CHARACTERIZATION OF PERMAFROST CORES FROM THE INUVIK-TUKTOYAKTUK CORRIDOR

Permafrost, or ground that remains below 0°C for two or more years, is the binding agent holding many northern landscapes from collapse. The sensitivity and impacts of climate change on permafrost is primarily related to the nature and amount of ground ice in the host materials that may potentially lose cohesion with thaw, and may develop terrain effects from subsidence, termed thermokarst. The magnitude of thermokarst development is largely a function of the abundance of excess ice, i.e., ice that exceeds the pore space of the host sediments.

This study analyzed three ice-rich cores (BH-1, BH-4, and BH-8) recording a variety of depositional environments, along the Inuvik-Tuktoyaktuk Highway, NWT. 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. Ice-rich diamictons are present near the base of the BH-1 and BH-4 cores. These diamictons are fine-grained and have δ¹⁸O water isotope values of -18 to -20 ‰, with a co-isotope slope less than the local meteoric water line. These values are more enriched than primary glacial diamictons in the area, suggesting these diamicton bodies have been modified by thaw and refrozen with younger Holocene water. A prominent 4 m thick massive ice body is present in BH-1 between the diamicton and the peat's base. Water isotopes from the massive ice body are depleted relative to the values from the rest of the cores and fall on the local meteoric water line, suggesting the preservation of buried ground ice. Core BH-8 contains ice-rich silt and clay near the base 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.

Collectively, these deposits suggest preservation of a relict permafrost landscape affected by thaw in the early Holocene, followed by subsequent stabilization and permafrost aggradation. Since the distribution and abundance of ground ice is 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.