The degradation of permafrost due to global warming has pronounced adverse effects, including damage to the infrastructure and climate feedback mechanisms through the release of CO₂. Numerical simulations are often used to predict the speed at which frozen ground is thawing. One essential parameter for these simulations is the ice content, due to its increased heat conductivity and nonlinear behavior during phase changes. Despite its importance, ice content is normally only recorded sporadically as it is difficult to collect measurements at high spatial resolution.

Geophysical methods, which investigate the physical properties of the subsurface, have the potential to estimate the spatial distribution of ice content. Geoelectric measurements are sensitive to the existence of ice since the electrical resistivity of ice is orders of magnitudes greater than that of unfrozen water. However, a quantitative estimate of ice content from resistivity alone is difficult because large resistivities may also be caused by low porosities. Therefore, DC resistivity is sometimes combined with seismic methods to reduce ambiguity.

The high-frequency induced polarization (HFIP) method is capable of measuring ice content as a stand-alone technique. HFIP measures the complex electrical resistivity over a broad frequency range, typically up to 200 kHz. In this frequency range the data is sensitive to an additional property, that is, the dielectric permittivity which represents the material’s capability to be polarized by an electric field. The permittivity of ice exhibits a unique behavior in this frequency range, and therefore HFIP may be used to estimate ice content at the field scale. In order to convert this concept into to a practical method, several challenges must be considered. These include the removal of undesired electromagnetic coupling, efficient data acquisition, the inversion of the raw data to obtain useful images of the subsurface, and the conversion of the frequency dependent resistivity into ice content.

Here, we discuss the progress that has been made in recent years to overcome some of these challenges. Data acquisition relies on the Chameleon II equipment that was designed specifically for HFIP measurements. The Chameleon II is one of the few measuring devices that can perform HFIP measurements on field scale and is able to minimize the undesired coupling between electrical components. Subsurface images are obtained through a 2-D inversion of all frequencies separately, followed by the calculation of ice content using a 2-component model where the electrical properties of the ice fraction and the non-ice fraction are considered. We demonstrate the feasibility of the method using recent case histories from alpine and subarctic permafrost areas. We also show by comparison with independent estimates obtained from drill cores that the obtained estimates are sufficiently accurate. We suggest that this method is ready for practical application and may contribute to the understanding of permafrost degradation processes and to the prediction of the future development of permafrost regions under global warming conditions.

How to cite: Hördt, A., Sugand, M., and Schulz, R.: Ice content estimation in the frozen subsurface with an innovative geophysical method: high-frequency induced polarization, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8707, https://doi.org/10.5194/egusphere-egu24-8707, 2024.

This study investigates the changes in shallow cryo-hydrogeological layers over time using Ground Penetrating Radar (GPR) in the unique Arctic environment of the Fuglebekken catchment on Spitsbergen Island. Accurate identification of permafrost changes is essential for understanding geotechnical and environmental processes, making precise monitoring imperative. GPR has proven to be a valuable non-destructive method, providing high-resolution spatially distributed data in permafrost regions and overcoming environmental limitations inherent in Arctic areas.

Utilizing a 250 MHz shielded antenna, GPR measurements facilitated the identification of the groundwater layer and changes in the top border of permafrost at different seasons in the Fuglebekken catchment. A distinctive aspect of this research involved the repetition of GPR profiles at the same location during three different seasons, enabling the observation of temporal variations in subsurface conditions across different seasons. These profiles were complemented by strategically placed boreholes and piezometers recording ground temperature at various depths and groundwater levels, providing key data for the validation and correlation of GPR results. Additionally, drone-based digital elevation models (DEM) were employed during GPR data processing to enhance the accuracy of results.

In the majority of recorded profiles, GPR measurements captured well-defined reflections of subsurface features. The emphasis is on revealing changes over time in the study area by distinguishing geological structures from the groundwater and upper permafrost boundaries. The study convincingly demonstrated the efficacy of GPR in capturing underground time-lapse changes throughout the studied area. The comprehensive insights gained through GPR offered distinct advantages over traditional methods reliant on limited borehole data, especially in terms of demonstrating spatial changes. Integration of GPR data with ground temperature measurements from boreholes and the use of Drone-based DEM during data processing provided a holistic perspective on the evolving nature of permafrost borders, significantly enhancing the accuracy and reliability of the findings.

Comprehending spatial and temporal variations in permafrost borders is critical for predicting the impacts of climate change and guiding geotechnical and environmental management strategies. This research serves as a valuable reference for future studies aiming to explore permafrost conditions in polar regions, offering a comprehensive framework for more effective monitoring and management practices.

How to cite: Izadi Yazdanabadi, M., Marciniak, A., Oryński, S., Wawrzyniak, T., and Osuch, M.: Time-lapse GPR Measurements for Observing Shallow Cryo-Hydrogeological Borders in Spitsbergen's Fuglebekken Catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10315, https://doi.org/10.5194/egusphere-egu24-10315, 2024.

The permafrost-covered areas in polar regions face rapid changes in the current climate. While the active layer and permafrost zone near the surface are well-studied, the precise boundaries of the bottom permafrost remain unclear. Consequently, there is insufficient accuracy in understanding the overall shape of permafrost between the upper and lower boundaries. The evolution of deep cryotic structures, influenced by subsurface factors, is also relatively unknown.

In this study, based on the results of seismic reflection imaging we propose a hypothesis regarding the permafrost shape in the coastal area of Svalbard, Southern Spitsbergen. Additional Ground penetrating radar survey using a low-frequency antenna, as well as results of previous researches based on multiple geophysical methods, allowed for correlation of the obtained seismic results with surface observations. The entire methods were complemented by synthetic modeling, in order to better understand the obtained data. The work emphasizes the importance of recognizing not only the upper active layer but also the bottom permafrost boundary and its transition zone due to the underestimated potential role in observing climatic changes. The estimated bottom permafrost border ranges from 70 m below the surface near the shore to 180 m deep further inland, with a continuous frozen matrix layer identified between 40 m and 100 m depth. We also present a hypothesis about the possible presence of subsea permafrost in the Hornsund.

Factors such as seawater intrusions, isostatic uplift of deglaciated areas, and surface-related processes influencing permafrost evolution may lead to extensive changes in the hydrology and geology of polar regions in the future. Therefore, global attention and scientific efforts are essential for monitoring, geophysical imaging, and understanding the characteristics and evolution of deep permafrost structures. The research presented here forms the basis for a full understanding of permafrost evolution and degradation, and should be repeated across the globe to monitor climate change on a worldwide scale.

How to cite: Marciniak, A., Majdański, M., Dobiński, W., and Cader, J.: The hypothesis of the bottom of the permafrost in Spitsbergen and its overall "shape" - a case study from Hornsund, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7507, https://doi.org/10.5194/egusphere-egu24-7507, 2024.

The Hudson Bay Railway (HBR) serves as the singular land pathway connecting the Pas to Churchill, Manitoba, Canada. Hence, it is an essential means of transportation for northern communities, enabling the transport of both goods and individuals. However, it has faced many operational challenges because of its remote geographical location and the permafrost conditions it passes over. Over its 1000-kilometre length, the permafrost conditions transition. The railway starts in the isolated permafrost zone in its most southern portions before passing over discontinuous permafrost and then reaching continuous permafrost in its northern section. One of the unique operational challenges present at bridge crossings is the phenomena of “frost jacking”.

Frost jacking refers to the upward displacement of pile bridge foundations caused by forces generated from frost heave in the surrounding ground. If the driving force from frost heave exceeds the frictional resisting forces anchoring a pile into the ground, uplift occurs. When designing pile foundations in cold regions, the potential effects of frost jacking must be considered, as any significant differential heave between piers or the abutments can lead to track geometry issues that affect operations and, in extreme cases, require bridge maintenance. However, research on frost jacking experienced by operational infrastructure has been very limited, which hinders the ability to account for its impacts.

The Horn Creek Crossing on the Hudson Bay Railway is a 30-metre-long, steel ballast deck bridge supported by H-piles. Over a 10-year period, the foundations of the bridge underwent hundreds of millimetres of differential heave before repairs were completed to level the structure in July 2022. Because of the bridge’s remote location, there is limited information on the rate and timing of when frost jacking occurred. Therefore, in 2022, a multi-sensor monitoring program was designed and subsequently installed on the bridge with the purpose of collecting data to explore the mechanism of frost jacking at this site.

Preliminary results from the first monitored winter season resulted in an average upward movement of 33 mm of the spans surrounding the northern pier. This upward movement occurred throughout the winter and ended when daily average temperatures became above 0°C. Afterwards, limited recovery was present in the spring when temperatures rose and was measured to be 11 mm, less than the upward movement measured. The monitoring process is still ongoing, with the aim of identifying longer-term trends and analyzing the outcomes of the repair work. Furthermore, using this site as the location of known differential heave at a railway bridge, methods are being developed to explore whether a parallel data source (track geometry data) can capture patterns and rates of seasonal differential heave at this and other bridges along the HBR.

How to cite: Arpin, N., Take, A., and Beddoe, R.: Railways on Permafrost: Unique Challenges Observed at Bridge Crossings along the Hudson Bay Railway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13170, https://doi.org/10.5194/egusphere-egu24-13170, 2024.

Permafrost thawing in the Alps and elsewhere is leading to infrastructure failure. Implementation of protective measures is therefore necessary to avoid incidents and damage to both infrastructure and the environment. Existing methods for thermal stabilization of permafrost are not directly applicable to the particular conditions of the Alps. For instance, traditional passive thermal stabilization techniques do not provide rapid and substantial soil stabilization. Meanwhile, active methods present financial constraints and have not yet achieved complete efficiency. Here we present a novel solar-powered thermal stabilization system to effectively protect Alpine permafrost and the most vulnerable infrastructure built on it from the impacts of global warming. To understand how these thermal stabilization methods affect the permafrost, numerical simulations using the SNOWPACK model are performed for the Schilthorn Alpine permafrost site (Switzerland, 2900 m a.s.l.). First, the natural permafrost conditions in the soil are simulated as reference state. Then, thermal stabilization components are included and their effect is quantified and evaluated.

To demonstrate the working principle of the thermal stabilization system and to gauge its performance and requirements, a laboratory-scale prototype demonstrator of the system was built and experimental data of the prototype are compared to numerical simulations of a digital twin. The setup includes the components of the thermal stabilization system, which are a cooling pipe for generating a cold barrier layer, as well as temperature, soil moisture, and heat flux sensors for measuring the conditions and processes occurring in the permafrost sample. This data is used to assess the performance and efficiency of the thermal stabilization system. Measurement results indicate that a frozen barrier layer at the level of the pipes can be created and maintained, avoiding heat penetration deeper into the soil and keeping the permafrost sample frozen during the time of the experiment.

Findings from the prototype experiment combined with numerical modeling and optimized engineering will enable advanced engineering design and physical process understanding of effective thermal stabilization systems even considering further impact of climate change.

How to cite: Sharaborova, E., Huwald, H., and Lehning, M.: Developing, Testing, and Modeling of an Innovative Thermal Stabilization Method for Alpine Permafrost Protection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13291, https://doi.org/10.5194/egusphere-egu24-13291, 2024.

The Alpine region undergoes a faster and more pronounced climate change than surrounding lowlands and, therefore, is a time machine showing the things to come in a changing climate and environment. Under the influence of a robust warming trend, witnessing an ascent of >1°C since the 1980s significant effects are visible and measurable in atmosphere, biosphere, hydrosphere, and most apparently the cryosphere.

The Virtual Alpine Observatory is an assemblage comprising European Alpine Observatories, high alpine research facilities, data archives, and supercomputing centers, seamlessly interwoven through shared infrastructure and collaborative research pursuits. It is the answer to how the complex Alpine environmental system can be addressed by an interdisciplinary, cross-border collaborating research paradigm. At its core, the primary objective is to orchestrate collective endeavors aimed at observing, comprehending, and prognosticating the ramifications of climate change on the Alpine expanse. This extends to the multifaceted facets of the environment in multiple aspects.

This alliance of researchers and data-gathering institutions spanning the Alpine landscape and analogous mountainous terrains in Europe propels the exploration of data patterns transcending national boundaries. In doing so, it creates a reservoir of data, knowledge and scientific approaches that surpasses the cumulative understanding derived from its individual constituents.

In the upcoming discourse, we illuminate the network's future goals, composition, unveil forthcoming research initiatives, expound upon data availabilities, and deliberate on the trajectories that lie ahead for collaborative efforts.

The VAO network is substantially funded by the Bavarian State Ministry of the Environment and Consumer Protection.

How to cite: Krautblatter, M., Stammberger, V., Einhellinger, B., Theiler, H., Zeitler, R., Zebisch, M., Ludewig, E., Marton, P., Cotte, N., Močnik, G., Leuenberger, M., Decurtins, S., and Kraushaar, S.: The Virtual Alpine Observatory (VAO) acting to better observe, understand, forecast and react to climate change in a combined Network of European High-Altitude Research Stations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22269, https://doi.org/10.5194/egusphere-egu24-22269, 2024.

Thermokarst lakes are among the most common and dynamic landscape features in ice-rich permafrost regions. They form due to melting of ground ice and subsequent ground subsidence. Their presence and dynamic behavior do not only influence the carbon exchange with the atmosphere by accelerating permafrost thaw and facilitating the production of methane, but also have an impact on soil hydrology as well as biophysical fluxes between atmosphere and land surface, such as energy and water transfer. These feedbacks have implications for both the regional and global climate and are therefore highly relevant when investigating the climate response to changes in permafrost systems under different future carbon emission and warming scenarios. Despite their significant role in the climate system, thermokarst lakes are only rudimentarily or not at all represented in Earth system models. Because the involved hydrological processes are complex and depend on small-scale sub-surface heterogeneities that are difficult to measure, we treat them as probabilistic and use a stochastic approach to create a model of thermokarst lake dynamics (formation, expansion and drainage). More specifically, we utilize common stochastic approaches, such as the Poisson process and Brownian motion, as tools to simulate changes in lake density, size distributions and fractions of water and drained area. Recent advancements in remote sensing offer an opportunity to use high-resolution satellite data products for model calibration and the parameterization of inherent and/or climate-induced thermokarst lake dynamics. We expect our approach and the results of our simulations to contribute to a more accurate representation of permafrost dynamics in Earth system models.

How to cite: Reinken, C., Brovkin, V., de Vrese, P., Nitze, I., and Bergstedt, H.: Stochastic modelling of thermokarst lake distributions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8919, https://doi.org/10.5194/egusphere-egu24-8919, 2024.

The impact of climate warming on permafrost and the potential of climate feedback resulting from permafrost thawing have recently received remarkable attention. Climate warming promotes an increase in permafrost temperature and active layer thickness, which, in turn, affect the stability of northern ecosystems, threaten infrastructure, and cause the release of carbon dioxide and methane into the atmosphere. The timing and the rate of permafrost degradation are two of the major factors in determining the anticipated negative impacts of climate warming on the Arctic ecosystems and infrastructure. The results of permafrost and active layer temperature observations (from the ground surface down to 1.5 m) at the three North Slope Borough communities of Point Lay, Wainwright, and Utqiagvik will be presented in this paper. Ground temperatures were measured both in natural conditions around the villages and under residential and commercial buildings to estimate the impact of infrastructure on permafrost stability. Generally, for all three villages, permafrost is still thermally stable. The mean annual ground temperature at 1.5-m depth is typically below -4°C for both natural conditions and under the elevated above ground engineering structures. One of the exceptions is thermokarst depressions such as deep troughs or ponds filled with water within and outside of the village of Point Lay. The mean annual water temperature at the bottom of some of these ponds with the water depth more than 0.5 m approaches the 0°C threshold, and in some cases even exceeds it, which can trigger development of a talik under these depressions. This may accelerate permafrost degradation at these locations with certain negative consequences for the stability of the village infrastructure and may manifest in numerous hazards for the residents. The methods of stabilization of permafrost and mitigation of adverse impacts of permafrost degradation will be discussed in this presentation. To enhance our understanding of possible future rates and pathways of permafrost degradation and to predict the consequences to residents, accurate high spatial resolution permafrost models are needed. Establishment of these models is possible only by integrating available high-resolution environmental data and by the assimilation of existing field and remote sensing data and observations into these models. The use of high-resolution (30x30 m) stand-alone permafrost dynamics GIPL2 model will be discussed to illustrate how changes in climate and further development of infrastructure will affect permafrost and people in this area.

How to cite: Romanovsky, V., Nicolsky, D., Farquharson, L., Rybakov, S., and Wright, T.: Permafrost stability in and around three North Slope Borough communities in Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4217, https://doi.org/10.5194/egusphere-egu24-4217, 2024.

Thawing of permafrost soils results in drastic changes in soil biogeochemistry and plant community composition. Specifically, the thawing process in subarctic regions can transform previously stable permafrost soils, home to slow growing, shallow-rooted shrubs into water-saturated, oxygen-depleted soils with fast-growing, deep-rooted graminoids. This change in soil biogeochemistry, along with the distinct characteristics and requirements of these contrasting plant types, leads to the hypothesis that the way these plants interact with the soil may impact biogeochemical cycles. Consequently, this could result in changes in the amounts and ratios of released greenhouse gases, influencing climate-relevant processes. On the one hand, tall graminoids may increase CO₂ fixation. On the other hand, root exudation might prime the formation of CH₄ and the root internal CH₄ transport protecting it from oxidation outweighing increased CO₂ fixation in thawed permafrost soils as compared to intact permafrost soil.

To explore this idea, we conducted a study in Stordalen, Abisko, Sweden, at a permafrost site with three different thawing stages. Sampling locations in intact, intermediately, and fully thawed permafrost soil were selected, each with varying densities of shrubs and graminoids. Representative plants were sampled to analyze the quantity and composition of root exudates. Data on soil redox potential at different depths were combined with porewater geochemical parameters like the amount and speciation of dissolved iron, dissolved organic carbon, inorganic nitrogen species, dissolved porewater gases, and soil microbial functional genes. Net emissions of CO₂, CH₄, and N₂O were tracked using static gas flux chambers. 

Most reducing redox conditions were observed in fully thawed soils compared to intact and intermediately thawed permafrost soils. Additionally, redox potentials decreased at greater depth in the soil and with higher graminoid density. At the same time graminoid roots exuded larger amounts of organic carbon than shrub roots with a high fraction of easily available organic molecules. We relate the decreasing redox potentials with increasing graminoid density to the rapid depletion of available electron acceptors such as iron(III) caused by an increased supply of easily available organic molecules through root exudation. This, in turn, might prime CH₄ production, indicated by increased porewater CH₄ at depth. Given the net CH₄ flux increase at an increased porewater CH₄ at depth, we suggest that this is partly from CH₄-priming and partly from aerenchyma transport of CH₄ from the soil to the atmosphere (Ström et al. 2005). Since thawing permafrost areas are rapidly expanding and contribute to climate change, the plant-specific alterations of these contrasting rhizosphere biogeochemical systems are important to consider altering greenhouse gas fluxes and warming potentials.

Ström, L. et al. Species-specific Effects of Vascular Plants on Carbon Turnover and Methane Emissions from Wetlands. Biogeochemistry 75, 65–82 (2005).

How to cite: Mollenkopf, M., Lenge, K., Joshi, P., Wild, B., Dorrepaal, E., Monteux, S., Kappler, A., and Muehe, M.: Plant-specific rhizosphere influences on soil redox and soil biogeochemistry affect methane release from thawing permafrost soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12030, https://doi.org/10.5194/egusphere-egu24-12030, 2024.

Permafrost degradation, freezing and thawing processes, and poor drainage due to underlain frozen ground have far-reaching consequences on soil hydrology and biology and, thus, on the redox dynamic in soils of the Arctic. Assessing the redox status of these soils is essential for understanding soil organic matter decomposition processes and can be done by temporal measurements in the field, analyses of redox-sensitive elements, or identification of microbial species or enzymes in redox process chains. While such approaches provide snippets of the complex redox dynamic, publications reporting long-term in-situ redox potential (E_H) measurements in arctic permafrost soils are scarce. Limited accessibility to study sites and technical limitations in measuring the redox potential in a frozen environment may be two reasons for this research gap.

But how does the redox potential develop in permafrost soils at different depths in the active layer during the summer? What happens during freezing and thawing? Finally, do thawing/degrading permafrost soils show different patterns compared to intact permafrost?

We approached these research questions by installation of a unique soil monitoring setup at 3 sites near Fairbanks, Alaska, in August 2021. An intact permafrost soil (active layer depth about 50 cm) was equipped with 3 redox electrodes (for E_H) and 3 hydra probes (for water content and soil temperature) in the topsoil and subsoil, respectively, and connected to a logger unit allowing continuous measurement of these parameters in both depths every 15 minutes. In addition, two sites with advanced permafrost degradation (permafrost level below 100 cm) were equipped in the same way. One degraded site featured large water contents, representing a wet thaw scenario, while the other site was well-drained, representing a dry thaw scenario, thus representing different endmembers of the ongoing climate-change induced permafrost thaw.

Here, we present the first 2 years of soil monitoring in a discontinuous permafrost area in Interior Alaska from 09/2021 to 09/2023. Overall, pH values of all soils varied between 4.5-6.3. The dry thaw scenario showed oxic conditions (i.e., E_H >600 mV) in top- and subsoil, while water contents were low. The wet thaw scenario exhibited high topsoil redox potentials (i.e., E_H >500 mV), while subsoil redox potential was lower (i.e., E_H <500 mV). High water contents in both intact permafrost and wet thaw scenario demonstrated a pronounced zero curtain effect over several months during the long winter season due to the release of latent heat during freezing. We further detected a strong 200-600 mV decrease in E_H in the topsoil of the intact permafrost active layer during the summer season, reaching reducing conditions 1-3 months after seasonal thaw. Redox measurements in the subsoil of the intact permafrost active layer, which was about 25 cm below the topsoil measuring depth and about 5 cm above the frozen ground, revealed E_H of >400 mV in the summer period (August to October), suggesting less oxygen consumption in this recently thawed permafrost subsoil.

How to cite: Liebmann, P., Vogel, C., Barta, J., Urich, T., Kholodov, A., Varsadiya, M., Waqas, M., Wang, H., Donnerhack, O., Shibistova, O., Wessel-Bothe, S., Mansfeldt, T., and Guggenberger, G.: Long-term soil redox dynamics of intact and degraded permafrost in Interior Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16607, https://doi.org/10.5194/egusphere-egu24-16607, 2024.

Arctic permafrost, with inherent low microbial activity, has historically immobilized soil organic matter (OM) and other substances such as mercury (Hg). Derived from both natural sources (e.g., forest fires, volcanism) and human activities, Hg is a highly toxic contaminant.

As permafrost thaws, microbial activity reactivates, leading to the degradation of soil OM. Simultaneously, Hg, once sequestered with OM, is released into the environment. However, the extent of Hg remobilization and its subsequent fate remain uncertain. To address this knowledge gap, we are developing a continental model that focuses on the fate of Hg, particularly from permafrost, within the context of Arctic climate change.

Given the strong affinity of Hg to OM, their cycles within the terrestrial biosphere are intricately interconnected. Leveraging the foundational framework of the ORCHIDEE land surface model, which mechanistically represents the production, transport, and transformation of organic carbon in soils and permafrost, we are integrating the Hg cycle.

This model will be evaluated using available observational data, including soil cores with vertical and latitudinal gradients, as well as measurements of Hg riverine exports on a pan-Arctic scale. Then, the model will be used to estimate the quantities of Hg emitted into the atmosphere and rivers during permafrost thawing, along with the associated timing. Different climate change scenarios from CMIP6 will be used to assess the sensitivity of permafrost thaw and Hg emissions to varying climatic conditions.

How to cite: Sereni, L., Guenet, B., and Angot, H.: The impact of climate change on mercury in permafrost: insights from the ORCHIDEE-MICT-PEAT-LEAK model , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1475, https://doi.org/10.5194/egusphere-egu24-1475, 2024.

Permafrost soils contain twice as much carbon as earth’s atmosphere and almost twice as much mercury as is stored in the total of all other soils, the ocean, and the atmosphere (Schuster et al., 2018). Significant nitrogen stocks have also been identified in permafrost (Strauss et al., 2022). The CRREL Permafrost Tunnel near Fairbanks, Alaska provides access to 500 meters of 40,000 year syngenetic permafrost. This is predominantly ice and carbon rich loess with ice wedges, segregated ice, and some large thermokarst cave ice features that are attributed to sudden permafrost thaw. The walls and ceiling of the Tunnel provide ready access to these varied permafrost soil and ice types. Above the Tunnel modern syngenetic permafrost is accessible via trenching and coring.

We surveyed the entire surface area of the walls and ceiling of the Tunnel with light distance and ranging (LiDAR). Return intensity values from different laser wavelengths allowed us to quantify exposed ice features versus ice cemented silt. Full LiDAR coverage of the entire tunnel interior after all artificial, floor, and extreme values were removed totaled 10,753,495 individual points. From this, we calculate 90.5 % of the surface area of the Tunnel walls and ceiling are represented by ice cemented silt and gravel and the remaining 9.5 % are ice features. Of the ice, 89.9 % are ice wedges and 10.1 % is thermokarst cave ice.

Based on these measurements, we collected roughly 80 SIPRE cores of frozen silt and ice features in the Tunnel and from modern permafrost above the Tunnel. Thawed soil and water ice were analyzed for major ions, trace metals, stable water isotopes, and carbon and nitrogen.

Major ion and trace metal concentrations are higher in ice wedges than replacement thermokarst cave ice. Mercury concentrations in ice cemented silt (n=28; 42.9 ng/g +/- 11.0), ice wedges (n=32; 54.0 ng/g +/- 16.3), thermokarst cave ice (n=17; 32.5 ng/g +/- 20.0), and the active layer above the Tunnel (n=5; 47.4 ng/g +/- 10.8) are similar to the 43 ng/g soil reported by Schuster et al. (2018). Carbon and nitrogen concentrations are greater in replacement thermokarst cave ice than in ice wedges and this is indicative of their formation during high intensity summer erosion events. Ice wedge total dissolved nitrogen (n= 30; 5.4 +/- 4.0 mg/L) and dissolved organic carbon (n= 30; 22.7 +/- 6.6 mg/L) values are greater than total dissolved nitrogen (n= 12; 2.9 +/- 4.3 mg/L) and dissolved organic carbon (n= 12; 17.4 +/- 21.0 mg/L) in thermokarst cave ice. Our values for yedoma permafrost inside the Permafrost Tunnel (n=28; 1.9 +/-0.6 kgN/cubic meter) and active layer above the Tunnel (n=5; 1.4 +/-0.5 kgN/cubic meter) are similar to the values of 0.9 kgN/cubic meter for yedoma and 1.6 kgN/cubic meter for active layer soils presented in Strauss et al. (2022).

Schuster PF, et a. Permafrost stores a globally significant amount of mercury. Geophysical Research Letters. 2018 Feb 16;45(3):1463-71.

Strauss J, et al. A globally relevant stock of soil nitrogen in the Yedoma permafrost domain. Nature Communications. 2022 Oct 14;13(1).

How to cite: Douglas, T., Barker, A., Gelvin, A., Brodylo, D., and Strauss, J.: Mercury, carbon, and nitrogen characteristics of Permafrost From 40,000 years old to modern age in Interior Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4466, https://doi.org/10.5194/egusphere-egu24-4466, 2024.

Permafrost peatlands constitute a reservoir of highly labile components such as dissolved organic carbon (DOC), macro- and micro-nutrients, and toxic elements. Fast thawing of permafrost peatlands in most of climate warming scenarios will lead to the mobilisation of dissolved components from soils to rivers and lakes. Permafrost peatlands situated in western Siberia are especially vulnerable to thawing, as they contain the largest soil water and ice resources in the northern hemisphere.  Half of the volume of ice resources is in form of dispersed ice on the soil top layer (0-3 m) [1]. Dispersed ice is enriched in dissolved components, which may be highly reactive and even provide sizable contributions to the hydrological system via suprapermafrost flow [2]. However, contributions from local soil column-scale in the context of micro-environments potential deepening of the active layer remain to be assessed.

To characterize the dissolved fraction of dispersed peat ice, a study was performed in Tazovsky, a representative site located in a continuous permafrost zone in Siberia. Four peat cores (0-180 cm depth) were collected along a gradient from the bog to mineral-fen. DOC, nutrients and trace elements were analysed for both the porewater (active layer) and dispersed ice (frozen layer). Lateral and in-depth approaches were employed to quantify the pools of dissolved components. Preliminary results show an enrichment of highly labile components in the frozen layer, consistent with previous findings in the discontinuous permafrost zone [3]. We hypothesize that the highest concentrations of DOC and certain macro/micro-nutrients in the frozen layer are mostly driven by downwards colloidal migration during the freezing phase. These organic and inorganic nutrients may be released due to progressive thawing, and eventually become bioavailable for microbial uptake. Consequently, the production of CO₂ may increase, contributing to the ongoing climate change.

[1] W. H. Pollard and H. M. French, « A first approximation of the volume of ground ice, Richards Island, Pleistocene Mackenzie delta, Northwest Territories, Canada », Can. Geotech. J., vol. 17, n^o 4, p. 509-516, november 1980, doi: 10.1139/t80-059.

[2] A. G. Lim et al., « Dispersed ground ice of permafrost peatlands: Potential unaccounted carbon, nutrient and metal sources », Chemosphere, vol. 266, p. 128953, march 2021, doi: 10.1016/j.chemosphere.2020.128953.

[3] D. M. Kuzmina et al., « Dispersed ice of permafrost peatlands represents an important source of labile carboxylic acids, nutrients and metals », Geoderma, vol. 429, p. 116256, january 2023, doi: 10.1016/j.geoderma.2022.116256.

How to cite: Perez-Serrano, L., Loiko, S., Artem, L., Pokrovsky, O., and Rols, J.-L.: Labile components as geochemical tracers at the soil column-scale in permafrost peatlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8439, https://doi.org/10.5194/egusphere-egu24-8439, 2024.

Arctic ecosystems are changing rapidly due to climate warming. Increased air temperature increases shrub proportions in plant communities at large scales, and increased soil moisture associated with permafrost thawing favours herbaceous cover at local scales. Changes in vegetation community composition or soil moisture could particularly affect the biogeochemical cycling of elements in arctic environments through the variation in the proportion of slow-cycling woody biomass and in the mineralisation rates of organic matter with soil water saturation. Nitrogen (N), often considered to limit primary production in these ecosystems, could be particularly affected by these changes. Biological fixation of atmospheric dinitrogen represents a major input of N in these systems and is catalysed by nitrogenase enzymes that contain either Molybdenum (Mo) or Vanadium (V). Thus, the concentrations, stocks and bioavailability of these two lithogenic trace elements (TE) may be key factors in alleviating the N constraint on primary productivity and vegetation change. Understanding their biogeochemical cycles is therefore crucial for our comprehension of changes in arctic environments.

Our study evaluated the concentrations and stocks of Mo and V   in vegetation and soils of different subarctic habitats with different soil characteristics and vegetation communities in a mire and a tundra ecosystem at Abisko, northern Sweden. Mo was more concentrated in the biomass of herbaceous species than in shrubs, resulting in higher stocks in the biomass of herbaceous-dominated habitats than in shrub-dominated habitats. Conversely, V concentrations and stocks were not different between the two vegetation types. In soils, Mo concentrations were globally the same between deep and surface horizons (0.38 mg kg^-1), whereas V concentrations were globally higher in deep horizons than at the surface (61.0 to 22.9 mg kg^-1, respectively). Accordingly, enrichment factors of the surface horizons compared to deep horizons showed that Mo was highly enriched at the surface (EF > 1 and up to > 8), highlighting the importance of surface processes on Mo cycling. V was not enriched in the tundra but presented EF values similar to Mo in the mire, indicating a locally higher influence of surface processes in this ecosystem. Exploring the possible reasons behind these behaviours, we found that 1) atmospheric deposition seems to play little role in their concentrations in surface soils, 2) soil pH and redox conditions could partially explain the surface enrichment of these two elements through their sorption on organic matter and metallic oxides.

We conclude that global and local changes in plant communities in arctic ecosystems could decrease Mo and V litter fluxes with increased shrub cover, with a greater impact on the Mo cycle than on V due to the stronger influence of surface processes on the Mo cycle. We also highlight the importance of local factors for TE speciation that would control the bioavailability of these elements for organisms. Altogether, these results underline the need to consider the changes in TE cycling in regard to their importance for underlying processes controlling major elements (C, N) dynamics in the changing Arctic.

How to cite: Potier, H. M. G., Raynaud, X., Alexis, M. A., Agnan, Y., Allain, A., and Castrec-Rouelle, M.: Impact of plant community composition and soil characteristics on Mo and V cycling in subarctic habitats at Abisko, Northern Sweden., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9490, https://doi.org/10.5194/egusphere-egu24-9490, 2024.

Around 65% of the Arctic coastline consists of permafrost. Rising global air temperatures cause these permafrost grounds to thaw which leads to the release of organic matter and sediments into the coastal ocean. This influences coastal ecosystem functioning and may further enhance atmospheric warming due to greenhouse gas emissions when the released carbon decomposes. Permafrost organic carbon enters the coastal ocean either through coastal erosion or through fluvial discharge and both fluxes are expected to increase in the future. The Canadian Beaufort Sea receives material from both sources, the region has some of the highest erosion rates in the Arctic and receives additional input through the Mackenzie River, the largest sediment supplier to the Arctic Ocean. To reliably estimate the current and future impacts of permafrost carbon on the coastal ocean and its potential climate feedback, we need to distinguish between these two sources whose fluxes may respond differently to ongoing Arctic change. However, we still lack reliable methods to do so.

Here we propose a multiproxy approach to distinguish between sources of permafrost organic carbon by combining organic with inorganic geochemical tracers, grain size and grain shape data on a land-coast-ocean transect in the Mackenzie River Delta. The combined data pinpoints to differences in sediment source, composition, degradation, and transport pathways of both fluvially-discharged and coastally-eroded carbon. Degradation processes of organic and inorganic matter are tightly coupled, but do change within different environments (salinity, energy regimes). By combining degradation state (stable isotopes) and transport indicators (such as grain roundness) with source region tracers (XRF, radiogenic isotopes) we aim to gain insights into the interaction, transition, and origin of this different kind of matter. If successful, this approach can be applied and compared to other Arctic delta environments to fully understand the impacts of increased permafrost thaw and changing river discharge patterns on the coastal Arctic Ocean.

How to cite: Madaj, L., van Crimpen, F., Whalen, D., Bröder, L., Langens, T., Bosse-Demers, T., and Vonk, J.: Fluvial versus coastal input of permafrost organic carbon - insights from the Canadian Beaufort Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11455, https://doi.org/10.5194/egusphere-egu24-11455, 2024.

The Arctic Ocean is currently changing at a high rate, and projections over the next decades include an increase in water temperature and retreat of sea ice, as well as increased input of freshwater and land-derived material released by permafrost thaw. These changes might substantially alter marine biogeochemical cycles and primary production, with repercussions for the Arctic Ocean greenhouse gas balance as well as ocean acidification. The large and shallow continental shelf seas north of Siberia are particularly affected by these changes as they receive land-derived material from strong coastal erosion and large rivers such as Ob, Yenisey and Lena. In recent studies, we have shown a transition from predominantly land- to marine-derived organic matter in sediments from the coast to the shelf break based on isotopes and biomarkers, an increased decomposition state of land-derived organic matter, as well as a decrease in sediment and water column nitrogen concentrations. We here combine this understanding with incubation experiments to assess the impact of these gradients on benthic CO₂ production and nutrient remineralization. We found that fresh, land-derived organic matter typical for near-shore environments showed highest decomposability to CO₂ in controlled, aerobic laboratory incubations, as indicated by correlations of CO₂ production with concentrations of terrigenous biomarkers (lignin, high molecular weight n-alkanes), and biomarker proxies indicating the decomposition state of these compounds. Fresh, land-derived organic matter was also associated with highest ammonium and nitrite release to the water column, measured during on-board incubation of intact sediment cores. The opposite pattern was observed for phosphate and silicate fluxes that were highest in more marine-influenced settings. Our data suggest that increased input of land-derived organic matter to the Siberian Arctic Ocean shelves could promote benthic decomposition processes near the coast, including CO₂ release that might contribute to the strong ocean acidification already observed in the region. Furthermore, the different controls on nutrient fluxes indicate a de-coupling of nitrogen, phosphorus and silicon remineralization, with implications for nutrient limitation and primary production in the Arctic Ocean.

How to cite: Wild, B., Sauerland, L., Ray, N. E., Gangnus, I., Yakushev, E., Gustafsson, Ö., Dudarev, O., and Semiletov, I.: Land-derived organic matter drives benthic carbon and nutrient cycling on the Siberian Arctic Ocean shelves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8513, https://doi.org/10.5194/egusphere-egu24-8513, 2024.

The permafrost in the Northern Hemisphere holds approximately 50% of the global soil organic carbon, constituting a reservoir that is twice the size of atmospheric carbon storage. Permafrost carbon plays a vital role in governing the global carbon cycle through its reactivity and accessibility to microbial respiration to release greenhouse gases. Existing studies have revealed spatial variability of degradation of coastally-exported organic matter across regimes in the East Siberian Arctic Shelf Seas. While the degradation patterns and ambient rates are reasonably constrained for the Laptev Sea, these aspects are less well understood for the Kara Sea. Here, we quantified carbon isotopes (¹³C and ¹⁴C), TOC, specific surface area, lipid biomarkers, and lignin phenols along a Kara Sea cross-shelf transect to assess terrigenous organic matter degradation, and compare patterns with three East Siberian cross-shelf transects (Kara Sea, Laptev Sea, Western East Siberian Sea, and Eastern East Siberian Sea). The data demonstrate the highest degradation rate constant of 2.5 kyr^-1 in the Eastern East Siberian Sea, a moderate value of 2.0 kyr^-1 in the Laptev Sea, and the lowest value of 1.2 kyr^-1 in the Western East Siberian Sea. Intriguingly, no statistical trend in degradation was observed across the Kara Sea. The recalcitrant fractions of terrestrial organic carbon are determined to be largest (50%) in the Western East Siberian Sea, moderate (31%) in the Eastern East Siberian Sea, and smallest (11%) in the Laptev Sea. The spatial variabilities in degradation rate constants and recalcitrant fractions are likely attributed to different organic carbon speciation across regimes on land, e.g., from fibrous plant residues to mineral-associated organic carbon, and potential biological controls (e.g., priming effect) during transport.

How to cite: Wu, J., Matsubara, F., Wild, B., Mollenhauer, G., Stein, R., Fahl, K., Xiao, X., and Gustafsson, Ö.: Quantifying cross-shelf degradation of terrigenous organic carbon in Eurasian Arctic Shelf Seas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6884, https://doi.org/10.5194/egusphere-egu24-6884, 2024.