Iron (Fe) minerals possess a huge specific surface area and high adsorption affinity, usually considered as rust tanks of organic carbon (OC), playing an important role in global carbon storage. Microorganisms can change the chemical form of Fe by producing Fe-chelating agents such as side chains and form a stable complex with Fe(III), which makes it easier for microorganisms to use. However, in seasonal frozen soil thawing, the succession of soil Fe-cycling microbial communities and their coupling relationship with Fe oxides and Fe-bound organic carbon (Fe-OC) remains unclear. We characterized changes in the Fe phase, Fe-OC, Fe-oxidizing bacteria (FeOB), and Fe-reducing bacteria (FeRB) in the subsoil and analyzed the microbial mechanism underlying Fe-OC changes in alpine grassland by constructing a composite structural equation model (SEM). We found that the Fe(III) content consistently exceeded that of Fe(II). Among the three types of Fe oxides, organically complex Fe (Fe-p) decreased from 2.54 to 2.30 gkg(-1), whereas the opposite trend was observed for poorly crystalline Fe (Fe-o). The Fe-OC content also decreased (from 10.31 to 9.47 gkg(-1); p < 0.05). Fe-cycling microorganisms were markedly affected by the thawing of frozen soil (except FeRB). Fe-p and Feo directly affected changes in Fe-OC. Soil moisture (SM) and FeOB were significant indirect factors affecting Fe-OC changes. Freeze-thaw changes in the subsoil of alpine grassland in Central Asia significantly affected FeOB and Fe oxides, thus affecting the Fe-OC content. To the best of our knowledge, this was the first study to examine the influence of Fe-cycling microorganisms on the Fe phase and Fe-OC in the soil of alpine grassland in Central Asia. Overall, our findings provide scientific clues for exploring the biogeochemical cycle process in future climate change.

Mountain permafrost extends over a vast area throughout the Chilean and Argentinean Andes, making it a key component of these mountain ecosystems. To develop an overview of the current state of knowledge on southern Andean permafrost, it is essential to outline appropriate research strategies in a warmer climate context. Based on a comprehensive review of existing literature, this work identifies eight main research themes on mountain permafrost in the Chilean and Argentinean Andes: paleoenvironmental reconstructions, permafrost-derived landforms inventories, permafrost distribution models, internal structure analysis, hydrogeochemistry, permafrost dynamics, geological hazards, and transitional landscape studies. This extensive review work also highlights key debates concerning the potential of permafrost as a water resource and the factors influencing its distribution. Furthermore, we identified several challenges the scientific community must address to gain a deeper understanding of mountain permafrost dynamics. Among these challenges, we suggest tackling the need to broaden spatial focus, along with the use of emerging technologies and methodologies. Additionally, we emphasize the importance of developing interdisciplinary approaches to effectively identify the impacts of climate change on mountain permafrost. Such efforts are essential for adequately preparing scientists, institutional entities, and society to address future scenarios.

Over the past decades, the cryosphere has changed significantly in High Mountain Asia (HMA), leading to multiple natural hazards such as rock-ice avalanches, glacier collapse, debris flows, landslides, and glacial lake outburst floods (GLOFs). Monitoring cryosphere change and evaluating its hydrological effects are essential for studying climate change, the hydrological cycle, water resource management, and natural disaster mitigation and prevention. However, knowledge gaps, data uncertainties, and other substantial challenges limit comprehensive research in climate-cryosphere-hydrology-hazard systems. To address this, we provide an up-to-date, comprehensive, multidisciplinary review of remote sensing techniques in cryosphere studies, demonstrating primary methodologies for delineating glaciers and measuring geodetic glacier mass balance change, glacier thickness, glacier motion or ice velocity, snow extent and water equivalent, frozen ground or frozen soil, lake ice, and glacier-related hazards. The principal results and data achievements are summarized, including URL links for available products and related data platforms. We then describe the main challenges for cryosphere monitoring using satellite-based datasets. Among these challenges, the most significant limitations in accurate data inversion from remotely sensed data are attributed to the high uncertainties and inconsistent estimations due to rough terrain, the various techniques employed, data variability across the same regions (e.g., glacier mass balance change, snow depth retrieval, and the active layer thickness of frozen ground), and poor-quality optical images due to cloudy weather. The paucity of ground observations and validations with few long-term, continuous datasets also limits the utilization of satellite-based cryosphere studies and large-scale hydrological models. Lastly, we address potential breakthroughs in future studies, i.e., (1) outlining debris-covered glacier margins explicitly involving glacier areas in rough mountain shadows, (2) developing highly accurate snow depth retrieval methods by establishing a microwave emission model of snowpack in mountainous regions, (3) advancing techniques for subsurface complex freeze-thaw process observations from space, (4) filling knowledge gaps on scattering mechanisms varying with surface features (e.g., lake ice thickness and varying snow features on lake ice), and (5) improving and cross-verifying the data retrieval accuracy by combining different remote sensing techniques and physical models using machine learning methods and assimilation of multiple high-temporal-resolution datasets from multiple platforms. This comprehensive, multidisciplinary review highlights cryospheric studies incorporating spaceborne observations and hydrological models from diversified techniques/methodologies (e.g., multi-spectral optical data with thermal bands, SAR, InSAR, passive microwave, and altimetry), providing a valuable reference for what scientists have achieved in cryosphere change research and its hydrological effects on the Third Pole.

As an essential link between terrestrial and climatic ecosystems, vegetation has been altered by the soil hy-drological environment associated with frozen soil thaw. However, it is not clear whether fluctuating soil moisture (SM) within the frozen soil zone alters the hydrologic environment to alleviate water stress in plants further, and there are scant previous studies at large scale on whether there is a threshold for SM on vegetation greening. This study integrated SM monitoring data at 125 stations from existing studies, then quantified the advantages of six remote sensing/reanalysis SM products: QTP-DNN-Sm, Global Land Data Assimilation System (GLDAS-Noah), European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5-Land), European Space Agency Climate Change Initiative (ESA CCI), Global-SM, and QTP-SM. Moreover, we assessed the influence of single and multiple regional environmental elements (temperature, precipitation, land surface temperature (LST), normalized difference vegetation index (NDVI), and snow) on SM, as well as identified four trends of SM and vegetation growth for 51.26% of the Tibetan Plateau (TP). The results are as follows: 1) The overall performance of QTP-DNN-Sm products was slightly better than that of Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, and ERA5-Land, with higher median Pearson correlation coefficient (R) value (0.685, 0.686, 0.699, 0.704, 0.300, and 0.582 for QTP-DNN-Sm, Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, and ERA5-Land, respectively) and lowest median unbiased Root Mean Square Error (ubRMSE) (0.061, 0.064, 0.068, 0.064, 0.042, 0.076, and 0.047 m3/m3 for QTP-DNN-Sm, Global-SM, GLDAS-Noah, QTP-SM, ESA CCI, ERA5-Land, and ESA CCI, respectively). 2) NDVI in the frozen soil zone was the best variable to explain SM based on the GeoDetector-based factor detection, and interaction detection results indicated that the interaction between NDVI and temperature was gradually emerging to explain SM from permafrost zones to seasonally frozen ground zones. 3) The nonlinear relationship function between SM and NDVI showed that vegetation growth in 47.76% of the area (mainly distributed in the Changjiang River, Yarlung Zangbo River, and Yellow River basins) was more influenced by phenology. Thresholds existed in 3.49% of TP, where the cumulative effect of SM affects vegetation growth. In 0.65% of the regions, vegetation growth experienced eco-physiological processes of positive relief of water stress and physical processes of negative damage. The ease with which SM altered vegetation growth trends was consistent with the degradation degree of frozen soil type. Although the percentage of regions where the thresholds exist is relatively small, the positive/negative effects of the complex localized inter between SM and vegetation in these regions could threaten the balance and stability of fragile alpine ecosystems sustained by permafrost.

The vegetation and ecosystem in the source region of the Yangtze River and the Yellow River (SRYY) are fragile. Affected by climate change, extreme droughts are frequent and permafrost degradation is serious in this area. It is very important to quantify the drought-vegetation interaction in this area under the influence of climate-permafrost coupling. In this study, based on the saturated vapor pressure deficit (VPD) and soil moisture (SM) that characterize atmospheric and soil drought, as well as the Normalized Differential Vegetation Index (NDVI) and solar-induced fluorescence (SIF) that characterize vegetation greenness and function, the evolution of regional vegetation productivity and drought were systematically identified. On this basis, the technical advantages of the causal discovery algorithm Peter-Clark Momentary Conditional Independence (PCMCI) were applied to distinguish the response of vegetation to VPD and SM. Furthermore, this study delves into the response mechanisms of NDVI and SIF to atmospheric and soil drought, considering different vegetation types and permafrost degradation areas. The findings indicated that low SM and high VPD were the limiting factors for vegetation growth. The positive and negative causal effects of VPD on NDVI accounted for 47.88% and 52.12% of the total area, respectively. Shrubs were the most sensitive to SM, and the response speed of grassland to SM was faster than that of forest land. The impact of SM on vegetation in the SRYY was stronger than that of VPD, and the effect in the frozen soil degradation area was more obvious. The average causal effects of NDVI and SIF on SM in the frozen soil degradation area were 0.21 and 0.41, respectively, which were twice as high as those in the whole area, and SM dominated NDVI (SIF) changes in 62.87% (76.60%) of the frozen soil degradation area. The research results can provide important scientific basis and theoretical support for the scientific assessment and adaptation of permafrost, vegetation, and climate change in the source area and provide reference for ecological protection in permafrost regions.

The concentration and isotopic composition of mercury (Hg) were studied in frozen soils along a southwest-northeast transect over the Himalaya-Tibet. Soil total Hg (Hg-T) concentrations were significantly higher in the southern slopes (72 +/- 54 ng g(-1), 2SD, n = 21) than those in the northern slopes (43 +/- 26 ng g(-1), 2SD, n = 10) of Himalaya-Tibet. No significant relationship was observed between Hg T concentrations and soil organic carbon (SOC), indicating that the Hg-T variation was not governed by SOC. Soil from the southern slopes showed significantly negative mean delta Hg-202 (-0.53 +/- 0.50 parts per thousand, 2SD, n = 21) relative to those from the northern slopes (-0.12 +/- 0.40 parts per thousand, 2SD, n = 10). The delta Hg-202 values of the southern slopes are more similar to South Asian anthropogenic Hg emissions. A significant correlation between 1/Hg-T and delta Hg-202 was observed in all the soil samples, further suggesting a mixing of Hg from South Asian anthropogenic emissions and natural geochemical background. Large ranges of Delta Hg-199 (-0.45 and 0.24 parts per thousand) were observed in frozen soils. Most of soil samples displayed negative Delta Hg-199 values, implying they mainly received Hg from gaseous Hg(0) deposition. A few samples had slightly positive odd-MIF, indicating precipitation-sourced Hg was more prevalent than gaseous Hg(0) in certain areas. The spatial distribution patterns of Hg-T concentrations and Hg isotopes indicated that Himalaya-Tibet, even its northern part, may have been influenced by transboundary atmospheric Hg pollution from South Asia. (C) 2019 Elsevier Ltd. All rights reserved.

With the global warming, the permafrost on the Qinghai-Tibetan Plateau (QTP) is degrading significantly, which brings potential threats to the major engineering projects built in or on it, e. g., the Qinghai-Tibet Highway, Qinghai-Tibet Railway, and Xinjiang-Tibet Highway. This study uses advanced survey and statistical methods to reveal the spatial distribution characteristics, development patterns, influencing factors, and formation mechanisms of the damages on the pavement induced by permafrost thawing and freeze-thaw cycles to identify their development process, evolution patterns, and different types of underlying permafrost. This will provide suggestions and guidance to the relevant departments in the decision-making, planning, design, and construction and maintenance of the running or future engineering projects on the QTP.

The object of the research is the behavior of axial compressed piles in the foundations on continuous permafrost soils under global warming. There is a degradation of permafrost soils at present. The permafrost layer is vertically divided into two parts: 1) the top, the active layer; 2) the bottom, the frozen mass. The active layer of soil thaws in summer and freezes in winter. Frozen soil behaves as a rock in winter and as a liquid mass on some soil thickness in summer. Accordingly, the surface forces acting on the pile surface in winter time disappear in the entire melted liquid soil layer in summer time. We considered the design of a pile by the condition of the first kind buckling (form) under axial compression. We took into account the conditions when the depth of the base thawing soil increases in the upper part of the pile at the stages of operation (in the summertime of the pile operation). In addition, we considered the calculation of the pile length under the same conditions at a given load on the pile at the stage of its design. To forecast the piles operating time in pile foundations or individual piles during global warming on the Earth, an algorithm for calculating pile length at the design stage is proposed. The paper provides a numerical example of calculating the pile operational life in the solid frozen soil of the foundation in an oil pipeline support.

Seasonally frozen soil (SFS) is a critical component of the Cryosphere, and its heat-moisture-deformation characteristics during freeze-thaw processes greatly affect ecosystems, climate, and infrastructure stability. The influence of solar radiation and underlying surface colors on heat exchange between the atmosphere and soil, and SFS development, remains incompletely understood. A unidirectional freezing-thawing test system that considers solar radiation was developed. Subsequently, soil unidirectional freezing-thawing tests were conducted under varying solar radiation intensities and surface colors, and variations in heat flux, temperature, water content, and deformation were monitored. Finally, the effects of solar radiation and surface color on surface thermal response and soil heat-moisture-deformation behaviors were discussed. The results show that solar radiation and highabsorptivity surfaces can increase surface heat flux and convective heat flux, and linearly raise surface temperature. The small heat flux difference at night under different conditions indicates that soil ice-water phase change effectively stores solar energy, slowing down freezing depth development and delaying rapid and stable frost heave onset, ultimately reducing frost heave. Solar radiation causes a significant temperature increase during initial freezing and melting periods, yet its effect decreases notably in other freezing periods. Soil heatwater-deformation characteristics fluctuate due to solar radiation and diurnal soil freeze-thaw cycles exhibit cumulative water migration. Daily maximum solar radiation of 168 W/m(2) and 308 W/m(2) can cause heatmoisture fluctuations in SFS at depths of 6 cm and 11 cm, respectively. The research findings offer valuable insights into the formation, development, and use of solar radiation to mitigate frost heave in SFS.

Global warming has caused changes in the area and thickness of permafrost on the Qinghai-Tibet Plateau and prompted the transition from permafrost to seasonally frozen soil, which has affected the soil moisture, soil temperature, and distribution of plant roots. This, in turn, affects grassland vegetation productivity and aboveground/belowground biomass. In this study, we took Qinghai Province in the northeastern Qinghai-Tibet Plateau as the research area to model the spatial pattern of grassland biomass and then evaluated the potential influence of frozen soil type information on aboveground and belowground biomass. Our research shows that there are significantly more biomass observations in seasonally frozen soil regions than in permafrost regions. However, when we ignore the type of frozen soil, the model does not show more accurate simulation in seasonally frozen soil regions, mainly because the stronger correlation between permafrost biomass and environmental factors, such as precipitation, compensates for the lack of observational data. In addition, we found that the biomass estimation error can be reduced significantly by building different models for each type of frozen soil, which implies that the type of frozen soil has an important impact on grassland biomass. Therefore, in considering the effects of future climate warming, more attention should be given to the impact of changes in frozen soil type on regional vegetation productivity. In addition, our investigation contributes a benchmark dataset of above- and belowground vegetation carbon storage in different frozen soil types, which provides the research community with useful information for optimizing process-based carbon cycle models.