The distribution of segregated ice and soluble ions in near-surface permafrost were investigated in hummocky terrain near Inuvik, Northwest Territories. Soil water content profiles from analyses of drill cores indicate that ice-poor permafrost developed beneath a permafrost table aggrading at approximately 4 cm/a, but an ice-rich zone, 10 to 20 cm thick, was observed beneath a permafrost table that had remained stable for about a decade. Ice-rich intervals 10 to 30 cm thick were observed immediately beneath both a thaw unconformity formed in 1981 and an older, deeper unconformity. In profile, the correspondence between zones of cation and ice enrichment suggests soluble materials were incorporated into permafrost during development of near-surface aggradational ice. Moisture enrichment below an experimentally degrading permafrost table was negligible. Similar ice contents beneath the present permafrost table and the deep thaw unconformity, and the preservation of ice-poor intervals immediately above the 1981 and deep thaw unconformities indicate limited vertical ice enrichment. The estimated rates of ice accumulation in two-decade-old permafrost are on the order of mm/a, but ice accumulation above older unconformities indicates that, in aggregate, these initial rates decrease with time. The ground ice and soluble cations sequestered in near-surface permafrost comprise an important pool of water and nutrients that may be released into the active layer during periods of deeper thaw.

[1] Low-centered ice wedge polygons in the Big Lake Delta Plain of the outer Mackenzie Delta are unusual because their bounding ramparts appear to have a single ridge. Twenty-two ice wedges in the area were examined between 2006 and 2009 to describe their morphology and diagnose their growth processes. The ground above ice wedges had a subtle microtopography, with ridges of 0.12 m relief and 4.0 m total width, bisected by troughs only 0.05 m wide and 0.09 m deep. The troughs, initially obscured by vegetation growth and organic matter, were underlain by ice wedges with average widths that increased downward in the uppermost 1 m of permafrost from 0.03 to 0.95 m. "Shoulders" on the ice wedges indicated vertical growth stages. Temperatures near the top of permafrost were favorable to thermal-contraction cracking, and ice veins connected to the top of wedge ice were observed in the active layer at five sites. These observations indicate the ice wedges are syngenetic and active, although without dating control, we cannot unequivocally dismiss the possibility that the wedges are epigenetic features that were truncated by a recent thaw unconformity. Muted relief above the ice wedges, which is uncommon above epigenetic ice wedges, was largely due to aggradation of the surface. Secondary ice wedges have not developed within the polygons, suggesting that climate variability has not led to polygon network development in this area. Wedge ice occupied only about 1.5% of the uppermost 1 m of permafrost, a much smaller volumetric proportion than in epigenetic settings.

Lake-bottom temperatures have been measured for several years at two lakes with littoral terraces on north-central Richards Island, a residual pond of the Illisarvik experimental drained lake site, and a taiga lake near Inuvik. The tundra lakes possess distinct thermal regimes: in (1) the deep central pools;(2) shallows where winter ice may reach bottom; and (3) on littoral terraces, where water depth is less than 1 m. In summer, the tundra lakes are uniformly well mixed and reach similar lake-bottom temperatures at all depths. In winter, conditions vary, depending on the proximity of the ice cover to lake bottom. The annual mean lake-bottom temperatures have been about 3 C in the deep central pools, 0 C in the shallow pools, and À2 C on the terraces of the tundra lakes. For the taiga lake, where late-winter ice cover reaches only about half the thickness of the two tundra lakes, annual lake-bottom temperatures follow the same pattern as in the central pools of the tundra lakes, but the mean temperature is over 5 C. If the thermal regime of the taiga lake is an analogue for tundra conditions following climate warming, then the width of lakes with through taliks on Richards Island may decline by between 20 and 100 m. At equilibrium, about 45% of the lakes and 20% of the surface area of Richards Island may then be underlain by taliks that penetrate permafrost.

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Permafrost conditions were examined near the Dempster Highway embankment on Peel Plateau, Northwest Territories. Ground temperatures were recorded in 2013-2015 at five sites at the embankment toe and at two sites in undisturbed (control) tundra. Annual mean ground temperatures at approximately 5 m depth ranged from −2.2 to 0.0°C at the embankment toe and were −1.8 and −2.6°C at control sites. Permafrost is degrading beside the road at four of five sites. Thaw depths are greater at the embankment toe, where deep snow accumulates, than in undisturbed tundra. A numerical model was used to examine the influence of varying snow cover properties on the ground thermal regime. Simulations indicated that delaying the onset of deep (1 m) snow accumulation and (or) prolonging the duration of the same total accumulation accelerates removal of latent heat from the active layer, increases sensible ground cooling, and results in reduced thaw depth. Furthermore, reducing snow depth and increasing snow density may rapidly raise the permafrost table, lower ground temperatures at the embankment toe, and cool permafrost at depth over several years. In consequence, mechanical snow removal and (or) compaction should be investigated as an active management strategy for mitigating permafrost degradation in ice-rich settings.Arctic Science Downloaded from www.nrcresearchpress.com by 44.224.250.200 on 07/04/20For personal use only. limite du pergélisol, baisser les températures du sol au pied du remblai et refroidir le pergélisol profond sur une période de plusieurs années. Par conséquent, on devrait considérer le déneigement mécanique et (ou) le compactage de neige comme stratégie active de gestion afin d'atténuer la dégradation du pergélisol en milieux riches en glace.Mots-clés : pergélisol, infrastructure, autoroutes, régime thermique, couverture de neige.