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Samuel Gagnon


Postdoctoral fellow

Department of geography, Université de Montréal

Université de Montréal
Quebec, Canada





Projet de recherche

The role of vegetation and ground ice on the thermal resistance of permafrost and the release of soil carbon due to climate change


The dynamics of the active layer (AL; the layer above permafrost that thaws in summer and freezes in winter) plays a central role in the release of carbon from Arctic soils because it dictates the portion of soil available for microbial decomposition. Vegetation cover properties are critical in modulating the surface energy balance, energy input and its diffusion into the AL. AL dynamics is also influenced by ground ice, particularly in the transition zone (TZ), an area at the interface between permafrost and the AL. This zone is very ice-rich and requires an exponential input of thermal energy to thaw. Therefore, both the vegetation cover and the TZ act as an "energy buffer" to limit temperature rise in permafrost, which can slow the progression of the AL and limit, for a time, permafrost degradation and carbon decomposition.


The goal of this project is to investigate the indirect effects of ground surface vegetation and TZ changes on AL dynamics.

More specifically to:

  1. Characterize and compare the physical properties of different permafrost layers (AL, upper permafrost TZ, deep permafrost) and assess how these layers contribute to the resilience and vulnerability of surface ecosystems by investigating energy transfers;
  2. highlight the interactions between changes at the ground surface (surface hydrology ↔ soil moisture ↔ vegetation ↔ snow) and their impacts on the permafrost thermal regime; and
  3. identify the short (1-5 years), medium (5-100 years) and long-term (>100 years) impacts of rapid and gradual disturbances of surface conditions on the surficial geomorphology, permafrost thermal regime and biogeochemical processes that occur in the AL.

Study sites

Fieldwork will be conducted at Bylot Island, Nunavut, in late May 2021 when the AL is still predominantly frozen. This study site was chosen because of the extensive environmental monitoring of experimental sites to compare a range of vegetation and hydrological changes occurring in the Arctic and expected to occur over the next few decades. The sites simulate the effect of fertilization on vegetation with annual nutrient addition (18 plots), the effect of increased air temperatures with micro-chambers (12 plots), and monitor the effect of shrubification in a site where the erect shrub population accounts for 80% of the vegetation cover (12 plots). A total of 42 plots on which the plant community has already been described will be used in order to obtain a good spatial representativeness of the different sites and the bioclimatic zone.

Material and methods

Boreholes up to ~2-3 m deep will be drilled on each plot to study soil cryostratigraphy. Permafrost cores will then be examined to measure the cryostructures present (CT-scan), ice content, thermal conductivity of each horizon (non-stationary state probe), oxygen isotopy, major ions (elemental analyzer) and organic carbon content. Laboratory experiments will also be conducted to determine the relative effects of factors affecting the formation of the TZ. These experiments will be conducted with the environmental simulator at Université de Montréal, which will allow the recreation of weather conditions down to -25°C and thermal shocks (cold or heat waves with an average rate of ±2°C h-1). A large-scale permafrost cell (2 m long, 1.5 m wide, 1.5 m high) will be used to simulate the formation of the TZ under controlled conditions.

Expected results

This work will provide a better understanding of the diversity of active layer and permafrost dynamics at the landscape scale, increase knowledge of the transition zone and determine the role of the transition zone and vegetation on carbon storage and release processes in Arctic environments.

Location of the research site

Scientific communications

Gagnon, S., Allard, M., 2020. Changes in ice‐wedge activity over 25 years of climate change near Salluit, Nunavik (northern Québec, Canada). Permafrost and Periglacial Processes, 31: 69-84. DOI: 10.1002/ppp.2030.

Gagnon, S., 2018. Pergélisol: un retrait progressif. Pages 12-13 in Brousseau, Y., Mercier, G. (Editors). Le Québec d'une carte à l'autre. Géographie, Presses de l’Université du Québec. Quebec, Canada.

Gagnon, S., Allard, M., Nicosia, A., 2018. Diurnal and seasonal variations of tundra CO2 emissions in a polygonal peatland near Salluit, Nunavik, Canada. Arctic Science, 4(1): 1-15. DOI: 10.1139/as-2016-0045.

Gagnon, S., L’Hérault, E., Lemay, M., Allard, M., 2016. New low-cost automated system of closed chambers to measure greenhouse gas emissions from the tundra. Agricultural and Forest Meteorology, 228-229: 29-41. DOI: 10.1016/j.agrformet.2016.06.012.

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