Seasonal variation characteristics and influencing factors of dissolved organic carbon of soil water in permafrost peatlands of the Great Hing'an Mountains in summer and autumn.

Dissolved organic carbon (DOC) plays a crucial role in the assessment of greenhouse gas emission and carbon balance in peatlands. However, limited research has been conducted on the seasonal variations and properties of soil water DOC content at different depths in the permafrost peatlands of the Great Hing'an Mountains. In this study, we analyzed the seasonal patterns of soil water DOC contents (surface, 10 cm, 20 cm, 30 cm, 40 cm, and permafrost layer) the permafrost peatlands of the Great Hing'an Mountains (Tuqiang Forestry Bureau), and investigated the influencing factors, such as electrical conductivity, dissolved oxygen, HCO3- concentration, pH value, oxidation-reduction potential, and CO2 content. The stability of DOC was assessed by using UV-Vis spectrum. There were significant seasonal dynamics of DOC content in soil water, with higher contents in autumn and lower content in summer, ranging from 55.7 to 188.1 mg·L-1. There were significant differences in DOC content among different soil depths, with the highest levels detected in the permafrost layer. The DOC content showed a significantly positive correlation with pH value and electrical conductivity, while showed a significantly negative correlation with redox potential, HCO3- concentration, and dissolved oxygen content. Additionally, there was a significantly positive correlation between DOC and CO2 contents. The dissolved CO2 content in soil water increased with soil depth, with the highest content observed in the permafrost layer. Results of spectral analysis showed higher aromaticity in autumn compared to summer, indicating greater stability of DOC during the autumn season. Our results clarified the seasonal variations of soil water DOC in permafrost peatlands of the Great Hing'an Mountains and could provide important data to understand the carbon cycling in the region.

Changing microbiome community structure and functional potential during permafrost thawing on the Tibetan Plateau.

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.

Responses of soil microbes and enzymes to long-term warming incubation in different depths of permafrost peatland soil.

Soil microbes and enzymes mediate soil carbon-climate feedback, and their responses to increasing temperature partly affect soil carbon stability subjected to the effects of climate change. We performed a 50-month incubation experiment to determine the effect of long-term warming on soil microbes and enzymes involved in carbon cycling along permafrost peatland profile (0-150 cm) and investigated their response to water flooding in the active soil layer. Soil bacteria, fungi, and most enzymes were observed to be sensitive to changes in temperature and water in the permafrost peatland. Bacterial and fungal abundance decreased in the active layer soil but increased in the deepest permafrost layer under warming. The highest decrease in the ratio of soil bacteria to fungi was observed in the deepest permafrost layer under warming. These results indicated that long-term warming promotes recalcitrant carbon loss in permafrost because fungi are more efficient in decomposing high-molecular-weight compounds. Soil microbial catabolic activity measured using Biolog Ecoplates indicated a greater degree of average well color development at 15 °C than at 5 °C. The highest levels of microbial catabolic activity, functional diversity, and carbon substrate utilization were found in the permafrost boundary layer (60-80 cm). Soil polyphenol oxidase that degrades recalcitrant carbon was more sensitive to increases in temperature than ß-glucosidase, N-acetyl-ß-glucosaminidase, and acid phosphatase, which degrade labile carbon. Increasing temperature and water flooding exerted a synergistic effect on the bacterial and fungal abundance and ß-glucosidase, acid phosphatase, and RubisCO activity in the topsoil. Structural equation modeling analysis indicated that soil enzyme activity significantly correlated with ratio of soil bacteria to fungi and microbial catabolic activity. Our results provide valuable insights into the linkage response of soil microorganisms, enzymes to climate change and their feedback to permafrost carbon loss.

Permafrost microbial communities and functional genes are structured by latitudinal and soil geochemical gradients.

Permafrost underlies approximately one quarter of Northern Hemisphere terrestrial surfaces and contains 25-50% of the global soil carbon (C) pool. Permafrost soils and the C stocks within are vulnerable to ongoing and future projected climate warming. The biogeography of microbial communities inhabiting permafrost has not been examined beyond a small number of sites focused on local-scale variation. Permafrost is different from other soils. Perennially frozen conditions in permafrost dictate that microbial communities do not turn over quickly, thus possibly providing strong linkages to past environments. Thus, the factors structuring the composition and function of microbial communities may differ from patterns observed in other terrestrial environments. Here, we analyzed 133 permafrost metagenomes from North America, Europe, and Asia. Permafrost biodiversity and taxonomic distribution varied in relation to pH, latitude and soil depth. The distribution of genes differed by latitude, soil depth, age, and pH. Genes that were the most highly variable across all sites were associated with energy metabolism and C-assimilation. Specifically, methanogenesis, fermentation, nitrate reduction, and replenishment of citric acid cycle intermediates. This suggests that adaptations to energy acquisition and substrate availability are among some of the strongest selective pressures shaping permafrost microbial communities. The spatial variation in metabolic potential has primed communities for specific biogeochemical processes as soils thaw due to climate change, which could cause regional- to global- scale variation in C and nitrogen processing and greenhouse gas emissions.

(Un)frozen foundations: A study of permafrost construction practices in Russia, Alaska, and Canada.

The Arctic is rapidly warming posing a significant threat to underlying permafrost. Permafrost degradation has already resulted in extensive damage to the Arctic's built infrastructure, putting communities and industries at risk. Projected climate warming will further reduce the capacity of permafrost to support infrastructure, thereby requiring a rethinking of construction and development of permafrost regions in the future. This paper focuses on three Arctic regions with a substantial presence of population and infrastructure on permafrost: USA (Alaska), Canada, and Russia. The three regions' permafrost construction practices are examined in order to identify best practices and major gaps. We identify a lack of standardized, codified construction guidelines; an absence of permafrost-geotechnical monitoring in communities; barriers to integrating climate scenarios into future planning; limited data sharing; and low numbers of permafrost professionals as major constraints limiting the region's resilience in the face of climate change. Refining building practices and standards, implementing operational permafrost monitoring systems, developing downscaled climate projections, and integrating local knowledge will minimize the impacts of permafrost degradation under rapidly warming climatic conditions.

Structure, stability, and potential function of groundwater microbial community responses to permafrost degradation on varying permafrost of the Qinghai-Tibet Plateau.

The ongoing permafrost degradation under climate warming has modified aboveground biogeochemical processes mediated by microbes, yet groundwater microbial structure and function as well as their response to permafrost degradation remain poorly understood. We separately collect 20 and 22 sub-permafrost groundwater samples from Qilian Mountain (alpine and seasonal permafrost) and Southern Tibet Valley (plateau isolated permafrost) on the Qinghai-Tibet Plateau (QTP) to investigate the effects of permafrost groundwater characteristics on the diversity, structure, stability, and potential function of bacterial and fungal communities. Regional discrepancy of groundwater microbes between two permafrost regions reveals that permafrost degradation might reshape microbial community structure, increase community stability and potential functions relevant to carbon metabolism. Bacterial community assembly in permafrost groundwater is governed by deterministic processes, whereas fungal communities are mainly controlled by stochastic processes, suggesting that bacterial biomarkers might provide the better 'early warning signals' to permafrost degradation in deeper layers. Our study highlights the importance of groundwater microbes in ecological stability and carbon emission on the QTP.

Laboratory growth capacity of an invasive cyanobacterium (Microcystis aeruginosa) on organic substrates from surface waters of permafrost peatlands.

Within a global warming trend, invasive cyanobacteria, abundant in tropical and temperate regions, can migrate northward and colonize thermokarst lakes in permafrost-affected territories. For a better understanding of the cyanobacterial proliferation mechanism in those lakes, we performed laboratory growth of typical invasive cyanobacteria, Microcystis aeruginosa, onto various organic-rich solutions representative of permafrost peatlands. Aqueous leachates of lichen, moss and peat were the most favorable substrates for massive growth. The growth in the presence of all organic substrates produced an increase in solution pH by two units and a sizable (30-50%) decrease in the concentration of dissolved organic carbon. The observed increase in the dissolved organic carbon aromaticity degree likely reflected preferential cyanobacterial uptake of aliphatic, optically transparent organic substances. Cyanobacterial growth over a bloom period can create a carbon sink (uptake of 2.5 and 8.3 g C-CO2 m-2 d-1) that can offset the net heterotrophic status of thermokarst lakes in permafrost peatlands, thus switching the lake status from a C source to a C sink. Therefore, predictions of future carbon exchanges with the atmosphere in surface waters of permafrost peatlands require explicit accounting for the possibility of invasive cyanobacterial growth.

Soil contamination by diesel fuel destabilizes the soil microbial pools: Insights from permafrost soil incubations.

Arctic contamination by diesel fuel (DF) is of great concern because of the uncertain feedback of permafrost carbon (C) and soil microbiota to DF in the context of climate change in high latitudes. We conducted a laboratory incubation experiment with a gradient of DF addition ratios to examine the responses of the soil microbiota of the typical permafrost soils in the tundra ecosystems of the Norilsk region (Siberia). The study revealed initial heterogeneity in the microbial activity of the studied soils (Histic Gleyic Cryosols (CR-hi,gl), Turbic Cryosols (CR-tu), Turbic Spodic Folic Cryosols (CR-tu,sd,fo), Gleyic Fluvisols (FL-gl)). We applied the two-pool model for evaluation of the effect of DF on the proportions of C pools and revealed significant differences between soil types in the fast and slow C pools in response to DF addition. The results showed that DF addition treatments had varying effects on the fast and slow C pools, microbial activity, and microbial community structure in the studied soils. For minor exceptions, DF dramatically accelerated C loss from the slow C pool in all soil types. We assume that differences in C pool and microbiota responses to DF addition were caused by soil texture and changes in microbial community structure. We isolated Serratia proteamaculans, S. liquefaciens, S. plymuthica, Rhodococcus erythropolis, Pseudomonas antarctica, P. libanensis, P. brassicacearum, and P. chlororaphis from the DF-polluted soils. These species are recommended for bioremediation to mitigate the DF contamination of permafrost soils, especially regarding climate change and the sustainable well-being of Arctic ecosystems.

RNA Viruses Linked to Eukaryotic Hosts in Thawed Permafrost.

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.

A globally relevant stock of soil nitrogen in the Yedoma permafrost domain.

Nitrogen regulates multiple aspects of the permafrost climate feedback, including plant growth, organic matter decomposition, and the production of the potent greenhouse gas nitrous oxide. Despite its importance, current estimates of permafrost nitrogen are highly uncertain. Here, we compiled a dataset of >2000 samples to quantify nitrogen stocks in the Yedoma domain, a region with organic-rich permafrost that contains ~25% of all permafrost carbon. We estimate that the Yedoma domain contains 41.2 gigatons of nitrogen down to ~20 metre for the deepest unit, which increases the previous estimate for the entire permafrost zone by ~46%. Approximately 90% of this nitrogen (37 gigatons) is stored in permafrost and therefore currently immobile and frozen. Here, we show that of this amount, ¾ is stored >3 metre depth, but if partially mobilised by thaw, this large nitrogen pool could have continental-scale consequences for soil and aquatic biogeochemistry and global-scale consequences for the permafrost feedback.

Bacterial functional redundancy and carbon metabolism potentials in soil, sediment, and water of thermokarst landscapes across the Qinghai-Tibet Plateau: Implications for the fate of permafrost carbon.

Permafrost thaw create widespread thermokarst landscapes. As a result, distinct habitats are provided to harbor different bacterial communities in degraded permafrost soil (PBCs), thermokarst lake sediment (SBCs), and lake water (WBCs), driving carbon metabolism differentially. In this study, we investigated functional diversity and redundancy, and carbon metabolism potentials of PBCs, SBCs, and WBCs in thermokarst landscapes across the Qinghai-Tibet Plateau. The results showed that PBCs and SBCs had higher taxonomic and functional alpha diversity than WBCs, while WBCs had lower functional redundancy. WBCs had the highest beta diversity followed by SBCs and PBCs, suggesting strong determination of taxonomic variations on functional differences. Community assembly processes also had significant influences on beta diversity, especially for SBCs. Metabolism pathways of carbohydrate metabolism, methane metabolism, and carbon fixation were enriched differentially in PBCs, SBCs, and WBCs, suggesting different C fate in distinct habitats. Carbohydrate metabolism data suggested that PBCs might have stronger potentials to mineralize a greater diversity of organic carbon substrate than SBCs and WBCs, promoting degradation of organic carbon stocks in degraded permafrost soils. Methane metabolism data showed that SBCs had a stronger methanogenesis potential followed by PBCs and WBCs, while PBCs had a stronger methane oxidation potential. High abundance of genes involving in formaldehyde assimilation might suggested that a large proportion of produced methane might be assimilated by methanotrophs in the thermokarst landscapes. Both aerobic and anaerobic carbon fixation pathways were enriched in PBCs. The results added our understanding of functional properties and biogeochemical carbon cycles in thermokarst landscapes, improving our abilities in accurate modeling of carbon dynamics and the ultimate fate of permafrost carbon in a warming world.

Approaches for the complex assessment of polychemical pollution of permafrost-affected soils and the upper layer of permafrost.

The analysis of about 200 samples taken from 42 permafrost-affected soil profiles was carried out on four key sites in different regions of cryolithozone (West Siberia, Central, North, and North-East Yakutia) characterized by different active layer depths and soil lithology. The aim of the study was to determine the influence of different processes of cryogenic mass-exchange on the redistribution and accumulation of major pollutants such as petroleum products, acid-soluble forms of trace elements, polycyclic hydrocarbons, and technogenic radionuclides transferred via atmospheric transport or after the local anthropogenic impact in different soil horizons of Cryosols and in the upper layers of permafrost. Samples were analyzed using modern precise techniques (direct γ-spectrometric measurements with Ge(Li) and NaI(Tl) detectors; fluorometric method; reversed-phase high-performance liquid chromatography; spectrofluorimetric detection; atomic absorption spectrometry with flame atomization). The study has shown that processes (cryoturbations, frost heaving, gelifluction along with fluvial processes) that strongly affect Cryosols' profile structure can also lead to the active migration and accumulation of local and global pollutants in the middle and lowermost suprapermafrost soil horizons. The accumulation of some pollutants in suprapermafrost horizons of cryogenic soils and in the upper layers of permafrost (in particular, petroleum products and mobile forms of trace elements) can be associated with a combination of factors, such as the relatively light particle size distribution, relatively weak manifestation of cryoturbation processes, and low thickness of the active layer (about 40-60 cm). The integral calculation of the geoaccumulation index values has shown that all of the groups of human-affected soil horizons are moderately to extremely polluted by petroleum hydrocarbons (and at a relatively lower level by trace elements) and the maximum pollution stands for the suprapermafrost horizons as well as in cryoturbated or buried fragments of organogenic matter in some cases. The maxima of the heavy PAH content in permafrost-affected soils can be confined to horizons enriched with anthropogenic inclusions and artifacts (for example, construction slag, coal) and to individual horizons of soils buried as a result of both cryogenic and alluvial processes. The specific activity of the technogenic radionuclide cesium in cryogenic soils revealed its association mainly with the surface organogenic and organomineral horizons of the studied profiles and rarely observed in the cryoturbated fragments of these horizons in the middle and suprapermafrost layers of soil profiles. The necessity of the complex analytical assessment of the permafrost-affected soils has been revealed especially in case of studying of the ecological state of the anthropogenically affected Cryosols.

Carbon and nitrogen cycling dynamics following permafrost thaw in the Northwest Territories, Canada.

Rapid climate warming across northern high latitudes is leading to permafrost thaw and ecosystem carbon release while simultaneously impacting other biogeochemical cycles including nitrogen. We used a two-year laboratory incubation study to quantify concomitant changes in carbon and nitrogen pool quantity and quality as drivers of potential CO2 production in thawed permafrost soils from eight soil cores collected across the southern Northwest Territories (NWT), Canada. These data were contextualized via in situ annual thaw depth measurements from 2015 to 2019 at 40 study sites that varied in burn history. We found with increasing time since experimental thaw the dissolved carbon and nitrogen pool quality significantly declined, indicating sustained microbial processing and selective immobilization across both pools. Piecewise structural equation modeling revealed CO2 trends were predominantly predicted by initial soil carbon content with minimal influence of dissolved phase carbon. Using these results, we provide a first-order estimate of potential near-surface permafrost soil losses of up to 80 g C m-2 over one year in southern NWT, exceeding regional historic mean primary productivity rates in some areas. Taken together, this research provides mechanistic knowledge needed to further constrain the permafrost­carbon feedback and parameterize Earth system models, while building on empirical evidence that permafrost soils are at high risk of becoming weaker carbon sinks or even significant carbon sources under a changing climate.

Microbiome assembly in thawing permafrost and its feedbacks to climate.

The physical and chemical changes that accompany permafrost thaw directly influence the microbial communities that mediate the decomposition of formerly frozen organic matter, leading to uncertainty in permafrost-climate feedbacks. Although changes to microbial metabolism and community structure are documented following thaw, the generality of post-thaw assembly patterns across permafrost soils of the world remains uncertain, limiting our ability to predict biogeochemistry and microbial community responses to climate change. Based on our review of the Arctic microbiome, permafrost microbiology, and community ecology, we propose that Assembly Theory provides a framework to better understand thaw-mediated microbiome changes and the implications for community function and climate feedbacks. This framework posits that the prevalence of deterministic or stochastic processes indicates whether the community is well-suited to thrive in changing environmental conditions. We predict that on a short timescale and following high-disturbance thaw (e.g., thermokarst), stochasticity dominates post-thaw microbiome assembly, suggesting that functional predictions will be aided by detailed information about the microbiome. At a longer timescale and lower-intensity disturbance (e.g., active layer deepening), deterministic processes likely dominate, making environmental parameters sufficient for predicting function. We propose that the contribution of stochastic and deterministic processes to post-thaw microbiome assembly depends on the characteristics of the thaw disturbance, as well as characteristics of the microbial community, such as the ecological and phylogenetic breadth of functional guilds, their functional redundancy, and biotic interactions. These propagate across space and time, potentially providing a means for predicting the microbial forcing of greenhouse gas feedbacks to global climate change.

Reduced methane emissions in former permafrost soils driven by vegetation and microbial changes following drainage.

In Arctic regions, thawing permafrost soils are projected to release 50 to 250 Gt of carbon by 2100. This data is mostly derived from carbon-rich wetlands, although 71% of this carbon pool is stored in faster-thawing mineral soils, where ecosystems close to the outer boundaries of permafrost regions are especially vulnerable. Although extensive data exists from currently thawing sites and short-term thawing experiments, investigations of the long-term changes following final thaw and co-occurring drainage are scarce. Here we show ecosystem changes at two comparable tussock tundra sites with distinct permafrost thaw histories, representing 15 and 25 years of natural drainage, that resulted in a 10-fold decrease in CH4 emissions (3.2 ± 2.2 vs. 0.3 ± 0.4 mg C-CH4  m-2  day-1 ), while CO2 emissions were comparable. These data extend the time perspective from earlier studies based on short-term experimental drainage. The overall microbial community structures did not differ significantly between sites, although the drier top soils at the most advanced site led to a loss of methanogens and their syntrophic partners in surface layers while the abundance of methanotrophs remained unchanged. The resulting deeper aeration zones likely increased CH4 oxidation due to the longer residence time of CH4 in the oxidation zone, while the observed loss of aerenchyma plants reduced CH4 diffusion from deeper soil layers directly to the atmosphere. Our findings highlight the importance of including hydrological, vegetation and microbial specific responses when studying long-term effects of climate change on CH4 emissions and underscores the need for data from different soil types and thaw histories.

Warming promotes soil CO2 and CH4 emissions but decreasing moisture inhibits CH4 emissions in the permafrost peatland of the Great Xing'an Mountains.

Permafrost peatlands, as large soil carbon pools, are sensitive to global warming. However, the effects of temperature, moisture, and their interactions on carbon emissions in the permafrost peatlands remain unclear, when considering the availability of soil matrixes. The permafrost peatland (0-50 cm soil) in the Great Xing'an Mountains was selected to explore the deficiency. The cumulative carbon dioxide (CO2) and methane (CH4) emissions from soil were measured under different temperatures (5 °C, 10 °C, and 15 °C) and moisture content (130%, 100%, and 70%) treatments by the indoor incubation. The results showed that the soil carbon and nitrogen matrix determined soil carbon emissions. Warming affected the availability of soil carbon and nitrogen substrates, thus stimulating microbial activity and increasing soil carbon emissions. With soil temperature increasing by 10 °C, soil CO2 and CH4 emission rates increased by 5.1-9.4 and 3.8-6.4 times respectively. Warming promoted soil carbon emissions, and the decrease of moisture content promoted CO2 emissions but inhibited CH4 emissions in the permafrost peatland. Soil moisture and the carbon and nitrogen matrix determined the intensity of CO2 and CH4 emissions. The results were important to assess soil carbon emissions from permafrost peatlands under the impact of future climate warming and to formulate carbon emission reduction policies.

Organic carbon, and major and trace elements reside in labile low-molecular form in the ground ice of permafrost peatlands: a case study of colloids in peat ice of Western Siberia.

The fate of organic carbon (OC), nutrients and metals accumulated in thawing permafrost ice is at the forefront of environmental studies in the Arctic. In contrast to a fairly good understanding of the chemical nature of dissolved OC (DOC) and metals in surface Arctic waters, the speciation and colloidal status of solutes accommodated in the dispersed ground ice remain virtually unknown. Here we used a size fractionation procedure (centrifugal ultrafiltration) to quantify the proportion of colloidal (3 kDa to 0.45 µm) and conventionally dissolved low molecular weight (LMW<3 kDa) fractions of DOC, and major and trace elements in the porewater and ice of 5 peat cores sampled along a 400 km permafrost and climate gradient in the largest peatland in the world, the Western Siberian Lowland (WSL). We discovered that the strong (a factor of 2 to 10) increase in the total dissolved (<0.45 µm) concentration of DOC and most major and trace elements in the peat ice relative to the peat porewater from the thawed layer was essentially linked to an increase in the LMW<3 kDa fraction. This increase in the potentially bioavailable fraction in the peat ice relative to the porewater was especially pronounced for DOC, P and many trace elements including metal micronutrients, and was observed throughout all permafrost zones. This contrasted with element distribution in the upper (thaw) layer, where the majority of these elements were present in the colloidal pool. Following previous experiments on permafrost peatland surface waters, we hypothesized that the freeze-thaw cycles of peat porewater were responsible for generation of the LMW fraction in the bottom part of the peat core. Results of this study demonstrate that carbon, and macro- and micro-nutrients as well as trace metals in ground ice of permafrost peatlands are essentially present in a low molecular weight (<3 kDa) and potentially bioavailable form that can strongly impact the riverine export fluxes of solutes during permafrost thaw.

Methane release from carbonate rock formations in the Siberian permafrost area during and after the 2020 heat wave.

Anthropogenic global warming may be accelerated by a positive feedback from the mobilization of methane from thawing Arctic permafrost. There are large uncertainties about the size of carbon stocks and the magnitude of possible methane emissions. Methane cannot only be produced from the microbial decay of organic matter within the thawing permafrost soils (microbial methane) but can also come from natural gas (thermogenic methane) trapped under or within the permafrost layer and released when it thaws. In the Taymyr Peninsula and surroundings in North Siberia, the area of the worldwide largest positive surface temperature anomaly for 2020, atmospheric methane concentrations have increased considerably during and after the 2020 heat wave. Two elongated areas of increased atmospheric methane concentration that appeared during summer coincide with two stripes of Paleozoic carbonates exposed at the southern and northern borders of the Yenisey-Khatanga Basin, a hydrocarbon-bearing sedimentary basin between the Siberian Craton to the south and the Taymyr Fold Belt to the north. Over the carbonates, soils are thin to nonexistent and wetlands are scarce. The maxima are thus unlikely to be caused by microbial methane from soils or wetlands. We suggest that gas hydrates in fractures and pockets of the carbonate rocks in the permafrost zone became unstable due to warming from the surface. This process may add unknown quantities of methane to the atmosphere in the near future.