Ground ice and soluble cations in near-surface permafrost, Inuvik, Northwest Territories, Canada

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. Copyrigh

Physical and chemical characteristics of the active layer and permafrost, Herschel Island, western Arctic Coast, Canada

Physical and geochemical characteristics of near-surface permafrost and the impact of permafrost degradation on soil and water chemistry were investigated at five sites on Herschel Island, Yukon Territory. The distribution of soluble cations, moisture and organic matter content in turbic cryosols from undisturbed terrain indicated a thaw unconformity 50 to 80 cm below the base of the present active layer. Palaeoactive-layer depth, estimated at between 90 and 100 cm, is less than at comparable sites in the Mackenzie Delta area. The difference may be due to the comparative proximity of Herschel Island to the Beaufort Sea coastline in the early Holocene. Soluble cations in permafrost and the active layer of static cryosols at recently disturbed sites were two orders of magnitude higher than in the active layer at undisturbed sites. Na+ was the dominant cation in undisturbed permafrost, recently disturbed ground, and surface runoff derived from disturbed areas. Although degradation of permafrost following terrain disturbance has resulted in surface salinization, a condition detrimental to vegetation growth, leaching of soluble salts from disturbed areas has occurred over time. These processes have produced a range of soil conditions that contribute to the floristic diversity of Herschel Island. Copyrigh

Distribution and activity of ice wedges across the forest-tundra transition, western arctic Canada

Remote sensing, regional ground temperature and ground ice observations, and numerical simulation were used to investigate the size, distribution, and activity of ice wedges in fine-grained mineral and organic soils across the forest-tundra transition in uplands east of theMackenzie Delta. In the northernmost dwarf-shrub tundra, ice wedge polygons cover up to 40% of the ground surface, with the wedges commonly exceeding 3m in width. The largest ice wedges are in peatlands where thermal contraction cracking occurs more frequently than in nearby hummocky terrain with fine-grained soils. There are fewer ice wedges, rarely exceeding 2m in width, in uplands to the south and none have been found in mineral soils of the tall-shrub tundra, although active icewedges are found there throughout peatlands. In the spruce forest zone, small, relict ice wedges are restricted to peatlands. At tundra sites, winter temperatures at the top of permafrost are lower in organic than mineral soils because of the shallow permafrost table, occurrence of phase change at 0°C, and the relatively high thermal conductivity of icy peat. Due to these factors and the high coefficient of thermal contraction of frozen saturated peat, ice wedge cracking and growth is more common in peatlands than in mineral soil. However, the high latent heat content of saturated organic active layer soils may inhibit freezeback, particularly where thick snow accumulates,making the permafrost and the ice wedges in spruce forest polygonal peatlands susceptible to degradation following alteration of drainage or climate warming