Antarctic soils are heavily affected by climate change in terms of properties and ecosystem functions. With increasing global temperatures, the frequency of freeze and thaw cycles of Antarctic soils will increase, thus affecting their mechanical behavior, with varying responses in erosion. This study quantitatively evaluated the effect of increasing frequency of freezing-thawing (F-T) cycles on rheological properties of four soils from the maritime Antarctica. Using an amplitude sweep test, the effects of 1, 5 and 9F-T cycles on soil micromechanics were evaluated and compared to a reference soil without F-T. These rheological parameters were determined: (i) the linear viscoelastic strain interval (LVR) (gamma LVR), (ii) the shear stress at the end of the LVR (rLVR), (iii) the maximum shear stress (rmax), (iv) the strain at the yield point (gamma YP), and (v) the storage and loss modulus at the yield point (G'YP). F-T cycles influenced soil rheological properties. Higher F-T frequency either increased or decreased gamma LVR and gamma YP, depending on the soil material. A 35% increase in rLVE occurred after one F-T cycle; however, at the fifth cycle a decrease of approximately 27% occurred, when compared to one cycle treatment, reaching similar values of no F-T. But after nine cycles, rLVE increased again by approximately 29% compared to previous treatment. The resistance and elasticity of the Antarctic soil microstructure showed great variation among the different soils, while soils with different textures behaved similarly for some rheological properties. Rheometry was confirmed as a method with little soil material consumption, however, soil rheology of Antarctic soils requires further studies to disentangle its interactions with soil chemical properties.

In the context of climate change, research on frozen soils has attracted much attention in recent years, and numerous research papers have been published on these topics in the last decade. However, the present status and developmental trends in frozen soils research have not been reported systematically. Herein, a bibliometric analysis was conducted using 7,108 research papers on frozen soils published between 2010 and 2019. The results indicate that: (a) although the number of articles published increased from 432 in 2010 to 1,066 in 2019, the average number of citations per paper reached a maximum of 5.40 in 2014, and subsequently decreased to 2.99 in 2019; (b) China, the USA, and Canada ranked first to third in terms of total papers; (c) the most popular author keywords were boreal, tundra, Landsat, lakes, decomposition, dissolved organic carbon, permafrost thaw, and carbon cycle; and (d) the five most popular research topics in 2010-2019 were the characteristics and factors influencing frozen soils, the Arctic carbon cycle under the background of its complex environment, permafrost changes on the Qinghai-Tibet Plateau in the context of climate change, ancient frozen soils in various historical periods, and frozen soils in the Arctic.

Recently, very active studies have been undertaken on the response and stability of permafrost carbon pool and key biogeochemical processes in permafrost regions to climate warming. By observing the significant differences in microbial community structure in regions of seasonal frost and permafrost, it is evident that microbes play key roles in the conversion of permafrost carbon. This paper reviews research progress at the cutting edges on the conversion and decomposition of permafrost carbon to climate warming and subsequent changes in microbial activities over the past decade. Findings indicated that: (1) Freezethaw cycles of soils in the active layer in permafrost regions showed an increasing annual trend and the existing survival patterns of permafrost microbes may be altered by the increasing freeze-thaw frequency; and (2) Soil microbes are an essential part of the cold-regions ecosystem and they play vital roles in soil carbon and nitrogen cycling, the mineralization and decomposition of soil organic matter. Thus, climate warming and subsequent permafrost degradation affect the conversion and decomposition of permafrost carbon, resulting in changes in CO2 and CH4 emissions, soil environmental factors, and soil microbial community structures. The laws for governing permafrost carbon conversion and the self-regulation mechanisms of soil microbes are important for natural ecosystems and environments in cold regions, and affect the strengths of greenhouse gas sources and sinks in permafrost regions.

The influence of seasonally frozen ground (SFG) on water, energy, and solute fluxes is important in cold climate regions. The hydrological role of permafrost is now being actively researched, but the influence of SFG has received less attention. Intuitively, SFG restricts (snowmelt) infiltration, thereby enhancing surface runoff and decreasing soil water replenishment and groundwater recharge. However, the reported hydrological effects of SFG remain contradictory and appear to be highly site- and event-specific. There is a clear knowledge gap concerning under what physiographical and climate conditions SFG is more likely to influence hydrological fluxes. We addressed this knowledge gap by systematically reviewing published work examining the role of SFG in hydrological partitioning. We collected data on environmental variables influencing the SFG regime across different climates, land covers, and measurement scales, along with the main conclusion about the SFG influence on the studied hydrological flux. The compiled dataset allowed us to draw conclusions that extended beyond individual site investigations. Our key findings were: (a) an obvious hydrological influence of SFG at small-scale, but a more variable hydrological response with increasing scale of measurement, and (b) indication that cold climate with deep snow and forest land cover may be related to reduced importance of SFG in hydrological partitioning. It is thus increasingly important to understand the hydrological repercussions of SFG in a warming climate, where permafrost is transitioning to seasonally frozen conditions.

While the composition and diversity of soil microbial communities play a central and essential role in biogeochemical cycling of nutrients, they are known to be shaped by the physical and chemical properties of soils and various environmental factors. This study investigated the composition and diversity of microbial communities in 48 samples of seasonally frozen soils collected from 16 sites in an alpine wetland region (Lhasa River basin) and an alpine forest region (Nyang River basin) on the Tibetan Plateau using high-throughput sequencing that targeted the V3-V4 region of 16S rRNA gene. The dominant soil microbial phyla included Proteobacteria, Acidobacteria, and Actinobacteria in the alpine wetland and alpine forest ecosystems, and no significant difference was observed for their microbial composition. Linear discriminant analysis Effect Size (LEfSe) analysis showed that significant enrichment of Hymenobacteraceae and Cytophagales (belonging to Bacteroidetes) existed in the alpine wetland soils, while the alpine forest soils were enriched with Alphaproteobacteria (belonging to Proteobacteria), suggesting that these species could be potential biomarkers for alpine wetland and alpine forest ecosystems. Results of redundancy analysis (RDA) suggest that the microbial community diversity and abundance in the seasonally frozen soils on the Tibetan Plateau were mainly related to the total potassium in the alpine wetland ecosystem, and available potassium and soil moisture in the alpine forest ecosystem, respectively. In addition, function prediction analysis by Tax4Fun revealed the existence of potential functional pathways involved in human diseases in all soil samples. These results provide insights on the structure and function of soil microbial communities in the alpine wetland and alpine forest ecosystems on the Tibetan Plateau, while the potential risk to human health from the pathogenic microbes in the seasonally frozen soils deserves attention. (C) 2020 Elsevier B.V. All rights reserved.

In this article, we consider the problem of thermal response of the near-surface ice-rich permafrost to the effects of linear infrastructure and current climate change. First, we emphasize the scientific and practical significance of the study and briefly describe permafrost conditions and related hazards in the study area. Then we present a mathematical model which accounts for the actual process of soil thawing and freezing and consists of two nonlinear equations: heat conduction and moisture transfer. Numerical calculations were made to predict temperature and moisture conditions in the railroad embankment, taking into account solar radiation, snow cover, rainfall infiltration, and evaporation from the surface. The numerical results indicate that moisture migration and infiltration play the primary role in the development of frost heaving and thaw settlement. During winter, the frost-heave extent is monotonously increased due to pore moisture migration to the freezing front. Strong volume expansion (dilatation) is observed near the surface of the active layer with the onset of the warm season and meltwater infiltration. Settlement of the upper layers of the soil occurs in the summer months (June-August) when there is intense evaporation due to drying. Autumn rains stop the process of thaw settlement by increasing the soil moisture. The above processes are repeated cyclically every year. A frozen core shifts to the shaded side of the embankment under the influence of variations in the solar radiation. Over time, the total moisture content of the frozen core is increased which increases differential heaving and negatively affects the stress-strain state in the embankment. The quantitative and qualitative characteristics of the processes of frost heaving and thaw settlement are obtained in the annual and long-term cycles.

Widespread degradation of ice wedges has been observed during the last decades in numerous areas within the continuous permafrost zone of Eurasia and North America. To study ice-wedge degradation, we performed field investigations at Prudhoe Bay and Barrow in northern Alaska during 2011-2016. In each study area, a 250-m transect was established with plots representing different stages of ice-wedge degradation/stabilization. Field work included surveying ground- and water-surface elevations, thaw-depth measurements, permafrost coring, vegetation sampling, and ground-based LiDAR scanning. We described cryostratigraphy of frozen soils and stable isotope composition, analyzed environmental characteristics associated with ice-wedge degradation and stabilization, evaluated the vulnerability and resilience of ice wedges to climate change and disturbances, and developed new conceptual models of ice-wedge dynamics that identify the main factors affecting ice-wedge degradation and stabilization and the main stages of this quasi-cyclic process. We found significant differences in the patterns of ice-wedge degradation and stabilization between the two areas, and the patterns were more complex than those previously described because of the interactions of changing topography, water redistribution, and vegetation/soil responses that can interrupt or reinforce degradation. Degradation of ice wedges is usually triggered by an increase in the active-layer thickness during exceptionally warm and wet summers or as a result of flooding or disturbance. Vulnerability of ice wedges to thermokarst is controlled by the thickness of the intermediate layer of the upper permafrost, which overlies ice wedges and protects them from thawing. In the continuous permafrost zone, degradation of ice wedges rarely leads to their complete melting; and in most cases wedges eventually stabilize and can then resume growing, indicating a somewhat cyclic and reversible process. Stabilization of ice wedges after their partial degradation makes them better protected than before degradation because the intermediate layer is usually 2 to 3 times thicker on top of stabilized ice wedges than on top of initial ice wedges in undisturbed conditions. As a result, the likelihood of formation of large thaw lakes in the continuous permafrost zone triggered by ice-wedge degradation alone is very low. (C) 2017 Elsevier B.V. All rights reserved.