Ground ice, organic carbon and soluble cations in tundra permafrost and active-layer soils near a Laurentide ice divide in the Slave Geological Province, N.W.T., Canada

Abstract

<jats:p>Abstract. The central Slave Geological Province is situated near a divide of the Laurentide Ice Sheet and it differs from the western Canadian Arctic, where thaw-induced landscape changes in Laurentide ice-marginal environments are already abundant. Although much of the terrain in the central Slave Geological Province is mapped as predominantly bedrock and ice-poor, glacial deposits of varying thickness occupy significant portions of the landscape, creating a mosaic of conditions. Some evidence of ice-rich ground, a key determinant of thaw-induced landscape change, exists. Carbon and soluble cation content in permafrost are largely unknown in the area. Twenty-four boreholes with depths up to ten metres were drilled in tundra north of Lac de Gras to address these regional gaps in knowledge and to better inform projections and generalizations at coarser scale. Excess-ice contents of 20–60 %, likely remnant Laurentide basal ice, are common in till and thaw subsidence of metres to more than ten metres is possible. Beneath organic terrain and in fluvially-reworked sediment, aggradational ice is found. The abundant ground-ice poses long-term challenges for engineering, and it makes the area susceptible to thaw-induced landscape change and mobilization of sediment, solutes and carbon several metres deep. The characteristics of landscape changes, however, are expected to differ from ice-marginal landscapes of western Arctic Canada, for example, based on subsurface properties. Average soil organic-carbon storage is approximately 8 and 14 kg C m−2 for the depth ranges 0–1 m and 0–3 m. The concentration of total soluble cations in mineral soils is much lower than at other previously studied locations in the western Canadian Arctic. Permafrost in the study area contains much more ground ice than expected, and slightly less organic carbon and fewer soluble cations than well studied areas in the western Canadian Arctic. As these differences are strongly related to geology and glacial history, this study may inform investigations in other parts of the Slave Geological Province and its data can support scenario simulations of future trajectories of permafrost thaw at continental and circumpolar scales. </jats:p>