materials along the coast. The results of this study suggest that existing estimates of permafrost distribution for southeastern Labrador require adjustments to better reflect the abundance of peatland permafrost complexes to the south of the regional sporadic discontinuous permafrost limit. This study constitutes the first dedicated peatland permafrost inventory for Labrador and provides an important baseline for future mapping, modelling, and climate change adaptation strategy development in the region.

Multi-decadal degradation and fragmentation of palsas and peat plateaus in coastal Labrador, northeastern Canada

“…We also expect palsas to be less resilient than peat plateaus because palsas are described as taller (Zoltai 1972, Thie 1974, International Permafrost Association Terminology Working Group 2005, leading to greater surrounding snow accumulation (Olvmo et al 2020), and cover less area, making them more susceptible to edge collapse (Thie 1974). This study will contribute to local and regional adaptation strategies related to permafrost thaw and ecosystem change and complements ongoing research on the distribution, thermal properties, and contemporary characteristics of peatland permafrost in coastal Labrador (Beer et al in review, Way et al 2018, Wang et al 2023.…”

“…The distribution of permafrost in Labrador follows a latitudinal gradient, with continuous permafrost predicted to persist at high latitudes and high elevations in the Torngat Mountains, and discontinuous or isolated patches of permafrost further south (Heginbottom et al 1995). High densities of permafrost peatlands were recently identified in lowland locations along the Labrador Sea coastline (figure 1) (Wang et al 2023), and an analysis of 20 permafrost peatlands describes palsas and peat plateaus in Labrador as being small, fragmented, and irregularly shaped (Beer et al in review). Unlike the peatland permafrost found in some parts of northern Québec (Cyr and Payette 2010, Jean and Payette 2014a, 2014b, peatland permafrost in coastal Labrador is also non-forested and is instead characterized by lichens (e.g.…”

“…Seven permafrost peatlands, located along a north to south transect from near the communities of Hopedale (55.7 • N) to Red Bay (51.7 • N), were selected for this study (figure 1 and table 1). Study sites were selected from an inventory of likely permafrost peatlands in coastal Labrador (Wang et al 2023) and consist of palsa sites (n = 2), peat plateau sites (n = 3), and mixed palsa and peat plateau sites (n = 2). Sites broadly represent the spatial extent of peatland permafrost in their respective regions (figure 1).…”

“…While field visits to BB1, BB2, MT-P, and SC were not possible due to their more remote locations, the authors did visit similar sites during surveys of other permafrost peatlands for prior work (e.g. Wang et al 2023).…”

“…Peatland permafrost is found in both continental and coastal areas of northern Canada but was previously thought to be uncommon in the northeastern region of Labrador. Notwithstanding, a recent study identified large areas of peatland permafrost along the Labrador Sea coastline (Wang et al 2023), including in regions previously mapped as having little to no permafrost (e.g. Fewster et al 2020, Hugelius et al 2020, Olefeldt et al 2021.…”