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Climate change is rapidly transforming Arctic landscapes where increasing soil temperatures speed up permafrost thaw. This exposes large carbon stocks to microbial decomposition, possibly worsening climate change by releasing more greenhouse gases. Understanding how microbes break down soil carbon, especially under the anaerobic conditions of thawing permafrost, is important to determine future changes. Here, we studied the microbial community dynamics and soil carbon decomposition potential in permafrost and active layer soils under anaerobic laboratory conditions that simulated an Arctic summer thaw. The microbial and viral compositions in the samples were analyzed based on metagenomes, metagenome-assembled genomes, and metagenomic viral contigs (mVCs). Following the thawing of permafrost, there was a notable shift in microbial community structure, with fermentative Firmicutes and Bacteroidota taking over from Actinobacteria and Proteobacteria over the 60-day incubation period. The increase in iron and sulfate-reducing microbes had a significant role in limiting methane production from thawed permafrost, underscoring the competition within microbial communities. We explored the growth strategies of microbial communities and found that slow growth was the major strategy in both the active layer and permafrost. Our findings challenge the assumption that fast-growing microbes mainly respond to environmental changes like permafrost thaw. Instead, they indicate a common strategy of slow growth among microbial communities, likely due to the thermodynamic constraints of soil substrates and electron acceptors, and the need for microbes to adjust to post-thaw conditions. The mVCs harbored a wide range of auxiliary metabolic genes that may support cell protection from ice formation in virus-infected cells.ImportanceAs the Arctic warms, thawing permafrost unlocks carbon, potentially accelerating climate change by releasing greenhouse gases. Our research delves into the underlying biogeochemical processes likely mediated by the soil microbial community in response to the wet and anaerobic conditions, akin to an Arctic summer thaw. We observed a significant shift in the microbial community post-thaw, with fermentative bacteria like Firmicutes and Bacteroidota taking over and switching to different fermentation pathways. The dominance of iron and sulfate-reducing bacteria likely constrained methane production in the thawing permafrost. Slow-growing microbes outweighed fast-growing ones, even after thaw, upending the expectation that rapid microbial responses to dominate after permafrost thaws. This research highlights the nuanced and complex interactions within Arctic soil microbial communities and underscores the challenges in predicting microbial response to environmental change.

Remote northern communities in Canada face energy challenges due to their reliance on fossil fuels. Small modular reactors (SMRs) show promise as a sustainable solution to this issue, as they can reduce greenhouse gas emissions and promote sustainable development. However, SMRs require specific structural and geotechnical design paradigms for implementation and operation in permafrost regions, which are adversely affected by climate change and permafrost degradation. This study presents the potential of SMRs for sustainable energy production in the northern context. We provide an overview of SMRs and highligh their position in Canada's energy transition in northern regions. Additionally, we discuss the challenges associated with designing and implementing SMRs in northern regions. Our study contributes to the growing body of literature on SMRs in permafrost regions and highlights the need for further research and policy development to support their adoption. [ABSTRACT FROM AUTHOR]

Metabolism in stream ecosystems alters the fate of organic carbon (OC) received from surrounding landscapes, but our understanding of in‐stream metabolic processes in boreal ecosystems remains limited. Determining the factors that regulate OC metabolism will help predict how the C balance of boreal streams may respond to future environmental change. In this study, we addressed the question: what controls OC metabolism in boreal headwater streams draining catchments with discontinuous permafrost? We hypothesized that metabolism is collectively regulated by OC reactivity, phosphorus availability, and temperature, with discharge modulating each of these conditions. We tested these hypotheses using a combination of laboratory experiments and whole‐stream ecosystem metabolism measurements throughout the Caribou‐Poker Creeks Research Watershed (CPCRW) in Interior Alaska, USA. In the laboratory experiments, respiration and dissolved OC (DOC) removal were both co‐limited by the supply of reactive C and phosphorus, but temperature and residence time acted as stronger controls of DOC removal. Ecosystem respiration (ER) was largely predicted by discharge and site, with some variance explained by gross primary production (GPP) and temperature. Both ER and GPP varied inversely with watershed permafrost extent, with an inverse relationship between temperature and permafrost extent providing one plausible explanation. Our results provide some of the first evidence of a functional response to permafrost thaw in stream ecosystems and suggest the role of metabolism in landscape C cycling may increase as climate change progresses. Plain Language Summary: Rivers and streams can transform organic matter received from the surrounding landscape through the metabolic activity of microbes and other organisms. In boreal streams, little is known about ecosystem metabolism and whether respiration rates might change as warming‐induced permafrost thaw progresses. To understand if and how permafrost thaw is affecting stream microbial activity, we compared respiration rates in streams draining areas with different amounts of permafrost and used lab experiments to test which factors are currently limiting microbial activity. We found that metabolic rates were greatest in streams where the most permafrost thaw had occurred. This pattern could be explained by warmer water temperature promoting faster rates of microbial activity and less flashy flow conditions allowing more time for microbes to break down organic matter before it is flushed downstream. This newly documented relationship between permafrost thaw and stream respiration should be considered in efforts to better incorporate in‐stream processes into broader carbon cycling models. Key Points: Stream ecosystem respiration increased with permafrost thaw, likely due to warmer temperature and a more stable flow regimeWithin individual streams, ecosystem respiration was positively correlated with both discharge and gross primary productionRespiration was most limited by temperature and residence time in lab experiments, with additional co‐limitation by carbon and phosphorus [ABSTRACT FROM AUTHOR]

The landscape and landforms in permafrost regions are transforming due to climate change and permafrost thaw. This study uses optical and radar remote sensing, alongside spatial analysis, to examine thermokarst features and their driving factors in the source region of the Yangtze River (SRYR) on the central Tibetan Plateau. We analyse the distribution, interaction, and key environmental factors influencing thermokarst ponds and ground surface deformation, which are the two widespread and noticeable thermokarst features. Since the 1960s, the number of small water bodies has doubled from approximately ~2 × 104 to ~4 × 104 by the 2020s, with the median size of these water bodies decreasing from 2.3 × 104 m2 to 1.4 × 104 m2. The permafrost terrain has an average subsidence rate of 6.8 mm/a. About 50.9% of the SRYR exhibits evident thermokarst features. Surficial geological factors, especially geomorphology and slope, are primary factors in shaping the spatial distributions of thermokarst features. Both seasonal deformation and long‐term subsidence rates are more pronounced in areas with thermokarst ponds. However, once pond coverage exceeds around 5%, the amplifying effect on long‐term subsidence rates and seasonal deformation diminishes. The investigation further reveals that the relationship between seasonal deformation and long‐term subsidence is not strictly linear and that the combined increase in seasonal deformation and long‐term subsidence applies only to areas with seasonal deformation below approximately 20 mm. Beyond this threshold, the long‐term subsidence rate is no longer exacerbated by increased seasonal deformation. [ABSTRACT FROM AUTHOR]

This article uses the Resilient Community Development frame to explore how the residents from two coastal settlements in the Russian Arctic cope with the long-term effects of climate change, permafrost thaw and challenging socio-economic conditions. Semi-structured interviews were conducted in 2019 in Tiksi and Bykovsky (Republic of Sakha, Russia). These narratives were coded and qualitatively analyzed using the aforementioned framing as a guideline. This article shows that migration, mobility, culture, history, identity and extended networks play a key role in the way that these residents cope with disturbances and upheavals. Sharing past experiences and specific ways to interact with their natural environment, other neighbors and the land they live in are pivotal for the local social configuration and can underpin identity processes. This analysis demonstrates that residents' narratives regarding socio-economic challenges, climate change and permafrost thaw can inform us about short-term concerns, but also how to enhance long-term community resilience. [ABSTRACT FROM AUTHOR]

Our knowledge on permafrost carbon (C) cycle is crucial for understanding its feedback to climate warming and developing nature-based solutions for mitigating climate change. To understand the characteristics of permafrost C cycle on the Tibetan Plateau, the largest alpine permafrost region around the world, we summarized recent advances including the stocks and fluxes of permafrost C and their responses to thawing, and depicted permafrost C dynamics within this century. We find that this alpine permafrost region stores approximately 14.1 Pg (1 Pg=1015 g) of soil organic C (SOC) in the top 3 m. Both substantial gaseous emissions and lateral C transport occur across this permafrost region. Moreover, the mobilization of frozen C is expedited by permafrost thaw, especially by the formation of thermokarst landscapes, which could release significant amounts of C into the atmosphere and surrounding water bodies. This alpine permafrost region nevertheless remains an important C sink, and its capacity to sequester C will continue to increase by 2100. For future perspectives, we would suggest developing long-term in situ observation networks of C stocks and fluxes with improved temporal and spatial coverage, and exploring the mechanisms underlying the response of ecosystem C cycle to permafrost thaw. In addition, it is essential to improve the projection of permafrost C dynamics through in-depth model-data fusion on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

High-latitude warming is increasing soil temperatures and driving permafrost thaw, potentially altering soil nutrient conditions by enhancing microbial mineralization and making nutrients from previously frozen soils accessible for plant and microbial use. Increases in soil nutrient concentrations may alter plant community processes and, consequently, carbon (C) fluxes. We conducted an experiment in a boreal permafrost peatland, monitoring forest floor C flux and functional traits of the entire moss and vascular plant communities to the addition of nutrients at 20 and 40 cm soil depths and under closed and open canopy conditions. Plant functional trait responses were investigated at both community level (using community-weighted means) and intraspecific scales. Using fertilizer additions, we emulated nutrient increases at different depths in the soil profile, replicated at high and low canopy cover sites to assess the influence of light availability. Our results demonstrate rapid responses of vascular plant community-level traits as well as ecosystem respiration and gross primary productivity to fertilization treatments under low canopy cover, suggesting an influence of local environmental variation. We found that moss community-level traits played a more important role in mediating C flux response to nutrient fertilization than vascular plants but led to little change in C sink–source dynamics. This provides insight into existing ambiguities of the response of boreal C fluxes to increased nutrient availability following soil warming and permafrost thaw: Local environmental conditions and moss community can strongly mediate the response, whereas vascular plant communities may play a more minor role. However, our results suggest that these changes may not alter overall C sink–source dynamics of peatlands in the near term. [ABSTRACT FROM AUTHOR]

ABSTRACT Climate change is rapidly transforming Arctic landscapes where increasing soil temperatures speed up permafrost thaw. This exposes large carbon stocks to microbial decomposition, possibly worsening climate change by releasing more greenhouse gases. Understanding how microbes break down soil carbon, especially under the anaerobic conditions of thawing permafrost, is important to determine future changes. Here, we studied the microbial community dynamics and soil carbon decomposition potential in permafrost and active layer soils under anaerobic laboratory conditions that simulated an Arctic summer thaw. The microbial and viral compositions in the samples were analyzed based on metagenomes, metagenome-assembled genomes, and metagenomic viral contigs (mVCs). Following the thawing of permafrost, there was a notable shift in microbial community structure, with fermentative Firmicutes and Bacteroidota taking over from Actinobacteria and Proteobacteria over the 60-day incubation period. The increase in iron and sulfate-reducing microbes had a significant role in limiting methane production from thawed permafrost, underscoring the competition within microbial communities. We explored the growth strategies of microbial communities and found that slow growth was the major strategy in both the active layer and permafrost. Our findings challenge the assumption that fast-growing microbes mainly respond to environmental changes like permafrost thaw. Instead, they indicate a common strategy of slow growth among microbial communities, likely due to the thermodynamic constraints of soil substrates and electron acceptors, and the need for microbes to adjust to post-thaw conditions. The mVCs harbored a wide range of auxiliary metabolic genes that may support cell protection from ice formation in virus-infected cells.IMPORTANCEAs the Arctic warms, thawing permafrost unlocks carbon, potentially accelerating climate change by releasing greenhouse gases. Our research delves into the underlying biogeochemical processes likely mediated by the soil microbial community in response to the wet and anaerobic conditions, akin to an Arctic summer thaw. We observed a significant shift in the microbial community post-thaw, with fermentative bacteria like Firmicutes and Bacteroidota taking over and switching to different fermentation pathways. The dominance of iron and sulfate-reducing bacteria likely constrained methane production in the thawing permafrost. Slow-growing microbes outweighed fast-growing ones, even after thaw, upending the expectation that rapid microbial responses to dominate after permafrost thaws. This research highlights the nuanced and complex interactions within Arctic soil microbial communities and underscores the challenges in predicting microbial response to environmental change.

Rainfall frequency and intensity are expected to increase in the Arctic, with potential detrimental impacts on permafrost, leading to enhanced thawing and carbon release to the atmosphere. However, there have been very few studies on the effect of discrete rain events on permafrost in the Arctic and sub-Arctic. Conducting controlled rainfall experiments within permafrost landscapes can provide an improved understanding of the effect of changing intensity, duration, and timing of rain events on permafrost tundra ecosystems. Here, we describe the design and implementation of the Next-Generation Ecosystem Experiment Arctic Rainfall Simulator (NARS), a variable intensity (4–82 mm/h) rainfall simulator that can be used to study the effects of rainfall on permafrost stability. The NARS design includes a 3D-printed 4 cm H-flume and uses an eTape resistivity sensor that was calibrated (R2 = 0.9–0.96) to measure discharge from the system. NARS is designed to be lightweight, simple to construct, and can be easily deployed in remote locations. As a field validation of updated rainfall simulator design and modernized controls, NARS was tested on the Seward Peninsula, AK. Because of its portability, versatility in deployment, dimensions, and rainfall intensity, NARS represents a methodological innovation for researching the impacts of rainfall on permafrost environments. HIGHLIGHTS Rainfall is expected to increase in the Arctic over the next century.; The effects of rainfall on permafrost stability are poorly understood.; We developed a variable intensity rainfall simulator for use in remote areas.; The new rainfall simulator is lightweight and modernizes simulator controls.; The simulator can be used to study rain effects on permafrost.;

Permafrost soils in the northern hemisphere are known to harbor large amounts of soil organic matter (SOM). Global climate warming endangers this stable soil organic carbon (SOC) pool by triggering permafrost thaw and deepening the active layer, while at the same time progressing soil formation. But depending, e.g., on ice content or drainage, conditions in the degraded permafrost can range from water-saturated/anoxic to dry/oxic, with concomitant shifts in SOM stabilizing mechanisms. In this field study in Interior Alaska, we investigated two sites featuring degraded permafrost, one water-saturated and the other well-drained, alongside a third site with intact permafrost. Soil aggregate- and density fractions highlighted that permafrost thaw promoted macroaggregate formation, amplified by the incorporation of particulate organic matter, in topsoils of both degradation sites, thus potentially counteracting a decrease in topsoil SOC induced by the permafrost thawing. However, the subsoils were found to store notably less SOC than the intact permafrost in all fractions of both degradation sites. Our investigations revealed up to net 75% smaller SOC storage in the upper 100 cm of degraded permafrost soils as compared to the intact one, predominantly related to the subsoils, while differences between soils of wet and dry degraded landscapes were minor. This study provides evidence that the consideration of different permafrost degradation landscapes and the employment of soil fractionation techniques is a useful combination to investigate soil development and SOM stabilization processes in this sensitive ecosystem. [ABSTRACT FROM AUTHOR]

Rainfall frequency and intensity are expected to increase in the Arctic, with potential detrimental impacts on permafrost, leading to enhanced thawing and carbon release to the atmosphere. However, there have been very few studies on the effect of discrete rain events on permafrost in the Arctic and sub-Arctic. Conducting controlled rainfall experiments within permafrost landscapes can provide an improved understanding of the effect of changing intensity, duration, and timing of rain events on permafrost tundra ecosystems. Here, we describe the design and implementation of the Next-Generation Ecosystem Experiment Arctic Rainfall Simulator (NARS), a variable intensity (4-82mm/h) rainfall simulator that can be used to study the effects of rainfall on permafrost stability. The NARS design includes a 3D-printed 4 cm H-flume and uses an eTape resistivity sensor that was calibrated (R2? 0.9-0.96) to measure discharge from the system. NARS is designed to be lightweight, simple to construct, and can be easily deployed in remote locations. As a field validation of updated rainfall simulator design and modernized controls, NARS was tested on the Seward Peninsula, AK. Because of its portability, versatility in deployment, dimensions, and rainfall intensity, NARS represents a methodological innovation for researching the impacts of rainfall on permafrost environments. [ABSTRACT FROM AUTHOR]

Permafrost thaw is a major potential feedback source to climate change as it can drive the increased release of greenhouse gases carbon dioxide (CO2 ) and methane (CH4 ). This carbon release from the decomposition of thawing soil organic material can be mitigated by increased net primary productivity (NPP) caused by warming, increasing atmospheric CO2 , and plant community transition. However, the net effect on C storage also depends on how these plant community changes alter plant litter quantity, quality, and decomposition rates. Predicting decomposition rates based on litter quality remains challenging, but a promising new way forward is to incorporate measures of the energetic favorability to soil microbes of plant biomass decomposition. We asked how the variation in one such measure, the nominal oxidation state of carbon (NOSC), interacts with changing quantities of plant material inputs to influence the net C balance of a thawing permafrost peatland. We found: (1) Plant productivity (NPP) increased post-thaw, but instead of contributing to increased standing biomass, it increased plant biomass turnover via increased litter inputs to soil; (2) Plant litter thermodynamic favorability (NOSC) and decomposition rate both increased post-thaw, despite limited changes in bulk C:N ratios; (3) these increases caused the higher NPP to cycle more rapidly through both plants and soil, contributing to higher CO2 and CH4  fluxes from decomposition. Thus, the increased C-storage expected from higher productivity was limited and the high global warming potential of CH4 contributed a net positive warming effect. Although post-thaw peatlands are currently C sinks due to high NPP offsetting high CO2 release, this status is very sensitive to the plant community's litter input rate and quality. Integration of novel bioavailability metrics based on litter chemistry, including NOSC, into studies of ecosystem dynamics, is needed to improve the understanding of controls on arctic C stocks under continued ecosystem transition.

Climate warming holds the potential to cause extensive drying of wetlands in the Arctic, but the warming-drying effects on belowground ecosystems, particularly micro-eukaryotes, remain poorly understood. We investigated the responses of soil micro-eukaryotic communities, including fungi, protists, and microbial metazoa, to decadal drainage manipulation in a Siberian wet tundra using both amplicon and shotgun metagenomic sequencing. Our results indicate that drainage treatment increased the abundance of both fungal and non-fungal micro-eukaryotic communities, with key groups such as Ascomycota (mostly order Helotiales), Nematoda, and Tardigrada being notably abundant in drained sites. Functional traits analysis showed an increase in litter saprotrophic fungi and protistan consumers, indicating their increased activities in drained sites. The effects of drainage were more pronounced in the surface soil layer than the deeper layer, as soils dry and warm from the surface. Marked compositional shifts were observed for both communities, with fungal communities being more strongly influenced by drainage-induced vegetation change than the lowered water table itself, while the vegetation effect on non-fungal micro-eukaryotes was moderate. These findings provide insights into how belowground micro-eukaryotic communities respond to the widespread drying of wetlands in the Arctic and improve our predictive understanding of future ecosystem changes.

The source region of the Yangtze River (SRYR, 1.4 × 105 km2 above Zhimenda station) on the Tibetan Plateau (TP) has 78% permafrost coverage. The streamflow depth increased at a rate of 2.5 mm/a since 2000. Quantification of the water contribution brought by permafrost thawing is a difficult task. In this study, we used Sentinel‐1 data and the SBAS‐InSAR technique to monitor terrain deformation from September 2016 to December 2021, and then utilized the long‐term deformation rate to assess ground ice meltwater release and the seasonal deformation to evaluate water storage in the active layer. Results reveal that 55.3% of the terrain in the SRYR has subsidence >2.5 mm/a, indicating widespread ground ice melting. The release rate of ground ice meltwater is 4.3 mm/a in the entire SRYR, above 6 mm/a at the Dangqu and Tuotuo River subbasins. The water release rate is relatively small (∼3%) in comparison to the streamflow depth of 151 mm per year during the investigation period of 2017–2021. We did not detect a strong increasing or decreasing trend among the 5‐year seasonal deformation, which reflects that the total soil water content in the active layer did not change significantly during the short investigation period. The results provide a data basis for ground ice richness and loss information in the SRYR and help to understand the impact of permafrost thawing on the regional water cycle in the permafrost environment. Plain Language Summary: The Yangtze River is the longest river in China; its source region (1.4 × 105 km2, above Zhimenda station) has 78% permafrost coverage and a 935 km3 ground ice reserve. The hydrological processes may have been significantly impacted by the permafrost degradation over the past few decades. This study presented a quantitative analysis of the effects of permafrost thawing on the water balance using terrain deformation derived from InSAR monitoring. Subsidence rates and seasonal deformation were first used combined to estimate permafrost thawing release water. The entire source region of the Yangtze River experienced extensive thaw subsidence and ground ice melting, and the rate of ground ice meltwater release was 4.3 mm per year during 2016–2021. The 5‐year seasonal deformation for 2017 to 2021 did not show strong increasing or decreasing trends. It suggests that the water storage in the active layer doesn't have significant changes. It may also suggest that most of the water from melting ground ice is released as surface or subsurface runoff and the supply to the active layer is small during the investigation period. Key Points: Quantitative analysis of the effects of permafrost thawing on the water balance in the permafrost‐affected watershedSubsidence rates and seasonal deformation were used combined to evaluate the amount of ground ice melting release waterRunoff depth of 4.3 mm/a by ground ice melting water and small variation of active layer water storage in the study area during 2016–2021 [ABSTRACT FROM AUTHOR]

Large amounts of carbon sequestered in permafrost on the Tibetan Plateau (TP) are becoming vulnerable to microbial decomposition in a warming world. However, knowledge about how the responsible microbial community responds to warming-induced permafrost thaw on the TP is still limited. This study aimed to conduct a comprehensive comparison of the microbial communities and their functional potential in the active layer of thawing permafrost on the TP. We found that the microbial communities were diverse and varied across soil profiles. The microbial diversity declined and the relative abundance of Chloroflexi, Bacteroidetes, Euryarchaeota , and Bathyarchaeota significantly increased with permafrost thawing. Moreover, warming reduced the similarity and stability of active layer microbial communities. The high-throughput qPCR results showed that the abundance of functional genes involved in liable carbon degradation and methanogenesis increased with permafrost thawing. Notably, the significantly increased mcrA gene abundance and the higher methanogens to methanotrophs ratio implied enhanced methanogenic activities during permafrost thawing. Overall, the composition and functional potentials of the active layer microbial community in the Tibetan permafrost region are susceptible to warming. These changes in the responsible microbial community may accelerate carbon degradation, particularly in the methane releases from alpine permafrost ecosystems on the TP. [ABSTRACT FROM AUTHOR]

Rapid, ongoing permafrost thaw of peatlands in the discontinuous permafrost zone is exposing a globally significant store of soil carbon (C) to microbial processes. Mineralization and release of this peat C to the atmosphere as greenhouse gases is a potentially important feedback to climate change. Here we investigated the effects of permafrost thaw on peat C at a peatland complex in western Canada. We collected 15 complete peat cores (between 2.7 and 4.5 m deep) along four chronosequences, from elevated permafrost peat plateaus to saturated thermokarst bogs that thawed up to 600 years ago. The peat cores were analysed for peat C storage and peat quality, as indicated by decomposition proxies (FTIR and C/N ratios) and potential decomposability using a 200‐day aerobic laboratory incubation. Our results suggest net C loss following thaw, with average total peat C stocks decreasing by ~19.3 ± 7.2 kg C m−2 over <600 years (~13% loss). Average post‐thaw accumulation of new peat at the surface over the same period was ~13.1 ± 2.5 kg C m−2. We estimate ~19% (±5.8%) of deep peat (>40 cm below surface) C is lost following thaw (average 26 ± 7.9 kg C m−2 over <600 years). Our FTIR analysis shows peat below the thaw transition in thermokarst bogs is slightly more decomposed than peat of a similar type and age in permafrost plateaus, but we found no significant changes to the quality or lability of deeper peat across the chronosequences. Our incubation results also showed no increase in C mineralization of deep peat across the chronosequences. While these limited changes in peat quality in deeper peat following permafrost thaw highlight uncertainty in the exact mechanisms and processes for C loss, our analysis of peat C stocks shows large C losses following permafrost thaw in peatlands in western Canada. [ABSTRACT FROM AUTHOR]

Rivers originating from the Tibetan Plateau (TP) provide water to more than 1 billion people living downstream. Almost 40% of the TP is currently underlain by permafrost, which serves as both an ice reserve and a flow barrier and is expected to degrade drastically in a warming climate. The hydrological impacts of permafrost thaw across the TP, however, remain poorly understood. Here, we quantify the permafrost change on the TP over 1980–2100 and evaluate its hydrological impacts using a physically‐based cryospheric‐hydrological model at a high spatial resolution. Using the ensemble mean of 38 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), the near‐surface permafrost area and the total ground ice storage are projected to decrease by 86.4% and 61.6% during 2020–2100 under a high‐emission scenario, respectively. The lowering of the permafrost table and removal of permafrost as a flow barrier would enhance infiltration and raise subsurface storage capacity. The diminished water supply from ground ice melt and enhanced subsurface storage capacity could jointly reduce annual runoff and lead to exacerbated regional water shortage when facing future droughts. If the most severe 10‐year drought in the historical period occurs again in the future, the annual river runoff will further decrease by 9.7% and 11.3% compared with the historical dry period due to vanishing cryosphere in the source area of Yellow and Yangtze River. Our findings highlight the importance to get prepared for the additional water shortage risks caused by pervasive permafrost thaw in future water resources management across the TP. Plain Language Summary: Permafrost is the subsurface material that stays frozen for at least two consecutive years. It is both an ice reserve and a flow barrier, the degradation of which will lead to mobilized meltwater and enhanced infiltration at the same time. Here, we employ a physically‐based, cryospheric‐hydrological model to examine the changes in permafrost hydrology across the TP in a warming climate. As permafrost degradation progresses, the deepening of permafrost table and the complete thaw of permafrost would result in enhanced hydraulic connectivity and subsurface storage capacity. These changes could lead to reduced runoff and exacerbated water shortage when facing future droughts, calling for adaptive water management measures to address the potential challenges resulting from the vanishing cryosphere across the Third Pole region. Key Points: Pervasive permafrost degradation is projected in the future on the Tibetan Plateau using a physically‐based cryospheric hydrological modelThe near‐surface permafrost area and ground ice storage are expected to decrease by 86.4% and 61.6% during 2020–2100 under a warm scenarioThe diminished water supply and enhanced subsurface storage capacity could jointly exacerbate water shortage when facing future droughts [ABSTRACT FROM AUTHOR]

Retrogressive thaw slumps, which are a type of landslide disturbance caused by thawing of ice-rich permafrost, are increasing in size, intensity, and frequency in the Arctic because of climate warming. The formation of thaw slumps on lake shorelines in the Mackenzie Delta region (Northwest Territories, Canada) has been shown to increase water clarity, which may increase exposure risk of aquatic biota to potentially harmful ultraviolet (UV) radiation. To test this, we inferred temporal trends in UV exposure for the cladoceran Chydorus (Family Chydoridae, Class Branchiopoda) in a slump-affected lake and a neighbouring undisturbed lake by measuring absorbance at UV wavelengths in Chydorus subfossil carapaces isolated from lake-sediment cores. There was no statistically significant difference in Chydorus carapace UV-absorbance measures between the slump-affected and the undisturbed lake, despite notable differences in dissolved organic carbon and water clarity. No increase in Chydorus UV-absorbance measures occurred in the slump-impacted lake following re-initiation of slumping in the ~ 1990s, but a steady increase in UV absorbance was observed in both lakes since ~ 1800, independent of slump formation. Overall, the results of this study suggest that retrogressive thaw slumping did not substantially increase Chydorus exposure to potentially harmful UV radiation. As benthic taxa, Chydorus are likely able to find refuge among the dense macrophyte beds that develop in slump-affected lakes, which would provide shading from UV radiation. [ABSTRACT FROM AUTHOR]

Anticipated permafrost thaw in upcoming decades may exert significant impacts on forest soil nitrogen (N) dynamics. The rate of soil N mineralization (Nmin) plays a crucial role in determining soil N availability. Nevertheless, our understanding remains limited regarding how biotic and abiotic factors influence the Nmin of forest soil in response to permafrost thaw. In this study, we investigated the implications of permafrost thaw on Nmin within a hemiboreal forest based on a field investigation along the degree of permafrost thaw, having monitored permafrost conditions for eight years. The results indicate that permafrost thaw markedly decreased Nmin values. Furthermore, Nmin demonstrated positive associations with soil substrates (namely, soil organic carbon and soil total nitrogen), microbial biomass carbon and nitrogen, and soil moisture content. The decline in Nmin due to permafrost thaw was primarily attributed to the diminished quality and quantity of soil substrates rather than alterations in plant community composition. Collectively, our results underscore the pivotal role of soil substrate and microbial biomass in guiding forest soil N transformations in the face of climate-induced permafrost thaw. [ABSTRACT FROM AUTHOR]

Abstract Rivers originating from the Tibetan Plateau (TP) provide water to more than 1 billion people living downstream. Almost 40% of the TP is currently underlain by permafrost, which serves as both an ice reserve and a flow barrier and is expected to degrade drastically in a warming climate. The hydrological impacts of permafrost thaw across the TP, however, remain poorly understood. Here, we quantify the permafrost change on the TP over 1980–2100 and evaluate its hydrological impacts using a physically‐based cryospheric‐hydrological model at a high spatial resolution. Using the ensemble mean of 38 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), the near‐surface permafrost area and the total ground ice storage are projected to decrease by 86.4% and 61.6% during 2020–2100 under a high‐emission scenario, respectively. The lowering of the permafrost table and removal of permafrost as a flow barrier would enhance infiltration and raise subsurface storage capacity. The diminished water supply from ground ice melt and enhanced subsurface storage capacity could jointly reduce annual runoff and lead to exacerbated regional water shortage when facing future droughts. If the most severe 10‐year drought in the historical period occurs again in the future, the annual river runoff will further decrease by 9.7% and 11.3% compared with the historical dry period due to vanishing cryosphere in the source area of Yellow and Yangtze River. Our findings highlight the importance to get prepared for the additional water shortage risks caused by pervasive permafrost thaw in future water resources management across the TP.

Climate warming leads to widespread permafrost thaw with a fraction of the thawed permafrost carbon (C) being released as carbon dioxide (CO2), thus triggering a positive permafrost C-climate feedback. However, large uncertainty exists in the size of this model-projected feedback, partly owing to the limited understanding of permafrost CO2 release through the priming effect (i.e., the stimulation of soil organic matter decomposition by external C inputs) upon thaw. By combining permafrost sampling from 24 sites on the Tibetan Plateau and laboratory incubation, we detected an overall positive priming effect (an increase in soil C decomposition by up to 31%) upon permafrost thaw, which increased with permafrost C density (C storage per area). We then assessed the magnitude of thawed permafrost C under future climate scenarios by coupling increases in active layer thickness over half a century with spatial and vertical distributions of soil C density. The thawed C stocks in the top 3 m of soils from the present (2000-2015) to the future period (2061-2080) were estimated at 1.0 (95% confidence interval (CI): 0.8-1.2) and 1.3 (95% CI: 1.0-1.7) Pg (1 Pg = 1015 g) C under moderate and high Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5, respectively. We further predicted permafrost priming effect potential (priming intensity under optimal conditions) based on the thawed C and the empirical relationship between the priming effect and permafrost C density. By the period 2061-2080, the regional priming potentials could be 8.8 (95% CI: 7.4-10.2) and 10.0 (95% CI: 8.3-11.6) Tg (1 Tg = 1012 g) C year-1 under the RCP 4.5 and RCP 8.5 scenarios, respectively. This large CO2 emission potential induced by the priming effect highlights the complex permafrost C dynamics upon thaw, potentially reinforcing permafrost C-climate feedback. [ABSTRACT FROM AUTHOR]

Long‐term (1991–2018) thaw tube measurements highlight widespread permafrost thaw and ground surface (GS) subsidence over a large portion of northwest Canada. Statistically significant positive trends in thaw penetration (TP), measured with respect to a fixed datum, were observed at 18 of 28 sites with data that span three decades at a median rate of 0.8 cm a−1. This rate implies thawing of about 22 cm of permafrost over the study period. Similarly significant trends in GS subsidence occurred at 21 of 28 sites, at a median rate of 0.4 cm a−1. In contrast with TP and GS elevation, long‐term trends in active layer thickness (ALT) were less consistent, with 10 of 28 sites having statistically significant trends indicating increasing ALT (median rate: 0.6 cm a−1), and 7 sites having trends indicating decrease in ALT (median: 0.3 cm a−1). The ALT measurements underestimated the thawing of ice‐rich permafrost due to GS subsidence. Sites with high rates of thaw had relatively warm permafrost, deep snow cover, and poor drainage. Masking of ice‐rich permafrost degradation by ALT measurements has important implications for modeling permafrost thaw and climate change reporting. Accurate simulation of ice‐rich permafrost thaw is conceivable for sites where conditions are well‐defined. However, the prediction of subsidence and TP at regional or broader scales is only possible in general terms due to variation in surface conditions and ground ice content. Trends in TP and GS subsidence more accurately characterize ice‐rich permafrost degradation than trends in ALT. Plain Language Summary: Measurements from instruments that account for changes in the ground surface (GS) elevation indicate that permafrost has thawed, and the GS has subsided in the past three decades over a large area in northwest Canada. Traditional measurements that do not account for changes in the GS elevation mask how much permafrost is thawing and are therefore less useful for tracking the effects of climate change in permafrost areas where there is a significant amount of ice in the ground. The results of this study also highlight that it may be difficult to predict permafrost degradation and GS subsidence over large areas using simulations because conditions such as vegetation, soil wetness, snow, and ground ice content may vary over short distances and strongly affect the rates of thawing. Key Points: Permafrost thaw and ground surface subsidence are widespread in northwest CanadaActive layer thickness (ALT) measurements poorly represent the magnitude of permafrost thaw in ice‐rich settingsALT is widely used in climate change reporting, but it may be a poor indicator of climate change at ice‐rich sites [ABSTRACT FROM AUTHOR]

Northern lakes disproportionately influence the global carbon cycle, and may do so more in the future depending on how their microbial communities respond to climate warming. Microbial communities can change because of the direct effects of climate warming on their metabolism and the indirect effects of climate warming on groundwater connectivity from thawing of surrounding permafrost, especially at lower landscape positions. Here we used shotgun metagenomics to compare the taxonomic and functional gene composition of sediment microbes in 19 peatland lakes across a 1600‐km permafrost transect in boreal western Canada. We found microbes responded differently to the loss of regional permafrost cover than to increases in local groundwater connectivity. These results suggest that both the direct and indirect effects of climate warming, which were respectively associated with loss of permafrost and subsequent changes in groundwater connectivity interact to change microbial composition and function. Archaeal methanogens and genes involved in all major methanogenesis pathways were more abundant in warmer regions with less permafrost, but higher groundwater connectivity partly offset these effects. Bacterial community composition and methanotrophy genes did not vary with regional permafrost cover, and the latter changed similarly to methanogenesis with groundwater connectivity. Finally, we found an increase in sugar utilization genes in regions with less permafrost, which may further fuel methanogenesis. These results provide the microbial mechanism for observed increases in methane emissions associated with loss of permafrost cover in this region and suggest that future emissions will primarily be controlled by archaeal methanogens over methanotrophic bacteria as northern lakes warm. Our study more generally suggests that future predictions of aquatic carbon cycling will be improved by considering how climate warming exerts both direct effects associated with regional‐scale permafrost thaw and indirect effects associated with local hydrology. [ABSTRACT FROM AUTHOR]

Thermokarst lagoons represent the transition state from a freshwater lacustrine to a marine environment, and receive little attention regarding their role for greenhouse gas production and release in Arctic permafrost landscapes. We studied the fate of methane (CH4) in sediments of a thermokarst lagoon in comparison to two thermokarst lakes on the Bykovsky Peninsula in northeastern Siberia through the analysis of sediment CH4 concentrations and isotopic signature, methane-cycling microbial taxa, sediment geochemistry, lipid biomarkers, and network analysis. We assessed how differences in geochemistry between thermokarst lakes and thermokarst lagoons, caused by the infiltration of sulfate-rich marine water, altered the microbial methane-cycling community. Anaerobic sulfate-reducing ANME-2a/2b methanotrophs dominated the sulfate-rich sediments of the lagoon despite its known seasonal alternation between brackish and freshwater inflow and low sulfate concentrations compared to the usual marine ANME habitat. Non-competitive methylotrophic methanogens dominated the methanogenic community of the lakes and the lagoon, independent of differences in porewater chemistry and depth. This potentially contributed to the high CH4 concentrations observed in all sulfate-poor sediments. CH4 concentrations in the freshwater-influenced sediments averaged 1.34 ± 0.98 µmol g-1, with highly depleted d13C-CH4 values ranging from -89‰ to -70‰. In contrast, the sulfate-affected upper 300 cm of the lagoon exhibited low average CH4 concentrations of 0.011 ± 0.005 µmol g-1 with comparatively enriched d13C-CH4 values of -54‰ to -37‰ pointing to substantial methane oxidation. Our study shows that lagoon formation specifically supports methane oxidizers and methane oxidation through changes in pore water chemistry, especially sulfate, while methanogens are similar to lake conditions. [ABSTRACT FROM AUTHOR]

Significant attention has been given to the way in which the soil nitrogen (N) cycle responds to permafrost thaw in recent years, yet little is known about anaerobic N transformations in thermokarst lakes, which account for more than one-third of thermokarst landforms across permafrost regions. Based on the N isotope dilution and tracing technique, combined with qPCR and high-throughput sequencing, we presented large-scale measurements of anaerobic N transformations of sediments across 30 thermokarst lakes over the Tibetan alpine permafrost region. Our results showed that gross N mineralization, ammonium immobilization, and dissimilatory nitrate reduction rates in thermokarst lakes were higher in the eastern part of our study area than in the west. Denitrification dominated in the dissimilatory nitrate reduction processes, being two and one orders of magnitude higher than anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA), respectively. The abundances of the dissimilatory nitrate reduction genes (nirK, nirS, hzsB, and nrfA) exhibited patterns consistent with sediment N transformation rates, while a diversity did not. The inter-lake variability in gross N mineralization and ammonium immobilization was dominantly driven by microbial biomass, while the variability in anammox and DNRA was driven by substrate supply and organic carbon content, respectively. Denitrification was jointly affected by nirS abundance and organic carbon content. Overall, the patterns and drivers of anaerobic N transformation rates detected in this study provide a new perspective on potential N release, retention, and removal upon the formation and development of thermokarst lakes. [ABSTRACT FROM AUTHOR]

The greenhouse gas (GHG) balance of boreal peatlands in permafrost regions will be affected by climate change through disturbances such as permafrost thaw and wildfire. Although the future GHG balance of boreal peatlands including ponds is dominated by the exchange of both carbon dioxide (CO2) and methane (CH4), disturbance impacts on fluxes of the potent GHG nitrous oxide (N2O) could contribute to shifts in the net radiative balance. Here, we measured monthly (April to October) fluxes of N2O, CH4, and CO2 from three sites located across the sporadic and discontinuous permafrost zones of western Canada. Undisturbed permafrost peat plateaus acted as N2O sinks (−0.025 mg N2O m−2 d−1), but N2O uptake was lower from burned plateaus (−0.003 mg N2O m−2 d−1) and higher following permafrost thaw in the thermokarst bogs (−0.054 mg N2O m−2 d−1). The thermokarst bogs had below‐ambient N2O soil gas concentrations, suggesting that denitrification consumed atmospheric N2O during reduction to dinitrogen. Atmospheric uptake of N2O in peat plateaus and thermokarst bogs increased with soil temperature and soil moisture, suggesting sensitivity of N2O consumption to further climate change. Four of five peatland ponds acted as N2O sinks (−0.018 mg N2O m−2 d−1), with no influence of thermokarst expansion. One pond with high nitrate concentrations had high N2O emissions (0.30 mg N2O m−2 d−1). Overall, our study suggests that the future net radiative balance of boreal peatlands will be dominated by impacts of wildfire and permafrost thaw on CH4 and CO2 fluxes, while the influence from N2O is minor. Plain Language Summary: The peatlands in the boreal biome of northwestern Canada have been a sink of the potent greenhouse gases (GHG) carbon dioxide (CO2) and nitrous oxide (N2O), and a source of methane (CH4) for many millennia. Now, climate change is transforming these boreal peat landscapes as more severe and frequent wildfires burn the forests and ground ice‐rich permafrost thaws. Wildfires and permafrost thaw alter soil biogeochemical conditions such as soil temperature, soil moisture, and water table depth. The changing conditions have immediate effects on GHG production, transport, and consumption in the soil, which are reasonably well understood for CO2 and CH4 but not for N2O. By measuring soil GHG concentrations at different depths and GHG exchange between soil and atmosphere with static chambers, we showed that N2O exchange from different peat surfaces responded differently depending on the two disturbance types. While burned peatland areas were close to neutral regarding N2O, the wet, thaw‐affected areas showed increased N2O uptake driven by high soil moisture contents, soil temperatures, and below‐atmospheric N2O soil gas concentrations. However, this minor N2O uptake can only offset less than 1% of the global warming potential of CH4 emissions from the thawing peatlands studied here. Key Points: Permafrost peatlands acted as sinks of nitrous oxide; thermokarst and wildfire caused increased and reduced uptake rates, respectivelyUptake of nitrous oxide in peat plateaus and thermokarst bogs increased with soil temperature, suggesting sensitivity to climate warmingImpacts of thermokarst and wildfire on nitrous oxide fluxes were minor compared to methane when expressed in carbon dioxide equivalents [ABSTRACT FROM AUTHOR]

The paper analyzed the number of ecological-trophic groups of microorganisms and the elemental composition of the active, permafrost and thawed layers of a typical flat mount frozen peatlands (plateau palsa) in the Nadym-Pur interfluves, Western Siberia, with part of it affected by fire. The number of ecological-trophic groups was found to change after permafrost thaw. The study revealed a relationship between the number of microorganisms and the content of some chemical elements in the soil profile of the plateau palsa in the Nadym-Pur interfluve. A statistically significant relationship was found between the most probable number of microorganisms (CFU/g) in different peat layers and the pH, the ash content and the content of calcium, magnesium, strontium, and iron.

Permafrost regions, characterised by extensive belowground excess ice, are highly vulnerable to rapid thaw, particularly in areas such as the Yedoma domain. This region is known to freeze-lock a globally significant stock of soil nitrogen (N). However, the fate of this N upon permafrost thaw remains largely unknown. In this study, we assess the impact of climate warming on the size and dynamics of the soil N pool in (sub-)Arctic ecosystems, drawing upon recently published data and literature. Our findings suggest that climate warming and increased thaw depths will result in an expansion of the reactive soil N pool due to the larger volume of (seasonally) thawed soil. Dissolved organic N emerges as the predominant N form for rapid cycling within (sub-)Arctic ecosystems. The fate of newly thawed N from permafrost is primarily influenced by plant uptake, microbial immobilisation, changes in decomposition rates due to improved N availability, as well as lateral flow. The Yedoma domain contains substantial N pools, and the partial but increasing thaw of this previously frozen N has the potential to amplify climate feedbacks through additional nitrous oxide (N _2 O) emissions. Our ballpark estimate indicates that the Yedoma domain may contribute approximately 6% of the global annual rate of N _2 O emissions from soils under natural vegetation. However, the released soil N could also mitigate climate feedbacks by promoting enhanced vegetation carbon uptake. The likelihood and rate of N _2 O production are highest in permafrost thaw sites with intermediate moisture content and disturbed vegetation, but accurately predicting future landscape and hydrology changes in the Yedoma domain remains challenging. Nevertheless, it is evident that the permafrost-climate feedback will be significantly influenced by the quantity and mobilisation state of this unconsidered N pool.

Model projections of permafrost thaw during the next century diverge widely. Here we used ecosys to examine how climate change will affect permafrost thaw in a polygonal tundra at Barrow AK. The model was tested against diurnal and seasonal variation in energy exchange, soil heat flux, soil temperature (Ts), and active layer depth (ALD) measured during 2014 and 2015, and interannual variation in ALD measured from 1991 to 2015. During RCP 8.5 climate change from 2015 to 2085, increases in Ta and precipitation (P) to 6.2 °C and 27% above current values, and in atmospheric CO2 concentrations (Ca) to763 μmol mol−1, altered energy exchange by increasing leaf area index of dominant sedge relative to that of moss. Increased Ca and sedge leaf area index imposed greater stomatal control of transpiration and reduced soil heat fluxes, slowing soil warming, limiting increases in evapotranspiration, and thereby causing gradual soil wetting. Consequently, increases in surface Ts and ALD of 2.4–4.7 °C and 21–24 cm above current values were modeled after 70 years. ALD increase was slowed if model boundary conditions were altered to improve landscape drainage. These rates were smaller than those of earlier modeling studies, some of which did not account for changes in vegetation, but are closer to those derived from current studies of warming impacts in the region. Therefore, accounting for climate change effects on vegetation density and composition, and consequent effects on surface energy budgets, will cause slower increases in Ts and ALD to be modeled during climate change simulations.

Wildfires in Arctic regions impact landforms via permafrost degradation and subsequent deformation that can last for many years. However, it remains uncertain on if and how much deformations occur, and what controls their magnitude, particularly during the first couple of years. Here, we examine the transient post‐fire deformation responses near the Batagaika megaslump, which is the world's largest retrogressive thaw slump at Batagay, Sakha Republic. There were wildfires in the summers of 2018 and 2019 on the same slope, which could trigger the formation of another megaslump; many fires occurred nearby in 2019. We use interferometric synthetic aperture radar (InSAR) to measure surface displacements, including both post‐fire and span‐fire images. We also perform onsite measurements of temperature and thaw depth around the two scars near Batagaika megaslump in 2019, 2020, and 2021 and around the 2014 scar in 2019. At the three fire scars formed in 2018 and 2019, we demonstrate year‐to‐year and location‐specific changes in the amplitude of subsidence, heave, and duration. The 2018 scar shows cumulative subsidences of up to 10 cm by March 2021, more clearly than the nearby 2019 scar. On the other hand, another 2019 scar adjacent to the 2014 scar shows up to 13 cm net subsidence during the first span‐fire year, although the subsiding area is limited. These diverse transient post‐fire responses demonstrate that under the yedoma area the spatial heterogeneities of the active layer depth and the timing of fires will control subsequent thermokarst processes. Plain Language Summary: Wildfires in Arctic regions impact landforms via permafrost degradation and subsequent deformation that can last for many years. However, it remains uncertain on if and how much post‐fire deformation has been taking place, and what controls the magnitude of ground deformation is unclear, especially in the first couple of years after the fire. Here, we examine the transient post‐fire responses to the three fire scars formed in 2018 and 2019 near Batagay, Northeast Siberia. Two of the fires occurred on the same slope as the "Batagaika crater," the world's largest surface depression initiated by deforestation in the 1970s. We used not only the satellite‐based imaging tool called Interferometric Synthetic Aperture Radar (InSAR) to detect the surface deformation signals but also onsite measurements to detect the spatial‐temporal depth changes of the active layer. The inferred transient post‐fire responses are rather diverse despite the shared climate, suggesting that the prefire depth to the permafrost table will play the most crucial role in controlling the subsequent subsidence. Key Points: Transient post‐fire deformations at the 2018 and two 2019 scars near Batagay were examined by satellite radar and onsite thaw depth dataThe northern 2019 scar subsided by 13 cm in the first span‐fire year, but the other two scars uplifted and started to subside during the next yearThe duration of frost heave is longer in the next year after fire than in the burned year because of more soil water in the active layer [ABSTRACT FROM AUTHOR]

Permafrost peatlands store globally significant amounts of soil organic carbon (SOC) that may be vulnerable to climate change. Permafrost thaw exposes deeper, older SOC to microbial activity, but SOC vulnerability to mineralization and release as carbon dioxide is likely influenced by the soil environmental conditions that follow thaw. Permafrost thaw in peat plateaus, the dominant type of permafrost peatlands in North America, occurs both through deepening of the active layer and through thermokarst. Active layer deepening exposes aged SOC to predominately oxic conditions, while thermokarst is associated with complete permafrost thaw which leads to ground subsidence, inundation and soil anoxic conditions. Thermokarst often follows active layer deepening, and wildfire is an important trigger of this sequence. We compared the mineralization rate of aged SOC at an intact peat plateau (∼70 cm oxic active layer), a burned peat plateau (∼120 cm oxic active layer), and a thermokarst bog (∼550 cm anoxic peat profile) by measuring respired 14C-CO2. Measurements were done in fall when surface temperatures were near-freezing while deeper soil temperatures were still close to their seasonal maxima. Aged SOC (1600 yrs BP) contributed 22.1 ± 11.3% and 3.5 ± 3.1% to soil respiration in the burned and intact peat plateau, respectively, indicating a fivefold higher rate of aged SOC mineralization in the burned than intact peat plateau (0.15 ± 0.07 versus 0.03 ± 0.03 g CO2-C m−2 d−1). None or minimal contribution of aged SOC to soil respiration was detected within the thermokarst bog, regardless of whether thaw had occurred decades or centuries ago. While more data from other sites and seasons are required, our study provides strong evidence of substantially increased respiration of aged SOC from burned peat plateaus with deepened active layer, while also suggesting inhibition of aged SOC respiration under anoxic conditions in thermokarst bogs.

Permafrost soil in high latitude tundra is one of the largest terrestrial carbon (C) stocks and is highly sensitive to climate warming. Understanding microbial responses to warming-induced environmental changes is critical to evaluating their influences on soil biogeochemical cycles. In this study, a functional gene array (i.e., geochip 4.2) was used to analyze the functional capacities of soil microbial communities collected from a naturally degrading permafrost region in Central Alaska. Varied thaw history was reported to be the main driver of soil and plant differences across a gradient of minimally, moderately, and extensively thawed sites. Compared with the minimally thawed site, the number of detected functional gene probes across the 15-65 cm depth profile at the moderately and extensively thawed sites decreased by 25% and 5%, while the community functional gene β-diversity increased by 34% and 45%, respectively, revealing decreased functional gene richness but increased community heterogeneity along the thaw progression. Particularly, the moderately thawed site contained microbial communities with the highest abundances of many genes involved in prokaryotic C degradation, ammonification, and nitrification processes, but lower abundances of fungal C decomposition and anaerobic-related genes. Significant correlations were observed between functional gene abundance and vascular plant primary productivity, suggesting that plant growth and species composition could be co-evolving traits together with microbial community composition. Altogether, this study reveals the complex responses of microbial functional potentials to thaw-related soil and plant changes and provides information on potential microbially mediated biogeochemical cycles in tundra ecosystems.

Peatlands at high latitudes have accumulated >400 Pg carbon (C) because saturated soil and cold temperatures suppress C decomposition. This substantial amount of C in Arctic and Boreal peatlands is potentially subject to increased decomposition if the water table (WT) decreases due to climate change, including permafrost thaw‐related drying. Here, we optimize a version of the Organizing Carbon and Hydrology In Dynamic Ecosystems model (ORCHIDEE‐PCH4) using site‐specific observations to investigate changes in CO2 and CH4 fluxes as well as C stock responses to an experimentally manipulated decrease of WT at six northern peatlands. The unmanipulated control peatlands, with the WT <20 cm on average (seasonal max up to 45 cm) below the surface, currently act as C sinks in most years (58 ± 34 g C m−2 year−1; including 6 ± 7 g C–CH4 m−2 year−1 emission). We found, however, that lowering the WT by 10 cm reduced the CO2 sink by 13 ± 15 g C m−2 year−1 and decreased CH4 emission by 4 ± 4 g CH4 m−2 year−1, thus accumulating less C over 100 years (0.2 ± 0.2 kg C m−2). Yet, the reduced emission of CH4, which has a larger greenhouse warming potential, resulted in a net decrease in greenhouse gas balance by 310 ± 360 g CO2‐eq m−2 year−1. Peatlands with the initial WT close to the soil surface were more vulnerable to C loss: Non‐permafrost peatlands lost >2 kg C m−2 over 100 years when WT is lowered by 50 cm, while permafrost peatlands temporally switched from C sinks to sources. These results highlight that reductions in C storage capacity in response to drying of northern peatlands are offset in part by reduced CH4 emissions, thus slightly reducing the positive carbon climate feedbacks of peatlands under a warmer and drier future climate scenario. [ABSTRACT FROM AUTHOR]

Abstract Northern lakes are important sources of CH4 in the atmosphere under the background of permafrost thaw and winter warming. We synthesize studies on thermokarst lakes, including various carbon sources for CH4 emission and the influence of thermokarst drainage on carbon emission, to show the evasion potential of ancient carbon that stored in the permafrost and CH4 emission dynamics along with thermokarst lake evolution. Besides, we discuss the lake CH4 dynamics in seasonally ice-covered lakes, especially for under-ice CH4 accumulation and emission during spring ice melt and the possible influential factors for CH4 emission in ice-melt period. We summarize the latest findings and point out that further research should be conducted to investigate the possibility of abundant ancient carbon emission from thermokarst lakes under climate warming and quantify the contribution of ice-melt CH4 emission from northern lakes on a large scale.

ABSTRACT Arctic permafrost is thawing due to global warming, with unknown consequences on the microbial inhabitants or associated viruses. DNA viruses have previously been shown to be abundant and active in thawing permafrost, but little is known about RNA viruses in these systems. To address this knowledge gap, we assessed the composition of RNA viruses in thawed permafrost samples that were incubated for 97 days at 4°C to simulate thaw conditions. A diverse RNA viral community was assembled from metatranscriptome data including double-stranded RNA viruses, dominated by Reoviridae and Hypoviridae, and negative and positive single-stranded RNA viruses, with relatively high representations of Rhabdoviridae and Leviviridae, respectively. Sequences corresponding to potential plant and human pathogens were also detected. The detected RNA viruses primarily targeted dominant eukaryotic taxa in the samples (e.g., fungi, Metazoa and Viridiplantae) and the viral community structures were significantly associated with predicted host populations. These results indicate that RNA viruses are linked to eukaryotic host dynamics. Several of the RNA viral sequences contained auxiliary metabolic genes encoding proteins involved in carbon utilization (e.g., polygalacturosase), implying their potential roles in carbon cycling in thawed permafrost. IMPORTANCE Permafrost is thawing at a rapid pace in the Arctic with largely unknown consequences on ecological processes that are fundamental to Arctic ecosystems. This is the first study to determine the composition of RNA viruses in thawed permafrost. Other recent studies have characterized DNA viruses in thawing permafrost, but the majority of DNA viruses are bacteriophages that target bacterial hosts. By contrast RNA viruses primarily target eukaryotic hosts and thus represent potential pathogenic threats to humans, animals, and plants. Here, we find that RNA viruses in permafrost are novel and distinct from those in other habitats studied to date. The COVID-19 pandemic has heightened awareness of the importance of potential environmental reservoirs of emerging RNA viral pathogens. We demonstrate that some potential pathogens were detected after an experimental thawing regime. These results are important for understanding critical viral-host interactions and provide a better understanding of the ecological roles that RNA viruses play as permafrost thaws.

As arctic permafrost continues to thaw, previously inaccessible nitrogen (N) becomes available to N‐limited arctic plants. Increased N availability could enhance plant growth and thereby potentially offset climate‐induced carbon release. Arctic plants can take up newly available permafrost‐N locally upon release. However, in a topographically diverse arctic landscape, permafrost‐N may be transported along hillslopes, away from the point‐of‐release. The extent to which topographical N transport can impact arctic vegetation change depends on whether N is retained locally, captured by downslope recipient plant communities, or transported away.We used stable isotope labelling (15N) to simulate upslope release of ammonium (NH4+) and nitrate (NO3−) from thawing permafrost on an arctic hillslope, western Greenland. We tracked the plant species‐specific uptake of simulated permafrost‐released N from the upslope point‐of‐release to the bottom of the slope through 4 years.We found that arctic tundra plants successfully acquired locally released permafrost‐N, even in sloping terrain, and that N was strongly retained in the plant–soil system through multiple years. At the same time, we also importantly demonstrate that permafrost‐N can be transported and taken up by plants up to 30 m downslope from the point‐of‐release. Especially NO3− was more easily redistributed vertically within the soil column compared to NH4+ and therefore potentially more accessible to plants. Specifically, plant species with fast N uptake capacity and deep‐soil foraging strategies may have competitive advantages for capitalising on deep‐soil released and topographically transported permafrost‐N (here exemplified by Equisetum arvense and Salix glauca). Nevertheless, even mosses gained access to permafrost‐N via vertical and lateral redistribution on the slope. Ultimately, the intricate balance between strong local N retention, downslope transport and plant species‐specific uptake strategies may contribute to shaping arctic vegetation change.Synthesis. Across spatially complex arctic ecosystems, arctic plants can take up permafrost‐released N both at the local point‐of‐release and at a considerable distance downslope. The potential for arctic plants to take advantage of topographically transported permafrost‐N could lead to long‐term and landscape‐scale changes in species composition, plant productivity, and ultimately carbon and climate feedbacks across the Arctic. [ABSTRACT FROM AUTHOR]

Pipeline corridors have been rapidly increasing in length and density because of the ever growing demand for crude oil and natural gas resources in hydrocarbon-rich permafrost regions. Pipeline engineering activities have significant implications for the permafrost environment in cold regions. Along these pipeline corridors, the shrubification in the right-of-way (ROW) has been extensively observed during vegetation recovery. However, the hydrothermal mechanisms of this ROW shrubification have seldom been studied and thus remain poorly understood. This paper reviews more than 112 articles mainly published from 2000 to 2022 and focuses on the hydrothermal mechanisms of shrubification associated with environmental changes induced by the rapidly degrading permafrost from pipeline construction and around the operating pipelines under a warming climate. First, the shrubification from pipeline construction and operation and the ensuing vegetation clearance are featured. Then, key permafrost-related ROW shrubification mechanisms (e.g., from the perspectives of warmer soil, soil moisture, soil type, soil nutrients, topography and landscapes, and snow cover) are discussed. Other key influencing factors on these hydrothermal and other mechanisms are hierarchically documented as well. In the end, future research priorities are identified and proposed. We call for prioritizing more systematic and in-depth investigations and surveys, laboratory testing, long-term field monitoring, and numerical modeling studies of the ROW shrubification along oil and gas pipelines in permafrost regions, such as in boreal and arctic zones, as well as in alpine and high-plateau regions. This review can improve our understanding of shrubification mechanisms under pipeline disturbances and climate changes and help to better manage the ecological environment along pipeline corridors in permafrost regions. [ABSTRACT FROM AUTHOR]

Abstract Alaska’s North Slope is predicted to experience twice the warming expected globally. When summers are longer and winters are shortened, ground surface conditions in the Arctic are expected to change considerably. This is significant for Arctic Alaska, a region that supports surface infrastructure such as energy extraction and transport assets (pipelines), buildings, roadways, and bridges. Climatic change at the ground surface has been shown to impact soil layers beneath through the harmonic fluctuation of the active layer, and warmer air temperature can result in progressive permafrost thaw, leading to a deeper active layer. This study attempts to assess climate change based on the climate model data from the fifth phase of the Coupled Model Intercomparison Project and its impact on a permafrost environment in Northern Alaska. The predicted air temperature data are analyzed to evaluate how the freezing and thawing indices will change due to climate warming. A thermal model was developed that incorporated a ground surface condition defined by either undisturbed intact tundra or a gravel fill surface and applied climate model predicted air temperatures. Results indicate similar fluctuation in active layer thickness and values that fall within the range of minimum and maximum readings for the last quarter-century. It is found that the active layer thickness increases, with the amount depending on climate model predictions and ground surface conditions. These variations in active layer thickness are then analyzed by considering the near-surface frozen soil ice content. Analysis of results indicates that thaw strain is most significant in the near-surface layers, indicating that settlement would be concurrent with annual thaw penetration. Moreover, ice content is a major factor in the settlement prediction. This assessment methodology, after improvement, and the results can help enhance the resilience of the existing and future new infrastructure in a changing Arctic environment.

Permafrost characterizes ground conditions in most of the Arctic and is increasingly thawing. While environmental consequences of permafrost thaw are under intense scrutiny by natural and life sciences, social sciences' studies on local communities' perceptions of change is thus far limited. This hinders the development of targeted adaptation and mitigation measures. We present the results of a survey on communities' perceptions of permafrost thaw, with a focus on subsistence activities, carried out between 2019 and 2020 in Aklavik (Northwest Territories, Canada), Longyearbyen (Svalbard, Norway), and Qeqertarsuaq (Qeqertalik Municipality, Greenland). Results show that the majority of the 237 participants are well aware of the consequences of permafrost thaw on the landscape as well as the connection between increased air temperature and permafrost thaw. The majority perceive permafrost thaw negatively although they do not perceive it as a challenge in all life domains. Permafrost thaw is perceived as a major cause for challenges in subsistence activities, infrastructure, and the physical environment. Different perceptions within the three study communities suggests that perceptions of thaw are not solely determined by physical changes but also influenced by factors related to the societal context, including discourses of climate change, cultural background, and land use. [ABSTRACT FROM AUTHOR]

Climate change will likely increase the total streamflow in most headwaters on the Tibetan Plateau in the next decades, yet the response of runoff components to climate change and permafrost thaw remain largely uncertain. Here, we investigate the changes in runoff components under a changing climate, based on a high‐resolution cryosphere‐hydrology model (Spatial Processes in Hydrology model, SPHY) and multi‐decadal streamflow observations at the upstream (Jimai) and downstream stations (Maqu and Tangnaihai) in the source‐region of the Yellow River (SYR). We find that rainfall flow dominates the runoff regime in SYR (contributions of 48%–56%), followed by snowmelt flow (contributions of 26%/23% at Maqu/Tangnaihai). Baseflow is more important at Jimai (32%) than at the the downstream stations (21%–23%). Glacier meltwater from the Anyê Maqên and Bayankala Mountains contributes negligibly to the downstream total runoff. With increasing temperature and precipitation, the increase in total runoff is smaller in the warm and wet downstream stations than in the cold and dry upstream station. This is because of a higher increase in evapotranspiration and a larger reduction in snowmelt flow in the downstream region in response to a warming climate. With temperature increase, there is less increase in rainfall flow in the downstream region due to increased water loss through evapotranspiration. Meanwhile, the decline in snowmelt flow is larger further downstream, which can negatively impact the spring irrigation for the whole Yellow River basin that supports the livelihoods of 140 million people. Importantly, we find that baseflow plays an increasingly important role in the permafrost‐dominated upstream region with atmospheric warming and permafrost thaw, accompanied by decreased surface flow. These findings improve our current understanding of how different hydrological processes respond to climate change and provide insights for optimizing hydropower and irrigation systems in the entire Yellow River basin under a rapidly changing climate. [ABSTRACT FROM AUTHOR]

Thawing permafrost in northern latitudes has led to deepening active soil layers and fluctuating water tables. This could increase plant access to permafrost‐derived nitrogen (N), phosphorus (P) and other nutrients such as calcium (Ca) and magnesium (Mg), and subsequently increase plant productivity and ecosystem carbon storage and nutrient cycling. We hypothesized that deepening permafrost thaw and water table fluctuations would alter species‐specific foliar N:P ratios. Since there is often more P, Ca and Mg available in the deeper mineral soil layers and more N available in the shallow organic layers, we expected that deeply rooted species would decrease foliar N:P ratios due to root proximity to thawing mineral soil, and plants with shallower rooting systems mostly in the organic layer would increase foliar N:P ratios.We assessed foliar and canopy nutrient responses of seven vascular plant species in moist acidic tussock tundra vegetation in the northern foothills of the Alaska Range to variable soil thaw depths and water table levels induced by either a natural thermokarst gradient or a winter warming snow fence experiment.In both the natural thermokarst gradient and the warming experiment, wet or deeply thawed areas generally led to an increase in foliar nutrient concentrations and greater canopy mass and canopy nutrients. For the majority of species, foliar N:P ratios remained proportional or decreased in deciduous species in wet sites, with the exception of one shallowly rooted species that increased foliar N:P ratio in deeply thawed sites. Overall, plant acquisition of P was more related to water table level than to thaw depth, and water table modulated the canopy biomass response of the species at the warming experiment.Synthesis. Foliar N:P ratios suggest that plant species in this tussock tundra ecosystem are either remaining or becoming more N‐limited as thaw depth deepens and water table level rises, indicating that P is not likely to become the primary limiting nutrient with the progression of permafrost thaw. However, the amount of deeply thawed, wet areas that develop on the landscape as permafrost thaws will be important contributors in the total movement of nutrients above‐ground. [ABSTRACT FROM AUTHOR]

Climate warming in Arctic Canada, e.g., permafrost thaw, comprehensively impacts biota and the environment, which then affects the lives of people. This study aimed to investigate which perceived environmental and adaptation factors relate to self-rated well-being, quality of life, satisfaction with life (sum variable = life balance), self-rated health, and feeling of empowerment to face the changes related to permafrost thaw. The study sample was collected from one community using a questionnaire (n = 53) and analyzed by cross-tabulation. Results indicated that most participants had at least good well-being, quality of life, satisfaction with life, and a medium level of health, and over 40% assessed being empowered to face the changes related to permafrost thaw. Problems and challenges associated with permafrost thaw, e.g., health, traditional lifeways, and infrastructure, were recognized; these had impacts on life balance, feeling of empowerment, and self-rated health. Traditional knowledge regarding adaptation to face changes was seen as important. More adaptation actions from the individual to global level seemed to be needed. This study provides an overview of the situation in one area, but more research, with a larger study sample, should be conducted to achieve a deeper understanding of climate-related impacts on life and holistic well-being. [ABSTRACT FROM AUTHOR]

Climate change in Arctic landscapes may increase freeze–thaw frequency within the active layer as well as newly thawed permafrost. Freeze-thaw is a highly disruptive process that can deform soil pores and alter the architecture of the soil pore network with varied impacts to water transport and retention, redox conditions, and microbial activity. Our objective was to investigate how freeze–thaw cycles impacted the pore network of newly thawed permafrost aggregates to improve understanding of what type of transformations can be expected from warming Arctic landscapes. We measured the impact of freeze–thaw on pore morphology, pore throat diameter distribution, and pore connectivity with X-ray computed tomography (XCT) using six permafrost aggregates with sizes of 2.5 cm3 from a mineral soil horizon (Bw; 28–50 cm depths) in Toolik, Alaska. Freeze-thaw cycles were performed using a laboratory incubation consisting of five freeze–thaw cycles (−10 °C to 20 °C) over five weeks. Our findings indicated decreasing spatial connectivity of the pore network across all aggregates with higher frequencies of singly connected pores following freeze–thaw. Water-filled pores that were connected to the pore network decreased in volume while the overall connected pore volumetric fraction was not affected. Shifts in the pore throat diameter distribution were mostly observed in pore throats ranges of 100 µm or less with no corresponding changes to the pore shape factor of pore throats. Responses of the pore network to freeze–thaw varied by aggregate, suggesting that initial pore morphology may play a role in driving freeze–thaw response. Our research suggests that freeze–thaw alters the microenvironment of permafrost aggregates during the incipient stage of deformation following permafrost thaw, impacting soil properties and function in Arctic landscapes undergoing transition.

With rapid changes in climate and the seasonal amplitude of carbon dioxide (CO2) in the Arctic, it is critical that we detect and quantify the underlying processes controlling the changing amplitude of CO2 to better predict carbon cycle feedbacks in the Arctic climate system. We use satellite and airborne observations of atmospheric CO2 with climatically forced CO2 flux simulations to assess the detectability of Alaskan carbon cycle signals as future warming evolves. We find that current satellite remote sensing technologies can detect changing uptake accurately during the growing season but lack sufficient cold season coverage and near-surface sensitivity to constrain annual carbon balance changes at regional scale. Airborne strategies that target regular vertical profile measurements within continental interiors are more sensitive to regional flux deeper into the cold season but currently lack sufficient spatial coverage throughout the entire cold season. Thus, the current CO2 observing network is unlikely to detect potentially large CO2 sources associated with deep permafrost thaw and cold season respiration expected over the next 50 y. Although continuity of current observations is vital, strategies and technologies focused on cold season measurements (active remote sensing, aircraft, and tall towers) and systematic sampling of vertical profiles across continental interiors over the full annual cycle are required to detect the onset of carbon release from thawing permafrost.