Properties Of Permafrost Research Articles

Hydro-thermal boundary conditions at different underlying surfaces in a permafrost region of the Qinghai-Tibet Plateau

Hydro-thermal properties of permafrost and its distribution are sensitive to climate changes and human activities. Accurate and reasonable prediction on aforementioned information is important for eco-environment construction and vital infrastructures development. To model the current and future states of permafrost, it is a key challenge to effectively determine the upper hydro-thermal boundary conditions for permafrost models under changing climate and different underlying surfaces at proper spatial and temporal scales. An approach, combined regional climate downscaling method with model output statistics method, was developed to produce a time series of air temperature, surface temperatures, and surface unfrozen water contents for different underlying surfaces. It provided various climate and surface parameters at a spatial scale on the order of 102 m2 for engineering designs, which was used to predict boundary conditions under possible climate scenarios. The predicted and simulated models were calibrated and validated by the monitored data at an experimental site in Chumar, China, close to the Qinghai-Tibet Railway and the Qinghai-Tibet Highway. Results show that the multiple linear regression model (MLRM) can predict the current states and future changes of upper hydro-thermal boundary conditions for permafrost while the original states of natural surface are modified by natural or human factors on the condition of complicated climatic and complex topography regions. The statistical regression model (SRM) based on the outputs of regional climate model (RCM) and MLRM provides a simple method for the convenience of numerical calculation. These results also indicate the possible applications to other areas and situations.

On the freezing and thawing of groundwater

Analyses the thermal and Physico mechanical properties of permafrost received a convenient formula for calculating them with the economic development of the territory the spread of everfrozen soils

Electrical properties of permafrost in the Laptev sea coast: evidence from radio-wave measurements.

Electrical properties of permafrost in the Laptev sea coast: evidence from radio-wave measurements.

Электрические свойства мерзлых пород на побережье моря Лаптевых по данным радиоволновых измерений

Электрические свойства мерзлых пород на побережье моря Лаптевых по данным радиоволновых измерений

Variations in soil temperature from 1980 to 2015 in permafrost regions on the Qinghai-Tibetan Plateau based on observed and reanalysis products

Soil temperature is an important physical variable of soil and plays a key role in controlling the underground hydro-thermal processes in permafrost regions on the Qinghai-Tibetan Plateau (QTP). Daily soil temperatures were observed at five different vegetation cover sites (alpine wet meadow, alpine meadow, alpine steppe, alpine desert steppe and alpine desert) from 2012 to 2015 in permafrost regions on the QTP. The performance of three reanalysis soil temperature products (National Centers for Environmental Prediction Climate Forecast System and Climate Forecast System Reanalysis (CFSR), European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim), and Global Land Data Assimilation System (GLDAS- NOAH)) at four depths (0–10, 10–40, 40–100 and 100–200 cm) was evaluated using the observation data. The results revealed that the CFSR soil temperature products had the best performance at most sites and that GLDAS-NOAH and Era-Interim had the poorest performance. However, the original CFSR soil temperature products underestimated the lowest temperatures. The calibration models for CFSR soil temperature products were established using the observed daily soil temperature from 2013 to 2015 and were validated with observed data from 2012. The results showed that the calibrated CFSv2 products were closer to the observations at different depths in the study sites. Moreover, we investigated the variations of seasonal and annual mean soil temperature from 1980 to 2015 at depths of 0–10, 10–40, 40–100 and 100–200 cm using the soil temperature calibration results. It was found that the soil temperatures at different depths all warmed fastest in spring, more slowly in winter and slowest in autumn at most sites. In addition, the average annual soil temperature exhibited significant warming trends in the permafrost regions on the QTP. The effect was largest with alpine desert steppe and smallest with alpine wet meadow, with statistically significant rates of 0.0599, 0.0468, 0.0438, 0.0282 and 0.0145 °C/year in alpine desert steppe, alpine desert, alpine steppe, alpine meadow and alpine wet meadow, respectively. This research provides a foundation for understanding the thermal properties of permafrost on the Qinghai-Tibetan Plateau under climate change.

Transient Electromagnetic Surveys for the Determination of Talik Depth and Geometry Beneath Thermokarst Lakes

AbstractThermokarst lakes are prevalent in Arctic coastal lowland regions and sublake permafrost degradation and talik development contributes to greenhouse gas emissions by tapping the large permafrost carbon pool. Whereas lateral thermokarst lake expansion is readily apparent through remote sensing and shoreline measurements, sublake thawed sediment conditions and talik growth are difficult to measure. Here we combine transient electromagnetic surveys with thermal modeling, backed up by measured permafrost properties and radiocarbon ages, to reveal closed‐talik geometry associated with a thermokarst lake in continuous permafrost. To improve access to talik geometry data, we conducted surveys along three transient electromagnetic transects perpendicular to lakeshores with different decadal‐scale expansion rates of 0.16, 0.38, and 0.58 m/year. We modeled thermal development of the talik using boundary conditions based on field data from the lake, surrounding permafrost and a borehole, independent of the transient electromagnetics. A talik depth of 91 m was determined from analysis of the transient electromagnetic surveys. Using a lake initiation age of 1400 years before present and available subsurface properties the results from thermal modeling of the lake center arrived at a best estimate talk depth of 80 m, which is on the same order of magnitude as the results from the transient electromagnetic survey. Our approach has provided a noninvasive estimate of talik geometry suitable for comparable settings throughout circum‐Arctic coastal lowland regions.

An Estimation of Ground Ice Volumes in Permafrost Layers in Northeastern Qinghai-Tibet Plateau, China

The ground ice content in permafrost serves as one of the dominant properties of permafrost for the study of global climate change, ecology, hydrology and engineering construction in cold regions. This paper initially attempts to assess the ground ice volume in permafrost layers on the Qinghai-Tibet Plateau by considering landform types, the corresponding lithological composition, and the measured water content in various regions. An approximation demonstrating the existence of many similarities in lithological composition and water content within a unified landform was established during the calculations. Considerable knowledge of the case study area, here called the Source Area of the Yellow (Huanghe) River (SAYR) in the northeastern Qinghai-Tibet Plateau, has been accumulated related to permafrost and fresh water resources during the past 40 years. Considering the permafrost distribution, extent, spatial distribution of landform types, the ground ice volume at the depths of 3.0–10.0 m below the ground surface was estimated based on the data of 101 boreholes from field observations and geological surveys in different types of landforms in the permafrost region of the SAYR. The total ground ice volume in permafrost layers at the depths of 3.0–10.0 m was approximately (51.68 ± 18.81) km3, and the ground ice volume per unit volume was (0.31 ± 0.11) m3/m3. In the horizontal direction, the ground ice content was higher in the landforms of lacustrine-marshland plains and alluvial-lacustrine plains, and the lower ground ice content was distributed in the erosional platforms and alluvial-proluvial plains. In the vertical direction, the volume of ground ice was relatively high in the top layers (especially near the permafrost table) and at the depths of 7.0–8.0 m. This calculation method will be used in the other areas when the necessary information is available, including landform type, borehole data, and measured water content.

Elastic properties of saline permafrost during thawing by bender elements and bending disks

The elastic properties such as small-strain Young's, shear moduli and Poisson's ratio of permafrost are important parameters for analyzing the stress distribution and thaw-subsidence of permafrost and deformation of well casing embedded in permafrost. However, the deep natural permafrost warms up and even thaws due to energy extraction and its elastic properties change significantly with temperature. This paper presents elastic properties obtained by conducting laboratory testing of permafrost samples from the North Slope of Alaska. The testing specimens were conditioned from −10°C to −2°C at an interval of 2°C, and to 20°C for examining the temperature effects. The bending disks and bender elements were used to measure the compressional wave (P-wave) and shear wave (S-wave) velocities, respectively, for evaluating the small-strain elastic properties during thawing. Measurements were done in both horizontal and vertical directions for assessing anisotropy. The results show that the P- and S-wave velocities from this study partially overlap with in situ measurement data reported in the literature, and tend to be lower due to high salinity and lack of overburden effects, which is stronger on sandy permafrost. Results reveal anisotropy in the wave velocities in all types of permafrost tested, and the small-strain elastic properties of clay and silt permafrost exhibit no sharp change when the temperature crosses 0°C, likely due to non-uniform freezing point depression caused by the varying and high salinity among specimens. Finally, parameters were provided for predicting the confining pressure dependent small-strain Young's modulus, and regression equations were proposed for predicting the modulus number and exponent in Janbu's model based on permafrost dry density and moisture content.

Quantification of Arctic Soil and Permafrost Properties Using Ground-Penetrating Radar and Electrical Resistivity Tomography Datasets

Improving understanding of Arctic ecosystem climate feedback and parameterization of models that simulate freeze-thaw dynamics require advances in quantifying soil and snow properties. Due to the significant spatiotemporal variability of soil properties and the limited information provided by point-scale measurements (e.g., cores), geophysical methods hold potential for improving soil and permafrost characterization. In this study, we evaluate the use of a ground-penetrating radar (GPR) to estimate thaw layer thickness, snow depth, and ice-wedge characteristics in an ice-wedge-dominated tundra region near Barrow, AK, USA. To this end, we analyze GPR and point-scale measurements collected along several parallel transects at the end of the growing season and the end of frozen season. In addition, we compare the structural information extracted from the GPR data with electrical resistivity tomography (ERT) information about ice-wedge characteristics. Our study generally highlights the value of GPR data collected in the frozen season, when conditions lead to the improved GPR signal-to-noise ratio, facilitate data acquisition, and reduce acquisition-related ecosystem disturbance relative to growing season. We document for the first time that GPR data collected during the frozen season can provide reliable estimates of active layer thickness and geometry of ice wedges. We find that the ice-wedge geometry extracted from GPR data collected during the frozen season is consistent with ERT data, and that GPR data can be used to constrain the ERT inversion. Consistent with recent studies, we also find that GPR data collected during the frozen season can provide good estimates of snow thickness, and that GPR data collected during the growing season can provide reliable estimate thaw depth. Our quantification of the value of the GPR and ERT data collected during growing and frozen seasons paves the way for coupled inversion of the datasets to improve understanding of permafrost variability.

Electrical and seismic response of saline permafrost soil during freeze - Thaw transition

We conducted laboratory studies on the geophysical signals from Arctic saline permafrost soils to help understand the physical and mechanical processes during freeze-thaw cycles. Our results revealed low electrical resistivity (<20Ωm) and elastic moduli (7.7GPa for Young's modulus and 2.9GPa for shear modulus) at temperatures down to ~−10°C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze – thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law. Using an improved formulation of Archie's law with a variable cementation exponent, the unfrozen water content estimation showed a large variation depending on the choice of the resistivity data during either a freezing or thawing cycle. Combining the electrical and seismic results, we suggest that, rather than a large hysteresis in the actual unfrozen water content, the shift of the resistivity response may reflect the changes of the distribution pattern of the unfrozen water (or ice) in the soil matrix during repeated freeze and thaw processes. Collectively, our results provide an improved petrophysical understanding of the physical and mechanical properties of saline permafrost during freeze – thaw transitions, and suggest that large uncertainty may exist when estimating the unfrozen water content using electrical resistivity data.

Исследование устойчивости карстовой пещеры Хээтэй к динамическим воздействиям при взрывном способе разработки Усть-Борзинского месторождения известняков в Восточном Забайкалье

The article devotes to investigations the caves Heetey - natural monument Trans-Baikal Territory, in connection with the problem of their preservation during the blasting development of the nearby located Ust'-Borzinsky limestone deposits. Limestone processing is planned to open by a career with 5 ledges height of 15 m each. The characteristics of natural conditions, geological, and hydrogeological properties of permafrost enclosing rock massif, provides information about the shape, location and characteristics of ice cover, which affects on the dynamic stability of the cave and its elements. The analysis of the results of experimental studies of dynamic stability of karst cave Heetey to the effects of explosions in the development of the open method of Ust'-Borzinsky limestone deposits is presented. The main purpose of engineering and seismic measurements of vibrations of the rock mass enclosing Heetey cave was to study the amplitude and frequency content of vibrations to assess the seismic effect of explosions carried out in the near quarry with limestone mining. Actual measurements of the parameters of the rocks fluctuations in the cave Heetey included varying the total weight of the impact of charges, the distance from the source of vibrations to the registration points, the difference in the parameters of group explosions on the amplitude-frequency characteristics of wave propagation in a cave in the enclosing rock mass. The analysis of the results of field measurements of cave rock vibrations and calculations, of their dynamic stability taking into account the effect of the array of bottom cover of ice, filling with water of the cave and shielding devices is cited. Particular attention is paid to the effect of empty and filled with ice holes in the rock mass in the propagation of mechanical vibrations in it. Presented findings of scientific and applied pattern.

Coincident aboveground and belowground autonomous monitoring to quantify covariability in permafrost, soil, and vegetation properties in Arctic tundra

AbstractCoincident monitoring of the spatiotemporal distribution of and interactions between land, soil, and permafrost properties is important for advancing our understanding of ecosystem dynamics. In this study, a novel monitoring strategy was developed to quantify complex Arctic ecosystem responses to the seasonal freeze‐thaw‐growing season conditions. The strategy exploited autonomous measurements obtained through electrical resistivity tomography to monitor soil properties, pole‐mounted optical cameras to monitor vegetation dynamics, point probes to measure soil temperature, and periodic manual measurements of thaw layer thickness, snow thickness, and soil dielectric permittivity. The spatially and temporally dense monitoring data sets revealed several insights about tundra system behavior at a site located near Barrow, AK. In the active layer, the soil electrical conductivity (a proxy for soil water content) indicated an increasing positive correlation with the green chromatic coordinate (a proxy for vegetation vigor) over the growing season, with the strongest correlation (R = 0.89) near the typical peak of the growing season. Soil conductivity and green chromatic coordinate also showed significant positive correlations with thaw depth, which is influenced by soil and surface properties. In the permafrost, soil electrical conductivity revealed annual variations in solute concentration and unfrozen water content, even at temperatures well below 0°C in saline permafrost. These conditions may contribute to an acceleration of long‐term thaw in Coastal permafrost regions. Demonstration of this first aboveground and belowground geophysical monitoring approach within an Arctic ecosystem illustrates its significant potential to remotely “visualize” permafrost, soil, and vegetation ecosystem codynamics in high resolution over field relevant scales.

Distribution of near-surface permafrost in Alaska: Estimates of present and future conditions

High-latitude regions are experiencing rapid and extensive changes in ecosystem composition and function as the result of increases in average air temperature. Increasing air temperatures have led to widespread thawing and degradation of permafrost, which in turn has affected ecosystems, socioeconomics, and the carbon cycle of high latitudes. Here we overcome complex interactions among surface and subsurface conditions to map near-surface permafrost through decision and regression tree approaches that statistically and spatially extend field observations using remotely sensed imagery, climatic data, and thematic maps of a wide range of surface and subsurface biophysical characteristics. The data fusion approach generated medium-resolution (30-m pixels) maps of near-surface (within 1 m) permafrost, active-layer thickness, and associated uncertainty estimates throughout mainland Alaska. Our calibrated models (overall test accuracy of ~ 85%) were used to quantify changes in permafrost distribution under varying future climate scenarios assuming no other changes in biophysical factors. Models indicate that near-surface permafrost underlies 38% of mainland Alaska and that near-surface permafrost will disappear on 16 to 24% of the landscape by the end of the 21st Century. Simulations suggest that near-surface permafrost degradation is more probable in central regions of Alaska than more northerly regions. Taken together, these results have obvious implications for potential remobilization of frozen soil carbon pools under warmer temperatures. Additionally, warmer and drier conditions may increase fire activity and severity, which may exacerbate rates of permafrost thaw and carbon remobilization relative to climate alone. The mapping of permafrost distribution across Alaska is important for land-use planning, environmental assessments, and a wide-array of geophysical studies. • Novel-baseline assessment of permafrost properties in Alaska • Mapping permafrost in Alaska using Landsat and empirical modeling • Approximately 85% overall accuracy for near-surface permafrost distribution • Projected 16 to 24% loss of frozen ground in Alaska during 21st Century • Spatially explicit estimates of uncertainty and probability

Carbon and Nitrogen Properties of Permafrost over the Eboling Mountain in the Upper Reach of Heihe River Basin, Northwestern China

The sensitivity of soil carbon and nitrogen to warming is a major uncertainty in projections of climate. However, previous studies about soil organic carbon (SOC) stocks and potential emission predominantly concentrated on the shallow soil layer in high latitude ecosystems. In this study, we analyzed the SOC, total nitrogen (TN) and soil inorganic carbon (SIC) stocks, C/N ratios, and stable carbon isotope (δ13C) in the active layer and permafrost layer on the Eboling Mountain in the upper reach of Heihe River basin, northwestern China. Our results showed that the average stocks of SOC, TN, and SIC in permafrost layer above soil parent materials (71.7 kg m-2, 8.0 kg m-2, 34.7 kg m-2) were much higher than those in the active layer (44.3 kg m-2, 5.3 kg m-2, 12.2 kg m-2). The δ13C pattern in the soil profiles indicated that historical drainage conditions and pedogenesis were important factors in determining soil organic matter (SOM) stocks in this permafrost region. The δ13C and C/N ratios of the transient layer and some layers of permafrost implied that the degradation of SOM was different. These results highlight that carbon and nitrogen in permafrost regions with Alpine Kobresia meadow could make significant contribution to China’s terrestrial carbon cycle.

Warmer and wetter winters: characteristics and implications of an extreme weather event in the High Arctic

One predicted consequence of global warming is an increased frequency of extreme weather events, such as heat waves, droughts, or heavy rainfalls. In parts of the Arctic, extreme warm spells and heavy rain-on-snow (ROS) events in winter are already more frequent. How these weather events impact snow-pack and permafrost characteristics is rarely documented empirically, and the implications for wildlife and society are hence far from understood. Here we characterize and document the effects of an extreme warm spell and ROS event that occurred in High Arctic Svalbard in January–February 2012, during the polar night. In this normally cold semi-desert environment, we recorded above-zero temperatures (up to 7 °C) across the entire archipelago and record-breaking precipitation, with up to 98 mm rainfall in one day (return period of >500 years prior to this event) and 272 mm over the two-week long warm spell. These precipitation amounts are equivalent to 25 and 70% respectively of the mean annual total precipitation. The extreme event caused significant increase in permafrost temperatures down to at least 5 m depth, induced slush avalanches with resultant damage to infrastructure, and left a significant ground-ice cover (∼5–20 cm thick basal ice). The ground-ice not only affected inhabitants by closing roads and airports as well as reducing mobility and thereby tourism income, but it also led to high starvation-induced mortality in all monitored populations of the wild reindeer by blocking access to the winter food source. Based on empirical-statistical downscaling of global climate models run under the moderate RCP4.5 emission scenario, we predict strong future warming with average mid-winter temperatures even approaching 0 °C, suggesting increased frequency of ROS. This will have far-reaching implications for Arctic ecosystems and societies through the changes in snow-pack and permafrost properties.

Effect of permafrost properties on gas hydrate petroleum system in the Qilian Mountains, Qinghai, Northwest China.

The gas hydrate petroleum system in the permafrost of the Qilian Mountains, which exists as an epigenetic hydrocarbon reservoir above a deep-seated hydrocarbon reservoir, has been dynamic since the end of the Late Pleistocene because of climate change. The permafrost limits the occurrence of gas hydrate reservoirs by changing the pressure-temperature (P-T) conditions, and it affects the migration of the underlying hydrocarbon gas because of its strong sealing ability. In this study, we reconstructed the permafrost structure of the Qilian Mountains using a combination of methods and measured methane permeability in ice-bearing sediment permafrost. A relationship between the ice saturation of permafrost and methane permeability was established, which permitted the quantitative evaluation of the sealing ability of permafrost with regard to methane migration. The test results showed that when ice saturation is >80%, methane gas can be completely sealed within the permafrost. Based on the permafrost properties and genesis of shallow gas, we suggest that a shallow "gas pool" occurred in the gas hydrate petroleum system in the Qilian Mountains. Its formation was related to a metastable gas hydrate reservoir controlled by the P-T conditions, sealing ability of the permafrost, fault system, and climatic warming. From an energy perspective, the increasing volume of the gas pool means that it will likely become a shallow gas resource available for exploitation; however, for the environment, the gas pool is an underground "time bomb" that is a potential source of greenhouse gas.

Electrical Conductivity Imaging of Active Layer and Permafrost in an Arctic Ecosystem, through Advanced Inversion of Electromagnetic Induction Data

Characterizing the spatial variability of active layer and permafrost properties is critical for parameterizing process‐rich models that simulate feedbacks from Arctic ecosystem to a changing climate. Because of the sensitivity of electrical conductivity (EC) measurements to moisture content, salinity, and freeze state and the ease of collecting electromagnetic induction (EMI) data with portable tools (e.g., EM38, GEM2, or DUALEM) over large regions, EMI surveys hold great potential for Arctic ecosystem characterization. However, estimation of subsurface EC distribution from such data is challenging because of the insufficient amount of information such data provide towards finding a unique solution. The non‐uniqueness problem is often approached by fixing inversion constraints and initial models without a clear understanding of their possible effects on the obtained results. Here we developed a direct search method, which involves a grid‐based evaluation of one‐dimensional layered model parameters, to estimate EC distribution from EMI data and evaluate the influence of prior constraints, data information content, and solution non‐uniqueness. We applied the new method to EMI data acquired in Barrow, AK, as part of the Department of Energy Next‐Generation Ecosystem Experiments (DOE NGEE–Arctic). Results demonstrate the success of the developed approach for estimating models that reproduce recorded data within a specified range of uncertainty at each measurement location, as well as the value of different types of constraints. Importantly, the method can be used to quickly investigate the need for and effects of different priors at numerous measurement locations, since the time‐consuming simulation of the EMI signals from the multidimensional search grid is performed only once.

Fire at high latitudes: Data‐model comparisons and their consequences

AbstractFire is an endemic process at high latitudes, connected to a range of other land surface properties, such as land cover, biomass, and permafrost, and intimately linked to the carbon balance of the high‐latitude land surface. Much of our current understanding of these links and their climate consequences is through land surface models, so it is important to ensure that for their credibility, these models should be consistent with available data. Over the vast panboreal region, a key source of information on fire is satellite data. Comparisons between satellite‐based burned area data from the Global Fire Emissions Database and three dynamic vegetation models (LPJ‐WM, CLM4CN, and SDGVM) indicate that all models fail to represent the observed spatial and temporal properties of the fire regime. Although the three dynamic vegetation models give comparable values of the boreal net biome production (NBP), fire emissions are found to differ by a factor 4 between the models, because of widely different estimates of burned area and because of different parameterizations of the fuel load and combustion process. Including a more realistic representation of the fire regime in the models shows that for northern high latitudes, (i) severe fire years do not coincide with source years or vice versa, (ii) the interannual variability of fire emissions does not significantly affect the interannual variability of NBP, and (iii) overall biomass values alter only slightly, but the spatial distribution of biomass exhibits changes. We also demonstrate that it is crucial to alter the current representations of fire occurrence and severity in land surface models if the links between permafrost and fire are to be captured, in particular, the dynamics of permafrost properties, such as active layer depth. This is especially important if models are to be used to predict the effects of a changing climate, because of the consequences of permafrost changes for greenhouse gas emissions, hydrology, and land cover.

Effect of permafrost on the formation of soil organic carbon pools and their physical–chemical properties in the Eastern Swiss Alps

Abstract Current climatic conditions and the occurrence of discontinuous and sporadic permafrost in the Alps result in a low turnover rate and therefore accumulation of organic matter (OM) in soils. Alpine soils are thus highly sensitive to global warming that potentially promotes the mineralisation of soil organic matter (SOM). This process might increase the release of CO2 to the atmosphere. Our aim was to investigate the potential effect of permafrost thawing by the analysis of the physical–chemical soil properties of permafrost versus non-permafrost sites. Specifically, we i) quantified the SOM stocks at such sites, ii) characterised SOM and its physical and chemical fractions and iii) estimated the age range of the bulk soil and stable C-fraction (radiocarbon dating). In south-eastern Switzerland, two areas above the timberline and one below the timberline (where isolated permafrost was verified) were investigated in detail. At each site, the experimental set-up consisted in the comparison of nearby soils that were either influenced or not by permafrost. The C-stocks (down to the C horizon or rock surface) did not show a significant difference between permafrost and non-permafrost soils and were in the same range of 10–15 kg/m2 in alpine (grassland) and subalpine (forest) sites. Above the timberline, the bulk SOM showed a distinct higher age at permafrost sites compared to non-permafrost sites. This higher age was even more evident in the stable C-fraction (resistant to an H2O2 treatment), where ages of up to 11 ky in permafrost soils were recorded. The highest age obtained in the stable C-fraction in non-permafrost soils was around 4 ky. Consequently, climatic conditions and the occurrence of discontinuous permafrost resulted in a very low turnover rate of SOM. At the subalpine site, the difference between permafrost and non-permafrost sites was less. At both sites (alpine and subalpine), DRIFT (Diffuse Reflection Infrared Fourier Transform) was used to determine the functional groups in the bulk soil and in the stable C-fraction. In general, the stable C-fraction had a different composition compared to the bulk SOM at non-permafrost sites; this was mostly not the case at the permafrost sites. This confirms that different decomposition processes occur between permafrost and non-permafrost sites. Furthermore, permafrost sites accumulated more the low-density physical fractions of SOM that are potentially easily degradable. The obtained results suggest that a warmer climate may not necessarily lead to an increased CO2 release from SOM-degradation in permafrost soils compared to non-permafrost soils. High-alpine soils and OM furthermore integrate a multi-facetted response to the past and ongoing surrounding conditions. The melting of permafrost will most likely enhance vegetation growth, which to a certain degree will probably compensate for carbon losses on the long-term.

Structure and properties of ice-rich permafrost near Anchorage, Alaska

Abstract Geotechnical investigations in the vicinity of Anchorage, Alaska revealed a body of ice-rich permafrost up to 12 m thick and approximately 150 m long. Mean annual air temperature in Anchorage is + 2.2 °C which is unfavorable to the existence of permafrost. However, isolated masses of relic permafrost exist at temperatures close to 0 °C protected from rapid thawing by a thick layer of peat and soils with high ice content. Frozen soils found at the study site include silty clay of glacio-lacustrine origin with numerous layers of segregated ice up to 70 cm in thickness. The average volume of visible ice is 42.5%; and total gravimetric water content is 68%. With an average permafrost thickness of 9.5 m and an average thaw strain of 40%, the thaw settlement of the surface is expected to be at least 3.8 m after degradation of permafrost, an unacceptable deformation for any engineered structure on these soils.