Near-surface Permafrost Research Articles

Rockfall, glacier recession, and permafrost degradation: long-term monitoring of climate change impacts at the Open-Air-Lab Kitzsteinhorn, Hohe Tauern

Abstract. Since 2010, comprehensive geoscientific monitoring has been established in the summit region of the Kitzsteinhorn (“Open-Air-Lab Kitzsteinhorn”), which focuses on the investigation of high-alpine climate change impacts in four monitoring domains: air temperature, glaciation, permafrost, and rock stability. Air and near-surface permafrost temperatures are currently rising with mean rates of almost +0.1 °C yr−1. The thickness of the local cirque glacier is decreasing by more than 1 m yr−1. Rockwall monitoring demonstrates that rockfall activity in freshly deglaciated rockwall sections has increased by 1 order of magnitude. The intensity of the observed processes is most likely unprecedented in recent human history. This emphasizes the importance of long-term monitoring efforts such as those carried out at the Kitzsteinhorn for improved geophysical understanding and for safe and sustainable infrastructure operation in high-alpine environments.

Hysteresis of Northern Hemisphere permafrost to carbon dioxide emissions

Abstract Carbon dioxide removal (CDR) is proposed to limit the level of global warming and minimize the impacts of climate crises. However, how permafrost may respond to negative carbon emissions remains unknown. Here, the response of near-surface permafrost in the Northern Hemisphere is investigated based on idealized carbon dioxide (CO2) ramp-up (284.7–1138.8 ppm) and symmetric ramp-down model experiments. The results demonstrate that the timing of the minimum permafrost area lags the maximum CO2 concentration for decades, which is also observed in soil temperatures at different depths and active layer thicknesses. When the CO2 concentration is reversed to the preindustrial level, the permafrost area decreases by ~12% relative to the initial conditions, together with additional warming in the ground temperature at the top of the permafrost, indicating the hysteresis of permafrost to CO2 removal. The most profound hysteretic responses occur at high latitudes for soil temperatures owing to Arctic amplification, while at the southern margins of the permafrost zones for permafrost and active layer thickness that largely linked to the climate state. Moreover, the sensitivity of permafrost and the associated thermodynamic factors to CO2 change is generally lower during the CO2 ramp-down phase than during the ramp-up phase, likely due to the release of stored heat on land. The results reveal the behaviour of permafrost in response to negative carbon emissions, which is informative for the projections of permafrost towards carbon neutral targets. In addition, the results may provide a reference for permafrost-related tipping points (e.g., releasing long-term stored greenhouse gases and destabilising recalcitrant soil carbon) and risk management in the future.

Can dwarf birch (Betula nana) growth rings be used as indicators of permafrost degradation?

Accelerating Arctic permafrost thaw results in increasing methane emissions affecting regional and global climates, but the rate of permafrost disappearance can be difficult to estimate with remote sensing, field surveys and modelling. Here we investigate if the annual growth rings of the shrub Betula nana (dwarf birch) may be used to detect and monitor near-surface permafrost degradation. Whole B. nana samples were collected at Latnjajávri and Corrvosjávri, northernmost Sweden, and their annual growth rings were analysed regarding their potential as permafrost indicators. Permafrost disappeared in Latnjajávri between 1993 and 2001, whereas Corrvosjávri lost its frozen ground decades earlier. Annual growth rings from more than twenty B. nana shrubs at each site were measured and crossdated by serial sectioning, and then averaged into two separate shrub-ring chronologies. Growth rates were higher at Corrvosjávri than at Latnjajávri. Analysing the 1972–2015 period disclosed a stronger climate-growth relationship at Corrvosjávri, with significant correlations with summer temperatures. In Latnjajávri the association with climate was much weaker before the permafrost disappeared, but afterwards reached similar levels as at Corrvosjávri. Our results suggest that changes in the B. nana growth-climate relationship may be used to indicate permafrost degradation. Moreover, the strong correlation between summer temperature and shrub growth after disappearance of permafrost supports previous research that B. nana ring widths are useful climate proxies.

Post-fire stabilization of thaw-affected permafrost terrain in northern Alaska

In 2007, the Anaktuvuk River fire burned more than 1000 km2 of arctic tundra in northern Alaska, ~ 50% of which occurred in an area with ice-rich syngenetic permafrost (Yedoma). By 2014, widespread degradation of ice wedges was apparent in the Yedoma region. In a 50 km2 area, thaw subsidence was detected across 15% of the land area in repeat airborne LiDAR data acquired in 2009 and 2014. Updating observations with a 2021 airborne LiDAR dataset show that additional thaw subsidence was detected in < 1% of the study area, indicating stabilization of the thaw-affected permafrost terrain. Ground temperature measurements between 2010 and 2015 indicated that the number of near-surface soil thawing-degree-days at the burn site were 3 × greater than at an unburned control site, but by 2022 the number was reduced to 1.3 × greater. Mean annual ground temperature of the near-surface permafrost increased by 0.33 °C/yr in the burn site up to 7-years post-fire, but then cooled by 0.15 °C/yr in the subsequent eight years, while temperatures at the control site remained relatively stable. Permafrost cores collected from ice-wedge troughs (n = 41) and polygon centers (n = 8) revealed the presence of a thaw unconformity, that in most cases was overlain by a recovered permafrost layer that averaged 14.2 cm and 18.3 cm, respectively. Taken together, our observations highlight that the initial degradation of ice-rich permafrost following the Anaktuvuk River tundra fire has been followed by a period of thaw cessation, permafrost aggradation, and terrain stabilization.

Modelling permafrost distribution using the temperature at top of permafrost model in the boreal forest environment of Whatì, NT

Current permafrost models in Canadian boreal forests are generally of low spatial resolution as they cover regional or continental scales. This study aims to understand the viability of creating a temperature at the top of permafrost (TTOP) model on a local scale in the boreal wetland environment of Whatì, Northwest Territories from short-term field-collected temperature data. The model utilizes independent variables of vegetation, topographic position index, and elevation, with the dependent variables being ground surface temperature collected from 60 ground temperature nodes and 1.5 m air temperature collected from 10 temperature stations. In doing this, the study investigates the relationship vegetation and disturbance have on ground temperature and permafrost distribution. The model predicts that 31% of the ground is underlain by permafrost, based on a mean annual temperature at TTOP of &lt;0 °C. This model shows an accuracy of 62.5% when compared to cryotic assessment sites (CAS). Most inaccuracies, showing the limitations of the TTOP model, came from peat plateaus that had been burned in the most recent forest fire in 2014. These resulted in out-of-equilibrium permafrost and climatic conditions that TTOP cannot handle well. Commonly, permafrost mapping places Whatì in the extensive discontinuous zone, estimating that between 50% and 90% of the ground is underlain by permafrost. The study shows that a climatically driven TTOP model calibrated with CAS can be used to illustrate ground temperature heterogeneity from short-term data in boreal forest wetland environments. However, this approach likely underestimates permafrost extent and is perhaps not the best-suited modelling choice for near-surface permafrost, which is currently out of equilibrium with the current climate.

The evolution of Arctic permafrost over the last 3 centuries from ensemble simulations with the CryoGridLite permafrost model

Abstract. Understanding the future evolution of permafrost requires a better understanding of its climatological past. This requires permafrost models to efficiently simulate the thermal dynamics of permafrost over the past centuries to millennia, taking into account highly uncertain soil and snow properties. In this study, we present a computationally efficient numerical permafrost model which satisfactorily reproduces the current ground temperatures and active layer thicknesses of permafrost in the Arctic and their trends over recent centuries. The performed simulations provide insights into the evolution of permafrost since the 18th century and show that permafrost on the North American continent is subject to early degradation, while permafrost on the Eurasian continent is relatively stable over the investigated 300-year period. Permafrost warming since industrialization has occurred primarily in three “hotspot” regions in northeastern Canada, northern Alaska, and, to a lesser extent, western Siberia. We find that the extent of areas with a high probability (p3 m&gt;0.9) of near-surface permafrost (i.e., 3 m of permafrost within the upper 10 m of the subsurface) has declined substantially since the early 19th century, with loss accelerating during the last 50 years. Our simulations further indicate that short-term climate cooling due to large volcanic eruptions in the Northern Hemisphere in some cases favors permafrost aggradation within the uppermost 10 m of the ground, but the effect only lasts for a relatively short period of a few decades. Despite some limitations, e.g., with respect to the representation of vegetation, the presented model shows great potential for further investigation of the climatological past of permafrost, especially in conjunction with paleoclimate modeling.

Long-term responses of permafrost to the dual impacts of climate warming and engineering disturbance along the Qinghai-Tibet Highway

The sensitivity of near-surface permafrost to both climate warming and engineering disturbance is widely acknowledged. However, long-term responses of permafrost to the dual impacts of climate warming and engineering disturbances remain poorly understood. Using a 20-year dataset of ground temperature under roadway and natural ground surface, in this study not only we identify the thermal impacts of the Qinghai-Tibet Highway, in addition to those of climate warming, but also quantify the differences between these two impacts. The results show that variation rate of permafrost table under the highway was approximately 3.3 to 11.1 times greater than that under natural ground surface, along with a significant warming rate of permafrost under the highway. Under the dual thermal impacts of climate warming and engineering disturbances, the duration of ground frozen state at a depth of 0.5 m under roadway is 38.5 ± 6.36% shorter than that under natural ground surface. Meanwhile, rising rate of ground temperature at depth of 0.5 m beneath the asphaltic road surface is 51.7 ± 14.46% faster than that beneath the natural ground surface. This work underscores the importance for correctly understanding the response mechanisms and mitigative measures for hazards resulting from the dual impacts of climate warming and engineering disturbances, particularly by altering the heat absorption effect of asphalt pavement and by utilizing the roadbed cooling approaches.

Electrical Resistivity Tomography Investigation of Permafrost Conditions in a Thermokarst Site in Fairbanks, Alaska

&lt;abstract&gt; &lt;p&gt;The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Ωm and above 700 Ωm, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures.&lt;/p&gt; &lt;/abstract&gt;

The infrastructure cost of permafrost degradation for the Northern Hemisphere

Warming and resulting degradation of near-surface permafrost in cold regions across the globe has and will continue to lead to a series of hazards. These include land subsidence and weakening of the substrate’s bearing capacity, thus threatening infrastructure and the socioeconomics in permafrost regions. These potential hazards shorten the lifespan of infrastructure, increase the cost of infrastructure maintenance and replacement, which is of great importance to a variety of stakeholders. In Northern Hemisphere permafrost regions, more than 34% of the population and 44% of the infrastructure will be at high risk by the end of this century. Due to the degradation of permafrost, infrastructure will require an additional investment of approximately $205–572 billion to maintain the operation of engineering and service infrastructure in 2085, based on projections with a high greenhouse gas emissions scenario.

The hypothesis of the shape of the permafrost in Hornsund, Spitsbergen and the potential impact of its degradation on the Arctic

The areas covered by permafrost in the polar regions are vulnerable to rapid changes in the current climate. The well-studied near-surface active layer and permafrost zone are in contrast to the unknown exact shape of the bottom permafrost boundary. Therefore, the entire shape of permafrost between the upper and lower boundaries is not identified with sufficient accuracy. Since most of the factors affecting deep cryotic structures are subsurface in nature, their evolution in deeper layers is also relatively unclear. Here, we propose a hypothesis based on the results of geophysical studies regarding the shape of the permafrost in the coastal area of Svalbard, Southern Spitsbergen. In the article, we emphasize the importance of recognizing not only the uppermost active layer but also the bottom boundary of permafrost along with its transition zone, due to the underestimated potential role of its continuity in observing climate change. The lower permafrost boundary is estimated to range from 70 m below the surface in areas close to the shore to 180 m inland, while a continuous layer of an entirely frozen matrix can be identified with a thickness between 40 m and 100 m. We also hypothesized the presence of the possible subsea permafrost in the Hornsund. The influence of seawater intrusions, isostatic uplift of deglaciated areas, and surface-related processes that affect permafrost evolution may lead to extensive changes in the hydrology and geology of the polar regions in the future. For all these reasons, monitoring, geophysical imaging and understanding the characteristics and evolution of deep permafrost structures requires global attention and scientific efforts.

Environmental controls on observed spatial variability of soil pore water geochemistry in small headwater catchments underlain with permafrost

Abstract. Soil pore water (SPW) chemistry can vary substantially across multiple scales in Arctic permafrost landscapes. The magnitude of these variations and their relationship to scale are critical considerations for understanding current controls on geochemical cycling and for predicting future changes. These aspects are especially important for Arctic change modeling where accurate representation of sub-grid variability may be necessary to predict watershed-scale behaviors. Our research goal is to characterize intra- and inter-watershed soil water geochemical variations at two contrasting locations in the Seward Peninsula of Alaska, USA. We then attempt to identify the key factors controlling concentrations of important pore water solutes in these systems. The SPW geochemistry of 18 locations spanning two small Arctic catchments was examined for spatial variability and its dominant environmental controls. The primary environmental controls considered were vegetation, soil moisture and/or redox condition, water–soil interactions and hydrologic transport, and mineral solubility. The sampling locations varied in terms of vegetation type and canopy height, presence or absence of near-surface permafrost, soil moisture, and hillslope position. Vegetation was found to have a significant impact on SPW NO3- concentrations, associated with the localized presence of nitrogen-fixing alders and mineralization and nitrification of leaf litter from tall willow shrubs. The elevated NO3- concentrations were, however, frequently equipoised by increased microbial denitrification in regions with sufficient moisture to support it. Vegetation also had an observable impact on soil-moisture-sensitive constituents, but the effect was less significant. The redox conditions in both catchments were generally limited by Fe reduction, seemingly well-buffered by a cache of amorphous Fe hydroxides, with the most reducing conditions found at sampling locations with the highest soil moisture content. Non-redox-sensitive cations were affected by a wide variety of water–soil interactions that affect mineral solubility and transport. Identification of the dominant controls on current SPW hydrogeochemistry allows for qualitative prediction of future geochemical trends in small Arctic catchments that are likely to experience warming and permafrost thaw. As source areas for geochemical fluxes to the broader Arctic hydrologic system, geochemical processes occurring in these environments are particularly important to understand and predict with regards to such environmental changes.

Highly restricted near‐surface permafrost extent during the mid-Pliocene warm period

Accurate understanding of permafrost dynamics is critical for evaluating and mitigating impacts that may arise as permafrost degrades in the future; however, existing projections have large uncertainties. Studies of how permafrost responded historically during Earth's past warm periods are helpful in exploring potential future permafrost behavior and to evaluate the uncertainty of future permafrost change projections. Here, we combine a surface frost index model with outputs from the second phase of the Pliocene Model Intercomparison Project to simulate the near-surface (~3 to 4 m depth) permafrost state in the Northern Hemisphere during the mid-Pliocene warm period (mPWP, ~3.264 to 3.025 Ma). This period shares similarities with the projected future climate. Constrained by proxy-based surface air temperature records, our simulations demonstrate that near-surface permafrost was highly spatially restricted during the mPWP and was 93 ± 3% smaller than the preindustrial extent. Near-surface permafrost was present only in the eastern Siberian uplands, Canadian high Arctic Archipelago, and northernmost Greenland. The simulations are similar to near-surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario and provide a perspective on the potential permafrost behavior that may be expected in a warmer world.

The summer heatwave in 2022 and its role in changing permafrost and periglacial conditions at a historic mountain pass in the Eastern Alps (Hochtor, Hohe Tauern Range, Austria).

Air temperatures in Europe in 2022 had been the highest on record for the meteorological summer season [June, July and August (JJA)], with +1.3°C above the 1991-2020 average. We studied the effects of recent warming on permafrost and periglacial conditions at a historical mountain pass in the Eastern Alps (Hochtor, 2,576 m asl, 47.08°N, 12.84°E). We used ground temperature data (2010-2022), repeated electrical resistivity tomography measurements (2019, 2022) and auxiliary data dating back to Roman times. We quantified permafrost conditions, evaluated frost-related weathering and slope processes and assessed the impact of atmospheric warming on it. Results show that summer ground surface temperatures increased by 2.5°C between 1891-1920 and 1991-2020, whereas frost-related weathering and periglacial processes decreased. The summers of 2003, 2015, 2019 and 2022 were the four warmest ones in 1887-2022. Hochtor changed in 2010-2022 from an active permafrost site to an inactive one with supra-permafrost talik. A general three-layer structure was quantified for all three ERT profiles measured. The middle, 5-10m thick layer is ice-poor permafrost detected in 2019, whose existence, although smaller, was confirmed in 2022. Resistivity decreased at the three profiles by 3.9% to 5.2% per year, suggesting permafrost degradation. We interpret the resistivity changes between the summers of 2019 and 2022 as a long-term signal of permafrost degradation and not as the single effect of the summer heatwave in 2022. As our data show how rapidly permafrost degrades and as we face an even warmer climate for the remaining part of the 21st century, we expect that near-surface permafrost at the Hochtor site will soon be history.

Permafrost thaw induces short-term increase in vegetation productivity in northwestern Canada.

Over the past several decades, various trends in vegetation productivity, from increases to decreases, have been observed throughout Arctic-Boreal ecosystems. While some of this variation can be explained by recent climate warming and increased disturbance, very little is known about the impacts of permafrost thaw on productivity across diverse vegetation communities. Active layer thickness data from 135 permafrost monitoring sites along a 10° latitudinal transect of the Northwest Territories, Canada, paired with a Landsat time series of normalized difference vegetation index from 1984 to 2019, were used to quantify the impacts of changing permafrost conditions on vegetation productivity. We found that active layer thickness contributed to the observed variation in vegetation productivity in recent decades in the northwestern Arctic-Boreal, with the highest rates of greening occurring at sites where the near-surface permafrost recently had thawed. However, the greening associated with permafrost thaw was not sustained after prolonged periods of thaw and appeared to diminish after the thaw front extended outside the plants' rooting zone. Highest rates of greening were found at the mid-transect sites, between 62.4° N and 65.2° N, suggesting that more southernly sites may have already surpassed the period of beneficial permafrost thaw, while more northern sites may have yet to reach a level of thaw that supports enhanced vegetation productivity. These results indicate that the response of vegetation productivity to permafrost thaw is highly dependent on the extent of active layer thickening and that increases in productivity may not continue in the coming decades.

The Permafrost and Organic LayEr module for Forest Models (POLE-FM) 1.0

Abstract. Climate change and increased fire are eroding the resilience of boreal forests. This is problematic because boreal vegetation and the cold soils underneath store approximately 30 % of all terrestrial carbon. Society urgently needs projections of where, when, and why boreal forests are likely to change. Permafrost (i.e., subsurface material that remains frozen for at least 2 consecutive years) and the thick soil-surface organic layers (SOLs) that insulate permafrost are important controls of boreal forest dynamics and carbon cycling. However, both are rarely included in process-based vegetation models used to simulate future ecosystem trajectories. To address this challenge, we developed a computationally efficient permafrost and SOL module named the Permafrost and Organic LayEr module for Forest Models (POLE-FM) that operates at fine spatial (1 ha) and temporal (daily) resolutions. The module mechanistically simulates daily changes in depth to permafrost, annual SOL accumulation, and their complex effects on boreal forest structure and functions. We coupled the module to an established forest landscape model, iLand, and benchmarked the model in interior Alaska at spatial scales of stands (1 ha) to landscapes (61 000 ha) and over temporal scales of days to centuries. The coupled model generated intra- and inter-annual patterns of snow accumulation and active layer depth (portion of soil column that thaws throughout the year) generally consistent with independent observations in 17 instrumented forest stands. The model also represented the distribution of near-surface permafrost presence in a topographically complex landscape. We simulated 39.3 % of forested area in the landscape as underlain by permafrost, compared to the estimated 33.4 % from the benchmarking product. We further determined that the model could accurately simulate moss biomass, SOL accumulation, fire activity, tree species composition, and stand structure at the landscape scale. Modular and flexible representations of key biophysical processes that underpin 21st-century ecological change are an essential next step in vegetation simulation to reduce uncertainty in future projections and to support innovative environmental decision-making. We show that coupling a new permafrost and SOL module to an existing forest landscape model increases the model's utility for projecting forest futures at high latitudes. Process-based models that represent relevant dynamics will catalyze opportunities to address previously intractable questions about boreal forest resilience, biogeochemical cycling, and feedbacks to regional and global climate.

Performance of Climate Projections for Yukon and Adjacent Northwest Territories, 1991 – 2020

Permafrost foundation design recognizes the impact of climate change on soil bearing capacity, as described in Canadian guideline CSA PLUS 4011:19. There is, however, no guidance as to the climate scenarios most prudent to adopt for such design. We have compared climate change scenarios outlined in 2003 for the design of the proposed Mackenzie Gas Project (MGP) with climate data for 1991 – 2020 to determine the projections most representative of what did, in fact, occur. In Canada, the greatest change in climate during the last 50 years has been measured in the western Arctic, where fluctuations in annual air temperatures are regionally consistent. In this region, the rate of change in annual mean air temperature for 1971 – 2020 has ranged from 0.77 °C decade-1 at Inuvik, NT, to 0.30 °C decade-1 at Komakuk Beach, YT, with warming concentrated in winter. No statistically significant trends in total annual precipitation have been observed and these records are poorly correlated within the region. In 2003, 29 climate projections from seven global climate models were examined for the MGP and, in 2005, for research regarding forest fires in Yukon. The observed climate warming in Yukon and adjacent Northwest Territories during 1991 – 2020 was close to the upper projections for mean annual and winter air temperature. For example, at Inuvik the 2.3 °C increase observed in mean annual air temperature between 1961 – 90 and 1991 – 2020, exceeds the median projection for change by 2010 – 39 of +1.6 °C and approaches the upper value of +2.4 °C. No consistency between observed and projected precipitation has been determined. These results indicate that, when required, future projections of temperature in northwest Canada may prudently adopt higher or more extreme scenarios because they have been the most realistic to date. They imply that near-surface permafrost may soon become unsustainable in southern parts of the region and so site investi gations to locate thaw-stable soils will likely be cost effective for new projects.

Climate Indicators of Landslide Risks on Alaska National Park Road Corridors

Landslides along road corridors in Alaska national parks pose threats to public safety, visitor access, subsistence activities, and result in costly remediation of damaged infrastructure. Landslide risk in these areas, which contain near-surface permafrost, is associated with mean annual air temperatures (MAATs) above freezing and heavy precipitation events. Historical (1981–2020) values of MAAT and summer precipitation (JJA PCPT) from the fifth generation European Centre for Medium-Range Weather Forecasts (Reading, UK) atmospheric reanalysis (ERA5) were compared to mid-century (2021–2060) and late-century (2061–2100) downscaled climate model projections across Gates of the Arctic National Park and Preserve (GAAR), Denali National Park and Preserve (DENA), and Wrangell-St. Elias National Park and Preserve (WRST). ERA5 showed that all locations historically had MAAT values below freezing, but all three parks were warming significantly (0.3–0.6 °C per decade). Observed trends of MAAT from 18 stations showed warming trends with 11 of the 18 being significant at the 95% confidence level using the Mann–Kendall non-parametric test. Road corridor values are given for the: (1) proposed Ambler Road through GAAR, (2) Denali Park Road in DENA, and (3) McCarthy Road in WRST. Elevated risk from MAAT was projected in the mid-century period for the Denali Park Road and McCarthy Road and across all three park road corridors in the late-century period; elevated risk from JJA PCPT was projected in all periods for all road corridors.

Impact of wildfire on soil carbon and nitrogen storage and vegetation succession in the Nanweng'he National Natural Wetlands Reserve, Northeast China

In boreal regions, wildfires have a major impact on vegetation and permafrost. The ecosystem-protected Xing’an permafrost is sensitive to warming climate and wildfires, particularly on the southern margin of boreal coniferous forest and patchy permafrost zone. However, it remains unclear how fire disturbances are linked with changes in ecosystem composition and soil nutrients in the permafrost zones of Northeast China. Here, 13 years after the fire in the Yile’huli mountain knots, we investigated the parameters like vegetation cover, ground temperatures, active layer thickness, and soil carbon and nitrogen storage at burned and unburned sites of shrub wetlands. The fire resulted in ground warming of 0.1–5.0 °C at depths of 1.0–20.0 m and active layer deepening of 0.5 m, and gravimetric soil moisture content increasing of 26%-266%. Fire also increased the number of herbs and tall shrubs. After the fire, graminoids and tall shrubs increased significantly, and the species of herbs increased by five species. However, dwarf shrubs like Ledum palustre and Vaccinium uliginosum were missing from the burned site. A massive loss of total organic carbon (TOC) (248.40 t C/hm2) and nitrogen (TN) (11.87 t N/hm2) was observed by comparing their storage at burned and unburned sites. These results highlighted that the post-fire responses of vegetation cover and TOC and TN storage were dependent on the thermal regimes of near-surface permafrost and active layer, recovery of vegetation and organic layer, and soil moisture content. This study can provide an important reference for carbon storage and emission in boreal shrub wetlands under a warming climate and increasing fire disturbances.

Changes in near-surface permafrost temperature and active layer thickness in Northeast China in 1961–2020 based on GIPL model

Characteristics of active layer processes depend on the conditions of the ground surface, coupled water-heat balance, soil hydrology, and soil properties under frozen and thawed states at shallow depths. Mean annual temperature at the bottom of the active layer (MATBAL) and active layer thickness (ALT) are important metrics in studying the features of active layer processes and the thermal stability of permafrost. Affected by the changing climate, permafrost regions in Northeast China have undergone remarkable changes in the past 30 years, many of which are still ongoing. In Northeast China, however, model studies on examining hydrothermal dynamics and on changes in frozen ground have faced serious challenges, including a complex ecological environment and rugged terrains. In this study, the Geophysical Institute Permafrost Lab (GIPL) model was used to map temporal and spatial variations in MATBAL and ALT in Northeast China, where discontinuous, island, and sporadic permafrost coexists with seasonal frost. Using the parameters of ground surface temperature (GST) and soil properties as input, we applied the GIPL model to analyze the distributive characteristics of near-surface permafrost in Northeast China. The results indicate a sharply shrinking permafrost area from 5.49 × 105 to 2.29 × 105 km2 but rapidly rising rates of 0.17–0.83 °C/decade in MATBAL in Northeast China during the period from 1961 to 2020. Under a persistently warming climate, accelerating permafrost degradation will inevitably affect the hydrological environment, boreal ecosystem, soil biology, and engineering infrastructure. This work fills a gap in the distribution of MATBAL and ALT in Northeast China.

Landforms and degradation pattern of the Batagay thaw slump, Northeastern Siberia

Thaw slumps are clear indicators of rapid permafrost degradation. They form preferentially in near-surface ice-rich permafrost of northern high latitudes after initial thermal disturbance by the subsequent interplay of thermal (thawing of frozen deposits and melting of ice) and mechanical (slumping and erosion) processes. The largest known thaw slump on Earth – the Batagay megaslump – has been identified in sloping terrain on the Yana Upland in northern Yakutia. Its initiation began in the 1980s, with a current area of >0.8 km2. It continues to grow and has headwall retreat rates of up to 15 m per year. While various satellite remote sensing studies of the Batagay thaw slump have been undertaken, on-site studies characterizing internal landforms, terrain changes, and geomorphic processes have not yet been conducted. To fill this knowledge gap and to enhance our understanding of the dynamics of very large thaw slumps, our study employs on-site observations and detailed permafrost sampling combined with unoccupied aerial vehicle data from 2019. The latter were used to generate an orthomosaic, a digital surface model, hypsometric slope profiles and a map of relief types in the thaw slump. Within the Batagay thaw slump, the dynamic relationship between headwall morphology and slump floor is largely determined by the cryolithological structure of the permafrost horizons exposed across the headwall rising up to 55 m above the slump floor. Factors include the thickness and overall high volumetric ground-ice content (up to 87 %) of the cryostratigraphic horizons. Furthermore, the diurnal and seasonal insolation exposure of the headwall perimeter superimposes both thermal denudation activity and meltwater transport of eroded material. Thus, recent degradation patterns are linked to permafrost properties. Therefore, the Batagay thaw slump is not only a window into Earth's past as it reveals ancient permafrost, but its modern dynamics highlight that ongoing rapid permafrost thaw under present Arctic warming is directly influenced by its Quaternary geological and permafrost history.