Évolution couplée de la neige, du pergélisol et de la végétation arctique et subarctique

• Main Author: Barrère, Mathieu
• Other Authors: Dominé, Florent, Morin, Samuel
• Format: Thesis
• Language: French
• Published: Université Laval 2018
• Subjects: geo; envir; Arctic; Bylot Island; Umiujaq; Arctique*; Global warming; permafrost; Subarctic; subarctique*; Tundra; pergélisol
• Online Access: https://hdl.handle.net/20.500.11794/30263

Permafrost is a major component of the Earth climatic system. Global warming provokes the degradation of permafrost which favors biogeochemical activity in Arctic soils. The decomposition of organic matter increases and results in the release of high amounts of greenhouse gases (CO2 and CH4) to the atmosphere. By amplifying the greenhouse effect induced by human activities, this phenomenon may constitute one of the strongest positive feedbacks on global warming. Predicting these effects requires to study the evolution of the permafrost thermal regime and the factors governing it. The snowpack, because of its insulating effect, modulates the heat fluxes between permafrost and atmosphere most of the year. The snow insulating capacity depends on snow height and thermal conductivity. These two variables are highly dependent on climatic conditions and on the presence of vegetation. Here we monitor the snow and soil physical properties at a high Arctic site typical of herbaceous tundra (Bylot Island, 73°N), and at a low Arctic site situated at the limit between shrub and forest tundra (Umiujaq, 56°N). We use data from automatic measurement stations and manual measurements. A special attention is given to the snow thermal conductivity because very few data are available for Arctic regions. Results are interpreted in relation to vegetation type and atmospheric conditions. The numerical coupled model ISBA-Crocus is then used to simulate snow and soil properties at our sites. Results are compared to field data in order to evaluate the model capacity to accurately simulate the permafrost thermal regime. We managed to describe atmosphere-snow-vegetation interactions that shape the structure of Arctic snowpacks. Wind and the snow redistribution it induces are fundamental parameters governing snow height and thermal conductivity. A high vegetation cover (i.e. shrubs and forest) traps blowing snow and shields it from wind compaction. Vegetation growth thus favors the formation of an insulating snowpack which slows down or even ...