Sustainability of existing infrastructure and new projects in the Arctic rely on a detailed knowledge of the thermal and geotechnical properties of permafrost, which is required to adopt appropriate maintenance and construction practices and select proper structural and thermal engineering designs. Physical properties of permafrost are also used as input variables for the parameterization in thermal modelling and thaw settlement predictive models.
These data series were obtained following the ADAPT permafrost drilling protocol. For lower latitude sites, the top 2 meters of the permafrost, which do not include the active layer, was sampled. At higher latitudes in the continuous permafrost zone where it was difficult to drill into permafrost, only the first meter of permafrost was drilled. Each ADAPT site had two subsites. At each subsite, two boreholes were drilled into the permafrost table(for a maximum of 4 boreholes per ADAPT site) from the base of one of the three soil pits used for the active layer soil sampling.
The frozen cores were recovered for analysis of physical properties (ground ice content and structure, ground water content, grain-size determination, laboratory tests for thermal conductivity measurements) and carbon content. The top and bottom of each core segments (core segments had a maximum length of 30 cm ) were sub-sampled for C-H -N determination giving a minimum of 4 sub-samples per 30 cm. All sub-samples were analysed at the Centre d'études nordiques (CEN) Radiocarbon Dating Laboratory of the CEN, where the total mass content of carbon (C), nitrogen (N) and hydrogen (H) were also analysed, by combustion using a LECO CHN628 Elemental Analyzer. All permafrost sub-samples were 1) weighed for the determination of the bulk density of the soil, 2) dried and weighed again to determine the water content, and 3) ground and mixed using a mortar and pestle before a subsample was removed and analyzed. Conventional 14C dating was done at the CEN Radiocarbon Laboratory, and samples for 14C-AMS dating were prepared at CEN and dated at the University of California Riverside radiocarbon facility.
Cryostratigraphic analyses were done by X-ray computed tomography scans (CT-scans) of frozen cores with a Siemens Somatom 64 scanner at the Institut National de la Recherche Scientifique (INRS-ETE) in Québec City. The CT-Scan method is is a non-destructive (thus preserving sample integrity) approach to determine the physical properties of permafrost in undisturbed samples. The cores were scanned over their entire length with a slice thickness of 0.6 mm. According to the core diameter (100 mm), a pixel resolution of 0.2 x 0.2 mm is provided. By selecting a range of tomographic intensity values corresponding to each of the soil components (sediment, ice and gas), voxel classification and quantification of the soil components are achieved using a MATLAB script, therefore providing the fractional volume of the permafrost samples components (soil phase-diagram).
The cryostratigraphic, carbon, nitrogen, water content, and 14C data analyses were done on samples from 9 ADAPT sites: Arviat, Beaver Creek, Daring Lake, Vallée des Trois (VDT- Umiujaq), BGR (Umiujaq), SAS (Kuujjuarapik), Ward Hunt Island, Bylot Island and Churchill. Further details on ADAPT Standard Protocols are given at the ADAPT website.
