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ABSTRACT Research in geocryology is currently principally concerned with the effects of climate change on permafrost terrain. The motivations for most of the research are (1) quantification of the anticipated net emissions of CO₂and CH₄from warming and thaw of near‐surface permafrost and (2) mitigation of effects on infrastructure of such warming and thaw. Some of the effects, such as increases in ground temperature or active‐layer thickness, have been observed for several decades. Landforms that are sensitive to creep deformation are moving more quickly as a result, andRock Glacier Velocityis now part of the Essential Climate VariablePermafrostof the Global Climate Observing System. Other effects, for example, the occurrence of physical disturbances associated with thawing permafrost, particularly the development of thaw slumps, have noticeably increased since 2010. Still, others, such as erosion of sedimentary permafrost coasts, have accelerated. Geochemical effects in groundwater from trace elements, including contaminants, and those that issue from the release of sediment particles during mass wasting have become evident since 2020. Net release of CO₂and CH₄from thawing permafrost is anticipated within two decades and, worldwide, may reach emissions that are equivalent to a large industrial economy. The most immediate local concerns are for waste disposal pits that were constructed on the premise that permafrost would be an effective and permanent containment medium. This assumption is no longer valid at many contaminated sites. The role of ground ice in conditioning responses to changes in the thermal or hydrological regimes of permafrost has re‐emphasized the importance of regional conditions, particularly landscape history, when applying research results to practical problems. 

Abstract. Soil pore water (SPW) chemistry can vary substantially acrossmultiple scales in Arctic permafrost landscapes. The magnitude of thesevariations and their relationship to scale are critical considerations forunderstanding current controls on geochemical cycling and for predictingfuture changes. These aspects are especially important for Arctic changemodeling where accurate representation of sub-grid variability may benecessary to predict watershed-scale behaviors. Our research goal is tocharacterize intra- and inter-watershed soil water geochemical variations attwo contrasting locations in the Seward Peninsula of Alaska, USA. We thenattempt to identify the key factors controlling concentrations of importantpore water solutes in these systems. The SPW geochemistry of 18 locationsspanning two small Arctic catchments was examined for spatial variabilityand its dominant environmental controls. The primary environmental controlsconsidered were vegetation, soil moisture and/or redox condition, water–soilinteractions and hydrologic transport, and mineral solubility. The samplinglocations varied in terms of vegetation type and canopy height, presence orabsence of near-surface permafrost, soil moisture, and hillslope position.Vegetation was found to have a significant impact on SPW NO3-concentrations, associated with the localized presence of nitrogen-fixingalders and mineralization and nitrification of leaf litter from tall willowshrubs. The elevated NO3- concentrations were, however, frequentlyequipoised by increased microbial denitrification in regions with sufficientmoisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. Theredox conditions in both catchments were generally limited by Fe reduction,seemingly well-buffered by a cache of amorphous Fe hydroxides, with the mostreducing conditions found at sampling locations with the highest soilmoisture content. Non-redox-sensitive cations were affected by a widevariety of water–soil interactions that affect mineral solubility andtransport. Identification of the dominant controls on current SPWhydrogeochemistry allows for qualitative prediction of future geochemicaltrends in small Arctic catchments that are likely to experience warming andpermafrost thaw. As source areas for geochemical fluxes to the broaderArctic hydrologic system, geochemical processes occurring in theseenvironments are particularly important to understand and predict withregards to such environmental changes. 

Abstract Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO₂) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO₂flux across 181 ecosystems. We find an increase in the annual CO₂sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO₂losses have substantially impacted the CO₂balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming. 

Abstract Permafrost thaw causes the seasonally thawed active layer to deepen, causing the Arctic to shift toward carbon release as soil organic matter becomes susceptible to decomposition. Ground subsidence initiated by ice loss can cause these soils to collapse abruptly, rapidly shifting soil moisture as microtopography changes and also accelerating carbon and nutrient mobilization. The uncertainty of soil moisture trajectories during thaw makes it difficult to predict the role of abrupt thaw in suppressing or exacerbating carbon losses. In this study, we investigated the role of shifting soil moisture conditions on carbon dioxide fluxes during a 13‐year permafrost warming experiment that exhibited abrupt thaw. Warming deepened the active layer differentially across treatments, leading to variable rates of subsidence and formation of thermokarst depressions. In turn, differential subsidence caused a gradient of moisture conditions, with some plots becoming consistently inundated with water within thermokarst depressions and others exhibiting generally dry, but more variable soil moisture conditions outside of thermokarst depressions. Experimentally induced permafrost thaw initially drove increasing rates of growing season gross primary productivity (GPP), ecosystem respiration (R_eco), and net ecosystem exchange (NEE) (higher carbon uptake), but the formation of thermokarst depressions began to reverse this trend with a high level of spatial heterogeneity. Plots that subsided at the slowest rate stayed relatively dry and supported higher CO₂fluxes throughout the 13‐year experiment, while plots that subsided very rapidly into the center of a thermokarst feature became consistently wet and experienced a rapid decline in growing season GPP,R_eco, and NEE (lower carbon uptake or carbon release). These findings indicate that Earth system models, which do not simulate subsidence and often predict drier active layer conditions, likely overestimate net growing season carbon uptake in abruptly thawing landscapes.