Spatial and thermal characteristics of mountain permafrost, northwest canada

Abstract

Lewkowicz, A.G., Bonnaventure, P.P., Smith, S.L. and Kuntz, Z., 2012. Spatial and thermal characteristics of mountain permafrost, northwest Canada. Geografiska Annaler: Series A, Physical Geography, ••, ••–••. doi:10.1111/j.1468‐0459.2012.00462.x ABSTRACT An extensive network of monitoring stations was used to develop a mean annual air temperature map for the complex mountainous terrain in the southern Yukon and northern British Columbia, Canada (latitude 59° to 65° N). Air temperature lapse rates measured at screen height from valley bottoms up to treeline are normal in the maritime extreme southwest, normal but weak in much of the region, and inverted in the highly continental northernmost sites. Relationships between air and ground surface temperatures, expressed as freezing and thawing n‐factors, vary significantly with vegetation type and hence elevational band, with the lowest values for the forested zone and the highest for non‐maritime alpine tundra. Equilibrium modelling carried out for one site in the southern part of the region and one in the northern part illustrates the impacts of the differing n‐factors on trends in mean ground surface temperature with elevation. Ground thermal regimes determined at borehole locations vary greatly due to these climatic controls but are also affected by substrate. Valley‐bottom permafrost in the south is scattered, at temperatures just below 0°C, has a depth of zero annual amplitude of 2–3 m (due to latent heat effects) and may be only a few metres in thickness. Permafrost on bedrock summits is cold, has active layers >5 m thick, is >50 m thick and may be locally continuous. Given the range of air temperatures and n‐factors, permafrost is possible throughout the Yukon but higher temperatures southward and stronger lapse rates mean that a lower elevational limit exists in northern British Columbia.

A statistical approach to represent small-scale variability of permafrost temperatures due to snow cover

“…The investigated field sites show a similar spatial variability in GST, as reported by previous studies (e.g., Farbrot et al, 2011;Lewkowicz et al, 2012;Gruber and Hoelzle, 2001). However, other than in most previous studies, the sampling design with a large number of GST loggers facilitated estimating the distribution of GST, so that a statistical modeling approach for the small-scale variability could be validated.…”

“…(Etzelmüller et al, 1998) and observations of cold ice (< 0 • C) at the glacier front of Midtdalsbreen -an outlet glacier of Hardangerjøkulen (1400 m a.s.l. ; Liestøl and Sollid, 1980;Andersen, 1996;Hagen, 1978;Etzelmüller et al, 1998) -indicate permafrost at lower elevations, at least at snow-free sites (Lilleøren et al, 2013). Annual mean air temperature at the field site was −2.8 • C for 2012-2013.…”

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

“…The results of inverted SLRs on an annual basis are increased permafrost probabilities in valley bottoms in areas of high continentality while in more maritime environments, SLRs are gentle but normal, making permafrost less common at low elevations. In parts of northern British Columbia, therefore, a lower permafrost elevational limit exists (Lewkowicz et al, 2012). Changes in SLR from below to above treeline have been observed at widely spaced sites over multiple years, but their cause remains unknown .…”

“…Map of the study region showing intensive modelling sites (see Bonnaventure et al, 2012b) in relation to permafrost zones (Heginbottom et al, 1995) and climatic regions (Wahl et al, 1987 mainly subarctic continental, with long, cold winters and short, warm summers, varying with elevation and mountainside orientation (Natural Resources Canada, 2010). MAAT ranges from about 5 • C in the extreme southwest to <−10 • C on the highest peaks (Lewkowicz et al, 2012). The region can be sub-divided into six climatic regions largely based on physiography (Fig.…”

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

“…Several studies have been undertaken on this topic in European mountains (Haeberli, 1973;Grüber and Hoelzle, 2001;Luetschg et al, 2008;Farbrot et al, 2011Farbrot et al, , 2013Hasler et al, 2011;Pogliotti, 2011;Gisnås et al, 2014;Ardelean et al, 2015;Magnin et al, 2016;Beniston et al, 2017), in Japan (Ishikawa, 2003;Ishikawa and Hirakawa, 2000), in the Canadian Rocky Mountains (Harris, 1981;Lewkowicz and Ednie, Lewkowicz et al, 2012;Bonnaventure et al, 2012;Hasler et al, 2015), and most recently in the Andes (Apaloo et al 2012). The snow cover acts as a buffer layer controlling heat loss at the ground interface.…”