CR5.2

Abrupt permafrost thawing is expected to release large amounts of greenhouse gasses to the atmosphere, creating a positive feedback to climate warming. There is, however, still large uncertainty in the timing, duration, magnitude, and mechanisms controlling this process, which hampers accurate quantification of permafrost carbon climate feedback cycles. The current understanding supports that abrupt permafrost thaw will lead to surface inundation and create anaerobic landscapes, which dominantly produce methane during the decomposition process. Over time, natural succession and vegetation growth may decrease methane release and increase net carbon uptake. We investigated how rapid permafrost thawing and subsequent natural succession over time affect CO₂, CH₄, and N₂O release at a field site in northern Norway (69ᵒN), where recent abrupt degradation of permafrost created thaw ponds in palsa peat plateau-mire ecosystems. The site exhibits a natural gradient of permafrost thaw, which also corresponds to a strong hydrological gradient (i.e. dry peat plateau underlain by intact permafrost, seasonally inundated thaw slumps, thaw ponds, and natural succession ponds covered by sphagnum and sedges). Since 2017, we used a range of manual and automated techniques to measure changes in vegetation, soil and water microclimate, biogeochemistry, and soil CO₂, CH₄, and N₂O concentrations and fluxes across the permafrost thaw gradient. In the three-year observations, we show that abrupt permafrost thaw and land surface subsidence – both intermediate slumping and pond formation – increase net annual carbon loss. Permafrost thaw accelerated CO₂ release greatly in thaw slumps (177.5 gCO₂ m^-2) compared to intact permafrost peat plateau (59.0 gCO₂ m^-2). During the growing season, peat plateau was a small sink of atmospheric CH₄ (-2.5 gCH₄ m^-2), whereas permafrost thaw slumping and pond formation increased CH₄ release dramatically (ranging from 9.7 to 36.1 gCH₄ m^-2). Furthermore, CH₄ release continues to increase even in natural succession pond likely due to aerenchyma transport of CH₄ from deeper soil. The overall N₂O release was negligeable except in the bare soil peat plateau. The net radiative forcing of ecosystem carbon balance will depend on the carbon uptake from the natural succession of vegetation, but we show that greenhouse gas emissions continue to increase beyond abrupt permafrost thaw event towards natural succession.

How to cite: Lee, H., Christiansen, C., Althuizen, I., Michelsen, A., Dörsch, P., Westermann, S., and Risk, D.: Long lasting greenhouse gas emissions beyond abrupt permafrost thaw event in permafrost peatlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4211, https://doi.org/10.5194/egusphere-egu22-4211, 2022.

Peatlands comprise 19% of the permafrost area in the subarctic zone, they store 277 Pg of organic carbon. Peatlands in that area are represented by palsa mire. The palsa mire consists of frozen peat mounds (palsa), thermokarst depression and the wet bog without permafrost.

Climate change and thawing of permafrost leads to a change in soil moisture, both drying and wetting. This can lead to a change in the carbon balance of the ecosystem and increase or decrease the emission of greenhouse gases (CO₂ and CH₄).

The aim of the work was to study the effect of changes in soil moisture on the biological activity of palsa mire peat soils in the north of Western Siberia (65°18'52"N, 72°52'32"E). The studies were conducted in 2018-2021 in the northern taiga in the discontinuous permafrost zone.

The two palsas (Cryic Histosol) and the surrounding bog (Fibric Histosol) were examined. Palsa soils were characterized by high variability of the studied parameters; active layer thickness was 0.66±0.07 m, soil moisture - 30.98±2.49%, soil temperature - 8.31±0.45°C. The soils of the bog were characterized by the absence of permafrost, a higher soil temperature - 13.58±0.26°C and soil moisture - 74.59±0.26%. Despite the difference in the studied parameters of these ecosystems, no significant differences in biological activity were found (185.97±30.51 mgCO₂/m²/h).

Based on field measurements, 3 plots were identified with the same type of vegetation and soil temperature, but significantly differ in soil moisture. Depending on soil moisture, the plots were named “Dry” (25.73±1.89%), “Wet” (38.44±0.70%) and “Moist” (53.09±1.06%). Biological activity did not vary significantly between the studied sites but had a multidirectional dynamic in different years. This shows the complexity of palsa, their multifactorial nature and an ambiguous response to changes in moisture.

An added experiment was set up to change soil moisture - transplantation. Measured of CO₂ emissions from undisturbed peat soil of a large volume transferred from dry palsa to a wetting bog. And vice versa. The biological activity of the soils did not differ considerable both during wetting and draining. In different years, there was a vary dynamics in CO₂ emissions.

According to the results of the study, with climate change, thawing of permafrost and palsa degradation, there will be no significant CO₂ flux. This may be due to the multifactorial nature of ecosystems, a wide optimum of soil moisture for peat soils. The influence of additional factors is also significant: the size of the methanotrophic barrier, the transport of CO₂ with solutions over the surface of the palsa permafrost.

How to cite: Chuvanov, S., Matyshak, G., Trifonova, V., and Timofeeva, M.: Permafrost thawing and changes on peat biological activity of palsa mire in Western Siberia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-429, https://doi.org/10.5194/egusphere-egu22-429, 2022.

Wetland ecosystems play a significant role in organic carbon conservation; one meter layer of peat soils store over 30 percent of terrestrial organic carbon (Lal, 2008). Ecosystems have different sensitivity to climate change in different nature zones (IPCC, 2014) due to various moisture and temperature regime.

The aim in this work is to define effect of temperature and moisture on mineralization rate in peat soils in Northern and Southern taiga.

The samples of Cryic Histosol (WRB, 2014) were taken from Northern Taiga (65°18'52" N, 72°52'32" E). The samples of Fibric Histosol (WRB, 2014) were taken from Southern Taiga (55°40'04" N 36°42'49" E). In laboratory conditions, samples were brought to certain soil moisture (SM): 30, 60, 80, 100 % (Gritsch, 2015), temperature of incubation was ranging from 5 to 25 ◦C (equal-time method).

In all the cases basal respiration (BR) was growing with increasing of temperature. Samples of Cryic Histosol are more sensitive to changes both in temperature and moisture. BR varies from 0.58 ±0.26 (30% SM and 5 ◦C) to 13.53±0.22 mg C-CO₂/g/h (100% SM and 25 ◦C). Q₁₀ coefficient varies from 4.64 to 2.82 respectively (this coefficient demonstrates differences in the temperature sensitivity of soil respiration (Kirschbaum, 1995)). For samples of Fibric Histosol BR varies from 0.75±0.01 (30% SM and 5 ◦C) to 6.14±0.26 mg C-CO₂/g/h (100% SM and 25 ◦C). Q₁₀ coefficient varies from 2.70 to 2.18 respectively.

Influence of moisture and temperature on biological activity in all of the cases was statistically confirmed, but interaction of factors is significant only for Cryic Histosol. According to the results, Cryic Histosol is more sensitive to temperature and moisture change, than Fibric Histosol. Peat soils in the northern area are subjected to more rapid organic carbon mineralization after a change of hydrothermal regime, than southern peat soils. In conclusion, Q₁₀ coefficient variation indicates that soils with low soil moisture are more sensitive to temperature changes.

How to cite: Trifonova, V., Ryzhova, I., Matyshak, G., Chuvanov, S., and Tarkhov, M.: Effects of temperature and moisture manipulation on biological activity of Northern and Southern taiga peat soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-431, https://doi.org/10.5194/egusphere-egu22-431, 2022.

Subsurface hydrology in regions dominated by permafrost is expected to change as a response to global climate change. Groundwater transports energy as well as dissolved solutes such as contaminants and carbon. To investigate the changes in advected energy as well as potential implications for solute transport, we created a permafrost hillslope modeling study that simulates current day active layer hydrology as well as future conditions based on climate projections.

Simulations are conducted with a state-of-the-art physically based numerical model (ATS) and combine a generic modeling approach with site-specific boundary conditions representative of the Adventdalen valley in Svalbard. We find that in the current climate, the subsurface hydrothermal state of the active layer along the hillslope transect is affected by lateral groundwater flow through differences in moisture distribution up- and downhill. Although lateral heat advection along the transect was found to be negligible, we show that the moisture distribution by gravitationally-driven seepage flow along the hillslope leads to unexpected temperature differences between the uphill and downhill parts of the transect. A non-negligible warming effect is observed uphill, resulting in deeper active layer depths than downhill.

Additionally, preliminary results based on transport modeling indicate that solute migration is mostly longitudinal and slow due to low liquid saturation of the active layer in summer. Under warmer conditions (increased air temperatures), lateral heat advection is expected to increase with more available energy, but solute migration may be partially counteracted by a greater volume of unfrozen soil in summer caused by less saturated conditions closer to the surface.

Furthermore, we discuss the potential implications this has for subsurface transport of solutes and dissolved constituents, and highlight challenges for numerical modeling of these systems.

How to cite: Hamm, A. and Frampton, A.: Modeling groundwater flow and solute transport in the active layer of hillslope system in permafrost environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2251, https://doi.org/10.5194/egusphere-egu22-2251, 2022.

Zero Emissions Commitment (ZEC), the expected change in global temperature following the cessation of anthropogenic greenhouse gas emissions has recently been assessed by the Zero Emissions Commitment Model Intercomparison Project (ZECMIP). ZECMIP concluded that the component of ZEC from CO₂ emissions will likely be close to zero in the decades following the cessation of emissions. However, of the 18 Earth system models that participated in ZECMIP only two included a representation of the permafrost carbon feedback to climate change. To better assess the potential impact of permafrost carbon decay on ZEC a series of perturbed parameter experiments were conducted with an Earth system model of intermediate complexity. The experiment suggest that the permafrost carbon cycle feedback will directly add 0.06 [0.02 to 0.14]^oC to the benchmark ZEC value assesses 50 years after 1000 PgC of CO₂ has been emitted to the atmosphere. An additional 0.04 [0 to 0.06]^oC is likely to been added relative to the benchmark ZEC value from the thaw-lag effect unaccounted for in the ZECMIP experiment design. Overall we assess that the permafrost carbon feedback is unlikely to change the assessment that ZEC is close to zero on decadal timescales, however the feedback is expected to become more important over the coming centuries.

How to cite: MacDougall, A. H.: Estimated effect of the permafrost carbon stability on the zero emissions commitment to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2539, https://doi.org/10.5194/egusphere-egu22-2539, 2022.

Permafrost-affected mineral soils store large amounts of the soil organic matter (SOM) in high-latitude regions. These regions are large terrestrial carbon reservoirs and highly vulnerable to the global climate change. Global warming will cause rapid permafrost thaw and potentially accelerate decomposition of SOM. High-latitude regions, such as boreal and arctic ecozones, are regularly affected by wildfires with increasing intensity and frequency caused by global climate change. Wildfires produce pyrogenic organic matter (PyOM) during incomplete combustion of the fuel biomass. Little is known about the cycling of SOM and especially PyOM in permafrost-affected mineral soils, which limits our understanding of potential shifts in cycling and interaction with the soil mineral phase over time.

Here we study the fate of highly ¹³C-labelled (2-3 atm%) ryegrass organic matter and PyOM from the same feedstock (pyrolyzed at 400°C for 4h) during two years of in-situ incubation in boreal forest mineral soils. Soil cores (10 cm length and 6 cm diameter) were buried in the upper 10 cm of mineral soils under continuous and discontinuous to sporadic permafrost conditions at eleven forest locations (with six replicates) in Northern Canada. At the same locations, litter bags (green and rooibos teabags) were buried and soil temperatures were recorded. The soils cores were separated in three depth (0-3, 3-6 and 6-10 cm) to trace the vertical allocation of the applied organic matter. Density and particle fractionations are applied to identify mineral interactions of the ryegrass and pyrolyzed organic matter.

Preliminary δ¹³C results from the soil cores show a more extensive vertical allocation of ryegrass organic matter and PyOM in continuous permafrost-affected soils within the cores. This can be associated to the importance of freeze and thaw cycles for the carbon dynamics of permafrost-affected mineral soils. Tracing the labelled ryegrass organic matter and PyOM offers not only the opportunity to quantify the translocated fraction but also the decomposed proportion of the freshly added organic matter and thus understand short-term carbon dynamics. Preliminary results from the litter bags indicate a larger mass loss of slow cycling woody organic matter (rooibos tea) in discontinuous to sporadic permafrost-affected mineral soils, while larger mass losses of fast cycling organic matter (green tea) were observed in continuous permafrost-affected soils. These initial results indicate a complex cycling of organic matter in soils under different permafrost conditions.

How to cite: Schiedung, M., Bellè, S.-L., and Abiven, S.: Fate of pyrogenic and organic matter in permafrost-affected soils: A two years in-situ incubation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2733, https://doi.org/10.5194/egusphere-egu22-2733, 2022.

Permafrost has a huge potential as a source for greenhouse gas release under global warming. In this context, it is very important to understand biogeochemical mechanisms of permafrost-related greenhouse gas formation and capacity. As ice wedges are an essential component of ice-rich permafrost and often occupy a large volume fraction of permafrost deposits, it is necessary to study the their gas chemistry. The Batagay megaslump (Yana Uplands, Northeast Siberia) exposes ice-rich permafrost deposits (Ice Complex) that have formed in the Middle and Late Pleistocene. Previous studies suggest the ages of these deposits as MIS 4-2 and at least MIS 16 for the Upper and Lower Ice Complexes, respectively. In this study, we analyzed mixing ratios of gas in air bubbles occluded in ice wedges of both ice complexes. We extracted gas by both, wet and dry extraction methods that connected with a gas chromatography system to analyze CO₂, N₂O, and CH₄ concentrations. We observe CO₂ concentrations of 1.9–10.3%, N₂O of 0.1–8 ppm, and CH₄ of 30–170 ppm for the Lower Ice Complex, and CO₂ of 0.03–8.89%, N₂O of 0.3–70 ppm, and CH₄ of 5–980 ppm for the Upper Ice Complex. Greenhouse gas mixing ratios higher than atmospheric level indicate active microbial activity. This is supported by the δ(O₂/Ar) values, which range from –89.01 to –67.43% and from –98.07 to –47.06% for the Lower and Upper Ice Complexes, respectively. The highly depleted δ(O₂/Ar) values may indicate strong oxidation reactions by microbial activity and/or non-biological oxidation reactions. Even though there is no significant correlation between CO₂ and CH₄, abiotic CH₄ formation might be negligible because it is unlikely to occur under permanently frozen conditions. Interestingly, CH₄ and N₂O show a weak negative correlation in both ice complexes, which can be explained by the nitrogen compounds’ inhibitory effect for methanogenesis. The δ(N₂/Ar) values range from –8.06% to 33.86% for the Lower Ice Complex and from –5.49% to 30.64% for the Upper Ice Complex. Since nitrogen is more soluble in water than argon, this might indicate that ice wedges may have formed without a major contribution of snowmelt but mainly by dry snow compaction, which is also supported by the spherical shape of gas bubbles within the wedge ice. Furthermore, in ice the argon permeation coefficient is higher than that of nitrogen. Thus, high δ(N₂/Ar) values (>10%) are due to argon’s diffusion through ice. Our future research will focus on deciphering the biogeochemical process of greenhouse gas formation for both ice complexes by comparison with ice wedges from other Siberian locations which have experienced different biogeochemical conditions in the past.

How to cite: Park, H., Ko, N.-Y., Kim, J., Opel, T., Meyer, H., Wetterich, S., Fedorov, A., Shepelev, A., and Ahn, J.: Compositions and origins of greenhouse gas species in permafrost ice wedges at the Batagay megaslump, Yana Uplands, Northeast Siberia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3437, https://doi.org/10.5194/egusphere-egu22-3437, 2022.

Climate change affects the Arctic and Subarctic regions by exposing previously frozen permafrost to thaw, unlocking nutrients, changing hydrological processes, and boosting plant growth. As a result, Arctic tundra is subject to a shrub expansion, called “shrubification” at the expense of sedge species. Depending on intrinsic foliar properties of these plant species, changes in foliar fluxes with shrubification in the context of permafrost degradation may influence topsoil mineral element composition. Despite the potential implications for the fate of organic carbon in the topsoil, this remains poorly quantified. Here, we investigate vegetation foliar and topsoil mineral element composition (mineral elements that influence organic carbon decomposition: Si, K, Ca, P, Mn, Zn, Cu, Mo and V) from a typical Arctic tundra at Eight Mile Lake (Alaska, USA) across a natural gradient of permafrost degradation. Results show that foliar element concentrations are higher (up to 9 times; Si, K, Mo, and for some species Zn) or lower (up to 2 times; Ca, P, Mn, Cu, V, and for some species Zn) in sedge than in shrub species. This induces different foliar flux with permafrost degradation and shrubification. As a result, a vegetation shift over ~40 years from sedges to shrubs has resulted in lower topsoil concentrations in Si, K, Zn and Mo (respectively of 52, 24, 20 and 51%) in poorly degraded permafrost sites compared to highly degraded permafrost sites. For other mineral elements (Ca, P, Mn, Cu and V), the vegetation shift has not induced a marked changed in topsoil concentrations at this stage of permafrost degradation. This observed change in topsoil composition involving beneficial or toxic elements for decomposers is likely to influence organic carbon decomposition. These data can serve as a first estimate to assess the influence of other shifts in vegetation in Arctic tundra such as sedge expansion with wildfires.

How to cite: Villani, M., Mauclet, E., Agnan, Y., Druel, A., Jasinski, B., Taylor, M., Schuur, E. A. G., and Opfergelt, S.: Does vegetation shift in Arctic tundra upon permafrost degradation influence mineral element recycling in the topsoil?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4024, https://doi.org/10.5194/egusphere-egu22-4024, 2022.

Permafrost degradation caused by climate warming has potentially large impact on the hydro-eco environment in the Tibetan Plateau (TP) through affecting soil water redistribution, and it is critical to investigate the soil moisture changes and estimate their response to future climate conditions. In this study, we first analyzed the in-situ soil temperature and moisture data to examine the impact of active layer thickening on soil moisture redistribution. There is generally a “water-rich zone” around the bottom of the active layer at sites with the active layer thickness (ALT) greater than ~2 m, and a relative low soil moisture zone occurs approximately between the bottom of the root zone (~ 0.4 m) and the bottom of the active layer. However, at shallower-ALT sites (e.g., ALT< 2 m), a “soil water rich zone” occurs at the upper active layer rather than at the bottom of the active layer, and soil moisture at the deeper active layer generally shows a decreasing trend along soil depth. We used a process-based permafrost hydrology model to represent the above effects of active layer thickening on soil moisture redistribution through modifying the soil hydraulic profile. Model sensitivity runs indicate that soil moisture redistribution with active layer thickening is largely due to dramatic changes of hydraulic conductivity between the root zone and deeper layers (>~ 1m). The saturated hydraulic conductivity tends to increase a little in the root zoon and then show a sharp exponential decline along soil depth, while the pedo-transfer functions that are commonly used in models cannot reproduce this process well.

Our results indicate that shallower ALT helps to retain soil moisture in the soil root zone; however, when ALT increases to a certain depth, the root-zone soil layer tends to lose water because of little recharge from deeper (>~1m) soils due to the dramatical decreases in soil hydraulic conductivity. Therefore, active layer thickening may exacerbate soil drying in the root-zone, which will have negative impacts on the vegetation growth and performances of ecosystem functioning. We will further investigate the soil moisture changes under different climate scenarios in order to better project the future hydro-eco response in the TP permafrost region.

How to cite: Jiang, H., Yi, Y., Zhang, W., Chen, D., and Li, R.: Investigating the impact of active layer thickening on vertical soil moisture distribution in the Tibetan Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4672, https://doi.org/10.5194/egusphere-egu22-4672, 2022.

Climate change threatens the Earth’s biggest terrestrial organic carbon reservoir: permafrost soils. With climate warming, frozen soil organic matter may thaw and become available for microbial decomposition and subsequent greenhouse gas emissions. Permafrost soils are extremely heterogenous within the soil profile and between landforms. This heterogeneity in environmental conditions, carbon content and soil organic matter composition, potentially leads to different microbial communities with different responses to warming. The aim of the present study is to (1) elucidate these differences in microbial community compositions and (2) investigate how these communities react to warming.

We performed short-term warming experiments with permafrost soil organic matter from northwestern Canada. We compared two sites characterized by different glacial histories (Laurentide Ice Sheet cover during LGM and without glaciation), three landscape types (low-center, flat-center, high-center polygons) and four different soil horizons (organic topsoil layer, mineral topsoil layer, cryoturbated soil layer, and the upper permanently frozen soil layer). We incubated aliquots of all soil samples at 4 °C and at 14 °C for 8 weeks and analyzed microbial community compositions (amplicon sequencing of 16S rRNA gene and ITS1 region) before and after the incubation, comparing them to microbial growth, microbial respiration, microbial biomass and soil organic matter composition.

We found distinct bacterial, archaeal and fungal communities for soils of different glaciation history, polygon types and for different soil layers. Communities of low-center polygons differ from high-center and flat-center polygons in bacterial, archaeal and fungal community compositions, while communities of organic soil layers are significantly different from all other horizons. Interestingly, permanently frozen soil layers differ from all other horizons in bacterial and archaeal, but not fungal community composition.

The 8-week incubations led to minor shifts in bacterial and archaeal community composition between initial soils and those subjected to 14 °C warming. We also found a strong warming effect on the community compositions in some of the extreme habitats: microbial community compositions of (i) the upper permanently frozen layer and of (ii) low-center polygons differ significantly for incubations at 4 °C and 14 °C. Yet, the lack of a community change in horizons of the active layer suggests that microbes are adapted to fluctuating temperatures due to seasonal thaw events.

Our results suggest that warming responses of permafrost soil organic matter, if not frozen or water-saturated, may be predictable by current models. Process changes induced by short-term warming can be rather attributed to changes in microbial physiology than community composition.

This work is part of the EU H2020 project “Nunataryuk”.

How to cite: Rottensteiner, C., Martin, V., Schmidt, H., Hadžiabdić, L., Horak, J., Mohrlok, M., Urbina Malo, C., Wagner, J., A'Campo, W., Durstewitz, L., Lodi, R., Speetjens, N. J., Tanski, G., Fritz, M., Lantuit, H., Hugelius, G., and Richter, A.: Spatial variability shapes microbial communities of permafrost soils and their reaction to warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9891, https://doi.org/10.5194/egusphere-egu22-9891, 2022.

The arctic is warming at double the average global rate. This raises the concern that permafrost is beginning to thaw and could release large amounts of stored carbon, parts of which can be centuries old. If the total carbon release exceeds the carbon uptake the net ecosystem exchange (NEE) shifts from carbon sink to source, amplifying global warming. Here we present long-term eddy covariance (EC) data of a tundra ecosystem in northeast Siberia, showing the current NEE and its drivers in one of the most remote and coldest EC sites of the northern hemisphere. During the growing season the site is an overall carbon sink. The start of the carbon uptake quickly follows snowmelt and total growing season uptake is positively correlated with an earlier timing of the carbon uptake. While snowfall and the timing of snowmelt is highly variable no discernible trend can be seen in long-term data. In general, increased temperatures yield higher net carbon uptake during the growing season, although this effect levels off at roughly 20°C, likely due to the steadily decreasing solar radiation throughout the growing season. Because of the remoteness and extremely low temperatures, no winter measurements exist. However, machine learning gap filling suggests the site is a small net carbon source during most of the winter. This is in accordance with some of the recent findings at other sites and potentially offsets large parts of the growing season uptake. Thus, while the growing season initially might see increased terrestrial carbon uptake at higher regional temperatures, constraining yearly budgets with winter measurements is indispensable to get a full picture of changes in the total carbon budget of arctic tundra sites in Siberia.

How to cite: Hensgens, G., Vonk, J., Petrov, R., Karsanaev, S., Maximov, T., and Dolman, H.: The long-term Net Ecosystem Exchange of a remote Siberian high arctic site, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11774, https://doi.org/10.5194/egusphere-egu22-11774, 2022.