Widespread changes to near-surface permafrost in northern ecosystems are occurring through gradual top-down thaw and more abrupt localized thermokarst development. Both thaw types are associated with a loss of ecosystem services, including soil hydrothermal and mechanical stability and long-term carbon storage. Here, we analyzed relationships between the vascular understory, basal moss layer, active layer thickness (ALT), and greenhouse gas fluxes along a thaw gradient from permafrost peat plateau to thaw bog in Interior Alaska. We used ALT to define four distinct stages of thaw: Stable, Early, Intermediate, and Advanced, and we identified key plant taxa that serve as reliable indicators of each stage. Advanced thaw, with a thicker active layer and more developed thermokarst features, was associated with increased abundance of graminoids and Sphagnum mosses but decreased plant species richness and ericoid abundance, as well as a substantial increase in methane emissions. Early thaw, characterized by active layer thickening without thermokarst development, coincided with decreased ericoid cover and plant species richness and an increase in CH4 emissions. Our findings suggest that early stages of thaw, prior to the formation of thermokarst features, are associated with distinct vegetation and soil moisture changes that lead to abrupt increases in methane emissions, which then are perpetuated through ground surface subsidence and collapse scar bog formation. Current modeling of permafrost peatlands will underestimate carbon emissions from thawing permafrost unless these linkages between plant community, nonlinear active layer dynamics, and carbon fluxes of emerging thaw features are integrated into modeling frameworks.

Prairie Pothole wetlands have large temporal changes in water status. The wetlands are often flooded, with water above the soil surface during the early growing season, while becoming dry during the later growing season or for years under strong drought. We used the eddy covariance technique to assess the potential for ecosystem carbon sequestration as a natural climate solution in a large Prairie Pothole wetland in southern Alberta (Frank Lake wetland complex) that was dominated by the emergent macrophyte, Schoenoplectus acutus L. (bulrush). We made ecosystem-scale measurements of CO2 and CH4 exchange over two growing seasons during a time-period with environmental conditions that were warmer and drier than the climate normal. In particular, the study was conducted while the wetland had been experiencing a decade-long drought based on the Standardized Precipitation Evapotranspiration Index. To provide perspective on the longer-term temporal variability of ecosystem carbon exchange processes, we also used LandSat NDVI measurements of vegetation greenness, calibrated with eddy covariance measurements of ecosystem CO2 exchange during 2022-23, to estimate carbon sequestration capacity during 1984-2023, a period that included several wet-dry cycles. Our measured growing season-integrated net CO2 uptake values were 47 and 70 g C m-2 season-1 in 2022 and 2023, respectively. Including the measured low methane emissions (converted to CO2 equivalents based on a Sustained Global Warming Potential) only changed the net sink to 40 and 67 g C m-2 season-1 in 2022 and 2023, respectively. Despite drought conditions over the last decade, measured ecosystem carbon sequestration values were close to average values during 1984-2023, based on NDVI measurements and model carbon flux calculations. Our results demonstrated net carbon sequestration as a natural climate solution in a Prairie Pothole wetland, even during a time-period that was not expected to be favourable for carbon sequestration because of the drought conditions.

The Net Ecosystem Carbon Balance (NECB) is a crucial metric for understanding integrated carbon dynamics in Arctic and boreal regions, which are vital to the global carbon cycle. These areas are associated with significant uncertainties and rapid climate change, potentially leading to unpredictable alterations in carbon dynamics. This mini-review examines key components of NECB, including carbon sequestration, methane emissions, lateral carbon transport, herbivore interactions, and disturbances, while integrating insights from recent permafrost region greenhouse gas budget syntheses. We emphasize the need for a holistic approach to quantify the NECB, incorporating all components and their uncertainties. The review highlights recent methodological advances in flux measurements, including improvements in eddy covariance and automatic chamber techniques, as well as progress in modeling approaches and data assimilation. Key research priorities are identified, such as improving the representation of inland waters in process-based models, expanding monitoring networks, and enhancing integration of long-term field observations with modeling approaches. These efforts are essential for accurately quantifying current and future greenhouse gas budgets in rapidly changing northern landscapes, ultimately informing more effective climate change mitigation strategies and ecosystem management practices. The review aligns with the goals of the Arctic Monitoring and Assessment Program (AMAP) and Conservation of Arctic Flora and Fauna (CAFF), providing important insights for policymakers, researchers, and stakeholders working to understand and protect these sensitive ecosystems.

Vulnerability of peat plateaus to global warming was analyzed in northeastern European Russia. A laboratory experiment on artificial incubation of peat was carried out to analyze the resilience of organic matter of frozen peat bogs (palsas) to decomposition. The rate of mineralization of peat organic matter was calculated from data on the CO2 and CH4 emissions from the peat incubated at a temperature of +4 degrees C under artificial aerobic and anaerobic conditions during 1300 days. Peat samples were taken from the active layer (AL), transitional layer (TL), and permafrost layer (PL). The delta 13C and delta 15N isotopes and the C/N, O/C, and H/C ratios were determined as indicators of change in the decomposition rate of organic matter. By the 1300th day of the experiment under aerobic conditions, the total CO2 amount released from the analyzed samples (per 1 g of carbon) was 10.24-37.4 mg C g-1 (on average, 25.76 mg C g-1), while under anaerobic conditions, it was only 2.1-3.38 mg C g-1 (on average, 3.15 mg C g-1). The CH4 emission was detected only in the peat from the transitional layer in very small quantities. The incubation experiment results support the hypothesis that peat plateaus are resilient, especially under anaerobic conditions, regardless the ongoing climate warming.

The mechanical behavior of Methane Hydrate-Bearing Sediment (MHBS) is essential for the safe exploitation of Methane Hydrate (MH). In particular, the pore size and physicochemical characteristics of MHBS significantly influence its mechanical behavior, especially in clayey grain-cementing type MHBS. This study employs the Distinct Element Method (DEM) to investigate both the macroscopic and microscopic mechanical behavior of clayey grain-cementing type MHBS, focusing on variations in pore size and physicochemical characteristics. To accomplish this, we propose a Thermo-Hydro-Mechanical-Chemical-Soil Characteristics (THMCS) DEM contact model that incorporates the effects of pore size and physicochemical characteristics on the strength and modulus of MH. This THMCS model is validated using experimental data available in the literature. Using the proposed contact model, we conducted a series of investigations to explore the mechanical behavior of MHBS under conventional loading paths, including isotropic and drained triaxial tests using the DEM. The numerical results indicate that smaller pore sizes and lower water content-key physicochemical characteristics resulting from variations in electrochemical properties and the intensity of the electric field-can lead to reduced shear strength and stiffness due to the increased breakage of aggregates and weakened cementation. Additionally, heating was found to further accelerate the process of structural damage in MHBS.

To safely and effectively explore the natural methane hydrate, it is crucial to examine the mechanical behavior of methane hydrate-bearing sediments (MHBSs). Natural methane hydrate unevenly distributes in pores or bonds with soil particles in MHBS, changing the mechanical behavior of MHBS including stiffness, shear strength, and dilatancy. This paper presents an anisotropic critical state model for MHBS considering hydrate pore-filling and cementing effects. Based on the unified critical state model for both clay and sand, an equivalent hydrate ratio is defined to address pore-filling effect. Cohesive strength and its hardening law are introduced to characterize hydrate cementation. To describe the anisotropic behavior, the inherent anisotropy of soil particles and hydrates are modeled separately, and rotation hardening is introduced to describe the stress-induced anisotropy. Comparisons with existing triaxial tests of both synthetic and natural MHBS demonstrate that the proposed model comprehensively describes the mechanical behavior of MHBS. Detailed predictions indicate that hydrate pore-filling affects the hydrate-dependent stiffness and dilatancy of MHBS, which become more pronounced with increasing hydrate saturation. Cementing effect increases the initial stiffness and peak strength of MHBS. The pronounced influence of inherent anisotropic parameters on pre-peak stress-strain relation of MHBS is noted, and increasing hydrate saturation enhances the effect of hydrate anisotropy. These predictions contribute to a better understanding of the relation between hydrate morphologies and MHBS mechanical properties.

Permafrost regions of Qilian Mountains in China are rich in gas hydrate resources. Once greenhouse gases in deep frozen layer are released into the atmosphere during hydrate mining, a series of negative consequences occur. This study aims to evaluate the impact of hydrate thermal exploitation on regional permafrost and carbon budgets based on a multi-physical field coupling simulation. The results indicate that the permeability of the frozen soil is anisotropic, and the low permeability frozen layer can seal the methane gas in the natural state. Heat injection mining of hydrates causes the continuous melting of permafrost and the escape of methane gas, which transforms the regional permafrost from a carbon sink to a carbon source. A higher injection temperature concentrates the heat and causes uneven melting of the upper frozen layer, which provides a dominant channel for methane gas and results in increased methane emissions. However, dense heat injection wells cause more uniform melting of the lower permafrost layer, and the melting zone does not extend to the upper low permeability formation, which cannot provide advantageous channels for methane gas. Therefore, a reasonable and dense number of heat injection wells can reduce the risk of greenhouse gas emissions during hydrate exploitation.

Climate change in the northern circumpolar regions is rapidly thawing organic-rich permafrost soils, leading to the substantial release of dissolved CO2 and CH4 into river systems. This mobilization impacts local ecosystems and regional climate feedback loops, playing a crucial role in the Arctic carbon cycle. Here, we analyze the stable carbon (delta 13C) and radiocarbon (F14C) isotopic compositions of dissolved CO2 and CH4 in the Sagavanirktok and Kuparuk River watersheds on the North Slope, Alaska. By examining spatial and seasonal variations in these isotopic signatures, we identify patterns of carbon release and transport across the river continuum. We find consistent CO2 isotopic values along the geomorphological gradient, reflecting a mixture of geogenic and biogenic sources integrated throughout the watershed. Bayesian mixing models further demonstrate a systematic depletion in 13C and 14C signatures of dissolved CO2 sources from spring to fall, indicating increasing contributions of aged carbon as the active layer deepens. This seasonal deepening allows percolating groundwater to access deeper, older soil horizons, transporting CO2 produced by aerobic and anaerobic soil respiration to streams and rivers. In contrast, we observe no clear relationships between the 13C and 14C compositions of dissolved CH4 and landscape properties. Given the reduced solubility of CH4, which facilitates outgassing and limits its transport in aquatic systems, the isotopic signatures are likely indicative of localized contributions from streambeds, adjacent water saturated soils, and lake outflows. Our study illustrates that dissolved greenhouse gases are sensitive indicators of old carbon release from thawing permafrost and serve as early warning signals for permafrost carbon feedbacks. It establishes a crucial baseline for understanding the role of CO2 and CH4 in regional carbon cycling and Arctic environmental change.

Below their ice shells, icy moons may offer a source of chemical energy that could support microbial life in the absence of light. In the Arctic, past and present glacial retreat leads to isostatic uplift of sediments through which cold and methane-saturated groundwater travels. This fluid reaches the surface and freezes as hill-shaped icings during winter, producing dark ice-water interfaces above water ponds containing chemical energy sources. In one such system characterized by elevated methane concentrations - the Lagoon Pingo in Adventdalen, Svalbard, Norway (similar to 10 mg/L CH4, <0.3 mg/L O-2, -0.25 degrees C, pH 7.9), we studied amplicons of the bacterial and archaeal (microbial) 16S rRNA gene and transcripts in the water pond and overlaying ice. We found that active chemolithoautotrophic sulfur-oxidizing microorganisms (Sulfurimonas, Thiomicrorhabdus) dominate a niche at the bottom of the ice that is in contact with the anoxic water reservoir. There, the growing ice offers surfaces that interface with water and hosts favorable physico-chemical conditions for sulfide oxidation. The detection of anaerobic methanotrophs further suggests that throughout the winter, a steady-state dark and cold methane sink occurs under the ice in two steps: first, methane is oxidized to carbon dioxide and sulfates are concomitantly reduced to sulfides by the activity of anaerobic methanotrophs (ANME) ANME-1a and sulfate-reducing bacteria (SRB) SEEP-SRB1 consortia; and second, energy from sulfides is used by sulfur-oxidizing microorganisms to fix carbon dioxide into organic carbon. Our results underscore that ice-covered and dark ecosystems are hitherto overlooked oases of microbial life and emphasize the need to study microbial communities in icy habitats.

The mechanics of methane hydrate-bearing sediments (MHBS) have been broadly investigated over recent years in the context of methane-gas production or climate-change effects. Their mechanical investigation has mainly been carried out using models constructed from experimental data obtained for laboratory-formed MHBS. Along with the dominant effects of hydrate saturation and morphology within the host soil pores, this study recognizes the effective pressure at which the hydrate is formed as a key factor in the MHBS mechanics. A state-of-the-art experimental study has been conducted in order to isolate the effect of the hydrate formation pressure, for use as a model parameter. Two generalized mechanical prediction models that incorporate the effect of the hydrate formation pressure are developed in this work: (a) an analytical shear strength prediction, and (b) an empiric graphical model for predicting volumetric changes along a given stress path. The models are related to a novel data representation which enables the analysis of a few individual test outcomes as a whole, through a volume-change mapping that describes the complex influence of the volumetric effect of hydrate in MHBS, under combined hydrostatic and deviatoric loading scenarios. In this study, we delve into a specific configuration of hydrate morphology, hydrate saturation, and host soil type, enabling a distinctive fundamental geotechnical investigation and the development of a conceptual modeling approach. The paper describes the approaches by which the MHBS properties can be extracted for other MHBS samples (than those examined in this work) having different host soils and hydrate pore-space morphologies.