Rapid Thawing Research Articles

Influence of Seasonal Temperature Variations on Electromagnetic Characteristics of Frozen Soils by the Degree of Thawing and Freezing

Seasonal temperature fluctuations in frozen soils cause changes in their ice content which are accompanied by resistivity changes and electromagnetic emission. This study examines the periodic seasonal variation in apparent resistivity of permafrost soils based on field measurements of the surface impedance in the 100–1000 kHz frequency range. The characteristic changes in soil temperature and apparent resistivity associated with particular time periods are presented. The data show that the apparent resistivity values are consistent with the degree of soil freezing. Rapid freezing or thawing of the active layer causes electromagnetic emission in frozen soils. These features can be used to monitor and predict changes in permafrost conditionsunder climatic or anthropogenic impacts.

Cryopreservation and post-thaw characterization of dissociated human islet cells.

The objective of this study is to optimize the cryopreservation of dissociated islet cells and obtain functional cells that can be used in single-cell transcriptome studies on the pathology and treatment of diabetes. Using an iterative graded freezing approach we obtained viable cells after cooling in 10% dimethyl sulfoxide and 6% hydroxyethyl starch at 1°C/min to –40°C, storage in liquid nitrogen, rapid thaw, and removal of cryoprotectants by serial dilution. The expression of epithelial cell adhesion molecule declined immediately after thaw, but recovered after overnight incubation, while that of an endocrine cell marker (HPi2) remained high after cryopreservation. Patch-clamp electrophysiology revealed differences in channel activities and exocytosis of various islet cell types; however, exocytotic responses, and the biophysical properties of voltage-gated Na+ and Ca2+ channels, are sustained after cryopreservation. Single-cell RNA sequencing indicates that overall transcriptome and crucial exocytosis genes are comparable between fresh and cryopreserved dispersed human islet cells. Thus, we report an optimized procedure for cryopreserving dispersed islet cells that maintained their membrane integrity, along with their molecular and functional phenotypes. Our findings will not only provide a ready source of cells for investigating cellular mechanisms in diabetes but also for bio-engineering pseudo-islets and islet sheets for modeling studies and potential transplant applications.

Identifying Barriers to Estimating Carbon Release From Interacting Feedbacks in a Warming Arctic

The northern permafrost region holds almost half of the world's soil carbon in just 15% of global terrestrial surface area. Between 2007 and 2016, permafrost warmed by an average of 0.29°C, with observations indicating that frozen ground in the more southerly, discontinuous permafrost zone is already thawing. Despite this, our understanding of potential carbon release from this region remains not only uncertain, but incomplete. SROCC highlights that global-scale models represent carbon loss from permafrost only through gradual, top-down thaw. This excludes “pulse” disturbances – namely abrupt thaw, in which frozen ground with high ice content thaws, resulting in subsidence and comparatively rapid ongoing thaw, and fire – both of which are critically important to projecting future permafrost carbon feedbacks. Substantial uncertainty remains around the response of these disturbances to ongoing warming, although both are projected to affect an increasing area of the northern permafrost region. This is of particular concern as recent evidence indicates that pulse disturbances may, in some cases, respond nonlinearly to warming. Even less well understood are the interactions between processes driving loss of permafrost carbon. Fire not only drives direct carbon loss, but can accelerate gradual and abrupt permafrost thaw. However, this important interplay is rarely addressed in the scientific literature. Here, we identify barriers to estimating the magnitude of future emissions from pulse disturbances across the northern permafrost region, including those resulting from interactions between disturbances. We draw on recent advances to prioritize said barriers and suggest avenues for the polar research community to address these.

Decellularized xenogenic bone graft for repair of segmental bone defect in rabbits.

Bone grafting is a preferred treatment option for the healing of large diaphyseal bone defects and is useful in the management of nonunion, delayed union, and tumor resection. To investigate a decellularization protocol of bovine cancellous bone for xenogenic implantation in radial bone defects in rabbits. Bovine bone scaffolds fabricated with various decellularization protocols viz phosphate buffer saline (PBS), 1% sodium dodecyl sulfate (SDS), and rapid freeze and thaw technique. The manufactured scaffolds were characterized by biomechanical testing, histological staining, and scanning electron microscopy. A 10 mm rabbit radius bone defect was repaired with autograft and SDS treated and rapid freeze and thaw in groups A, B, and C respectively. Healing was evaluated by radiography and histopathology at 0, 30, 60, and 90 days. The grafts were also checked for host tissue reaction and incorporation into the defect. The freeze and thaw group showed complete elimination of all cellular nuclei, regular arrangement of collagen fiber, and no significant difference in tensile strength compared to 1% SDS treated and native groups. The in vivo radiographic and histopathological study showed that the rapid freeze and thaw group had complete bridging of the bone gap defect with new bone formation and they were immunologically less reactive compared to group B. The in vitro and in vivo evaluation of the grafts suggested that freeze and thaw technique was most superior to all other techniques for effective decellularization and augmentation of bone healing with better integration of the graft into the host.

Development of Cyroprotectant Agent-free Cell Cryopreservation by Superflash Freezing of Micro-droplets

Cell cryopreservation is the only way to stop biological activity and is widely used to maintain backups of cells. Conventionally, at least a cryoprotectant agent (CPA) must be added to avoid forming damaging ice crystals and to vitrify water on the inside and outside of the cell. We developed a CPA-free cryopreservation method by superflash freezing based on inkjet cell printing, in that cells were ejected as micro-droplets and deposited on the liquid nitrogen-cooled substrate. The method cryopreserved mouse fibroblast cells at a viability almost as high as the conventional method using dimethyl sulfoxide. To improve the reproducibility and viability further, the thawing process is important as well as the cooling process. Next, we also developed an automatic thawing apparatus that transports the vitrified cells rapidly into a prewarmed medium using a spring hinge. The experimental results indicate that the combination of superflash freezing with the rapid thawing process using the apparatus would become a possible approach to circumvent the problems associated with the addition of CPAs.

Structure Characterization and Anti-Inflammatory Activity of Polysaccharides from Lingzhi or Reishi Medicinal Mushroom Ganoderma lucidum (Agaricomycetes) by Microwave-Assisted Freeze-Thaw Extraction.

A water-soluble polysaccharide (GLP-2) was isolated and purified from Ganoderma lucidum by the microwave-assisted freeze-thaw method. Microwave-assisted rapid thawing treatment can greatly improve the extraction yield of polysaccharides. The chemical structure of GLP-2 was analyzed with FT-IR, HPLC, GC-MS, and NMR spectrometry. It was proved that GLP-2 is mainly composed of β-1,3-glucose and β-1,6-glucose. The chain conformation of GLP-2 was analyzed by SEC-MALLS-RI, indicating that GLP-2 adopts semi-rigid chain conformation. Its molecular weight is 16.7 × 104, and its molecular size is about 61.2 nm. MTT assay indicated that GLP-2 was non-toxic to RAW 264.7 cells in vitro. The results of anti-inflammatory studies showed that GLP-2 can inhibit the production of NO, TNF-α, IL-1β, and IL-6 in RAW 264.7 macrophage stimulated by lipopolysaccharide (LPS). The above data showed that the extraction method used in this study can obtain a high-yield polysaccharide with anti-inflammatory activity.

Effect of ultrasonic thawing on the physicochemical properties, freshness, and protein-related properties of frozen large yellow croaker (Pseudosciaena crocea).

Ultrasonic treatment (UT) was used to thaw large yellow croaker in this study, and the effect of various ultrasonic power levels on the quality of large yellow croaker was evaluated after thawing. The effects of ultrasonic on water holding capacity (WHC), moisture distribution, thiobarbituric acid-reactive substance (TBARs), total volatile base nitrogen (TVB-N), ATP degradation (related to K value), surface color change, free amino acid (FAA) content, total sulfhydryl group (SH) content, Fourier transform infrared absorption spectra (FT-IR), fluorescence emission spectra, and microscopic observations of large yellow croaker myofibrillar proteins were investigated. The thawing times of the control sample, 200UT, 240UT, 280UT, and 320UT samples were 1750, 1190, 810, 580, and 570 s, respectively, which indicated that ultrasonic radiation could improve thawing efficiency. Additionally, ultrasonic thawing maintained better freshness and color and inhibited lipid oxidation. Compared with fresh samples, the TVB-N of large yellow croaker thawed by ultrasonication increased by 12.68%, and the K value increased by 0.9%. The 240UT sample had tightly arranged myofibrils and fewer changes in the structures of myogenic fibrillar proteins than the fresh samples, and the SH content of 240UT was decreased by 8.17%. Use of excessive ultrasonic power (320 W) damaged the protein microstructure and the microstructure of large yellow croaker. In conclusion, sample 240UT maintained the quality of large yellow croaker better with minimal damage, which is recommended for rapid thawing. PRACTICAL APPLICATION: Ultrasonic waves improve the thawing efficiency of large yellow croaker and maintain the freshness and color of the fish. According to results, sample 240UT exhibited slight changes in the structure of the myofibril protein, but excessive ultrasonic power destroyed the microstructure and protein structure. Appropriate ultrasonic treatment to the thawing of fish has good prospects.

Cryopreservation of aromatic ginger Kaempferia galanga L. by encapsulation-dehydration

Kaempferia galanga L. is an endangered multi-purpose medicinal plant in Family Zingiberaceae, the rhizomes of which are used for several ayurvedic formulations. Encapsulation-dehydration (ED) method was optimized for cryopreservation of shoot tips of K. galanga. Shoot tips (STs) bearing the apical meristem dissected from the established in vitro shoot cultures were preconditioned in MS+0.4 M sucrose prior to encapsulation in calcium alginate and the beads subsequently transferred to MS liquid+0.3 M sucrose for 3 days afterward dehydration inside the laminar airflow for 4 hours upon rapid freezing in LN and rapid thawing produced maximum 62.2% survival and 46.7% regeneration rates. Shoot regeneration was observed from the apical meristems exclusive of intermediary callus phase. The plantlets regenerated from cryopreserved STs transferred to the field were phenotypically analogous with the mother plant.

Remote sensing annual dynamics of rapid permafrost thaw disturbances with LandTrendr

Permafrost is warming globally which leads to widespread permafrost thaw. Particularly ice-rich permafrost is vulnerable to rapid thaw and erosion, impacting whole landscapes and ecosystems. Retrogressive thaw slumps (RTS) are abrupt permafrost disturbances that expand by several meters each year and lead to an increased soil organic carbon release. Local Remote Sensing studies identified increasing RTS activity in the last two decades by increasing number of RTS or heightened RTS growth rates. However, a large-scale assessment across diverse permafrost regions and at high temporal resolution allowing to further determine RTS thaw dynamics and its main drivers is still lacking.In this study we apply the disturbance detection algorithm LandTrendr for automated large-scale RTS mapping and high temporal thaw dynamic assessment to North Siberia (8.1×106km2). We adapted and parametrised the temporal segmentation algorithm for abrupt disturbance detection to incorporate Landsat+Sentinel-2 mosaics, conducted spectral filtering, spatial masking and filtering, and a binary machine-learning object classification of the disturbance output to separate between RTS and false positives (F1 score: 0.609). Ground truth data for calibration and validation of the workflow was collected from 9 known RTS cluster sites using very high-resolution RapidEye and PlanetScope imagery.Our study presents the first automated detection and assessment of RTS and their temporal dynamics at large-scale for 2001–2019. We identified 50,895 RTS and a steady increase in RTS-affected area from 2001 to 2019 across North Siberia, with a more abrupt increase from 2016 onward. Overall the RTS-affected area increased by 331% compared to 2000 (2000: 20,158ha, 2001–2019: 66,699ha). Contrary to this, 5 focus sites show spatio-temporal variability in their annual RTS dynamics, with alternating periods of increased and decreased RTS development, indicating a close relationship to thaw drivers. The majority of identified RTS was active from 2000 onward and only a small proportion initiated during the assessment period, indicating that the increase in RTS-affected area was mainly caused by enlarging existing RTS and not by new RTS. The detected increase in RTS dynamics suggests advancing permafrost thaw and underlines the importance of assessing abrupt permafrost disturbances with high spatial and temporal resolution at large-scales. Obtaining such consistent disturbance products will help to parametrise regional and global climate change models.

Cell Viability Assessment Using Fluorescence Vital Dyes and Confocal Microscopy in Evaluating Freezing and Thawing Protocols Used in Cryopreservation of Allogeneic Venous Grafts.

The authors present their contribution to the improvement of methods suitable for the detection of the freezing and thawing damage of cells of cryopreserved venous grafts used for lower limb revascularization procedures. They studied the post-thaw viability of cells of the wall of cryopreserved venous grafts (CVG) immediately after thawing and after 24 and 48 h culture at +37 °C in two groups of six CVG selected randomly for slow thawing in the refrigerator and rapid thawing in a water bath at +37 °C. The grafts were collected from multi-organ and tissue brain-dead donors, cryopreserved, and stored in a liquid nitrogen vapor phase for five years. The viability was assessed from tissue slices obtained by perpendicular and longitudinal cuts of the thawed graft samples using in situ staining with fluorescence vital dyes. The mean and median immediate post-thaw viability values above 70% were found in using both thawing protocols and both types of cutting. The statistically significant decline in viability after the 48-h culture was observed only when using the slow thawing protocol and perpendicular cutting. The possible explanation might be the “solution effect damage” during slow thawing, which caused a gentle reduction in the graft cellularity. The possible influence of this phenomenon on the immunogenicity of CVG should be the subject of further investigations.

Assessment of the effect of long-term seed storage on the viability of Matricaria chamomilla seeds after cryopreservation

The article presents the study of influences of cryopreservation on seed germination of Matricaria chamomilla. Four varieties «Moscow Region», «Karagandinskaya», «Aibolit» and «Old Lekar» are used in the work. The seeds of the test species are cryopreserved in liquid nitrogen, followed by defrosting at room temperature and rapid defrosting in a water bath at temperature +40 Ԩ. After cryopreservation the seeds are planted in Petri dishes and placed in a climate chamber for determination laboratory germination. It is noted that the best results are obtained in the defrosting variant at the room temperature. Therefore, the maximum germination rate for variety «Karagandinskaya» was 84.0%, energy of germination — 83.0%; for «Aibolit» variety was 82.0% and 81.0%, respectively; «Moscow Region» variety had a minimum germination rate — 13.0 % and energy of germination 10.0 %. While for the «Old Lekar» variety, the optimal thawing mode was rapid thawing in a water bath at the temperature +40Ԩ; seed germination was 63.0%, energy of germination — 62.0%. Thus, it is necessary for receiving more viable seeds of varieties of Matricaria chamomilla after freezing in liquid nitrogen to apply the slow mode of thawing at the room temperature +24 Ԩ.

Mercury in Sediment Core Samples From Deep Siberian Ice-Rich Permafrost

We determine Hg concentrations of various deposits in Siberia’s deep permafrost and link sediment properties and Hg enrichment to establish a first Hg inventory of late Pleistocene permafrost down to a depth of 36 m below surface. As Arctic warming is transforming the ice-rich permafrost of Siberia, sediment is released and increases the flux of particulates to the Arctic shelf seas through thawing coasts, lakeshores, and river floodplains. Heavy metals within soils and sediments are also released and may increasingly enter Arctic waters and the biological food chain. High levels of mercury (Hg) have been reported from shallow soils across the Arctic. Rapid thawing is now mobilizing sediment from deeper strata, but so far little is known about Hg concentrations in deep permafrost. Here, forty-one samples from sediment successions at seven sites and of different states of permafrost degradation on Bykovsky Peninsula (northern Yakutian coast) and in the Yukechi Alas region (Central Yakutia) were analyzed for Hg, total carbon, total nitrogen, and total organic carbon as well as grain-size distribution, bulk density, and mass specific magnetic susceptibility. We show average Hg concentrations of 9.72 ± 9.28 μg kg−1 in the deep sediments, an amount comparable to the few previous Arctic studies existing, and a significant correlation of Hg content with total organic carbon, total nitrogen, grain-size distribution, and mass specific magnetic susceptibility. Hg concentrations are higher in the generally sandier sediments of the Bykovsky Peninsula than in the siltier sediments of the Yukechi Alas. The ratio of Hg to total organic carbon in this study is 2.57 g kg−1, including samples with very low carbon content. We conclude that many deep permafrost sediments, some of which have been frozen for millennia, contain elevated concentrations of Hg and the stock of Hg ready to be released by erosion is of significance for the Arctic ecosystem. The Hg mobilized may accumulate on the way to or in the shallow sea, and where it enters into active biogeochemical cycles of aquatic systems it may concentrate in food webs. Our study highlights the need for better understanding Hg stocks and Hg release from permafrost.

Sources and composition of chemical pollution in Maritime Antarctica (King George Island), part 2: Organic and inorganic chemicals in snow cover at the Warszawa Icefield

The study area is located on King George Island, where 90% of the area is permanently glaciated. This study provides a comprehensive analysis of the inorganic and organic chemistry of snow cover in the icefield and a comparison against previous results obtained in fresh water. Snow samples were collected in the summer of 2017 in the Warszawa Icefield area. Sampling points are located along two transects: between the Arctowski Polish Polar Station and the Carlini Base (N = 4), and from the forefield to the upper part of Ecology Glacier (N = 5). In the snow samples, (1) basic ions, (2) major trace metals and metalloids (and B), and (3) polycyclic aromatic hydrocarbons (PAHs) were detected and quantified. Additionally, the parameters of pH, specific electrolytic conductivity (SEC25) and total organic carbon (TOC) were determined. The results show a low concentration of inorganic elements (<30 mg/L), TOC (<1 mg/L) and PAHs (0.11–1.4 ng/L) in collected snow samples. A slight increase in PAHs and heavy-metals concentration has been observed at the marginal parts of the icefield, which suggests the impact of scientific stations. Based on this result there is a need to conduct research on pollutant levels in ice cores on King George Island to assess the risk associated with rapid glacier thawing and pollution remobilisation.

Topographic and Ground‐Ice Controls on Shallow Landsliding in Thawing Arctic Permafrost

AbstractAn increase in Arctic shallow landsliding is a potential consequence of climate warming. Warmer summer‐air temperatures and larger rainfall events drive heat into the active layer, melting ice and decreasing soil shear stress. Topography has the potential to exacerbate landsliding by controlling the distribution of ground ice and the movement of water in the subsurface. We demonstrate that shallow Arctic landslides initiate in zero‐order drainage basins consistent with models of shallow landsliding in non‐permafrost environments. However, the low average slopes and low concavity of Arctic hillslopes cannot create pore‐water pressures high enough to generate landsliding. Instead, two‐dimensional slope stability modeling suggests that the vertical distribution of ground‐ice distributions controls landslide susceptibility. High ground‐ice concentrations close to the potential failure plane act as a stronger control than high average ice volumes or rapid thawing. Our results demonstrate that landslide susceptibility is strongly affected by topographic controls on ground ice and hydrology.

Projecting Permafrost Thaw of Sub‐Arctic Tundra With a Thermodynamic Model Calibrated to Site Measurements

AbstractNorthern circumpolar permafrost thaw affects global carbon cycling, as large amounts of stored soil carbon becomes accessible to microbial breakdown under a warming climate. The magnitude of carbon release is linked to the extent of permafrost thaw, which is locally variable and controlled by soil thermodynamics. Soil thermodynamic properties, such as thermal diffusivity, govern the reactivity of the soil‐atmosphere thermal gradient, and are controlled by soil composition and drainage. In order to project permafrost thaw for an Alaskan tundra experimental site, we used seven years of site data to calibrate a soil thermodynamic model using a data assimilation technique. The model reproduced seasonal and interannual temperature dynamics for shallow (5–40 cm) and deep soil layers (2–4 m), and simulations of seasonal thaw depth closely matched observed data. The model was then used to project permafrost thaw at the site to the year 2100 using climate forcing data for three future climate scenarios (RCP 4.5, 6.0, and 8.5). Minimal permafrost thawing occurred until mean annual air temperatures rose above the freezing point, after which we measured over a 1 m increase in thaw depth for every 1 °C rise in mean annual air temperature. Under no projected warming scenario was permafrost remaining in the upper 3 m of soil by 2100. We demonstrated an effective data assimilation method that optimizes parameterization of a soil thermodynamic model. The sensitivity of local permafrost to climate warming illustrates the vulnerability of sub‐Arctic tundra ecosystems to significant and rapid soil thawing.

Mapping and understanding the vulnerability of northern peatlands to permafrost thaw at scales relevant to community adaptation planning

Developing spatially explicit permafrost datasets and climate assessments at scales relevant to northern communities is increasingly important as land users and decision makers incorporate changing permafrost conditions in community and adaptation planning. This need is particularly strong within the discontinuous permafrost zone of the Northwest Territories (NWT) Canada where permafrost peatlands are undergoing rapid thaw due to a warming climate. Current data products for predicting landscapes at risk of thaw are generally built at circumpolar scales and do not lend themselves well to fine-scale regional interpretations. Here, we present a new permafrost vulnerability dataset that assesses the degree of permafrost thaw within peatlands across a 750 km latitudinal gradient in the NWT. This updated dataset provides spatially explicit estimates of where peatland thermokarst potential exists, thus making it much more suitable for local, regional or community usage. Within southern peatland complexes, we show that permafrost thaw affects up to 70% of the peatland area and that thaw is strongly mediated by both latitude and elevation, with widespread thaw occuring particularly at low elevations. At the northern end of our latitudinal gradient, peatland permafrost remains climate-protected with relatively little thaw. Collectively these results demonstrate the importance of scale in permafrost analyses and mapping if research is to support northern communities and decision makers in a changing climate. This study offers a more scale-appropriate approach to support community adaptative planning under scenarios of continued warming and widespread permafrost thaw.

Downstream Evolution of Particulate Organic Matter Composition From Permafrost Thaw Slumps

Permafrost soils, which store almost half of the global belowground organic carbon (OC), are susceptible to thaw upon climate warming. On the Peel Plateau of northwestern Canada, the number and size of retrogressive thaw slumps (RTS) has increased in recent decades due to rising temperatures and higher precipitation. These RTS features caused by the rapid thaw of ice-rich permafrost release organic matter dominantly as particulate organic carbon (POC) to the stream network. In this study, we sampled POC and streambank sediments along a fluvial transect (∼12 km) downstream from two RTS features and assessed the composition and degradation status of the mobilized permafrost OC. We found that RTS features add old, Pleistocene-aged permafrost POC to the stream system that is traceable kilometers downstream. The POC released consists mainly of recalcitrant compounds that persists within stream networks, whereas labile compounds originate from the active layer and appear to largely degrade within the scar zone of the RTS feature. Thermokarst on the Peel Plateau is likely to intensify in the future, but our data suggest that most of the permafrost OC released is not readily degradable within the stream system and thus may have little potential for atmospheric evasion. Possibilities for the recalcitrant OC to degrade over decadal to millennial time scales while being transported via larger river networks, and within the marine environment, do however, still exist. These findings add to our understanding of the vulnerable Arctic landscapes and how they may interact with the global climate.

A 43-ka mineral magnetic record of environmental variations from lacustrine sediments of Schirmacher Oasis, East Antarctica

Glacial-interglacial climatic and environmental variations recorded in lake-bed sediments of Schirmacher Oasis (SO), East Antarctica, are rare; limited data exist on the past behavior of the East Antarctic Ice Sheet (EAIS). In this work, we present the mineral magnetic properties of a radiocarbon-dated sediment core, spanning the past 43,000 years, from a land-locked lake L-49 in SO. We also performed Scanning Electron Microscopic-Energy Dispersive X-ray Spectroscopic (SEM-EDS) studies on magnetic extracts to confirm the magnetic mineralogy. The values of magnetic susceptibility (χlf) and saturation isothermal remanent magnetization (SIRM) are relatively low during the Holocene but high during the last glacial period. Sediments of the last glacial period are composed mainly of coarse-grained (multi-domain - MD) magnetite/titanomagnetite (high values of S20 – an MD proxy, low susceptibility of anhysteretic remanent magnetism (χARM)/SIRM ratio values and high S-ratio values) indicating a stronger intensity of physical weathering in the Lake L-49 catchment. The mineralogy is confirmed by SEM-EDS data for magnetic extracts. Principal Component Analysis (PCA) of the data suggests three processes affecting magnetic properties of the lake sediments, i.e., ferrimagnetic input, biogenic processes and aeolian input. During deglaciation, a shift in the magnetic properties is documented: a decrease in χlf values from 18.6 cal ka BP onwards suggests melting of the snow and ice in the catchment thus leading to a significant production of fine-grained iron oxide minerals. At ~12.77 cal ka BP, high values of χlf and S20 ratio indicates cooling which is related to the Antarctic Cold Reversal (ACR). The Early Holocene Climate Optimum is distinctly imprinted in our record as a sudden decrease in χlf values and an increase in magnetic grain size ratio values (indicating finer iron oxide grains), suggesting a rapid thawing of the ice-sheet in response to a warm climate. The Mid-Holocene Hypsithermal (from 5.8 to 3.5 cal ka BP) and Neoglaciation (3.6 cal ka BP onwards) that are evident in this study correspond with reconstructions from lake and marine sediment, and ice-core records from Antarctica.

黄河源区不同类型冻土土壤水分入渗特性

冻土土壤水分运动由于受到冻融过程的影响而显示其独特性，而目前对于不同类型冻土土壤水分入渗特性尚缺乏足够的认识。为此，以黄河源区康穷小盆地多下坡年冻土和上坡季节冻土区为例，结合季节降雨变化，基于大气降水、冻土土壤水分、冻结层上水等野外监测数据分析，采用HYDRUS-1D软件冻融模块进行土壤水分入渗模拟，对比分析了融化期多年冻土和季节冻土土壤水分运移过程的差异性，研究结果表明：①在快速融化阶段，降雨以地表径流为主，表层土壤水分含量增加，土壤下渗有限，冻结层上水位上升幅度较小；在稳定融化阶段，土壤水分含量增加，土壤水分下渗增强，受冻土层阻隔影响，多年冻土区冻结层上水水位上升幅度较大，季节冻土区土壤水分则以深层渗漏或侧向流动为主。②受到降雨强度、土壤质地、蒸散发、植被覆盖等因素的影响，降雨损失主要以地表径流为主，下坡各层土壤水分随冻结土壤融化自上而下逐渐增加并达到饱和状态，但上坡表层土壤不易达到饱水状态。③区域河流贯穿融区地下水发育，导致上坡冻结层上水位小幅度上升，下坡冻结层上水位的变化除受到降雨入渗的影响外，还受到融区地下水的影响，引起下坡冻结层上水位的快速上升。研究结果有助于深入了解全球气候变化背景下的冻土退化及其水文效应，进而为定量评估流域水资源脆弱性与区域生态敏感性提供科学依据。;The water movement of frozen soil shows its uniqueness due to the influence of freeze-thaw process. However, there is a lack of in-depth study on soil moisture infiltration characteristics of different types of frozen soil at present. Therefore, a slope cross-section at the small basin of Kangqiong in Source Area of the Yellow River is studied. This zone on the upper slope is covered by seasonally frozen ground and that on the down slope is covered by the permafrost. Based on the field observation, the data has been collected from various sources including atmospheric precipitation, soil moisture, and suprapermafrost water from May 2017 to October 2017. In addition, the soil moisture infiltration is numerically simulated by the freeze-thaw module of HYDRUS-1D software package. Based on seasonal rainfall variation, the difference of soil moisture infiltration in permafrost regions and seasonally frozen regions is statistically investigated during thawing period. The results are summarized in the following: 1) in the rapid thawing stage, the rainfall infiltration is dominated by surface runoff. The water content of surface soil increases, but the infiltration of soil is limited. So, the suprapermafrost water flow rises slightly. During the stable thawing stage, soil water content increases and soil moisture infiltration increases. Influenced by the barrier of permafrost layer, the suprapermafrost water flow in permafrost regions rises greatly. While in seasonally frozen regions, the soil moisture infiltration is dominated by deep leakage or lateral flow. 2) Influenced by rainfall intensity, soil texture, evapotranspiration and vegetation coverage, the rainfall loss is mainly caused by surface runoff. Soil moisture content of each layer on the down slope increases gradually from top to bottom with the thawing of frozen soil and reaches the saturation state. Soil moisture content in surface layer on the upper slope has been rising with time, but it can not reach a stable state. 3) The existence of regional talik groundwater leads to a small increase of the suprapermafrost water level on the upper slope. In addition to rainfall infiltration, the change of the suprapermafrost water on the down slope is also affected by talik groundwater, which causes the rapid rise of the suprapermafrost water level on the down slope. The results are helpful to understand the degradation of frozen soil and its hydrological effects under the background of global climate change. At the same time, it will provide scientific basis for quantitative assessment of water resources vulnerability and regional ecological sensitivity.

Two-stage air thawing as an effective method for controlling thawing temperature and improving the freshness of frozen pork loin

Reduction in the total thawing time for pork loin subjected to two-stage air thawing was investigated. The pork loins were frozen at −60 and −18 °C and stored for up to 6 months at the freezing temperature. Samples were thawed using constant-temperature air thawing (−1.5, 2, and 25 °C) and two-stage air thawing methods. In the two-stage air thawing method, the samples were thawed at 25 °C in the initial stage. When the core temperature of the sample reached −5 °C, the samples were transferred to −1.5 °C (25/-1.5 method) or 2 °C (25/2 method). The physicochemical properties of the thawed pork loins, including thawing loss, cooking loss, water holding capacity (WHC), volatile basic nitrogen (VBN), and thiobarbituric acid reactive substances (TBARS) were analyzed. Thawing at 25 °C was the most rapid thawing method, and the total thawing time were reduced effectively using two-stage air thawing. Generally, samples thawed by two-stage air thawing (25/-1.5, and 25/2 methods) exhibit better moisture related properties. The effects of the thawing methods on VBN content were minimal; only trace levels of TBARS were detected in the samples. Therefore, two-stage air thawing is expected to reduce the total thawing time and prevent meat quality deterioration caused by the freezing and thawing processes.