Melt Period Research Articles

Variation in Soil Hydrothermal after 29-Year Straw Return in Northeast China during the Freeze–Thaw Process

In seasonal agricultural frozen soil areas, the straw return may influence the freeze–thaw characteristics by changing the soil organic matter and porosity. Monitoring moisture and heat in the freeze–thaw period is significant for preventing spring waterlogging and reasonable planting arrangements. However, the effect of long-term straw return on the soil freeze–thaw process is still unclear. In this study, we investigated the dynamics of soil temperature (ST) and soil moisture (SM) between straw-return cropland (SF) for 29 consecutive years and no-fertilization cropland (NF) during freeze–thaw progress in northeast China. The soil in both sites underwent unidirectional freezing and bidirectional thawing processes. The soil freezing and thawing dates in the NF of the profile occurred earlier than that in the SF. The NF had higher frozen depth and freezing rate than the SF and exhibited a larger range of ST variation and higher heat transmission efficiency. The SM showed a declining trend before the ST started to decrease to a freezing point at different depths in both sites. The migrated SM in most soil layers decreased during monitoring. The relationship between SM and negative ST was a power function at different frozen depths. The SM decreased rapidly in the range of −2–0 °C in both sites. During phase changes, the SF and NF consumed 33.0 and 43.6 MJ m−2, respectively. The results can partially explain the response of straw return to soil hydrothermal variation during the freeze-thaw process. This study may provide an integral theory for effectively utilizing agricultural soil hydrothermal resource in northeast China.

Evaluation of navigation capacity in the Northeast Arctic passage: evidence from multiple factors

ABSTRACT Arctic ice is melting away as a result of global warming, making possible the further commercial exploitations of the Arctic shipping routes, both to satisfy the shipping demand and to avoid the growing Somali piracy. In this research, the hierarchical regression is utilized to examine the impact of natural and economic factors on the Northeast Arctic Route (NER) through sample data on cargo volume from 2011 to 2021. From the results, the natural factors related to sea ice have a negative impact on the navigability of the NER, whereas economic factors and sea ice melting periods have a positive impact. Additionally, all variables are standardized to compare their respective significances on the cargo volume. Furthermore, Russian energy exports have a greater impact on shipping capacity than other variables, followed by the number of ship transits. Finally, the interrupted time-series analysis is introduced to find that the project of Yamal liquefied natural gas (LNG) has a positive effect on the NER, which could not offset the side effect of the COVID-19 epidemic.

Observed Retrogressive Thaw Slump Evolution in the Qilian Mountains

Climate warming can lead to permafrost degradation, potentially resulting in slope failures such as retrogressive thaw slumps (RTSs). The formation of and changes in RTSs could exacerbate the degradation of permafrost and the environment in general. The mechanisms of RTS progression and the potential consequences on the analogous freeze–thaw cycle are not well understood, owing partly to necessitating field work under harsh conditions and with high costs. Here, we used multi-source remote sensing and field surveys to quantify the changes in an RTS on Eboling Mountain in the Qilian Mountain Range in west-central China. Based on optical remote sensing and SBAS-InSAR measurements, we analyzed the RTS evolution and the underlying drivers, combined with meteorological observations. The RTS expanded from 56 m2 in 2015 to 4294 m2 in 2022, growing at a rate of 1300 m2/a to its maximum in 2018 and then decreasing. Changes in temperature and precipitation play a dominant role in the evolution of the RTS, and the extreme weather in 2016 may also be a primary contributor to the accelerated growth, with an average deformation of −8.3 mm during the thawing period, which decreased slope stability. The RTS evolved more actively during the thawing and early freezing process, with earthquakes having potentially contributed further to RTS evolution. We anticipate that the rate of RTS evolution is likely to increase in the coming years.

Effects of Seasonal Freezing and Thawing on Soil Moisture and Salinity in the Farmland Shelterbelt System in the Hetao Irrigation District

Water resources are scarce, and secondary soil salinization is severe in the Hetao Irrigation District. Farmland shelterbelt systems (FSS) play a critical role in regulating soil water and salt dynamics within the irrigation district. However, the understanding of soil water and salt migration within FSS during the freeze–thaw period remains unclear due to the complex and multifaceted interactions between water and salt. This study focused on a typical FSS and conducted comprehensive monitoring of soil moisture, salinity, temperature, and meteorological parameters during the freeze–thaw period. The results revealed consistent trends in air temperature and soil temperature overall. Soil freezing durations exceeded thawing durations, and both decreased with an increasing soil depth. At the three critical freeze–thaw nodes, the soil moisture content at a 0–20 cm depth was significantly lower than at a 40–100 cm depth (p < 0.05). The soil water content increased with time and depth at varying distances from the shelterbelt, with an average increase of 7.63% after freezing and thawing. The surface water content at the forest edge (0.3H, 4H) was lower than inside the farmland (1H, 2H, 3H). Soil salt accumulation occurred during both freezing stable periods and melting–thawing periods in the 0–100 cm soil layer near the forest edge (0.3H, 4H), with the highest soil salinity reaching 0.62 g·kg−1. After the freeze–thaw period, the soil salt content in each layer increased by 11.41–47.26% compared to before the freeze–thaw period. Salt accumulation in farmland soil near the shelterbelt was stronger than in the far shelterbelt. The multivariate statistical model demonstrated goodness of fit for soil water and salt as 0.94 and 0.72, respectively, while the BP neural network model showed goodness of fit for soil water and salt as 0.82 and 0.85, respectively. Our results provide an efficient theoretical basis for FSS construction and agricultural water management practices.

Freeze-thaw characteristics and deformation monitoring of topsoil in highland pastoral areas under the influence of snow accumulation

Soil freeze–thaw processes and snowmelt infiltration have a significant impact on the hydrological cycle and ecosystem productivity in alpine pastoral areas. To investigate the driving mechanism of snow on soil freeze-thaw processes, a meteorological station was established in the southern part of Namatso Lake, Tibet to collect environmental data. The study included analyzing the relationship between soil temperature and humity, as well as assessing soil freeze-thaw characteristics and the evolution of soil frost heave over time. The freeze-thaw frequency was significantly 43% lower at the surface soil, and the freeze-thaw intensity decreased when the ground was snow-covered. During the initial freezing period, precipitation and soil humidity remain relatively low, and soil moisture decreases linearly with decreasing soil temperature, which occurs in the phenomenon of soil freeze-shrink. During the initial thawing period, snowmelt infiltration impacts soil humidity, and soil frost heave increases logarithmically, reaching a maximum of 5.2 mm, driven by freeze-thaw. Soil moisture decreases under topsoil evaporation in the later stage and again follows a linear trend with the soil temperature. This study not only reveals the correlation between soil temperature and humidity during different freeze-thaw periods but also enhances the understanding of soil deformation patterns under the influence of snow accumulation.

Cryoprotective role of vacuum infused inulin on the quality of artichoke: Interactive effects of freezing, thawing and storage period

Freezing of artichoke is a promising alternative to storing it in brine and canning. The perishable vegetable was vacuum infused with inulin to improve freezing tolerance. Artichokes with and without inulin were frozen by static, air blast and individual quick freezing (IQF) methods and thawed by microwave, 25 °C and 4 °C temperature levels at each month of 6-months storage. Process conditions were evaluated by multivariate analysis of variance (MANOVA) and were found significant on the quality parameters. Inulin infusion better conserved the aw, color, texture, ascorbic acid and overall integrity of artichokes during frozen storage. Inulin incorporation and IQF showed mutual positive effect on drip loss. Polyphenol oxidase (PPO) activity values fitted to 2nd order kinetic and the highest residuals were determined in static freezing. PPO showed alleviating effect on total phenolic content. Vacuum impregnation caused a color difference prior to freezing, but was found effective for maintaining color during storage. As a result, the use of quick freezing techniques together with the addition of cryoprotectant was effective in the preservation of artichoke quality attributes during frozen storage.

Climate change impacts on Central Asia: Trends, extremes and future projections

AbstractCentral Asia (CA) is among the world's most vulnerable regions to climate change. Increasing anthropogenic greenhouse gas concentrations (GHGs) are the primary forcing of the current and future climate system for the time scale of a century. By analysing observation datasets, we show that a warming of 1.2°C led to a decrease of 20% in snow‐depth CA during the last 70 years, especially over the mountains. In recent decades, longer summer times and fewer icing days (more than 20 days·year−1) have exposed unprecedented shock to CA's climate system's components. Furthermore, we analyse 442 model simulations from Coupled Model Inter‐comparison Project Phase 5 and 6 (CMIP5, CMIP6) and show that CMIP6 simulations are generally warmer and wetter than the CMIP5 ones in CA. For instance, under the highest emission scenarios (RCP8.5 and SSP5‐8.5), CMIP6 projects a 6.1°C increase, while CMIP5 projects a 5.3°C increase, suggesting CMIP6 anticipates greater warming with high emissions. In contrast to CMIP6, the CMIP5 precipitation trends suggest a potential nonlinear relationship between increased greenhouse gas emissions and changes in precipitation, though the impact is much less pronounced than the temperature changes. Our analysis shows that CMIP6 models are more sensitive to temperature rise than CMIP5 ones. Both simulation sets' ensemble means capture well the observed warming trend. The imposed snow‐melting leads to an increase in the run‐off in the vicinity of glaciers. Such climatic shifts lead to more flooding events in CA. Given the projected warming range of 2–6°C in CA at the end of the century in various scenarios and models, such warming trends might be catastrophic in this region. The seasonal cycle of the temperature change indicates an extension of the glacier's melting period under future scenarios with fossil‐fueled development. The models' uncertainty increases for the far‐future time‐slice, and warming larger than 4°C in CA is very likely among all the models and during all the seasons if no sustainable action is taken. This study also incorporates a detailed Köppen climate classification analysis, revealing significant shifts towards warmer climate categories in Central Asia, which may have profound implications for regional hydrological cycles and water resource management, particularly in the Amu Darya and Syr Darya river basins under warmer scenario by the end of the century. The Tundra and ice cap climate categories will lose more than 60% of their coverage at the end of the century compared to the historical period in the Amu Darya and Syr Darya river basins.

Seasonal freeze‒thaw processes impact microbial communities of soil aggregates associated with soil pores on the Qinghai–Tibet Plateau

BackgroundSeasonal freeze‒thaw (FT) processes alter soil formation and cause changes in soil microbial communities, which regulate the decomposition of organic matter in alpine ecosystems. Soil aggregates are basic structural units and play a critical role in microbial habitation. However, the impact of seasonal FT processes on the distribution of microbial communities associated with soil pores in different aggregate fractions under climate change has been overlooked. In this study, we sampled soil aggregates from two typical alpine ecosystems (alpine meadow and alpine shrubland) during the seasonal FT processes (UFP: unstable freezing period, SFP: stable frozen period, UTP: unstable thawing period and STP: stable thawed period). The phospholipid fatty acid (PLFA) method was used to determine the biomass of living microbes in different aggregate fractions.ResultsThe microbial biomass of 0.25–2 mm and 0.053–0.25 mm aggregates did not change significantly during the seasonal FT process while the microbial biomass of > 2 mm aggregates presented a significant difference between the STP and UTP. Bacterial communities dominated the microbes in aggregates, accounting for over 80% of the total PLFAs. The microbial communities of soil aggregates in the surface layer were more sensitive to the seasonal FT process than those in other soil layers. In the thawing period, Gram positive bacteria (GP) was more dominant. In the freezing period, the ratio of Gram-positive to Gram-negative bacterial PLFAs (GP/GN) was low because the enrichment of plant litter facilitated the formation of organic matter. In the freezing process, pores of 30–80 μm (mesopores) favored the habitation of fungal and actinobacterial communities while total PLFAs and bacterial PLFAs were negatively correlated with mesopores in the thawing process.ConclusionsThe freezing process caused a greater variability in microbial biomass of different aggregate fractions. The thawing process increased the differences in microbial biomass among soil horizons. Mesopores of aggregates supported the habitation of actinobacterial and fungal communities while they were not conducive to bacterial growth. These findings provide a further comprehension of biodiversity and accurate estimation of global carbon cycle.

Effects of the freeze–thaw process on sources and pathways of subsurface flow in an alpine hillslope on the northeastern Qinghai-Tibet Plateau

The impact of the freeze–thaw process on the active layer is reflected in the changed subsurface flow (SSF) process in cold alpine regions. Identifying sources and pathways of SSF in the freeze–thaw process is critical but difficult, and the related dominant factors and mechanisms are still unknown. In this paper, the effective identification and analysis of SSF are promoted based on field sampling data from the thawing (June) to freezing (September) period of 2022 in the Qinghai Lake basin on the northeastern Qinghai-Tibetan Plateau. By the proposed method with a high sampling frequency and refined sampling spatial scale, the sources and pathways of SSF are clearly identified. The results are as follows: (1) The soil temperature is considered the most fundamental factor affecting the SSF pathways, it influences water infiltration to the deep layer and the effect is extended to the saprolite and weathered bedrock layers. (2) Thawing promotes water to infiltrating into deep layer. 30 cm soil water contributes the most to SSF (2 %–86 %) in the thawing period, while the contribution difference of the water from the 30 cm, 60 cm, and 90 cm layers is small (ranging from 32 %–33 %, 24 %–26 %, and 32 %–35 %, respectively) in the thawed period. (3) Meanwhile, the soil water from different slope positions contribute differently to SSF, and the SSF from deep soil layer is transit in prolong paths and depths. It is caused by the out-of-sync water transit process in the hillslope. With continuing climate warming, we propose that the differences in the water sources of SSF across soil layers may decrease, while the differences in the transit processes of SSF across soil layers may increase.

Exploring the impact of inner and middle channel geometries on the melting rate of PCM-metal foam composition in a triplex tube heat exchanger

Triplex tube heat exchangers (TTHXs) are devices suitable for storing thermal energy with PCM because they shorten the melting and solidification periods. Studies in literature have revealed that pipe geometries significantly affect the melting performance of PCM in thermal energy storage with TTHX. In the pipe designs carried out in these studies, convection in the heat transfer fluid (HTF) and the heat transfer surface areas of the pipes were considered. However, in addition to convection in the HTF, heat transfer by conduction and convection within the PCM also significantly affects the melting performance. The novelty of this study was to investigate the effects of inner and middle channel combinations with different geometries in TTHX on conduction and natural convection mechanisms in PCM combined with metal foam. Numerical analyses were carried out for nine inner-middle channel combinations with three different metal foam porosity values (ε = 0.85, 0.90 and 0.95). At porosity values of 0.85 and 0.90, the highest melting rate was achieved with the triangle-triangle inner-middle channel combination within a certain period, and the charging time was shortened by 16.67 % and 14.44 %, respectively, compared to the base case (circle-circle). For the porosity value of 0.95, it was observed that the most suitable channel combination for melting performance was circle-circle, as natural convection flow became more dominant in heat transfer in liquid PCM. At the porosity value of 0.95, the charging time with TTHX containing the circle-circle combination decreased by values ​​ranging from 29.75 % to 59.86 % compared to other combinations.

A facile strategy for enhancement of heat storage rate in LHS units

LHS units suffer from long melting periods, resulting in overestimated amounts of PCMs for specific heat storage rate as well as larger surface areas for heat transfer. In this paper, we propose a facile strategy for the enhancement of heat storage rate in LHS units, with the contribution of natural convection by the addition of materials with low melting temperatures. Morphology analysis and preliminary experiments are conducted and the validity of the strategy proposed is verified. The principle of natural convection contribution is concluded from the observation of curved boundary of solid PCMs in morphology analysis, after the addition of materials with low melting temperature. The melting period is shortened by 44.8 % and the heat storage amount is augmented due to the existence of added materials. The effects of the novel strategy on heat storage enhancement are more obvious in the case of container with smaller size. As in the experiments of a prototype of LHS units, the heat storage rate is augmented by 31.09 %. The strategy proposed in this paper offers a facile method for the design of LHS units with fast melting and heat storage augment.

Differences in sediment provenance from rainfall and snowmelt erosion in the Mollisol region of Northeast China

AbstractDifferences in erosion patterns inevitably lead to different soil loss processes. However, the differences in sediment sources between rainfall and snowmelt erosion are not well studied. To address this gap, a study was conducted in a small agricultural catchment (3.5 km2) using the fingerprinting technique to quantify the various sources contributing to sediment, as well as determine the magnitude of sediment total nitrogen (TN), total phosphorus (TP), total potassium (TK) and soil organic matter (SOM) loads from three sources (cultivated land, unpaved roads and gullies) during the rainy season and spring thawing period. Sediment sources from 17 rainfall erosion and seven snowmelt erosion events of varying magnitudes were compared. The Collins and Bayesian mixing models, coupled with geochemical tracers (Cs, V, Cd, Pb and Ag), were applied to assess the contribution proportion of individual sediment sources to suspended sediment. According to the results obtained from the Bayesian mixing model with higher accuracy, cultivated land, unpaved roads and gullies contributed 60.3% (load‐weighted mean contribution [LMC] = 82.8%), 11.0% (LMC = 6.5%) and 28.7% (LMC = 10.7%) of the sediment in the rainy season, respectively. Cultivated land was the dominant sediment source for rainfall erosion, with high rainfall erosivity and sediment concentration. However, for snowmelt erosion, gullies were the primary sediment source (LMC = 66.2%), followed by cultivated land (LMC = 19.8%) and unpaved roads (load‐weighted = 14.0%). Meanwhile, in the spring thawing period, the contributions of unpaved roads to sediment were higher than in the rainy season. During the rainy season, the greatest contributions of TN, TP, TK and SOM were observed from cultivated land, with respective LMC values of 94.2%, 89.4%, 81.1% and 94.8%. With the increase of sediment contribution from gullies in the spring thawing period, its LMC of TN, TP, TK and SOM increased to 42.6%, 58.3%, 65.0% and 38.0%, respectively. The results of the study could be useful for understanding the processes of soil erosion, clarifying the driving mechanism of compound erosion, developing the compound erosion prediction model and optimizing the spatial configuration of erosion control measures.

GEOCRYOLOGICAL CONDITIONS OF THE FORMATION OF GIANT SPRING AUFEIS AT THE ANMANGYNDA RIVER (MAGADAN REGION) ACCORDING TO GEOPHYSICAL DATA

Giant aufeis fields, common in the Northeast of Russia, are the indicators of water exchange processes in cryosphere. The development of ideas about icing processes is relevant both from the fundamental point of view of studying the permafrost evolution, and from the practical point of view – for the development of aufeis hazard measures. The aufeis in the Anmangynda River basin (aufeis glade area 7 km2) is considered representative of the region, and its studies have been carried out since 1962. In 2022, during the period of maximum thawing of the active layer Electrical Resistivity Tomography (ERT) soundings were carried out at the aufeis glade aiming to identify underchannel taliks and flooded fault zones in bedrock, including local areas of groundwater discharge. It was found that within the main river channels there are underchannel taliks up to 30 m deep. According to the results of 2D inversion, local anomalies of low electrical resistivity mark groundwater filtration channels. In 3D geoelectrical models, pipe-like anomalies of low resistivity are identified in the areas of groundwater discharge, interpreted as filtration channels in the alluvium and the zone of exogenous fracturing in bedrock formed by sandy-clay shales, as well as linear vertical anomalies of low resistivity, interpreted as faults. On vertical sections of 3D resistive models, a connection between faults and filtration channels in alluvium and a layer of exogenous fracturing is traced. In the right bank of the valley, geoelectric signs of taliks in the bedrock, presumably associated with fault tectonics, have been established. It is assumed that the identified faults are the additional transit routes for groundwater in the Anmangynda River valley, along with the alluvial aquifer and the zone of exogenous fracturing of bedrock.

Stream water sourcing from high-elevation snowpack inferred from stable isotopes of water: a novel application of d-excess values

Abstract. About 80 % of the precipitation at the Colorado River's headwaters is snow, and the resulting snowmelt-driven hydrograph is a crucial water source for about 40 million people. Snowmelt from alpine and subalpine snowpack contributes substantially to groundwater recharge and river flow. However, the dynamics of snowmelt progression are not well understood because observations of the high-elevation snowpack are difficult due to challenging access in complex mountainous terrain as well as the cost and labor intensity of currently available methods. We present a novel approach to infer the processes and dynamics of high-elevation snowmelt contributions predicated upon stable hydrogen and oxygen isotope ratios observed in streamflow. We show that deuterium-excess (d-excess) values of stream water could serve as a comparatively cost-effective proxy for a catchment-integrated signal of high-elevation snowmelt contributions to catchment runoff. We sampled stable hydrogen and oxygen isotope ratios of the precipitation, snowpack, and stream water in the East River, a headwater catchment of the Colorado River, and the stream water of larger catchments at sites on the Gunnison River and Colorado River. The d-excess of snowpack increased with elevation; the upper subalpine and alpine snowpack (> 3200 m) had substantially higher d-excess compared to lower elevations (< 3200 m) in the study area. The d-excess values of stream water reflected this because d-excess values increased as the higher-elevation snowpack contributed more to stream water generation later in the snowmelt/runoff season. End-member mixing analyses based on the d-excess data showed that the share of high-elevation snowmelt contributions within the snowmelt hydrograph was on average 44 % and generally increased during melt period progression, up to 70 %. The observed pattern was consistent during 6 years for the East River, and a similar relation was found for the larger catchments on the Gunnison and Colorado rivers. High-elevation snowpack contributions were found to be higher for years with lower snowpack and warmer spring temperatures. Thus, we conclude that the d-excess of stream water is a viable proxy to observe changes in high-elevation snowmelt contributions in catchments at various scales. Inter-catchment comparisons and temporal trends of the d-excess of stream water could therefore serve as a catchment-integrated measure to monitor if mountain systems rely on high-elevation water inputs more during snow drought compared to years of average snowpack depths.

Effects of the hydrologic process and geochemistry on dissolved carbon in shallow groundwater surrounding Qinghai Lake

A high concentration of dissolved carbon in groundwater increases drinking water health risks and carbon transport. Understanding the comprehensive impact of hydrologic processes and geochemistry on dissolved carbon in shallow groundwater also is a fundamental prerequisite for estimating the carbon budget of lakes in the Tibetan Plateau. This study investigated the spatial–temporal characteristics of the hydrologic process, geochemistry and dissolved carbon in shallow groundwater by the stable isotope tracer method, Piper diagram and Boomerang envelope model. The driving factors of dissolved carbon in shallow groundwater were explored by correlation analysis and redundancy analysis. The results showed low dissolved inorganic carbon (DIC) concentrations and high dissolved organic carbon (DOC) concentrations during the thawing period and rainy season and high DIC concentrations and low DOC concentrations during the freezing period. The seepage velocity, soil carbon dioxide dissolution and gypsum dissolution were the main factors influencing DIC concentrations during the thawing period. The mineralization and decomposition of DOC and dissolution of carbonate rocks were the main factors influencing DIC concentrations during the freezing period. The concentrations of DOC were mainly controlled by the adsorption of Ca2+ and Mg2+, microbial activity and pollutants produced by human activities. Our results are useful for ecological sustainable development, human health, and research on the carbon transport in groundwater in the Tibetan Plateau.

Study on the formation mechanism and preventive measure of pot cover effect for subgrade in seasonal frozen soil area under freeze–thaw cycles

AbstractThe presence of an impervious cover layer inhibits the free evaporation of moisture in the soil during seasonal freeze–thaw cycles, leading to a phenomenon known as the pot cover effect. This can result in severe frost heave issues in airport runways, highway subgrades, railway subgrades, and other similar infrastructure. In this study, a disease investigation was conducted at a gas transmission station situated in an area with seasonally frozen soil. Meanwhile, the causes of moisture accumulation and frost heave in the lower part of concrete pavement slabs were analyzed. A coupled water–vapor–heat model for unsaturated frozen soil is then established to analyze the formation mechanism of the pot cover effect in the subgrade. Finally, the preventive effect of the impervious layer on moisture migration in the pot cover effect was analyzed. The results indicate that the pot cover effect causes a significant accumulation of moisture beneath the concrete pavement at the gas transmission station, resulting in a moisture content increase of 5%–35%. During the freezing period, the vapor of shallow soil migrates upward, while the liquid water remains unchanged. During the melting period, both vapor and liquid water migrate downward. The laying of the impervious layer can prevent moisture migration of the pot cover effect. When the impervious layer is placed on the freezing front (0°C), the prevention effect of the pot cover effect is the best.

Using Icepack to reproduce ice mass balance buoy observations in landfast ice: improvements from the mushy-layer thermodynamics

Abstract. Icepack (v1.1.0) – the column thermodynamics model of the Community Ice CodE (CICE) version 6 – is used to assess how changing the thermodynamics from the Bitz and Lipscomb (1999) physics (hereafter BL99) to the mushy-layer physics impacts the model performance in reproducing in situ landfast ice observations from two ice mass balance (IMB) buoys co-deployed in the landfast ice close to Nain (Labrador) in February 2017. To this end, a new automated surface retrieval algorithm is used to determine the in situ ice thickness, snow depth, basal ice congelation and snow-ice formation from the measured vertical temperature profiles. Icepack simulations are run to reproduce these observations using each thermodynamics scheme, with a particular interest in how the different physics influence the representation of snow-ice formation and ice congelation. Results show that the BL99 parameterization represents well the ice congelation but underrepresents the snow-ice contribution to the ice mass balance. In particular, defining snow-ice formation based on the hydrostatic balance alone does not reproduce the negative freeboards observed for several days in the IMB observations, resulting in an earlier snow-flooding onset, a positive ice thickness bias and reduced snow depth variations. We find that the mushy-layer thermodynamics with default parameters significantly degrades the model performance, overestimating both the congelation growth and snow-ice formation. The simulated thermodynamics response to flooding, however, better represents the observations, and the best results are obtained when allowing for negative freeboards in the mushy-layer physics. We find that the mushy-layer thermodynamics produces a larger variability in congelation rates at the ice bottom interface, alternating between periods of exceedingly fast growth and periods of unrealistic basal melt. This pattern is related to persistent brine dilution in the lowest ice layer by the congelation and brine drainage parameterizations. We also show that the mushy-layer congelation parameterization produces significant frazil formation, which is not expected in a landfast ice context. This behavior is attributed to the congelation parameterization not fully accounting for the conductive heat flux imbalance at the ice–ocean boundary. We propose a modification of the mushy-layer congelation scheme that largely reduces the frazil formation and allows for better tuning of the congelation rates to match the observations. Our results demonstrate that the mushy-layer physics and its parameters can be tuned to closely match the in situ observations, although more observations are needed to better constrain them.

Precipitation and relative humidity favours tree growth while air temperature and relative humidity respectively drive winter stem shrinkage and expansion

Forest ecosystems have a major role in sequestering atmospheric CO2 and as such, their resilience is of upmost importance. In the boreal forest, trees grow only during a short period when air temperature is favourable. During winter, trees have specific mechanisms to survive in the cold air temperature. In order to understand the response of trees to a changing climate, this study assessed the influence of environmental variables on three phases of tree radial variation (i.e., growth, shrinkage and expansion) during three periods of the year (i.e., growing season, freeze–thaw period, and winter). The three phases were extracted from stem radial variation measured for as much as 11 years on 12 balsam fir [Abies balsamea (L.) Mill.] trees located in a cold and humid boreal forest of eastern Canada. The random forest algorithm was used to model each phase during each period. Our results show that tree growth increased with high precipitation and high relative humidity. Stem shrinkage was affected mostly by solar radiation, precipitation and vapour pressure deficit during the growing season and was likely caused by tree transpiration. During both the freeze–thaw and winter season periods, stem shrinkage increased with decreasing air temperature. During the growing season, stem expansion was related to 1-day-lag solar radiation and 1-day-lag vapour pressure deficit, which are the same variables associated with shrinkage the preceding day. Stem expansion increased with increasing air temperature and relative humidity during the freeze–thaw and winter season periods, respectively. This study shows that sink-driven tree growth is promoted mostly under humid conditions while antecedent dry and warm conditions are required during the growing season for trees to assimilate carbon through photosynthesis.

Thermo-seismic performance of the novel thermal anchor pipe frame (TAPF) structure for supporting slope in earthquake-prone permafrost regions

The thermal anchor pipe frame (TAPF) structure is a new type of permafrost slope support technology, but its thermo-seismic characteristics are still unclear. In this paper, the coupled hydro-thermal-dynamic model of the thermal anchor pipe frame permafrost slope system is established. The cooling performance of the TAPF structure is investigated and the seismic responses are comparatively analyzed for different freeze-thaw periods. Results show that the presence of “elliptical” freezing cores with lower temperatures (which ranged from −3.94 to −5.36 °C) near the active layer at the end of the thawing period, which raised the permafrost table. The strip-shaped unfrozen moisture accumulation layer appears near the upper part of the thawing front at the highest temperature in the warm season. The peak acceleration response is the largest on October 15, 52.3% greater than the peak acceleration on April 15. The peak axial force of the thermal anchor pipe during the freezing period was 119 kN, which was 32.2% greater than that during the thawing period, and the peak total axial force after the earthquake appeared at the location of the freeze-thaw interface, and the axial force of the heat-transfer free section is greater than that of the anchored section. The frame structure is sensitive to earthquakes during the freezing period, and plastic bending damage may occur, especially at connection locations with thermal anchor pipes. Seasonal effects also have a strong influence on the shape of the acceleration response spectrum. The results can provide useful references for the maintenance and safe operation of permafrost slopes along the Qinghai-Tibet Project as well as for the seismic design of the new structure.

Landscape evolution and sediment delivery in a High Arctic proglacial lake, Ellesmere Island, Canadian Arctic Archipelago

AbstractGeophysical and morphosedimentary investigations were conducted at Strathcona Lake, a High Arctic proglacial lake and its catchment connected to the Taggart Lake Glacier, northwest corner of the Prince of Wales Icefield in Ellesmere Island (eastern Canadian Arctic Archipelago). The mapping of glaciomarine landforms and units provides, together with updated radiocarbon information, a framework for catchment evolution and sediment delivery to the lake during deglaciation and glacio‐isostatically induced relative sea level fall. A staircase of deltas with descending altitudes provide evidence for a spatially diachronous timing of ice retreat from the catchments around Strathcona Lake. Swath bathymetric mapping coupled with acoustic sediment stratigraphy show draped infills with a transition from marine to rhythmically bedded lacustrine sediments produced by hyperpycnal flows. Multiproxy investigations on a set of sediment cores highlight proglacial varves interrupted by rhythmites resulting from the erosion of fluvially incised glaciomarine sediments stored in the catchment. Pluricentimetric proglacial varves formed during the last century in response to periods of intense glacial melt, notably since the 21st century. The sedimentary record suggests the varved sediments from Strathcona Lake can be used to reconstruct the melting history of the Prince of Wales Icefield. This work provides a geomorphological, sedimentological, and geochemical framework that should guide future varve‐based reconstructions of glacial and climatic variability in Ellesmere Island.