In order to understand permafrost and paleoenvironmental conditions near the newly developed Inuvik-Tuktoyaktuk Highway (ITH), Northwest Territories, permafrost cores were collected in the winter of 2017 by the Northwest Territories Geological Survey and partners as part of the Sentinel Drilling program. This study analyzed five cores (BH-1, BH-2, BH-3, BH-4, and BH-8) situated within hilltops, riparian, and peatland terrains, recording various depositional environments. Cores were analyzed for cryostructures, water isotopes (δ18O and δ2H) and underwent radiocarbon dating to determine the origin of the sedimentary records and associated ground ice.
Collectively, these results indicate that deposits within low-relief areas (such peatlands and riparian zones) are characterized by hosting ice with enriched values, similar to modern-day, local isotopic composition., i.e., local precipitation values. BH-1, BH-3, and BH-4 all had an ice-poor diamict present at depth. The ice within these diamicts ranged from δ18O -23‰ to -19‰, with a co-isotope slope lower than the local meteoric water line; indicative of thawing during the Early Holocene warming, followed by subsequent stabilization and permafrost aggradation. Core BH-8 contained a fine-grained unit, with laminations, overlain by ~ 4m of peat. Radiocarbon dates and sedimentary structures indicate a shifting landscape with a local lake from ~11,500 to 9000 years ago, subsequently draining, developing epigenetic permafrost, and transitioning to syngenetic peat in the early Holocene. Lastly, deposits within high-relief areas, such as hummocky hills, show little evidence of being affected by Holocene thaw. The ice within BH-2, located on a hilltop, displays depleted Pleistocene values ranging between δ18O -30‰ to -27‰; at depths greater than 6-metres below the surface. Since the distribution and abundance of ground ice are strongly related to the geologic history of permafrost regions, future work will focus on placing these cores into a Quaternary geologic context and allow future trajectories of thermokarst to be identified.