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In the Canadian high Arctic, tabular massive ground ice is found extensively throughout the Eureka Sound Lowlands (ESL). This study evaluates the development of tabular massive ice in raised marine-deltaic sediments of the ESL based on new cryostratigraphic data from sites found between the coastline and the Holocene marine limit. At all sites, massive ice is found below laminated fine-grained marine sediments, and the upper contact between the ice and the overlying marine sediments is conformable and gradational. The concentration of major ions in the massive ice is orders of magnitude higher than expected for glacial ice, but Na/Cl molar ratios vary following elevation: the higher-elevation site has ratios similar to glacial ice, but sites at lower elevations have ratios closer to seawater. The δ18O values of the ice indicate that the main source of water is glacial meltwater but the δD-δ18O regression slope values suggest that the ice formed in an open system while receiving an influx that had a substantially different isotopic signature than the initial reservoir. The development of massive ice in the marine-deltaic sediments involves glacial meltwater recharging an aquifer beneath the Holocene marine sediments with a contribution of 1-10% of seawater. [ABSTRACT FROM AUTHOR]

Knowledge of the amount of unfrozen water and its migration in permafrost soils is important for understanding physico‐chemical and biological processes. Here, we developed sub‐routines in FREZCHEM and embedded them in the WATEREGO2 soil environmental model to: (a) estimate unfrozen water content under changing soil temperatures and water–ice phase changes; and (b) determine the effects of Van der Waals (VdW) and rheological forces driven by seasonal temperature variations on the transport of residual water and the long‐term evolution of ground ice content over depths of 30 m. Together, the seasonal thermal regime and associated VdW and rheological forces on the transport of residual water lead to the evolution of distinct zones of ice‐enrichment: near the surface of permafrost, at 3–5 m, 11–13 m and 17–19 m depth. The depths of ice enrichment are a function of soil thermal diffusivity, and the time needed to evolve the ground ice content is dependent on soil type, soil water chemistry and permafrost temperature. The model can explain observed variations with depth in ground ice content of icy permafrost soils and indicate that these conditions evolve over time. The findings can be used to assess the stability of permafrost to climate change under different temperature scenarios. [ABSTRACT FROM AUTHOR]

Abstract: 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, δ18O may not always be able to identify thaw unconformities; however the calculation of the 18O enrichment factors between ice and water (ε18Oi−w) may be used to determine position of thaw unconformities in permafrost, if thaw events are followed by permafrost aggradation. The approach of using ε18Oi−w provides additional information regarding past permafrost conditions that can complement change in cryostructures observed along natural exposures. [Copyright &y& Elsevier]

Abstract: Retrogressive thaw slumps are one of the most dramatic thermokarst landforms in periglacial regions. This study investigates the impacts of one stable and two active thaw slumps on the geochemistry of streams in the Stony Creek watershed (Peel Plateau, NWT, Canada). The objective of this study is to elucidate the geochemical processes associated with ground ice ablation in retrogressive thaw slumps and the geochemical evolution of slump runoff to streams. This is accomplished by describing the geochemical composition of runoff across active mega-slumps, impacted and pristine tundra streams, as well as that of the ice-rich permafrost exposed in the slump headwalls. In the Stony Creek watershed, runoff derived from active and stable thaw slumps is characterized by a Ca(Mg)–SO4 geochemical facies with conductivity and solute concentrations approximately one order of magnitude higher than in pristine streams. The elevated solute concentrations in the slump runoff are directly related to thawing of highly weatherable Late Pleistocene age ice-rich and solute-rich permafrost exposed in the headwalls of slumps, which has solute concentrations nearly 100 times higher than those measured in the uppermost 1–2m (i.e., above the early Holocene thaw unconformity). An examination of ionic relations revealed a strong relation between Ca2+ and SO4 2− and (Ca2++Mg2+)–SO4 2−, suggestive that sulfate dissolution is the main process responsible for the geochemical composition of slump impacted streams. Thaw slumps significantly impact the geochemistry of streams, by increasing their solute load well above that of pristine streams along any reach of impacted streams. Unlike shallow active layer disturbances, the thaw slumps can degrade permafrost to depths of 10m or more and the impacts of abundant slump activity on stream geochemistry can be detected at the 10^2 km2 watershed-scale. [Copyright &y& Elsevier]

ABSTRACT This paper reviews contributions to permafrost isotope geochemistry published between 2007 and 2012 and proposes future research directions. It focuses on: (1) the origin and age of ground ice; (2) geochemistry and water movement in the active and transient layers; and (3) geochemistry and water movement in deep permafrost. The use of isotope geochemistry to study permafrost-related processes has grown significantly over the last few years. These processes have been elucidated by combining geochemical and isotope measurements from different components of permafrost. Such combination has yielded new insights, for example, into the water source and transfer processes that lead to the formation of ground ice, as well as groundwater movement and residence time in permafrost. Permafrost isotope geochemistry has a promising future and should provide valuable tools for the study of a rapidly changing permafrost environment. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20–40cm of loose cryotic sediments and sandstone boulders. This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O–H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting δ18O profiles and regression slope values between the uppermost 6cm of the buried massive ice (upward convex δ18O profile and S D-18O =5.1) and that below it (progressive increase in δ18O and S D-18O =6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex δ18O profile in the uppermost 6cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured δ18O profile is 0.2 ⋅ 10−3 mm yr−1, a value that is more similar to net ice removal rates derived from 3He data from cobbles in Beacon Valley till (7.0 ⋅ 10−3 mm yr−1) than sublimation rates computed based on current climate (0.1–0.2mm yr−1). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size). [Copyright &y& Elsevier]

Abstract: Endostromatolites (cf. fissure calcretes), which possess microbial evidence for a biogenic origin, are also thought to preserve isotopic biosignatures. In this study, a multi-proxy approach combining (micro)morphological, geochemical and isotopic analyses of middle Holocene age endostromatolites within sub-horizontal fissures in dolomitic limestone outcrops in the Haughton impact crater region (Devon Island, NU) was used to determine their origin (abiotic versus biogenic) and to identify potential isotope biosignatures. The micro-morphologies of the endostromatolites revealed some structures typical of a physico-chemical origin, whereas the presence of rod-shape particles and filamentous structures was more reminiscent of biologically-induced forms. The endostromatolites have δ 13C and δ 18O compositions reaching maximum values of 7.2‰ and −11.2‰, respectively. Positive relations between the elemental (Mg, Sr) and isotopic (δ 18O and δ 13C) composition of the endostromatolites are indicative of an evaporative enrichment process of the meteoric water infiltrating the fissures prior to calcite precipitation. However, the positive δ 13CTOC–δ 13CCaCO3 relation in the endostromatolites is strongly indicative that they were microbially-mediated. In support of a microbial origin, mostly aerobic heterotrophic bacteria that have been linked to both carbonate dissolution and mineralization were observed in the microbial diversity of the endostromatolites. However, the results are inconclusive to attribute the formation of the endostromatolites solely to a biologically-induced mineralization, but instead, favor a more complex origin that involved abiotic (evaporation), and to some extent, biological processes prior to and during calcite precipitation. Considering that the endostromatolites result from microbially-influenced mineralization, the effects of physico-chemical processes on the geochemical and isotopic composition of the endostromatolites were much greater than the effect of the biological processes. Thus, it seems that preservation of isotopic biosignatures in secondary carbonate precipitates is dependent on the sequence of processes generating chemical and isotopic modifications of the solution prior to calcite precipitation, the mechanism and condition (equilibrium or kinetic) of formation and post-fossilization alteration processes. [Copyright &y& Elsevier]

This study examines the physical and geochemical properties of near-surface sediments, as well as the geochemical and stable O–H–C isotope composition of (ground)surface waters in and around the Haughton impact structure region (Devon Island, Nunavut) to determine the types of weathering (mechanical, (bio)chemical) and their relative contribution in this polar desert environment. The surface sediments collected from the Allen Bay and Thumb Mountain formations surrounding the impact crater are dominated by sand-sized particles; whereas the impact melt breccias inside the crater have a greater abundance of silt-sized particles. The subsurface sediments in the Allen Bay formation show a near equal amount of sand- and silt-sized particles. However, the micromorphologies of the sand-sized particles collected at the surface revealed that these grains, irrespective of the local geology, were heavily fractured. By contrast, fractures and rounded pits are observed on the surface of the sand grains located within the active layer; whereas those located just above the permafrost table have only rounded cavities on their surface. The (ground)waters also show variations in their solute concentration with depth; the highest concentrations being found in the groundwaters near the top of permafrost. Taken together, these observations suggest that there is a progressive evolution from a mechanically dominated weathering regime near the surface, to increasing chemical weathering with depth. The transition from mechanical weathering near the surface to increasing chemical weathering with depth can be attributed to the decreasing frequency and intensity of mechanical weathering processes (i.e., frost action, wetting–drying, thermal dilation) with depth, and to the presence of permafrost, which allows a greater availability of water for chemical aqueous reactions at the base of the active layer. Cette étude examine les propriétés physiques et géochimiques de sédiments près de la surface ainsi que la composition géochimique et la composition des isotopes stables O–H–C des eaux souterraines et de surface dans la région de la structure d’impact Haughton et autour de celle-ci (île Devon, Nunavut) afin de déterminer le type de météorisation (mécanique, (bio)chimique) et leur contribution relative dans cet environnement de désert polaire. Les sédiments de surface recueillis des formations d’Allen Bay et de Thumb Mountain entourant le cratère d’impact comprennent surtout des particules de la taille du sable, alors que les brèches de fusion d’impact à l’intérieur du cratère présentent plus de particules de la taille du silt. Les sédiments sous la surface dans la Formation d’Allen Bay montrent des quantités presque égales de particules de la taille du sable et du silt. Toutefois, la micromorphologie des particules de la taille du sable recueillies à la surface révèle que ces grains étaient grandement fracturés, peu importe la géologie locale. Cependant, des fractures et de petites dépressions arrondies sont observées à la surface des grains de sable situés dans la couche active, alors que les particules situées tout juste au-dessus de la nappe du pergélisol ne présentent que des cavités arrondies à leur surface. Les eaux souterraines présentent aussi des variations de concentration de soluté avec la profondeur; les plus hautes concentrations se retrouvent dans les eaux de surface près du sommet du pergélisol. Prises ensemble, ces observations suggèrent qu’il existe une évolution progressive d’un régime d’altération principalement mécanique près de la surface à une altération de plus en plus chimique avec la profondeur. La transition d’une altération mécanique à proximité de la surface à une altération chimique plus poussée avec la profondeur peut être attribuée à la fréquence et l’intensité décroissantes des processus d’altération mécanique (c.-à-d. l’action du gel, les cycles de mouillage et séchage, la dilatation thermique) avec la profondeur et à la présence du pergélisol qui permet une plus grande disponibilité d’eau pour des réactions chimiques aqueuses à la base de la couche active. [ABSTRACT FROM AUTHOR]

Abstract: Acidic SO4–Ca–Fe waters are discharging from sandstone bedrock overlying pyrite-rich shales along the Dempster Highway near Eagle Plains, northern Yukon Territory. Although evidence of acid drainage was present prior to the construction of the Dempster Highway in the 1970''s, the removal of surficial sediments during its construction amplified the release of acidity by allowing the active layer to penetrate into the freshly exposed pyrite-rich shale. Acid drainage originating from the excavated area has a pH value averaging 3.1±0.3 and over 5 g/L of dissolved solids (SO4 2− =3915 mg/L, Fetotal =459 mg/L, Ca2+ =418 mg/L and Altotal =83.6 mg/L) whereas the unaffected drainage has a pH greater than 4.4 and total dissolved solids in the 100 to 200 mg/L range. Geochemical modeling of the surface waters and active layer pore water using PHREEQC hydrogeochemical computer code predicted saturation in Fe-hydroxide and Fe-sulfate minerals, which is confirmed by the observation of abundant ferrihydrite precipitates along the acidified stream. The solute concentrations of the acidified stream and active layer soluble ions versus SO4 plot on very similar slopes, suggesting a recycling of solutes. It is suggested that the effect of seasonal freeze-thaw of the active layer plays an important role in sustaining acidity in the stream. Freeze-back of the acid waters in the active layer produces both Fe-sulfate minerals and residual sulfuric acid. During the thaw season, this acidity is released, thus enhancing further dissolution of alumino-silicate minerals. The release of these contaminants, including acidity, not only causes a perturbation of the water quality, but also has a negative impact on the sensitive Arctic ecosystem, by disturbing the local permafrost conditions. [Copyright &y& Elsevier]

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl − , NO 3 − , ClO 4 − and ClO 3 − in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl − and NO 3 − isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO 4 − /NO 3 − ratios and NO 3 − isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO 3 − /ClO 4 − in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO 3 − , possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ∼10 to 30 kyr near the glacier to 70–200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization. [ABSTRACT FROM AUTHOR]