Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Geological Province, Northwest Territories, Canada

Abstract

Abstract. The central Slave Geological Province is situated 450–650 km from the presumed spreading centre of the Keewatin Dome of the Laurentide Ice Sheet, and it differs from the western Canadian Arctic, where recent 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 in some areas, creating a mosaic of permafrost conditions. Limited evidence of ice-rich ground, a key determinant of thaw-induced landscape change, exists. Carbon and soluble cation contents in permafrost are largely unknown in the area. Twenty-four boreholes with depths up to 10 m were drilled in tundra north of Lac de Gras to address these regional gaps in knowledge and to better inform projections and generalizations at a coarser scale. Excess-ice contents of 20 %–60 %, likely remnant Laurentide basal ice, are found in upland till, suggesting that thaw subsidence of metres to more than 10 m is possible if permafrost were to thaw completely. Beneath organic terrain and in fluvially reworked sediment, aggradational ice is found. The variability in abundance of 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 nature and spatial patterns of landscape changes, however, are expected to differ from ice-marginal landscapes of western Arctic Canada, for example, based on greater spatial and stratigraphic heterogeneity. Mean organic-carbon densities in the top 3 m of soil profiles near Lac de Gras are about half of those reported in circumpolar statistics; deeper deposits have densities ranging from 1.3–10.1 kg C m−3, representing a significant additional carbon pool. The concentration of total soluble cations in mineral soils is lower than at previously studied locations in the western Canadian Arctic. This study can inform permafrost investigations in other parts of the Slave Geological Province, and its data can support scenario simulations of future trajectories of permafrost thaw. Preserved Laurentide basal ice can support new ways of studying processes and phenomena at the base of an ice sheet.

Lateral thermokarst patterns in permafrost peat plateaus in northern Norway

“…As such, our ability to quantify and represent the physical evolution of permafrost landscapes is critical to provide robust predictions of the environmental and climatic changes to come (Aas et al, 2019;Andresen et al, 2020;Teufel and Sushama, 2019). While permafrost affects about 14 million square kilometers in the Northern Hemisphere (Obu et al, 2019), the ground thermal response to climatic signal and morphological changes of permafrost are governed by processes occurring within a spatial scale of a few meters (Gisnås et al, 2014;Jones et al, 2016;Martin et al, 2019;Way et al, 2018).…”

Effect of surficial geology mapping scale on modelled ground ice in Canadian Shield terrain

“…Surficial units that appeared on the national-scale mapping retained their model parameter values from the GIMC. Units that were not represented at the national scale were assigned parameters based on a review of surficial geology-ground ice associations informed by the map unit legends and observations from prior investigations (e.g., Dredge et al, 1999;Kerr et al, 1996;Subedi et al, 2020;Wolfe, 1998;Wolfe et al, 2017).…”

“…unconsolidated sediments and heterogeneity in surficial materials, and thus ground ice abundance, in some areas of the Canadian Shield due to the scale of the mapping (Kokelj et al, 2023;O'Neill et al, 2019;Wolfe et al, 2021). Subedi et al (2020) demonstrated the underestimation of relict ice abundance near Lac de Gras, where glacial ice was interpreted from coring, but where no relict ice is modelled on the GIMC due the lack of mapped thicker till units. Though broad-scale products may poorly represent empirical evidence of ice-rich permafrost (Kokelj et al, 2023), ground ice information from small-scale mapping such as the International Permafrost Association (IPA) Circum-Arctic Map of Permafrost and Ground-Ice Conditions (IPA map; Brown et al, 2002) and the GIMC are used in generalized assessments of infrastructure risks and costs related to permafrost thaw (e.g., Clark et al, 2022;Hjort et al, 2018;Streletskiy et al, 2023), as more detailed ground ice information is not available in a standardized digital form for Canada or worldwide.…”

Landscape influence on permafrost ground ice geochemistry in a polar desert environment, Resolute Bay, Nunavut

“…Next to ground thermal regime, geomorphology and ground ice conditions are two defining factors of permafrost degradation processes (Spence et al 2020). Incidentally, these factors can also have important ramifications for the geochemistry of permafrost, which depends on permafrost history and on ice formation processes (Pollard and Bell, 1998;Kokelj and Burns, 2003;Murton et al, 2015;Schirrmeister et al, 2013;Subedi et al 2020;Tank et al 2020). Permafrost history relates to the timing and processes of permafrost formation and degradation.…”

“…The development of a vegetation cover, the accumulation of insulating organic matter in the active layer and the formation of ice at the bottom of the active layer can also slowly raise the permafrost table in epigenetic permafrost, creating a quasisyngenetic upper permafrost layer of aggradational ice called the intermediate layer, which, along with the frequently thawed transient layer on top of it, form the transition zone at the upper depths of permafrost (Shur, 1988;Kanevskiy et al, 2014). 6 Studies including both ground ice and permafrost geochemistry are relatively few (Fritz et al, 2011;Malone et al, 2013;Lamhonwah et al, 2016;Obu et al, 2017, Subedi et al 2020, as most are concerned with bulk densities in order to determine soil organic carbon content (McGuire et al, 2009;Tarnocai et al, 2009;Grosse et al, 2011b, Fouché et al, 2020. In addition, less is known about the drier High Arctic (Metcalfe et al, 2018), particularly the distribution of ground ice and its links with geochemistry (Robinson andPollard, 1998, Paquette et al, 2020b).…”