Slope failures resulting from thaw slumps in permafrost regions, have developed widely under the influence of climate change and engineering activities. The shear strength at the interface between the active layer and permafrost (IBALP) at maximum thawing depth is a critical factor to evaluate stability of permafrost slopes. Traditional direct shear, triaxial shear, and large-scale in-situ shear experiments are unsuitable for measuring the shear strength parameter of the IBALP. Based on the characteristics of thaw slumps in permafrost regions, this study proposes a novel test method of self-weight direct shear instrument (SWDSI), and its principle, structure, measurement system and test steps are described in detail. The shear strength of the IBALP under maximum thaw depth conditions is measured using this method. The results show that under the condition that the permafrost layer is thick underground ice and the active layer consists of silty clay with 20% water content, the test results are in good agreement with the results of field large-scale direct shear tests and are in accordance with previous understandings and natural laws. The above analysis indicates that the method of the SWDSI has a reliable theoretical basis and reasonable experimental procedures, and meets the needs of stability assessment of thaw slumps in permafrost regions. The experimental data obtained provide important parameter support for the evaluation of related geological hazards.

Thaw hazards in high-latitude and glaciated regions are becoming increasingly frequent because of global climate warming and human activities, posing significant threats to infrastructure stability and environmental sustainability. However, despite these risks, comprehensive investigations of thaw-hazard susceptibility in permafrost regions remain limited. Here, this gap is addressed by a systematic and long-term investigation of thaw hazards in China's Qinghai Province as a representative permafrost area. A detailed inventory of 534 thawhazard sites was developed based on remote sensing, field verification, and surveys by a UAV, providing critical data for susceptibility analysis. Eleven environmental factors influencing thaw hazards were identified and analyzed using information gain and Shapley additive explanation. By using the random forest model, a susceptibility map was generated, categorizing the study area into five susceptibility classes: very low, low, moderate, high, and very high. The key influencing factors include precipitation, permafrost type, temperature change rate, and human activity. The results reveal that 17.5 % of the permafrost region within the study area is classified as high to very high susceptibility, concentrated primarily near critical infrastructure such as the Qinghai-Tibet Railway, potentially posing significant risks to its structural stability. The random forest model shows robust predictive capability, achieving an accuracy of 0.906 and an area under the receiver operating characteristic curve of 0.965. These findings underscore the critical role of advanced modeling in understanding the spatial distribution and drivers of thaw hazards, offering actionable insights for hazard mitigation and infrastructure protection in permafrost regions under a changing climate.

Global warming results in more field soil suffering freeze-thaw cycles (FTCs). The environmental risk of microplastics-recognized as a global emerging contaminant-in soils undergoing FTCs remains unclear. In this study, the combined effects of FTCs and poly(butylene adipate-co-terephthalate) (PBAT) microplastics on microbial degradation of atrazine in Mollisols were investigated. Freeze-thaw cycles, rather than microplastics, significantly inhibited the biodegradation of atrazine in soil, with average inhibition ratios of 33.69% and 4.99% for FTCs and microplastics, respectively. Thawing temperature was the main factor driving the changes in soil microbial community structures and the degradation of atrazine. The degradable microplastics with an amendment level of 0.2% had different and limited effects on the dissipation of atrazine under different modes of FTCs. Among the four modes, microplastics only showed a trend toward promoting atrazine degradation under high-frequency and high-thawing-temperature FTCs. Across all modes, microplastics altered microbial interactions and ecological niches that included affecting specific bacterial abundance, module keystone species, microbial network complexity, and functional genes in soil. There's no synergistic effect between microplastics and FTCs on the degradation of atrazine in soil within a short-term period. This study provides critical insights into the ecological effects of the new biodegradable mulch film-derived microplastics in soil under FTCs.

The freeze-thaw erosion zone of the Tibetan Plateau (FTZTP) maintains an ecologically fragile system with enhanced thermal sensitivity under climate warming. Vegetation phenology in this cryosphere-dominated environment acts as a crucial biophysical indicator of climate variability, showing potentially amplified responses to environmental changes relative to other ecosystems. To investigate vegetation phenological characteristics and their climate responses, we derived key phenological parameters (the start, end and length of growing season-SOS, EOS, LOS) for the FTZTP from 2001 to 2021 using MODIS EVI data and analysed their spatiotemporal patterns and climatic drivers. Results indicated that the spatial distribution of phenology was highly heterogeneous, influenced by local climate, complex topography and diverse vegetation. SOS generally exhibited a delayed trend from east to west, while EOS was progressively later from the central plateau towards the southeast and southwest. Consequently, LOS shortened along both east-west and south-north gradients. Under sustained warming and wetting, the region experienced intensified freeze-thaw cycles, characterised by a delayed freeze-start, advanced thaw-end and shortened freeze-thaw duration. Both climate warming and freeze-thaw changes drove an overall significant advancement of SOS (-3.1 days/decade), delay of EOS (+2.2 days/decade) and extension of LOS (+5.3 days/decade) over the 21-year period. Notably, an abrupt phenological shift occurred around 2015. Prior to 2015, both SOS and EOS advanced, whereas afterward, SOS transitioned to a delaying trend and EOS exhibited a markedly stronger delay, leading to a pronounced extension of LOS. This regime shift was primarily attributed to changes in hydrothermal conditions controlled by climate warming and evolving freeze-thaw dynamics, with temperature being the dominant factor and precipitation exerting seasonally differential effects. Our findings elucidate the complex responses of alpine cryospheric ecosystems to climate change, revealing freeze-thaw processes as a key modulator of vegetation phenology.

Climate change is driving permafrost thaw, releasing previously frozen resources, such as nitrogen, to the soil active layer. In low-nitrogen systems, like boreal peatlands, this novel nitrogen source may benefit plant productivity. However, other resource limitations (for example, light) may limit plant access to thaw-front nitrogen. We used a stable isotope experiment to explore variations in understory boreal plant species' ability to take up different forms of newly released nitrogen from permafrost thaw under different canopy covers. This experiment occurred in a peatland in the sporadic discontinuous permafrost zone of the Northwest Territories, Canada. We added N-15 labelled ammonium, nitrate, and the amino acid glycine at the thaw front (40 cm depth) at two sites differentiated by high and low canopy cover and determined uptake of N-15 in leaves of several common and abundant boreal plant species. We found that the probability of plant uptake of thaw-front nitrogen was significantly greater at low canopy cover sites; however, nitrogen form, plant species, and foliar N-mass had no effect. We further found that Rubus chamaemorus had the highest foliar N-mass followed by Rhododendron groenlandicum, Chamaedaphne calyculata, and Vaccinium vitis-idaea. Our results demonstrate that access to nitrogen released from permafrost thaw by boreal plants may be mediated by light availability. Understanding the variation in site response to permafrost thaw contributes to our understanding of how boreal peatlands will change with ongoing climate change.

Permafrost thawing is a critical climate tipping point, with catastrophic consequences. Existing stabilization methods rely on refrigerant-based systems, such as thermosyphons and active refrigeration, which are capital-intensive, energy-demanding, or increasingly ineffective in warming climates. Most infrastructure built on permafrost requires continuous heat removal from the foundation as the underlying permafrost becomes progressively unstable. To address these challenges, we demonstrate a fully biomass-derived cooling geotextile that can effectively mitigate permafrost thawing through scalable nanoprocessing via a roll-to-roll fabrication (1.3 mmin-1). The cooling geotextile features a hierarchical three-layer design: a strong woven biomass scaffold, a permeable nonwoven fiber network, and an optimized porous coating layer with micro- and nano-structures. When anchored to bare ground, it extracts heat to the cold sky, enhances albedo from similar to 30% to 96.3%, and establishes a thermal barrier between soil and air. Engineered for Arctic durability, it withstands strong winds, extreme cold, and freeze-thaw cycles, exceeding the American National Engineering Handbook requirements (tensile strength 1,682 kg; tear strength 191 kg; puncture strength 61 kg). Field tests in West Lafayette, IN (40 degrees 25 ' 21 '' N, 86 degrees 55 ' 12 '' W) reveal up to 25 degrees C soil cooling under 500 Wm-2 irradiance. Its lightweight (0.8 kgm-2) and rollable attributes enable scalable and fast localized deployment. Simulations predict up to 12 degrees C surface cooling during Arctic summer (2020-2050), preventing up to 40,000 km2 of permafrost from thawing. Completely derived from biomass, cooling geotextile ensures a low carbon footprint (0.7 kgm-2), positioning itself as a sustainable solution for reinforcing Arctic coastline, reconstructing thawing landscape, and restoring the environment.

Substantial nitrous oxide (N2O) emissions from permafrost-affected regions could accelerate climate warming, given that N2O exhibits approximately 300 times greater radiative forcing potential than carbon dioxide. Pronounced differences exist in N2O emissions between freeze and thaw periods (FP and TP), but the mechanisms by which environmental factors regulate the production and emission of N2O during these two periods have not been thoroughly examined. We therefore combined static chamber gas chromatography, in-situ soil temperature (ST) and moisture (SM) monitoring, and 16S rRNA sequencing to investigate seasonal N2O variations in the Qinghai-Tibet Plateau (QTP) alpine meadow ecosystem, and assess the relative contributions of environmental and microbial drivers. Our findings indicate that N2O fluxes (-3.15 to 6.10 mu g m-2 h-1) fluctuated between weak sources and sinks, peaking during FP, particularly at its late stage with initial surface soil thawing. Soil properties affect N2O emissions by regulating denitrification processes and altering microbial community diversity. During the FP, ST fluctuations control N2O release by modifying mineral nutrient availability. During TP, soil texture modulates denitrification-driven N2O production through its effect on SM. Spring N2O pulses likely originate from microbial reactivation in thawed soil. N2O accumulated in frozen soil may gradually release during vertical profile thawing. On the QTP, a warmer and wetter climate scenario may alter N2O emissions by modifying the duration of the FP and TP and phase-specific hydrothermal allocation. This study provides mechanistic insights for predicting climate change impacts on N2O flux in fragile alpine meadow ecosystems.

Highlights What are the main findings? A density-based Freeze-Thaw Disturbance Index (FTDI) was proposed to quantify the spatial clustering of disturbance features. Higher FTDI values indicate a greater likelihood of surface thawing processes triggered by rising temperatures. What are the implications of the main findings? Regions with relatively high FTDI values often contain substantial amounts of organic carbon and may experience delayed vegetation green-up despite general warming trends. FTDI reflects the impact of potential freeze-thaw dynamic phase changes on the geomorphology and offers a new perspective for monitoring permafrost degradation.Highlights What are the main findings? A density-based Freeze-Thaw Disturbance Index (FTDI) was proposed to quantify the spatial clustering of disturbance features. Higher FTDI values indicate a greater likelihood of surface thawing processes triggered by rising temperatures. What are the implications of the main findings? Regions with relatively high FTDI values often contain substantial amounts of organic carbon and may experience delayed vegetation green-up despite general warming trends. FTDI reflects the impact of potential freeze-thaw dynamic phase changes on the geomorphology and offers a new perspective for monitoring permafrost degradation.Abstract The soil freeze-thaw process is a dominant disturbance in the seasonally frozen ground and the active layer of permafrost, which plays a crucial role in the surface energy balance, water cycle, and carbon exchange and has a pronounced influence on vegetation phenology. This study proposes a novel density-based Freeze-Thaw Disturbance Index (FTDI) based on the identification of the freeze-thaw disturbance region (FTDR) over the Qinghai-Tibet Plateau (QTP). FTDI is defined as an areal density metric based on geomorphic disturbances, i.e., the proportion of FTDRs within a given region, with higher values indicating greater areal densities of disturbance. As a measure of landform clustering, FTDI complements existing freeze-thaw process indicators and provides a means to assess the geomorphic impacts of climate-driven freeze-thaw changes during permafrost degradation. The main conclusions are as follows: the FTDR results that are identified by the random forest model are reliable and highly consistent with ground observations; the FTDRs cover 8.85% of the total area of the QTP, and mainly in the central and eastern regions, characterized by prolonged freezing durations and the average annual ground temperature (MAGT) is close to 0 degrees C, making the soil in these regions highly susceptible to warming-induced disturbances. Most of the plateau exhibits low or negligible FTDI values. As a geomorphic indicator, FTDI reflects the impact of potential freeze-thaw dynamic phase changes on the surface. Higher FTDI values indicate a greater likelihood of surface thawing processes triggered by rising temperatures, which impact surface processes. Regions with relatively high FTDI values often contain substantial amounts of organic carbon, and may experience delayed vegetation green-up despite general warming trends. This study introduces the FTDI derived from the FTDR as a novel index, offering fresh insights into the study of freeze-thaw processes in the context of climate change.

Suprapermafrost groundwater (SPG) plays a critical role in hydrological and ecological functioning of permafrost regions, yet its spatiotemporal dynamics and controlling mechanisms remain poorly understood on the Qinghai-Tibet Plateau (QTP). Here, we integrated in situ observations, geophysical surveys, and machine learning (ML) models (including XGBoost, LightGBM, and RandomForest) to investigate the seasonal variation, drivers, and projections of SPG dynamics in alpine meadow (AM) and alpine wet meadow (AWM) ecosystems. Results showed that SPG tables ranged from -1.1 to -0.1 m in AM and from -1.3 to -0.2 m in AWM during the warm season. SPG fluctuations were primarily driven by thaw depth (TD) and rainfall infiltration and exhibited similar seasonal patterns across both ecosystems. A greater TD was associated with a deeper SPG table, as deeper thawing expanded the unsaturated zone and enhanced vertical drainage, indicating an exponential relationship between TD and SPG table position, and a linear relationship with aquifer thickness. In contrast, rainfall infiltration increased shallow soil moisture and elevated SPG tables, with responses influenced by rainfall intensity, duration, and infiltration pathways. Spatial heterogeneity in SPG distribution was further shaped by vegetation structure and microtopographic variation. Furthermore, ML models projected that mean summer SPG table depths in the 2090s would increase by 0.06 m under SSP126 and 0.64 m under SSP585 in AWM ecosystems, and by 0.37 m under SSP126 and 0.87 m under SSP585 in AM ecosystems. These findings provide new insights into how climate warming affects hydrological processes in permafrost regions of the QTP.

Uneven displacement of permafrost has become a major concern in cold regions, particularly under repeated freezing-thawing cycles. This issue poses a significant geohazard, jeopardizing the safety of transportation infrastructure. Statistical analyses of thermal penetration suggest that the problem is likely to intensify as water erosion expands, with increasing occurrences of uneven displacement. To tackle the challenges related to mechanical behavior under cyclic loading, the New Geocell Soil System has been implemented to mitigate hydrothermal effects. Assessment results indicate that the New Geocell Soil System is stable and effective, offering advantages in controlling weak zones on connecting slopes and reducing uneven solar radiation. Consequently, the New Geocell Soil System provides valuable insights into the quality of embankments and ensures operational safety by maintaining displacement at an even level below 1.0 mm. The thermal gradient is positive, with displacement below 6 degrees C/m, serving as a framework for understanding the stability of the subgrade. This system also enhances stress and release the sealing phenomenon.