Permafrost Thaw Research Articles

Accelerated permafrost thaw and increased drainage in the active layer: Responses from experimental surface alteration

Erosion and infrastructure in the Arctic can change the thickness of the active layer which can subsequently alternate the thermal-hydrological regime and change the drainage patterns on slopes. Previous studies have shown that drainage can either decrease due to the movement of water occurring in deeper soil layers with lower permeability or increase due to the formation of features like gullies and channels.In a field experiment conducted in Qaanaaq, Greenland, the surface topography was altered by adding 35 cm soil in one treatment, removing 33 cm in another, while an untreated plot measuring 10 × 10 m was maintained for comparison purposes. The temperature and water content of these plots were monitored in the three following years. Based on field measurements, a 1-dimensional model was set up in CoupModel to simulate the field experiment and quantify changes in the thickness of the saturated zone and drainage as a consequence of the treatment.Both field observations and simulations show that the addition and removal of soil changed the thickness of the saturated layer in the active layer, which changed the thermal properties in the soil and, thus, the response of thawing or recovery of permafrost. The simulations showed that during the summer depressions there were higher water contents, which accelerated warming of the soil and increased permafrost thawing of 35.7 cm in depth. In contrast, raising the soil surface aggregated only 19.8 cm of permafrost due to higher buffering from lower water contents. Changed active layer thickness altered the thickness of the saturated zone, leading to changed drainage patterns: In depressions, first drainage occurs three days earlier, and maximum daily drainage is increased by 154% as compared to ambient conditions. In contrast, raising the surface delayed the runoff from the plot by up to eight days, and decreased the maximum daily drainage to 72%. Effects of the treatment were most pronounced during the first year after the experiment, with diminishing effects during the consecutive year as the system equilibrated to the new state. Results from our study can advance our understanding of impacts of both natural and human-induced surface alterations on active layer thickening and water movement in permafrost-affected areas, which ultimately affect the entire ecosystem and the living conditions for local communities.

Scaling waterbody carbon dioxide and methane fluxes in the arctic using an integrated terrestrial-aquatic approach

In the Arctic waterbodies are abundant and rapid thaw of permafrost is destabilizing the carbon cycle and changing hydrology. It is particularly important to quantify and accurately scale aquatic carbon emissions in arctic ecosystems. Recently available high-resolution remote sensing datasets capture the physical characteristics of arctic landscapes at unprecedented spatial resolution. We demonstrate how machine learning models can capitalize on these spatial datasets to greatly improve accuracy when scaling waterbody CO2 and CH4 fluxes across the YK Delta of south-west AK. We found that waterbody size and contour were strong predictors for aquatic CO2 emissions, attributing greater than two-thirds of the influence to the scaling model. Small ponds (<0.001 km2) were hotspots of emissions, contributing fluxes several times their relative area, but were less than 5% of the total carbon budget. Small to medium lakes (0.001–0.1 km2) contributed the majority of carbon emissions from waterbodies. Waterbody CH4 emissions were predicted by a combination of wetland landcover and related drivers, as well as watershed hydrology, and waterbody surface reflectance related to chromophoric dissolved organic matter. When compared to our machine learning approach, traditional scaling methods that did not account for relevant landscape characteristics overestimated waterbody CO2 and CH4 emissions by 26%–79% and 8%–53% respectively. This study demonstrates the importance of an integrated terrestrial-aquatic approach to improving estimates and uncertainty when scaling C emissions in the arctic.

The start of frozen dates over northern permafrost regions with the changing climate.

The soil freeze-thaw cycle in the permafrost regions has a significant impact on regional surface energy and water balance. Although increasing efforts have been made to understand the responses of spring thawing to climate change, the mechanisms controlling the global interannual variability of the start date of permafrost frozen (SOF) remain unclear. Using long-term SOF from the combinations of multiple satellite microwave sensors between 1979 and 2020, and analytical techniques, including partial correlation, ridge regression, path analysis, and machine learning, we explored the responses of SOF to multiple climate change factors, including warming (surface and air temperature), start date of permafrost thawing (SOT), soil properties (soil temperature and volume of water), and the snow depth water equivalent (SDWE). Overall, climate warming exhibited the maximum control on SOF, but SOT in spring was also an important driver of SOF variability; among the 65.9% significant SOT and SOF correlations, 79.3% were positive, indicating an overall earlier thawing would contribute to an earlier frozen in winter. The machine learning analysis also suggested that apart from warming, SOT ranked as the second most important determinant of SOF. Therefore, we identified the mechanism responsible for the SOT-SOF relationship using the SEM analysis, which revealed that soil temperature change exhibited the maximum effect on this relationship, irrespective of the permafrost type. Finally, we analyzed the temporal changes in these responses using the moving window approach and found increased effect of soil warming on SOF. In conclusion, these results provide important insights into understanding and predicting SOF variations with future climate change.

Continental heat storage: contributions from the ground, inland waters, and permafrost thawing

Abstract. Heat storage within the Earth system is a fundamental metric for understanding climate change. The current energy imbalance at the top of the atmosphere causes changes in energy storage within the ocean, the atmosphere, the cryosphere, and the continental landmasses. After the ocean, heat storage in land is the second largest term of the Earth heat inventory, affecting physical processes relevant to society and ecosystems, such as the stability of the soil carbon pool. Here, we present an update of the continental heat storage, combining for the first time the heat in the land subsurface, inland water bodies, and permafrost thawing. The continental landmasses stored 23.8 ± 2.0 × 1021 J during the period 1960–2020, but the distribution of heat among the three components is not homogeneous. The sensible diffusion of heat through the ground accounts for ∼90 % of the continental heat storage, with inland water bodies and permafrost degradation (i.e. latent heat) accounting for ∼0.7 % and ∼9 % of the continental heat, respectively. Although the inland water bodies and permafrost soils store less heat than the solid ground, we argue that their associated climate phenomena justify their monitoring and inclusion in the Earth heat inventory.

Priming effect stimulates carbon release from thawed permafrost.

Climate warming leads to widespread permafrost thaw with a fraction of the thawed permafrost carbon (C) being released as carbon dioxide (CO2 ), thus triggering a positive permafrost C-climate feedback. However, large uncertainty exists in the size of this model-projected feedback, partly owing to the limited understanding of permafrost CO2 release through the priming effect (i.e., the stimulation of soil organic matter decomposition by external C inputs) upon thaw. By combining permafrost sampling from 24 sites on the Tibetan Plateau and laboratory incubation, we detected an overall positive priming effect (an increase in soil C decomposition by up to 31%) upon permafrost thaw, which increased with permafrost C density (C storage per area). We then assessed the magnitude of thawed permafrost C under future climate scenarios by coupling increases in active layer thickness over half a century with spatial and vertical distributions of soil C density. The thawed C stocks in the top 3 m of soils from the present (2000-2015) to the future period (2061-2080) were estimated at 1.0 (95% confidence interval (CI): 0.8-1.2) and 1.3 (95% CI: 1.0-1.7) Pg (1 Pg = 1015 g) C under moderate and high Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5, respectively. We further predicted permafrost priming effect potential (priming intensity under optimal conditions) based on the thawed C and the empirical relationship between the priming effect and permafrost C density. By the period 2061-2080, the regional priming potentials could be 8.8 (95% CI: 7.4-10.2) and 10.0 (95% CI: 8.3-11.6) Tg (1 Tg = 1012 g) C year-1 under the RCP 4.5 and RCP 8.5 scenarios, respectively. This large CO2 emission potential induced by the priming effect highlights the complex permafrost C dynamics upon thaw, potentially reinforcing permafrost C-climate feedback.

SWAMP: A new experiment for simulating permafrost warming and active layer deepening on the Tibetan Plateau

Abstract Our knowledge on the responses of permafrost ecosystems to climate warming is critical for assessing the direction and magnitude of permafrost carbon‐climate feedback. However, most of the previous experiments have only been able to warm the air and surface soil, with limited effects on the permafrost temperature. Consequently, it remains challenging to realistically simulate permafrost thawing in terms of increased active layer (a layer freezing and thawing seasonally above permafrost) thickness under climate warming scenarios. Here, we presented the experimental design and warming performance of a novel experiment, Simulate Warming at Mountain Permafrost (SWAMP), the first one to successfully simulate permafrost warming and the subsequent active layer deepening in a swamp meadow situated on the Tibetan Plateau. Infrared heating was employed as above‐ground warming to elevate the temperature of the air and surface soil, and heating rods were inserted vertically in the soil to provide below‐ground warming for transmitting heat to the deep active layer and even to permafrost deposits. In 3 m diameter warmed circular plots, the air and the entire soil profile (from surface soil to 120 cm) was effectively heated, with an increase of approximately 2°C in the upper 60 cm, which progressively weakened with soil depth. Warming increased soil moisture across the growing season by inducing an earlier thawing of the soil. Values varied from 1.8 ± 1.8 to 12.3 ± 2.3% according to the soil depth. Moreover, during the growing season, the warmed plots had greater thaw depths and a deeper active layer thickness of 12.6 ± 0.8 cm. In addition, soil thawing duration was prolonged by the warming, ranging from 22.8 ± 3.3 to 49.3 ± 4.5 days depending on the soil depth. The establishment of SWAMP provides a more realistic simulation of warming‐induced permafrost thaw, which can then be used to explore the effect of climate warming on permafrost ecosystems and the potential permafrost carbon‐climate feedback. Notably, our experiment is more advantageous for investigating how deep soil processes respond to climate warming and active layer deepening, compare with experiments which use passive warming techniques such as open top chambers (OTCs).

Stress prediction of heated crude oil pipeline in permafrost region via fully coupled heat-moisture-stress numerical simulation and SVM algorithm

Large diameter crude oil transmission pipelines in unstable permafrost areas have been put into operation in China in recent dozen years. The perennial positive temperature operation of buried heating transmission pipelines leads to freeze–thaw of the soil around pipelines, and the axial stresses generated by thawing settlement of permafrost may induce fracture failure of weld crack. However, there are many shortcomings in existing frozen soil thawing settlement analysis and pipeline stress assessment methods, which makes it difficult to accurately analyze and predict the axial additional stress of pipelines induced by thawing settlement. Based on heat conduction and permafrost thawing consolidation settlement theory, numerical inversion analysis of centrifuge test was conducted to verify the accuracy of the finite element method. The key influencing factors such as wall thickness, insulation layer thickness, buried depth of pipe, and length of thawing settlement zone on the axial stress and strain state of buried pipeline under the condition of double pipe operation of Mo-da line were investigated. The results show that: Pipeline with an insulation layer, larger wall thickness and smaller buried depth is beneficial to improve the bearing capacity of buried pipeline under thawing settlement of permafrost. The axial stress varies nonlinearly with the increase of the thawing settlement zone length. Based on support vector regression (SVR) model, the axial stress prediction model of pipe crown and invert at different positions in the thaw settlement area was proposed and verified by field monitoring data of buried pipeline. The relative error between the prediction results and the field monitoring results is less than 15 %. This study can provide some theoretical support for the structural design of pipelines in thaw settlement area.

Thermal performance and heat transfer process of an expressway embankment with horizontal-thermosyphons in permafrost regions

Two-phase closed thermosyphon (TPCT) has been considered to be an effective measure to reduce soil temperatures and maintain engineering stabilities in permafrost, but deformations and cracks of a testing expressway with inclined insertion thermosyphon embankment (ITE) were found to be serious and aggravated year by year. Monitoring results from 2011 to 2018 indicate that uneven temperatures and permafrost thawing are main causes for the disease in ITE. To address this issue, a horizontal insertion thermosyphon embankment (HTE) was proposed in this paper. Numerical results show that thermal performance of HTE is much better than that of ITE. In October of the 20th service year, base temperatures of HTE at center, sunny and shady foot can be reduced to −2.3 °C, −1.2 °C and − 1.6 °C, respectively. Low-temperature (≤ − 1 °C) contours in HTE showed a layered and nearly symmetric distribution, covering almost the entire base width range. The width of −1.5 °C isotherm can be increased by 61%, and the estimated annual heat release of deep soils can be increased by 72% compared with ITE. The thermal enhancement of HTE is because the horizontal-thermosyphon doubles the contact surface with soils and heat dissipation, and effectively reduces the heat flux difference. The horizontal-thermosyphon could be considered for application in expressways built on permafrost stratum.

Unsustainable water supply from thawing permafrost on the Tibetan Plateau in a changing climate

Unsustainable water supply from thawing permafrost on the Tibetan Plateau in a changing climate

Integrating local environmental observations and remote sensing to better understand the life cycle of a thermokarst lake in Arctic Alaska

ABSTRACT On 29 June 2022, local observers reported the drainage of a 0.5 ha lake near Qikiqtaġruk (Kotzebue), Alaska, that prompted this collaborative study on the life cycle of a thermokarst lake in the Arctic. Prior to its drainage, the lake expanded from 0.13 ha in 1951 to 0.54 ha in 2021 at lateral rates that ranged from 0.25 to 0.35 m/year. During the drainage event, we estimate that 18,500 m3 of water drained from the lake into Kotzebue Sound, forming a 125-m-long thermo-erosional gully that incised 2 to 14 m in ice-rich permafrost. Between 29 June and 18 August 2022, the drainage gully expanded from 1 m to >10 m wide, mobilizing ~8,500 m3 of material through erosion and thaw. By reconstructing a pre-lake disturbance terrain model, we show that thaw subsidence occurs rapidly (0.78 m/year) upon transition from tundra to lake but that over a seventy-year period it slows to 0.12 m/year. The combination of multiple remote sensing tools and local environmental observations provided a rich data set that allowed us to assess rates of lake expansion relative to rates of sub-lake permafrost thaw subsidence as well as hypothesizing about the potential role of beavers in arctic lake drainage.

Variations of soil quality in the southern Qinghai-Tibet Plateau during 1980s to 2020s.

Climate warming and thawing of permafrost in the Qinghai-Tibet Plateau have resulted in soil erosion and the decline of soil quality. Determining the decadal variation of soil quality in the Qinghai-Tibet Plateau is the basis for scientific understanding of soil resources and the key to vegetation restoration and ecological reconstruction. In this study, we used eight indicators (including soil organic matter, total nitrogen, and total phosphorus) to eva-luate soil quality of montane coniferous forest zone (Tibet's natural geographical division zone Ⅱ) and montane shrubby steppe zone (zone Ⅳ) by calculating soil quality index (SQI) in the southern Qinghai-Tibet Plateau in the 1980s and 2020s. Variation partitioning (VPA) was used to examine the drivers for the heterogeneity of the spatial-temporal distribution of soil quality. The results showed that soil quality in each natural zone showed a downward trend in the past 40 years, with SQI of zone Ⅱ decreasing from 0.505 to 0.484 and that of zone Ⅳ decreasing from 0.458 to 0.425. The spatial distribution of soil nutrients and quality was heterogeneous, while soil nutrient conditions and quality in zone Ⅱ were better than those in zone Ⅳ in different periods. The VPA results indicated that the interaction of climate change, land degradation, and vegetation differences was the major cause of temporal variation in soil quality. Differences in climate and vegetation could better explain the spatial variation of SQI.

Continental and Glacial Runoff Fingerprints in the Canadian Arctic Archipelago, the Inuit Nunangat Ocean

AbstractRising temperatures and an acceleration of the hydrological cycle due to climate change are increasing river discharge, causing permafrost thaw, glacial melt, and a shift to a groundwater‐dominated system in the Arctic. These changes are funneled to coastal regions of the Arctic Ocean where the implications for the distributions of nutrients and biogeochemical constituents are unclear. In this study, we investigate the impact of terrestrial runoff on marine biogeochemistry in Inuit Nunangat (the Canadian Arctic Archipelago)—a key pathway for transport and modification of waters from the Arctic Ocean to the North Atlantic—using sensitivity experiments from 2002 to 2020 with an ocean model of manganese (Mn). The micronutrient Mn traces terrestrial runoff and the modification of geochemical constituents of runoff during transit. The heterogeneity in Arctic runoff composition creates distinct terrestrial fingerprints of influence in the ocean: continental runoff influences Mn in the southwestern Archipelago, glacial runoff dominates the northeast, and their influence co‐occurs in central Parry Channel. Glacial runoff carries micronutrients southward from Nares Strait in the late summer and may help support longer phytoplankton blooms in the Pikialasorsuaq polynya. Enhanced glacial runoff may increase micronutrients delivered downstream to Baffin Bay, accounting for up to 18% of dissolved Mn fluxes seasonally and 6% annually. These findings highlight how climate induced changes to terrestrial runoff may impact the geochemical composition of the marine environment, and will help to predict the extent of these impacts from ongoing alterations of the Arctic hydrological cycle.

Nitrous Oxide Dynamics in the Siberian Arctic Ocean and Vulnerability to Climate Change

AbstractNitrous oxide (N2O) is a strong greenhouse gas and stratospheric ozone‐depleting substance. Around 20% of global emissions stem from the ocean, but current estimates and future projections are uncertain due to poor spatial coverage over large areas and limited understanding of drivers of N2O dynamics. Here, we focus on the extensive and particularly data‐lean Arctic Ocean shelves north of Siberia that experience rapid warming and increasing input of land‐derived nitrogen with permafrost thaw. We combine water column N2O measurements from two expeditions with on‐board incubation of intact sediment cores to assess N2O dynamics and the impact of land‐derived nitrogen. Elevated nitrogen concentrations in water column and sediments were observed near large river mouths. Concentrations of N2O were only weakly correlated with dissolved nitrogen and turbidity, reflecting particulate matter from rivers and coastal erosion, and correlations varied between river plumes. Surface water N2O concentrations were on average close to equilibrium with the atmosphere, but varied widely (N2O saturation 38%–180%), indicating strong local N2O sources and sinks. Water column N2O profiles and low sediment‐water N2O fluxes do not support strong sedimentary sources or sinks. We suggest that N2O dynamics in the region are influenced by water column N2O consumption under aerobic conditions or in anoxic microsites of particles, and possibly also by water column N2O production. Changes in biogeochemical and physical conditions will likely alter N2O dynamics in the Siberian Arctic Ocean over the coming decades, in addition to reduced N2O solubility in a warmer ocean.

Melting of permafrost: rise of Zombies

Melting of permafrost: rise of Zombies

MOSSES OF THE WESTERN PART OF THE CHUKCHI HIGHLANDS. 3. INTERDEPENDENCE OF PERCENT COVER VALUES OF MOSSES AND VASCULAR PLANTS

In previous publications (Kholod, Afonina, 2023a, b) the dependences of the number of moss species and the values of moss percent cover in the western part of the Chukchi Highlands on a number of abiotic factors were considered. This article discusses the interdependence of the percent cover values of mosses and vascular plants in this area. On the slopes of most aspects, an increase in the percent cover values of vascular plants to a value of 65–75% is accompanied by an increase in the percent cover values of mosses (up to 40–70%), which decreases with a further increase in the percent cover values of vascular plants. Two groups of bryocenotypes, one of them being formed on dry, relatively steep slopes of the southern and western aspects with rapidly descending snow, and the other on wet, snow-covered gentle slopes of the northern and eastern aspects, characterize 2 types of natural environments of the Pleistocene-Holocene: cooling with active freezing of loose strata of slopes, and warming with intense permafrost melting and activation of slope processes, respectively. The linear relationship between the values of the percent cover of vascular plants and mosses, on the one hand, and the area of unpaved soil, on the other, is considered as a model of the settlement of soils by mosses during the transition from cold climatic epochs to warm ones. In such transitional epochs, vascular plants have an advantage in the percent cover values at the initial stage, then, with the growth of mosses, the increase in the percent cover values of vascular plants slows down, which is a manifestation of the regulatory influence of mosses through the availability of accessible water and a number of other parameters.

Warming, permafrost thaw and increased nitrogen availability as drivers for plant composition and growth across the Tibetan Plateau

Permafrost-affected ecosystems are subject to warming and thawing, which can increase the availability of subsurface nitrogen (N) with consequences in otherwise N-limited tundra and alpine vegetation. Here, we quantify the extent of warming and permafrost thawing and the corresponding effects on nitrogen availability and plant growth based on a 20-year survey across 14 sites on the Tibetan Plateau. The survey showed that most sites have been subject to warming and thawing and that the upper permafrost zone across all sites was rich in inorganic N, mainly as ammonium. We further explore the efficiency of plants to utilize 15N-labelled inorganic N over five years following 15N addition at the permafrost table far below the main root zone. The 15N experiment showed that deep-rooted plant species were able to utilize the labelled N. A SEM model suggests that changes in vegetation can be explained by both active layer warming and permafrost thawing and the associated changes in inorganic nitrogen availability. Our results highlight a feedback mechanism of climate warming, in which released plant-available N may favour deep-rooted plants. This can explain important changes in plant composition and growth across the sites on the Tibetan Plateau.

Vulnerability assessment of peatland complexes in the Hudson Plains (Ontario, Canada) to permafrost‐thaw‐induced landcover and hydrological change using a multiscale approach

AbstractThe Hudson Plains, Canada, is one of the largest, undisturbed peatland regions (370,000 km2) in the world. Air temperature in the Hudson Plains is increasing rapidly leading to unprecedented permafrost thaw. The region's remoteness has hindered our knowledge of how permafrost thaw alters peatland land cover and hydrological response at multiple scales. To assess which landscapes in the Hudson Plains are vulnerable to such disturbances, we analysed latitudinal distributions of land cover over a 300‐km transect spanning the sporadic (&lt;30% areal) to continuous (&gt;80% areal) permafrost zone in northern Ontario and quantified land cover changes over 40 years using multiple remote sensing datasets (lidar, air photographs, and high‐resolution satellite imagery). We then evaluated these landscapes at a fundamental hydrological unit, the peatland complex, identified five peatland complex types, and conceptualized their potential hydrological response using circuitry analogues. Over four decades, we found that permafrost peatlands declined by 4%, 8.5%, and 2% areal in the sporadic, discontinuous, and continuous permafrost zones, respectively. Circuitry analogues partitioned peatland complexes into their component peatland forms (e.g., permafrost peatland, bog, and fen) and represented each component's hydrological function using an electrical equivalent (e.g., generator, switch, and conductor). When interpreted at the landscape scale, circuitry analogues demonstrated latitudinal patterns in landscape structure (i.e., circuitry wiring) and indicated where permafrost thaw will have the greatest impact on landscape structure (i.e., rewiring) and therefore hydrological response. Based on these analyses, we suggest a 60‐km latitudinal segment (54.5°N to 54.9°N) where peatland complexes are most vulnerable to permafrost‐thaw‐induced land cover and hydrological change and should therefore be the focus of future research and monitoring efforts.

SATELLITE DATA IN THE STUDY OF THE ARCTIC LANDSCAPES THAWING UNDER THE CONDITIONS OF OIL AND GAS PRODUCTION

The issues of climate warming and permafrost thawing are considered. A procedure for assessing the Arctic landscapes thawing based on the calculation of the normalized differential snow index (NDSI) is proposed. The factual material over the data of the global permafrost monitoring network is presented. Monitoring studies have shown that according to the results of NDSI calculation, abnormally early snowmelt was detected in 5 cases out of 23 years of observation at the Urengoy meteorological station and in 4 cases out of 23 years at the Tarko-Sale meteorological station. The absence of snow was observed during the indicated period in 13 cases at the technogenic sites of the Urengoy field, and in 8 cases at the Tarko-Sale field. With early snowmelt, the snow index NDSI decreases, and the depth of the seasonally thawed layer increases at the sites of the Urengoy field. The NDSI index can be used directly in assessing the duration of snow cover and early snowmelt, and indirectly in studying the depth of seasonally thawed layer. The results obtained are important for predictive estimates of the rate and extent of thawing and permafrost deformation, and for the prevention of emergency situations in the oil and gas complex.

Polarimetric L-Band ALOS2-PALSAR2 for Discontinuous Permafrost Mapping in Peatland Regions

Recently, it has been shown that the long penetrating polarimetric L-band ALOS is very promising for boreal and subarctic peatland mapping and monitoring. The unique information provided by the Touzi decomposition, and the dominant-scattering-type phase in particular, on peatland subsurface water flow permits an enhanced discrimination of bogs from fens, two peatland classes that can hardly be discriminated using conventional optical remote sensing sensors and C-band polarimetric SAR. In this study, the dominant and medium-scattering phases generated by the Touzi decomposition are investigated for discontinuous permafrost mapping in peatland regions. Polarimetric ALOS2, LiDAR, and field data were collected in the middle of August 2014, at the maximum permafrost thaw conditions, over discontinuous permafrost distributed within wooded palsa bogs and peat plateaus near the Namur Lake (Northern Alberta). The ALOS2 image, which was miscellaneously calibrated with antenna cross talk (−33 dB) much higher than the actual ones, was recalibrated. This led to a reduction of the residual calibration error (down to −43 dB) and permitted a significant improvement of the dominant and medium-scattering-type phase (20∘ to −30∘) over peatlands underlain by discontinuous permafrost. The Touzi decomposition, Cloude–Pottier α-H incoherent target scattering decomposition, and the HH-VV phase difference were investigated, in addition to the conventional multipolarization (HH, HV, and VV) channels, for discontinuous permafrost mapping using the recalibrated ALOS2 image. A LiDAR-based permafrost classification developed by the Alberta Geological Survey (AGS) was used in conjunction with the field data collected during the ALOS2 image acquisition for the validation of the results. It is shown that the dominant- and scattering-type phases are the only polarimetric parameters which can detect peatland subsurface discontinuous permafrost. The medium-scattering-type phase, ϕs2, performs better than the dominant-scattering-type phase, ϕs1, and permits a better detection of subsurface discontinuous permafrost in peatland regions. ϕs2 also allows for a better discrimination of areas underlain by permafrost from the nonpermafrost areas. The medium Huynen maximum polarization return (m2) and the minimum degree of polarization (DoP), pmin, can be used to remove the scattering-type phase ambiguities that might occur in areas with deep permafrost (more than 50 cm in depth). The excellent performance of polarimetric PALSAR2 in term of NESZ (−37 dB) permits the demonstration of the very promising L-band long-penetration SAR capabilities for enhanced detection and mapping of relatively deep (up to 50 cm) discontinuous permafrost in peatland regions.

Novel selection of environment-friendly curing agents for thawing permafrost: Alkali-activated ground granulated blast-furnace slag

Permafrost thawing deformation due to the climate warming has been continuously increasing in the Qinghai-Tibet Plateau, which may influence the stability of local infrastructures and cause frequent subgrade diseases. Although the effectiveness of cement has been certified to solidify thawed permafrost, the usage of cement is gradually limited due to its energy consumption and CO2 emissions. The alkali-activated ground granulated blast-furnace slag (GGBS), as waste by-products, has been widely used in the application of soil stabilization under normal temperature, but there exist few investigations on its application in cold regions, such as permafrost regions. The study aims to investigate the effectiveness of calcium carbide residue (CCR)-GGBS and NaOH-GGBS as curing agents to solidify thawing permafrost cured at low temperature. Simultaneously, the conventional Portland cement (PC) is also selected as the comparison. Laboratory tests, containing the unconfined compressive strength (UCS), pH, electron microscopy (SEM)/ energy dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP) tests, were carried out to investigate the effect of different influence factors including alkali activator types, activator content, and curing time on the strength development. The experiment results showed that alkali-activated GGBS with the optimum activator content can effectively improve the strength of thawing permafrost at low temperature. Furthermore, on the basis of strength difference (ΔUCS) and strength growth rate (UCSgr), it demonstrates that the best approach to development strength is to combine 30% GGBS with 20% CCR or NaOH. The microstructure analysis showed that alkali-activated GGBS is conducive to the polymerization reaction, and the strength development is attributed to the formation of the dense skeleton structure. Finally, the efficacy of alkali-activated GGBS as an alternative and green curing agent to solidify thawing permafrost was confirmed based on the stabilization mechanism and analysis of environmental benefit.