Near‐surface ground ice in sediments of the Mackenzie Delta, Northwest Territories, Canada

The ice content of near‐surface permafrost was determined at more than 70 sites in the Mackenzie Delta, Northwest Territories. Willow and alder communities growing on aggrading surfaces with well‐drained sandy silts and ‘warm’ ground temperatures were underlain by permafrost with low ice content. Spruce forests above the level of annual flooding, lakeside alder communities in the central and southern delta, and sedge wetlands in the northern delta with moist silty loam soils, low sedimentation rates and ‘cold’ ground temperatures were underlain by medium to high ice‐content permafrost. Beneath spruce forests, a layer of near‐surface ice accumulation 1 to 2 m thick was underlain by alluvium bonded by pore ice. These profiles indicate that contemporary conditions favour near‐surface ice accumulation. The preservation of ice‐poor permafrost at depth demonstrates the limited vertical accumulation of near‐surface segregated ice. In contrast, at lakeshore alder or sedge wetlands, segregated ice extended at least 2 m below the base of the active layer, indicating that permafrost aggraded in a saturated environment. Development of ground ice in the Mackenzie Delta may elevate alluvial surfaces, modify the flooding regime, and thereby influence soil conditions and ecological succession. Copyright © 2005 John Wiley & Sons, Ltd.