Changes In Freezing Research Articles

Evaluation and mapping soil organic carbon in seasonally frozen ground on the Tibetan Plateau

Seasonally frozen ground (SFG) significantly contributes to global carbon sinks. Global warming and anthropogenic-induced disturbances threaten the carbon storage capacity of SFG. Challenges in evaluating the SFG carbon storage potential include the lack of understanding of the control mechanisms of soil organic carbon (SOC) variations and timely spatial estimates of SOC. In this study, we investigated SOC stocks in SFG in the Tibet Autonomous Region, China, in 2020 and 2021. We employed partial least squares structural equation modeling (PLS-SEM) to explore the effect of complex processes (interacting roles of climate, plant physiology and phenology, freeze–thaw cycle, soil environment, and C inputs) on SOC and mapped SOC stocks in the topmost 30 cm. We identified four causal pathways: (1) an indirect pathway representing the effect of climate on plant physiology and phenology through changes in freeze–thaw cycles and soil environment, (2) an indirect pathway representing the effect of climate on C inputs through changes in freeze–thaw cycles, soil environment and plant physiology and phenology, (3) an indirect pathway representing the effect of climate on freeze–thaw cycles, and (4) an indirect pathway representing the effect of climate on the soil environment through changes in freeze–thaw cycles. C inputs exerted the greatest control on SOC. The effect of these factors decreased with increasing soil depth. We used PLS-SEM to generate maps of SOC stocks in SFG at a 500 m resolution with a moderate accuracy. The estimated mean SOC stocks in the 0–30 cm layer reached 6.87 kg m−2, with a 95% confidence interval ranging from 6.2 to 7.5 kg m−2. Our results indicated that it is critical to consider the depth dependence of the direct and indirect effects of environmental factors when assessing the control mechanisms of SOC variations. In this work, we also demonstrated that spatially explicit SOC estimates based on timely investigations are important for assessing C stocks against the background of considerable environmental changes across the Tibetan Plateau.

Soil microbial legacies influence freeze–thaw responses of soil

Abstract Warmer winters with less snowfall are increasing the frequency of soil freeze–thaw cycles across temperate regions. Soil microbial responses to freeze–thaw cycles vary and some of this variation may be explained by microbial conditioning to prior winter conditions, yet such linkages remain largely unexplored. We investigated how differences in temperature history influenced microbial community composition and activity in response to freeze–thaw cycles. We collected soil microbial communities that developed under colder (high elevation) and warmer (low elevation) temperature regimes in spruce‐fir forests, then added each of these soil microbial communities to a sterile bulk‐soil in a laboratory microcosm experiment. The inoculated high‐elevation cold and low‐elevation warm microcosms were subjected to diurnal freeze–thaw cycles or constant above‐freezing temperature for 9 days. Then, all microcosms were subjected to a 7‐day above‐freezing recovery period. Overall, we found that the high‐elevation cold community had, relative to the low‐elevation warm community, a smaller reduction in microbial respiration (CO2 flux) during freeze–thaw cycles. Further, the high‐elevation cold community, on average, experienced lower freeze–thaw‐induced bacterial mortality than the warm community and may have partly acclimated to freeze–thaw cycles via increased lipid membrane fluidity. Respiration of both microbial communities quickly recovered following the end of the freeze–thaw treatment period and there were no changes in soil extractable carbon or nitrogen. Our results provide evidence that past soil temperature conditions may influence the responses of soil microbial communities to freeze–thaw cycles. The microbial community that developed under a colder temperature regime was more tolerant of freeze–thaw cycles than the community that developed under a warmer temperature regime, although both communities displayed some level of resilience. Taken together, our data suggest that microbial communities conditioned to less extreme winter soil temperatures may be most vulnerable to rapid changes in freeze–thaw regimes as winters warm, but they also may be able to quickly recover if mortality is low. Read the free Plain Language Summary for this article on the Journal blog.

The Effects of Freeze–Thaw Cycles on Methane Emissions From Peat Soils of a High-Altitude Peatland

The Qinghai– Tibet Plateau (QTP), which embodies the largest area of permafrost at mid–low altitudes of the world, has been experiencing rapid permafrost degradation and changes in freeze–thaw processes for the past decades. However, the responses and potential feedbacks of the methane flux from peatlands on the QTP to changing freeze–thaw cycles (FTCs) remain unknown. In this study, we collected peat soils from the Zoîgé peatlands, the largest peatland complex on the QTP, to examine methane emissions under simulated diurnal FTC scenarios. In incubation experiments of 15 days, two freeze–thaw temperature ranges of −5 to 4°C (mild) and −15 to 4°C (intense) were applied to two sets of peat soil samples, and each of them was characterized by 100% or 80% maximum water holding capacity (MWHC). The results showed that the peak of methane emission from the peat soil occurred after the first freeze–thaw cycle (FTC1), with the highest reaching a value of 0.103 mg kg soil−1·h−1. Generally, the cumulative methane emissions were elevated by FTCs, and relative higher rates of methane emissions were found for the 2nd FTC to the 15th FTC, compared with those from low-altitude peatlands. Methane emissions were significantly correlated to the export of dissolved organic carbon (DOC) and the activities of β-D-cellobiosidase and phenol oxidase in various freeze–thaw conditions. This study highlights the importance of FTCs in stimulating methane emissions and implies that methane emissions during FTCs from high-altitude peatlands would increase under a warmer climate in the future.

On the freeze–thaw cycles of shallow soil and connections with environmental factors over the Tibetan Plateau

Changes in the freeze–thaw cycles of shallow soil have important consequences for surface and subsurface hydrology, land–atmosphere energy and moisture interaction, carbon exchange, and ecosystem diversity and productivity. This work examines the shallow soil freeze–thaw cycle on the Tibetan Plateau (TP) using in–situ soil temperature observations in 0–20 cm soil layer during July 1982–June 2017. The domain and layer averaged beginning frozen day is November 18 and delays by 2.2 days per decade; the ending frozen day is March 9 and advances by 3.2 days per decade; the number of frozen days is 109 and shortens by 5.2 days per decade. Altitude and latitude combined could explain the spatial patterns of annual mean freeze–thaw status well. Stations located near 0 °C contour line experienced dramatic changes in freeze–thaw cycles as seen from subtropical mountain coniferous forest in the southern TP. Soil completely freezes from surface to 20-cm depth in 15 days while completely thaws in 10 days on average. Near-surface soil displays more pronounced changes than deeper soil. Surface air temperature strongly influences the shallow soil freeze–thaw status but snow exerts limited effects. Different thresholds in freeze–thaw status definition lead to differences in the shallow soil freeze–thaw status and multiple-consecutive-day approach appears to be more robust and reliable. Gridded soil temperature products could resolve the spatial pattern of the observed shallow soil freeze–thaw status to some extent but further improvement is needed.

Dominant influence of non-thawing periods on annual CO2 emissions from Zoige peatlands: Five-year eddy covariance analysis

Changes in freeze–thaw processes as a result of climate change significantly affect the carbon balance of terrestrial ecosystems, especially peatlands. The Qinghai-Tibetan Plateau contains substantial permafrost and seasonal frozen soils and its peatlands feature a huge carbon stock highly sensitive to global change. In this paper, we used an eddy covariance flux tower to monitor carbon fluxes on the Zoige peatlands with seasonal frozen soils on the eastern Qinghai-Tibetan Plateau from 2013 to 2017. Total net emissions (g C m−2 yr−1) over the monitoring period were 64.1, 106.7, 126.5 and 103.2 in the frozen, frozen-thawing, thawing and thawing-freezing periods; the corresponding weighted mean emission rates (g C m−2 d−1) were 0.36, 0.44, 0.64 and 0.38. Although net CO2 emissions were highest in the thawing period, emissions during the other periods accounted for approximately 68.4% of annual emissions. In fact, emissions during the two freeze–thaw periods were 1.7 times those during the thawing period despite the freeze–thaw periods lasting fewer days. CO2 emission correlated significantly with volumetric water content and soil temperature in the frozen period, with soil temperature and precipitation in the frozen-thawing period, and with precipitation in the thawing and thawing-freezing periods. Annual net CO2 emissions during each of the years were 57.2 g C m−2 yr−1 (2013), 108.3 g C m−2 yr−1 (2014), 41 g C m−2 yr−1 (2015), 62.9 g C m−2 yr−1 (2016) and 131.1 g C m−2 yr−1 (2017), and hydrological conditions were the primary determinant of interannual variations. Long-term continuous monitoring of carbon is essential to understand how freeze–thaw processes affect the ability of alpine peatland ecosystems to act as carbon sources and sinks.

Mimicking myofibrillar protein denaturation in frozen-thawed meat: Effect of pH at high ionic strength

This study aims at providing new insight on protein denaturation in freezing-thawing. Freezing-thawing minced pork reduced water-holding of myofibrils and increased surface hydrophobicity. One additional freezing-thawing cycle at slow freezing rate caused appearance of a 160 kDa myosin-4 fragment in SDS-PAGE, further decreased water-holding of myofibrils and increased surface hydrophobicity. Fresh minced pork was exposed to either high salt (2 M KCl) only or high salt with lower pH to mimic conditions in freezing. Exposure to high salt only increased water-holding of myofibrils and hence did not reproduce myofibrillar protein changes in freezing. Exposure to combinations of lower pHs and high salt decreased water-holding and increased surface hydrophobicity, suggesting myofibrillar protein denaturation occurred by a comparable mechanism as in freezing-thawing. We propose that exposure to decreased pH combined with high solute concentrations in the unfrozen water of frozen meat is the primary cause of myofibrillar protein denaturation in frozen-thawed meat.

Soil respiration of alpine meadow is controlled by freeze–thaw processes of active layer in the permafrost region of the Qinghai–Tibet Plateau

Abstract. Freezing and thawing action of the active layer plays a significant role in soil respiration (Rs) in permafrost regions. However, little is known about how the freeze–thaw processes affect the Rs dynamics in different stages of the alpine meadow underlain by permafrost in the Qinghai–Tibet Plateau (QTP). We conducted continuous in situ measurements of Rs and freeze–thaw processes of the active layer at an alpine meadow site in the Beiluhe permafrost region of the QTP and divided the freeze–thaw processes into four different stages in a complete freeze–thaw cycle, comprising the summer thawing (ST) stage, autumn freezing (AF) stage, winter cooling (WC) stage, and spring warming (SW) stage. We found that the freeze–thaw processes have various effects on the Rs dynamics in different freeze–thaw stages. The mean Rs ranged from 0.12 to 3.18 µmol m−2 s−1 across the stages, with the lowest value in WC and highest value in ST. Q10 among the different freeze–thaw stages changed greatly, with the maximum (4.91±0.35) in WC and minimum (0.33±0.21) in AF. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to total Rs of a complete freeze–thaw cycle (1692.98±51.43 g CO2 m−2) were 61.32±0.32 %, 8.89±0.18 %, 18.43±0.11 %, and 11.29±0.11 %, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as climate change and permafrost degradation continue, great changes in freeze–thaw process patterns may trigger more Rs emissions from this ecosystem because of a prolonged ST stage.

Predictive ability of climate change with the automated statistical downscaling method in a freeze–thaw agricultural area

Precipitation and temperature in freeze–thaw agricultural area have different patterns under global warming. In this study, a statistical relationship between large-scale changes in climate variables and local weather data was built by applying an automated statistical downscaling (ASD) model in the Sanjiang Plain in China. We evaluated the prediction ability of the ASD model in terms of spatial–temporal changes in freeze–thaw agricultural area, and the temperature and precipitation changes in the twenty-first century under the representative concentration pathway 4.5 (RCP4.5) scenario were estimated. The results revealed that the explained variances in temperature were higher than 0.93 during the calibration and verification periods, which demonstrated good simulation capacity. The R2 of precipitation was acceptable due to the randomness and complexity of daily precipitation. Based on the Geophysical Fluid Dynamics Laboratory Earth System Model with the Generalized Ocean Layer Dynamics component (GFDL-CM3), the regional climate simulation provided good predictions. By 2100, the average, maximum and minimum temperatures in this area could increase by 2.0–2.5 °C, 2.5 °C and 2.5–4.0 °C, respectively. In terms of the spatial distribution, temperatures could increase faster in the northern region and slower in the central and southern regions. The warming trends in summer and winter were more significant than those in spring and autumn. There was no significant change in annual precipitation in the twenty-first century (increased approximately 10 mm by 2100). Precipitation decreased obviously in July and August (approximately 0.4 mm/day), and other months showed an increasing trend (approximately 0.5–0.9 mm/day). There will be large spatial variation of precipitation in the future changes. The results could serve as a reference for assessing non-point source pollution and agricultural management.

Effect of Air Entraining Admixture on Concrete under Temperature Changes in Freeze and Thaw Cycles

The mechanism of air bubbles acting during freezing and thawing cycles considering various conditions has been studied by many researchers. On the other hand, simulation of the thermal stresses in concrete with finite element software is performed where the results have proved the capability of these methods. In this paper, stresses which are induced by temperature changes in the freezing and thawing cycles are investigated for non-air and air entrained concrete. Modelling procedures were implemented considering effects of aggregates, cement paste, and boundary conditions. The results have shown that air bubbles can play important role in uniform distribution of thermal stresses in concrete which may lead to decreased maximum stress that occurs in concrete. It can also cause the plastic strains in the interfacial transition zone (ITZ) to be controlled.

Freezing Eggs in a Warming World

Most discussions of population control focus on how many children people should have, but ignore issues to do with the timing, so there is little discussion of the value of delaying childbearing. Once we recognize that delaying childbearing can have a significant impact on the size of the population, and, therefore, on CO2e (carbon dioxide equivalent) emissions, our perspective on egg freezing changes significantly. In this article, I argue that, if we focus on future generations in general, rather than focusing only on the children who would be conceived using frozen eggs, policies permitting or encouraging the freezing of eggs may reduce potential harms to future generations. This, I argue, may block the objections to egg freezing for non-medical reasons which focus on the potential risks to the child (without requiring an appeal to the non-identity problem).

The effect of low-level laser irradiation on sperm motility, and integrity of the plasma membrane and acrosome in cryopreserved bovine sperm.

Background and ObjectiveFreezing changes sperm integrity remarkably. Cryopreservation involves cooling, freezing, and thawing and all these contribute to structural damage in sperm, resulting in reduced fertility potential. Low-level laser irradiation (LLLI) could increase energy supply to the cell and cause reactive oxygen species reduction (ROS), contributing to the restoration of oxygen consumption and adenosine triphosphate synthesis (ATP) in the mitochondria. Our goal was to analyze the effects of low-level laser irradiation on sperm motility and integrity of the plasma membrane and acrosome in cryopreserved bovine sperm.Study Design/Materials and MethodsWe analyzed 09 samples of bull semen (Bos taurus indicus), divided into three groups: a control group without laser irradiation, a 4J group subjected to a laser irradiation dose of 4 joules, and a 6J group subjected to dose of 6 joules. Samples were divided for the analysis of cell viability and acrosomal membrane integrity using flow cytometry; another portion was used for motion analysis. Irradiation was performed in petri dishes of 30 mm containing 3 ml of semen by an aluminum gallium indium phosphide laser diode with a wavelength of 660 nm, 30 mW power, and energy of 4 and 6 joules for 80 and 120 seconds respectively. Subsequently, the irradiated and control semen samples were subjected to cryopreservation and analyzed by flow cytometry (7AAD and FITC-PSA) using the ISAS - Integrated Semen Analysis System.ResultsFlow cytometry showed an increase in the percentage of live sperm cells and acrosome integrity in relation to control cells when subjected to irradiation of low-power laser in two different doses of 4 and 6 joules (p < 0.05). In the analysis of straightness, percentage of cell movement, and motility, a dose of 4 joules was more effective (p < 0.05).ConclusionWe conclude that LLLI may exert beneficial effects in the preservation of live sperm. A dose of 4 joules prior to cryopreservation was more effective than a dose of 6 joules in preserving sperm motility.

Changes in active-layer thickness and near-surface permafrost between 2002 and 2012 in alpine ecosystems, Qinghai–Xizang (Tibet) Plateau, China

Between 2002 and 2012, daily soil temperature measurements were made at 10 sites within five alpine ecosystems in the Beiluhe area of the central Qinghai–Tibet Plateau. Changes in freeze–thaw occurrence, active-layer thickness and near-surface permafrost temperature in barren, desert grassland, alpine steppe and alpine meadow ecosystems indicate that alpine ecosystems are sensitive to climate variability. During this time, the average onset of spring thawing at 50-cm depth advanced by at least 16days in all but the barren alpine settings, and the duration of thaw increased by at least 14days for all but the desert grassland and barren ecosystems. All sites showed an increase in active-layer thickness (ALT) and near-surface permafrost temperature: the average increase of ALT was ~4.26cm/a and the average increase in permafrost temperatures at 6m and 10m depths were, respectively, ~0.13°C and ~0.14°C. No apparent trend in mean annual air temperature was detected at the Beiluhe weather station. However, an increasing trend in precipitation was measured. This suggests that the primary control on the ALT increase was an increase in summer rainfall and the primary control on increasing permafrost temperature was probably the combined effects of increasing rainfall and the asymmetrical seasonal changes in subsurface soil temperatures.

Intravenous amantadine on freezing of gait in Parkinson’s disease: a randomized controlled trial

To compare the effects of intravenous amantadine and placebo therapy on freezing of gait in patients with Parkinson's disease, this randomized, double-blind, placebo-controlled, multicenter trial compared the efficacy of 5 days intravenous amantadine and placebo treatments on freezing of gait in 42 subjects randomly allocated 2:1 to amantadine or placebo groups. Changes in freezing of gait questionnaire (FOG-Q) scores and in unified Parkinson's disease rating scale (UPDRS) scores, from baseline to immediately (V1) and 1 month (V2) after treatments, were assessed. Among the 42 patients (amantadine n = 29, placebo n = 13, a mean age 65.5 ± 9.4 years and a mean FOG-Q score 17.4 ± 3.2), 40 subjects completed treatment. There was no significant group difference on the primary outcome measure as total FOG-Q score changes at V1. However a significant beneficial effect of amantadine on freezing was seen at V2 in the UPDRS Part II freezing and FOG-Q item 3 scores, and there was significant improvement in the UPDRS Part IV total score and in the UPDRS Part II getting out of bed score in the amantadine group at both V1 and V2. There was no serious adverse event reported during the study. The intravenous amantadine therapy did not show a significant improvement on overall FOG-Q scores in patients with moderate-to-severe freezing; however, it might be beneficial by attenuating freezing severity and improving patients' mobility. To prove this finding further studies with larger sample sizes are warranted in the future.

Accumulative strain of clays in cold region under long-term low-level repeated cyclic loading: Experimental evidence and accumulation model

In cold region, the seasonal effects like changes in freeze–thaw should be investigated with respect to their influence on permanent settlement of foundation under long-term low-level repeated cyclic loading. Thereby, the influence of freeze–thaw processes on the accumulative axial strain of clays under long-term low-level repeated cyclic loading was investigated by conducting cyclic tri-axial tests and a numerical model for calculating the accumulative axial strain was proposed based on the experience observation in this paper. The normalized accumulative axial strain of clays increases significantly subjected to one freeze–thaw cycle, then decreases and tends up to be stable with the subsequent freeze–thaw cycles. The normalized accumulative axial strain increases with the increasing repeated cyclic stress amplitude, moisture content of samples and the number of loading cycles, but decreases with the increasing confining pressure. The modification parameters ηFT and functions fampl, fC, fW and fN were proposed to consider the effects of the influence factors and were implemented into the accumulative strain model. In this model, all of the calculating procedures were explicit and all material constants of clays were presented. Therefore, the accumulative strain model can be used to predict the settlement of foundation under long-term low-level repeated cyclic loading in cold region.

Gating of Fear in Prelimbic Cortex by Hippocampal and Amygdala Inputs

The prefrontal cortex (PFC) regulates emotional responses, but it is unclear how PFC integrates diverse inputs to select the appropriate response. We therefore evaluated the contribution of basolateral amygdala (BLA) and ventral hippocampus (vHPC) inputs to fear signaling in the prelimbic (PL) cortex, a PFC region critical for the expression of conditioned fear. In conditioned rats trained to press for food, BLA inactivation decreased the activity of projection cells in PL, and reduced PL conditioned tone responses. In contrast, vHPC inactivation decreased activity of interneurons in PL and increased PL conditioned tone responses. Consistent with hippocampal gating of fear after extinction, vHPC inactivation increased fear and PL pyramidal activity in extinguished, but not in conditioned, rats. These results suggest a prefrontal circuit whereby hippocampus gates amygdala-based fear. Thus, deficient hippocampal inhibition of PFC may underlie emotional disorders, especially in light of reduced hippocampal volume observed in depression and PTSD.

Changing freeze‐thaw seasons in northern high latitudes and associated influences on evapotranspiration

AbstractSeasonal frozen states in the northern terrestrial cryosphere limit vegetation photosynthetic activities and evapotranspiration (ET) through cold temperature constraints to biological processes and chemical unavailability of water as a result of being frozen. Seasonal transitions of the landscape between predominantly frozen and thawed conditions are analogous to a biospheric and hydrological on/off switch, with marked differences in ET, vegetation productivity and other biological activity between largely dormant winter and active summer conditions. We investigated changes in freeze–thaw (FT) seasons and ET from 1983 to 2006 and their connections in the northern cryosphere by analyzing independent satellite remote sensing derived FT and ET records. Our findings show that the northern cryosphere (≥ 40°N) has experienced advancing (−2.5 days/decade; P = 0.005) and lengthening (3.5 days/decade; P = 0.007) non‐frozen season trends over the 24‐year period, coinciding with an upward trend (6.4 mm/year/decade; P = 0.014) in regional mean annual ET over the same period. Regional average timing of spring primary thaw and the annual non‐frozen period are highly correlated with regional annual ET (|r| ≥ 0.75; P &lt; 0.001), with corresponding impacts to annual ET of approximately 0.6 and 0.5% per day, respectively. The impact of primary fall freeze timing on ET is relatively minor compared with primary spring thaw timing. Earlier onset of the non‐frozen season generally promotes annual ET in colder areas but appears to suppress summer ET by increasing drought stress in the southernmost parts of the domain where water supply is the leading constraint to ET. The cumulative effect of future freeze‐thaw changes on ET in the region will largely depend on future changes of large‐scale atmosphere circulations and rates of vegetation disturbance and adaptation to continued warming. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Performance degradation and microstructure changes in freeze–thaw cycling for PEMFC MEAs with various initial microstructures

When the temperature of a fuel cell vehicle is repeatedly reduced to subzero temperatures, volume changes by water/ice transformations and frost heave mechanism can cause microstructural changes in membrane–electrode assemblies (MEA), and a resultant permanent decrease in the performance of fuel cell stacks. In this study, five MEAs manufactured by different methods, were tested under repeated freeze–thaw (F–T) cycles between −20 °C and 10 °C, and the variations in their electrochemical and microstructural characteristics were analyzed according to the initial microstructures. When the MEAs were prepared by spraying catalyst inks on polymer membranes, no significant microstructural changes were observed. In the case of two supplied MEAs, void formations at the electrolyte/electrode interface or vertical cracks within the catalyst layers were observed after 120 F–T cycles. Void formation seems to be responsible for performance degradation as a result of ohmic loss, but the effect of cracks in the catalyst layers was not confirmed. In 120 F–T cycles, activation overpotentials and concentration overpotentials did not increase significantly for any of the MEAs, even although gradual decreases in the electrochemically active surface area of the platinum catalysts and changes in the porous structure were observed.

Long-Term Changes in Ice Phenology of the Yellow River in the Past Decades

Abstract The authors quantitatively describe the changes in the characteristics of ice phenology including the flow rate and freeze/breakup dates of the Yellow River based on observations of the past 50 yr. In both the upper and lower reaches of the Yellow River, increasing temperature delays the freeze date and advances the breakup date, thus decreasing the number of freeze days and the expanse of river freeze. From 1968 to 2001, the freeze duration has shortened significantly by 38 days at Bayangaole and 25 days at Sanhuhe, respectively. From the early 1950s to the early 2000s, the changes in freeze and breakup dates have shortened the freeze duration in the lower reach of the Yellow River by 12 days. The flow rate has reduced from 500 to 260 m3 s−1, and the expanse of river freeze has also decreased significantly by about 310 km. In addition, in the lower reach of the river, the location of earliest ice breakup has shifted downstream significantly in the last 50 yr, although the location of earliest freeze exhibits little change.

Interdecadal changes in seasonal freeze and thaw depths in Russia

Seasonal freezing and thawing processes in cold regions play a major role in ecosystem diversity, productivity, and the Arctic hydrological system. Long‐term changes in seasonal freeze and thaw depths are also important indicators of climate change. Only sparse historical measurements of seasonal freeze and thaw depths are available for permafrost and seasonally frozen ground regions. Using mean monthly soil temperature data for 1930–1990 for 242 stations located throughout Russia, we employed a linear interpolation method to determine the depth of the 0°C isotherm based on soil temperature data measured between 0.2 m and 3.2 m depth. The relationship between available observed annual maximum freeze and thaw depths and our interpolated values indicates a perfect correlation. A comprehensive evaluation of long‐term trends in these new interpolated data for Russia indicates that in permafrost regions, active layer depths have been steadily increasing. In the period 1956–1990 the active layer exhibited a statistically significant deepening by approximately 20 cm. The changes in the seasonally frozen ground areas are even greater: The depth of the freezing layer decreased 34 cm between 1956 and 1990. Potential forcings of the observed changes include air temperature, freezing and thawing index, and snow depth. Correlation and multiple regression reveal that active layer depth is most strongly related to snow depth. Air temperature, both mean annual and thawing index, is also significantly related to changes in the active layer. Freeze depth is influenced most strongly by the freezing index and mean annual air temperature, although snow depth is also a significant contributor. Air temperature and snow depth have been changing less in the seasonally frozen ground regions of Russia compared to permafrost regions, although observed changes in freeze depth are greater than changes in active layer depth for 1930–1990. This indicates that the seasonally frozen ground regions of the Russian high latitudes are more susceptible to climate change than the Russian permafrost. However, as temperatures have been rising, especially in the high‐latitude continental regions, both permafrost and seasonally frozen ground regions are being greatly impacted. These changes can potentially result in increased river runoff and changes in discharge throughout the Russian Arctic drainage basin, as well as changes in high‐latitude ecosystems.

Acquisition of freezing tolerance in early autumn and seasonal changes in gall water content influence inoculative freezing of gall fly larvae, Eurosta solidaginis (Diptera, Tephritidae)

We examined seasonal changes in freeze tolerance and the susceptibility of larvae of the gall fly, Eurosta solidaginis to inoculative freezing within the goldenrod gall ( Solidago sp.). In late September, when the water content of the galls was high (~55%), more than half of the larvae froze within their galls when held at –2.5 °C for 24 h, and nearly all larvae froze at –4 or –6 °C. At this time, most larvae survived freezing at ≥ –4 °C. By October plants had senesced, and their water content had decreased to 33%. Correspondingly, the number of larvae that froze by inoculation at –4 and –6 °C also decreased, however the proportion of larvae that survived freezing increased markedly. Gall water content reached its lowest value (10%) in November, when few larvae froze during exposure to subzero temperatures ≥ –6 °C. In winter, rain and melting snow transiently increased gall water content to values as high as 64% causing many larvae to freeze when exposed to temperatures as high as –4 °C. However, in the absence of precipitation, gall tissues dried and, as before, larvae were not likely to freeze by inoculation. Consequently, in nature larvae freeze earlier in the autumn and/or at higher temperatures than would be predicted based on the temperature of crystallization ( T c) of isolated larvae. However, even in early September when environmental temperatures are relatively high, larvae exhibited limited levels of freezing tolerance sufficient to protect them if they did freeze.