Wind-driven snow conditions control the occurrence of contemporary marginal mountain permafrost in the Chic-Choc Mountains, south-eastern Canada: a case study from Mont Jacques-Cartier

Abstract

Abstract. We present data on the distribution and thermophysical properties of snow collected sporadically over 4 decades along with recent data of ground surface temperature from Mont Jacques-Cartier (1268 m a.s.l.), the highest summit in the Appalachians of south-eastern Canada. We demonstrate that the occurrence of contemporary permafrost is necessarily associated with a very thin and wind-packed winter snow cover which brings local azonal topo-climatic conditions on the dome-shaped summit. The aims of this study were (i) to understand the snow distribution pattern and snow thermophysical properties on the Mont JacquesCartier summit and (ii) to investigate the impact of snow on the spatial distribution of the ground surface temperature (GST) using temperature sensors deployed over the summit. Results showed that above the local treeline, the summit is characterized by a snow cover typically less than 30 cm thick which is explained by the strong westerly winds interacting with the local surface roughness created by the physiography and surficial geomorphology of the site. The snowpack structure is fairly similar to that observed on windy Arctic tundra with a top dense wind slab (300 to 450 kg m −3 ) of high thermal conductivity, which facilitates heat transfer between the ground surface and the atmosphere. The mean annual ground surface temperature (MAGST) below this thin and wind-packed snow cover was about −1 • C in 2013 and 2014, for the higher, exposed, blockfield-covered sector of the summit characterized by a sporadic herbaceous cover. In contrast, for the gentle slopes covered with stunted spruce (krummholz), and for the steep leeward slope to the southeast of the summit, the MAGST was around 3 • C in 2013 and 2014. The study concludes that the permafrost on Mont Jacques-Cartier, most widely in the Chic-Choc Mountains and by extension in the southern highest summits of the Appalachians, is therefore likely limited to the barren windexposed surface of the summit where the low air temperature, the thin snowpack and the wind action bring local cold surface conditions favourable to permafrost development.

Winters are changing: snow effects on Arctic and alpine tundra ecosystems

“…Both and Grünberg et al (2020) found that snow depth and, most likely, snow structural differences, lead to pronounced differences in mean soil temperature, soil temperature variability and timing of snowmelt, across different vegetation types. Multiple field based studies have found that the thermal impacts of variations in snow thickness over natural gradients can explain more of the spatial variability in ground temperatures than key climate variables such as mean annual air temperature (Granberg 1988;Davesne et al 2017;Pelletier et al 2019;Davis et al 2020;Garibaldi et al 2021;Kropp et al 2021). Some modelling studies have shown that deeper snow thicknesses found particularly in tall vegetation may altogether prevent the formation of permafrost in regions that would otherwise be climatically suitable (Smith and Riseborough 2002;Tutton and Way 2021;Way and Lapalme 2021).…”

Effects of meteorology and soil moisture on the spatio-temporal evolution of the depth hoar layer in the polar desert snowpack

“…The onset of a stable snowpack is known to be a critical factor for the soil surface thermal regime (Ling and Zhang, 2003), and hence for the temperature gradient into the snowpack. An early snow onset, as it occurred at WHI and RB in the fall of 2018, prevents rapid cooling of the soil because it is partially disconnected from atmospheric conditions (Ishikawa, 2003; Davesne and others, 2017). However, data from WHI show that the soil surface temperature cooled quite rapidly despite the presence of the snowpack (Figs 9a, c and Figs S3a, b).…”

A Distributed Temperature Profiling System for Vertically and Laterally Dense Acquisition of Soil and Snow Temperature

“…Spatially and temporally dense monitoring of temperature -acquired at hundreds of locations distributed across several square kilometers-have primarily focused on air (Alcoforado and Andrade, 2006;Holden et al, 2016;Hubbart et al, 2005;Whiteman et al, 2000) and ground surface temperature (Davesne et al, 2017;Gisnås et al, 2014;Gubler et al, 2011;Lewkowicz et al, 2012). For example, dense air temperature measurements from 1600 self-recording temperature sensors, across a domain extending from the Boise Basin, Idaho, to southern British Columbia, have been used to evaluate downscaling of air temperature from long-term weather stationsusing covariates that have established physical links to surface air temperature (Holden et al, 2016).…”