Ecosystem changes across a gradient of permafrost degradation in subarctic Québec (Tasiapik Valley, Nunavik, Canada)

• Published in: Arctic Science
• Main Authors: Pelletier, M., Allard, M., Levesque, E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Permafrost; Shrubification; Snow cover; Subarctic; Thermokarst; Pergélisol; Subarctique; Augmentation du couvert arbustif; Couverture de neige; Canada; Nunavik; Active layer thickness; Arctic; Ice; permafrost; subarctique*; toundra; Tundra; pergélisol
• Online Access: https://depot-e.uqtr.ca/id/eprint/11076/; https://depot-e.uqtr.ca/id/eprint/11076/1/LEVESQUE_E_197_ED.pdf; https://doi.org/10.1139/as-2016-0049

Abstract Permafrost thaw, tundra shrubification, and changes in snow cover properties are documented impacts of climate warming, particularly in subarctic regions where discontinuous permafrost is disappearing. To obtain some insight into those changes, permafrost, active layer thickness, vegetation, snow cover, ground temperature, soil profiles, and carbon content were surveyed in an integrated approach in six field plots along a chronosequence of permafrost thaw on an ice-rich silty soil. Historical air photographs and dendrochronology provided the chronological context. Comparison of the plots reveals a positive feedback effect between thaw settlement, increased snow cover thickness, shrub growth, increase in soil temperature, and the process of permafrost decay. By the end of the sequence permafrost was no longer sustainable. Along the estimated 90 year duration of the chronosequence, the originally centimeter-thin pedogenic horizons under mosses and lichens increased to a thickness of nearly 65 cm under shrubs and trees. Snow cover increased from negligible to over 2 m. The thickness of soil organic layers and soil organic matter content increased manyfold, likely a result of the increased productivity in the shrub-dominated landscape. The results of this study strongly suggest that permafrost ecosystems in the subarctic are being replaced under climate warming by shrub and forest ecosystems enriched in carbon on more evolved soils. Résumé Le dégel du pergélisol, l’augmentation du couvert arbustif de la toundra (« shrubification ») et les changements de propriétés de la couverture de neige constituent des impacts déjà connus du réchauffement du climat, particulièrement dans les régions subarctiques où le pergélisol discontinu est en voie de disparition. Afin d’obtenir un aperçu de ces changements, le pergélisol, l’épaisseur de la couche active, la végétation, la couverture de neige, la température au sol, les profils de sol et le contenu en carbone ont été examinés selon une approche intégrée dans six ...