No abstract

Permafrost underlies peatlands of the Great Slave region, Northwest Territories, Canada, but permafrost relations beneath other ecotopes of black spruce (Picea mariana), white birch (Betula papyrifera) and mixed forests remain unknown. Permafrost-ecotope relations examined over a 3 year period (2010-13) establish the occurrence and thermal state of permafrost under these different types of forest. Air temperatures and snow depths are regionally consistent. Ground temperature variation primarily reflects latent heat effects during the freezing season, with the duration of season-normalised active-layer freezeback explaining 76% of 1 m ground temperature variation among all sites except xeric peatland. Low apparent thermal diffusivities from substantial latent heat effects strongly attenuate ground temperature variation with depth, and yield zero annual amplitude depths of 7 m or less where annual mean ground temperatures range among sites from -1.4°C to 0.0°C. Extensive discontinuous permafrost conditions, related to the extent of forested ecotopes, are commonly in thermal disequilibrium. Whereas permafrost in peatlands may be ecosystem-protected, this represents only about 2% of the area of the region. Permafrost in other forested ecotopes, occurring in ice-rich unconsolidated sediments, is climate-driven and ecosystem-protected because of latent heat effects. Though the rate of permafrost degradation may be reduced, an eventual transition to isolated permafrost retained primarily within ecosystem-driven peatlands implies substantial reductions of permafrost extent in this region.

This open file reports on recent geoscience data collected and monitoring sites installed by the Geological Survey of Canada (GSC) in collaboration with Aboriginal Affairs and Northern Development Canada (AANDC), Northwest Territories Geoscience Office (NTGO), Government of the Northwest Territories (GNWT) Environment and Natural Resources (ENR) and the Department of Transport (DOT), BGC Engineering Inc., Carleton University, and the University of Ottawa. The report represents the first of several co-published GSC / NTGO Open File reports under the Climate Change Geoscience Program. A 2010-11 field program under the Transportation Risk in the Arctic to Climatic Sensitivity (TRACS) activity in the Climate Change Geoscience Program included extensive fieldwork in the Yellowknife area between June and September, 2010. Field data collection by the Geological Survey of Canada and Carleton University included 14 CRREL-cored boreholes and ecological descriptions at 48 sites. An additional 20 ecological site descriptions were made by University of Ottawa students. Collaborative work with BGC Engineering Inc. included field observations and soil analysis (grain size and Atterberg limits) at test pits along Highway 3, and 15 water-jet drilled holes for subsequent temperature cable installations. Numerous temperature measurement sites were also established with AANDC along a 170 km transect between Behchoko and Tibbitt Lake including six air temperature sites, six multi-channel near-surface temperature sites and seven water temperature sites. In March 2011, additional field data were collected including snow depths at 45 sites, densities at 18 sites, and ice thicknesses at eight pond sites. Snow depth transect surveys were also conducted at 11 sites along Highway 3, across the highway embankments and right-of-ways. These data were collected in order to provide baseline information regarding the nature and properties of permafrost in the Yellowknife area.

The distribution of ice-rich terrain is an important geotechnical consideration for the engineering of northern infrastructure. Lithalsas represent one form of ice-rich terrain that can be identified on the basis of surface geomorphology and cryostratigraphy. A total of 1,777 ice-rich lithalsas were mapped over 3,680 km2 using monochromatic stereo-pair airphotos, across the Great Slave Lowlands and Uplands, NWT, Canada. Boreholes indicate lithalsas in this region consist of ice-rich silt and clay, with segregated ice lenses up to 10 cm thick. Three distinct morphologies are recognized from LiDAR bare-earth DEMs including; (i) circular, (ii) linear and (iii) crescentic plan-view shapes, which exhibit hill-like or ridge-like forms up to 8 m in height and more than 100 m in width. The linear relationship between lithalsa height and width indicates that 1 cm of vertical growth may be accompanied by 15 cm of lateral growth at the peripheral edges. Lithalsa distribution is skewed towards lower elevations, with 97.7% located within the Great Slave Lowlands. These features predominately occur adjacent to water bodies and follow the regional distribution of frost susceptible glaciolacustrine silt and clay. Landscape associations suggest lithalsa formation is controlled by sedimentological, thermal and hydrological conditions. This Open File reports the first account of lithalsas within this region.

No abstract