Changes in ice‐wedge activity over 25 years of climate change near Salluit, Nunavik (northern Québec, Canada)

Abstract

To assess the direct impact of climate change on ice‐wedge (IW) degradation, 16 sites in the Narsajuaq river valley (Nunavik, Canada) that were extensively studied between 1989 and 1991 were revisited in 2016, 2017 and 2018. In total, 109 pits were dug to record soil characteristics and IW shapes and depths. Changes in surface conditions were also noted using side‐by‐side comparisons of recent (2017) and older (1989–1991) land and aerial photographs. During the past 25 years, the active layer reached depths that were 1.2–3.4 times deeper than in 1991, which led to the widespread degradation of IWs in the valley. Whereas 94% of the IWs unearthed in 1991 showed multiple recent growth structures, only 13% of the 55 IWs unearthed in 2017 still had some upgrowth stages left. IW tops are now consistently deeper than the main stages of the IWs measured in 1991. In August 2017, however, about half of the IWs had ice veins connecting them to the base of the active layer, an indication that the recent cooling spell (2010 to present) in the region was enough to reactivate frost cracking and IW growth. This paper highlights how sensitive the Arctic soil system can be to short‐term climate variations.

Modeled (1990–2100) variations in active‐layer thickness and ice‐wedge activity near Salluit, Nunavik (Canada)

“…Vegetation in the valley is mostly composed of deciduous shrubs (14.6%), graminoids (32.1%), or a mix of both (33.3%). The remaining 5.9% is a mix of mosses, Sphagnum sp., evergreen shrubs, forbs, and lichens 26 …”

“…Most notably, between 1989 and 1991, Kasper and Allard 10,14 investigated ice‐wedge activity and morphology using field observations in the Narsajuaq river valley near Salluit, Nunavik, Canada. In 2016, 2017 and 2018, Gagnon and Allard 26 revisited the same 16 study sites to investigate the impact of climate change on winter soil cracking frequency and morphology of ice‐wedge tops. They found that based on the depth of ice‐wedge tops, the active layer had sometime in the period reached depths that were 1.2–3.4 times greater than in 1991, which led to the widespread degradation of ice‐wedge tops in the valley.…”

Geomorphological controls over carbon distribution in permafrost soils: the case of the Narsajuaq river valley, Nunavik (Canada)

“…Annual precipitation totals 524 mm, about half consisting of snowfall (Charron 2015). Most of the valley floor is covered by graminoids (sedges, grasses, and rushes) (32.1%), low deciduous shrubs (14.6%), and a mix of both (33.3%) (Gagnon and Allard 2020a). The rest of the vegetation cover is a mix of mosses, evergreen shrubs, forb species, and lichens.…”

“…During the summers of 2016 and 2017, 16 sites with polygonal networks were investigated ( Fig. 2) (Gagnon and Allard 2020a). The sites are located on different terrace levels in the valley and have varying soil compositions, vegetation covers, and surface drainage conditions (see Gagnon and Allard 2020a).…”

“…In our study area, this means that upon thawing, the lower parts of polygonal peatlands and high fluvial terraces will not be able to interact with the atmosphere because of the high water table, unless remobilization processes expose Pagination not final (cite DOI) / Pagination provisoire (citer le DOI) them to surface conditions. Thermo-erosion gullying has been observed in the valley (Gagnon and Allard 2020a), causing tunnelling and ground collapse in the terraces and exposing deeper soil layers. In contrast, active-layer deepening and permafrost thaw in sites with a thin top organic layer on sand was observed to improve drainage due to the increased hydraulic conductivity of the deeper mineral layers.…”