Near-surface wedges of massive ice commonly outline polygons in tundra lowlands, but such polygons have been difficult to identify on hillslopes because soil movement flattens the ridges and infills the troughs that form beside and above the ice wedges. Over the past three decades, the active layer has thickened near the western Arctic coast of Canada and consequent thawing of ice wedges has been detected by remote sensing for flat terrain but not, generally, on hillslopes. Annual field surveys (1996-2018) at the Illisarvik field site of thaw depth and ground surface elevation show the mean subsidence rate above hillslope ice wedges has been up to 32 mm a(-1) since thaw depth reached the ice-wedge tops in 2007. Annual mean ground temperatures at the site are about -3.0 degrees C beneath late-winter snow depths characteristic of the ice-wedge troughs but about -5.3 degrees C under conditions of the intervening polygons. The rate of thaw subsidence is high for natural, subaerial disturbances because meltwater from the ice wedges runs off downslope. The rate is constant, because the thickness of seasonally thawed ground above the ice wedges and the ice content of the ground remain the same while the troughs develop. Observations of changes in surface elevation in northern Banks Island between the late 1970s and 2019 show troughs on hillslopes where none was previously visible. Development of these troughs creates regional thermokarst landscapes, distinct from the widely recognized results of thawing relict glacier ice, that are now widespread over Canada's western Arctic coastlands. Recognition of ice-wedge occurrence and accelerated thaw subsidence on hillslopes is important in the design of infrastructure proposed for construction in rolling permafrost terrain.

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.

In the lake-rich tundra uplands east of the Mackenzie Delta, almost one in ten lakes has been affected by retrogressive thaw slumping. In this study, we assessed water chemistry for 34 slump-affected and 39 undisturbed upland lakes across this region and found that environmental factors typically evoked to explain variation in tundra lake water quality including surficial geology and proximity to the treeline or coast were subordinate to the main driver, permafrost degradation. Thaw slump-affected lakes had elevated ionic concentrations and water clarity in comparison with undisturbed lakes. The strength of the ionic impact was positively associated with the proportion of catchment affected by slumping and inversely related to disturbance age. Slumping did not have a significant effect on total organic carbon (TOC) concentrations, although Water clarity increased significantly with decreasing age of disturbance. In lakes undisturbed by slumping. fire-induced active-layer deepening had a delectable influence on lake water ionic strength. Surficial deposits influenced TOC concentrations with the highest concentrations and colour in undisturbed lakes with lacustrine catchments. In a warming Arctic, thermokarst processes may increase in importance as a driver of ionic chemistry and optical properties of small lakes and ponds, and shifts in aquatic food webs can be anticipated. Copyright (C) 2009 John Wiley & Sons, Ltd. and Her Majesty the Queen in right of Canada.

Chemical data are presented for water from 22 lakes in small upland catchments (<20 ha) between Inuvik and Richards Island, Northwest Territories, Canada. Eleven of the basins appear pristine and I I are affected by thermokarst slumping. The mean dissolved organic carbon (DOC) concentration of the pristine lakes (16.3 mg/l) is greater than the mean concentration of lakes disturbed by thermokarst slumping (10.5 mg/l). In pristine lakes, mean concentrations of Ca, Mg and SO4 are 9.6, 3.6 and 11.1 mg/l, but in lakes affected by thermokarst, mean concentrations are 72.6, 26.8 and 208.2 mg/l, respectively. Soluble materials released from degrading permafrost are transported to lakes by surface runoff, elevating concentrations in lake water. The percentage of total basin area influenced by thermokarst is positively associated with ionic concentrations in lake water and inversely related to DOC. Thermokarst occupying as little as 2% of catchment area may modify the chemistry of lake water, and water quality may remain affected for several decades after slump development has ceased. Aerial photographs indicate that 5 to 15% of all lakes and ponds in four 49 km(2) areas between Inuvik and Richards Island are small (median size <2 ha) with catchments affected by thermokarst. Copyright (C) 2005 John Wiley & Sons, Ltd.