Supervised by:

Daniel Nadeau (Regular Member (Co-researcher))

Co-supervised by:

Florent Domine (Regular Member (Co-researcher))

Research project description

Impact of shrub expansion in the Arctic on the permafrost summer thermal regime

Introduction

Global warming in the polar regions is four times faster than the global average (Rantanen et al., 2022), implying major changes that threaten local ecosystems and large-scale climate (IPCC, 2022). One of these changes is shrub expansion in the Arctic tundra (McDermott et al., 2021). In winter, various studies have shown the wide variety of physical processes caused by shrubs and influencing the permafrost thermal regime (Dominé et al., 2022). In summer, the impact of these shrubs on the ground remains largely unknown (Oehri et al., 2022), undermining our ability to estimate the thickness of the active permafrost layer (which thaws in summer). However, this is crucial to the quantity of organic compounds stored for thousands of years that can be transformed into greenhouse gases by microbial metabolism (Schaefer et al., 2014).

Objectives

In order to fill this gap, the aim of our study is to compare the surface energy balance of neighbouring patches of herbaceous and shrubby tundra, in order to identify the mechanisms controlling permafrost thaw in summer. To this end, the components of the energy balance will be quantified, including radiative, latent and sensitive fluxes, as well as soil heat storage and fluxes. A better understanding of these processes will contribute to the improvement of climate models. A modelling component is also part of the study, where the CLASSIC model (Canadian Land Surface Scheme Including Biogeochemical Cycles) will be used for comparison with observations at the study site.

Study Sites

The study site is located in the Qarlikturvik valley on Bylot Island (73°N) in the Canadian Arctic Archipelago, where a fraction of the surface is covered by shrubs. We selected two relevant study sites: Tundra and Salix. The first is a herbaceous tundra environment with no shrubs, and the second features patches of Salix richardsonii shrubs around 40 cm tall. The study site is located a few kilometers from the Centre d'Études Nordiques research station on Bylot Island.

Material and methods

Preliminary instrumentation was deployed in the Qarlikturvik valley in summer 2023 to measure the components of the surface energy balance. At this site of grassy and shrubby tundra, preliminary data suggest a shallower active layer beneath the shrubs. However, issues of quantifying sensible and latent heat fluxes were encountered at the shrub site, limiting the scope of the work carried out. In addition, the high spatial variability of soil thermal properties prevents the generalization of this observation. Thus, sites with different soils will be studied in order to quantify the impact of soil properties on the energy balance. Consequently, a second site in a different geomorphological unit will be instrumented in summer 2024, enabling a more precise comparison of conditions in each environment and a better quantification of turbulent fluxes in the shrub environment.

References

Domine, F., […], (2022). Permafrost cooled in winter by thermal bridging through snow-covered shrub branches. Nature Geoscience, 15(7), 554–560. IPCC, 2022: Climate Change 2022: Impacts, Adaptation and Vulnerability. Cambridge University Press. Cambridge University Press, Cambridge, UK and New York, NY, USA, 3056 pp. McDermott, M. T., […], (2021). Willow drives changes in arthropod communities of northwestern Alaska: Ecological implications of shrub expansion. Ecosphere, 12(5). Oehri, J., […], (2022). Vegetation type is an important predictor of the Arctic Summer Land Surface Energy Budget. Nature Communications, 13(1). Rantanen, M., […], (2022b). The Arctic has warmed nearly four times faster than the globe since 1979. Communications Earth & amp; Environment, 3(1). Schaefer, K., […], (2014). The impact of the Permafrost Carbon Feedback on Global Climate. Environmental Research Letters, 9(8), 085003.

Research Site Coordinates