High-resolution stable water isotopes as tracers of thaw unconformities in permafrost: A case study from western Arctic Canada

The knowledge of past permafrost conditions is of importance to assess the potential magnitude of changes that periglacial environments may experience as a result of climate warming or disturbance. To assess if past thaw unconformities may be preserved from isotopic and geochemical discontinuities within permafrost, this study investigates the distribution of ground ice, stable water isotopes and major cations in two permafrost cores collected in a hummocky terrain site near Inuvik, Northwest Territories, Canada; a site where the evolution of the active layer during a recent period of permafrost degradation and subsequent aggradation was documented. Based on the high-resolution isotope geochemistry profiles, closed-system Rayleigh-type ionic segregation and isotope fractionation occurred during thermally-induced water migration into shallow permafrost and its freezing along a negative soil temperature gradient. Due to thermally-induced water migration into permafrost, delta O-18 may not always be able to identify thaw unconformities; however the calculation of the O-18 enrichment factors between ice and water (epsilon O-18(i-w)) may be used to determine position of thaw unconformities in permafrost, if thaw events are followed by permafrost aggradation. The approach of using epsilon O-18(i-w) provides additional information regarding past permafrost conditions that can complement change in cryostructures observed along natural exposures. Crown Copyright (C) 2014 Published by Elsevier B. V. All rights reserved.