Low Temperature Conditions Research Articles

Sustainable application of recycled plastics in asphalt pavement: Case study of a trial in Newtonville, Ontario, Canada

Global research on using plastic waste in asphalt roads highlights its benefits: recycling waste, reducing greenhouse gas emissions, and providing an alternative to non-renewable asphalt binders. This study aims to bridge the gap between laboratory results and field performance of recycled plastic-modified asphalt in cold regions, promoting broader adoption. Laboratory analysis of core samples was performed as part of a quality assurance program. High-temperature rutting resistance was evaluated using the Hamburg wheel tracking test, while low-temperature cracking resistance was assessed through semi-circular bending testing. Results show that the impact of recycled plastics and fibers on rutting resistance varies with temperature, with the greatest benefit at the highest temperatures. For low-temperature cracking resistance, polyethylene terephthalate (PET) fibers outperform mixed plastics by delaying crack propagation. Low-temperature conditioning can induce thermal shrinkage in the asphalt mixture, slightly moderating the effects of recycled plastics and fibers.

Innovative modeling on the effects of low-temperature stress on rice yields

Abstract The increasing frequency and intensity of low-temperature events in temperate and cold rice production regions threaten rice yields under climate change. While process-based crop models can project climate impacts on rice yield, their accuracy under low-temperature conditions has not been well-evaluated. Our six-year chamber experiments revealed that low temperatures reduce spikelet fertility from panicle initiation to flowering, grain number per spike during panicle development, and grain weight during grain filling. We examined the algorithms of spikelet fertility response to temperature used in crop models. Results showed that simulation performance is poor for crop yields if the same function was used at different growth stages outside the booting stage. Indeed, we replaced a parameter spikelet fertility algorithm of the ORYZA model and developed the function of estimating grain number per spike and grain weight. After that, the improved equation algorithm was applied to 10 rice growth models. New functions considered the harmful effects of low temperatures on rice yield at different stages. In addition, the threshold temperatures of the cold tolerance were set for different rice varieties. The improved algorithm enhances the model's ability to simulate rice yields under climate change, providing a more reliable tool for adapting rice production to future climatic challenges.

Disruption of the OsWRKY71 transcription factor gene results in early rice seed germination under normal and cold stress conditions

Abstract Background Early seed germination in crops can confer a competitive advantage against weeds and reduce the time to maturation and harvest. WRKY transcription factors regulate many aspects of plant development including seed dormancy and germination. Both positive and negative regulators of seed germination have been reported in many plants such as rice and Arabidopsis. Using a transient expression system, we previously demonstrated that OsWRKY71 is a negative regulator of gibberellin (GA) signaling in aleurone cells and likely forms a “repressosome” complex with other transcriptional repressors. Hence, it has the potential to impact seed germination properties. Results In this study, we demonstrate that OsWRKY71, a Group IIa WRKY gene, appeared at the same time as seed-bearing plants. Rice mutants lacking OsWRKY71 have seeds and embryos that germinate earlier than wildtype controls. In oswrky71 aleurone layers, α-amylase activity was hypersensitive to stimulation by GA3 and hyposensitive to inhibition by abscisic acid (ABA). Early germination in oswrky71 intact seeds was also hyposensitive to ABA. Transcriptomic profiling during embryo germination and early post-germination growth demonstrates that OsWRKY71 influences the expression of 9–17% of genes in dry and imbibing embryos. Compared to wildtype embryos, the mutant transcriptomes have large temporal shifts at 4, 8 and 12 h after imbibition (HAI). Importantly, many genes involved in the ABA-dependent inhibition of seed germination were downregulated in oswrky71-1. This mutant also displayed altered expression of multiple ABA receptors (OsPYLs/RCARs) that control ABA signaling and the VP1-SDR4-DOG1L branch of ABA signaling that promotes seed dormancy. Association studies reveal an OsWRKY71-containing quantitative trait locus involved in low-temperature seed germinability, qLTG-2. Indeed, oswrky71 seeds germinated early at 15 °C. Conclusions Rice Group-IIa WRKY transcription factor OsWRKY71 is a master regulator of germination that influences the expression of 9–17% of genes in dry and imbibing embryos. It is also most likely the primary candidate of low-temperature seed germinability QTL, qLTG-2. We propose that knockouts of OsWRKY71 can generate rice varieties with improved germination properties under normal or low-temperature conditions.

Ecological conditions of vineyards and the polymorphism of Saccharomyces cerevisiae strains as a prerequisite of terroir identification

Aim. The aim of the study was to assess whether the ecological conditions for vineyards and the phylogenetic analysis of Saccharomyces cerevisiae wine yeast strains isolated from several locations in the Odesa and Mykolayiv regions could be used for terroir identification. Methods. The study employed microbiological, analytical, expedition, cartographic, and comparative assessment methods. Phylogenetic analysis was conducted using the MEGA software program, and VIN-CAD-UKR software was used for the vineyard cadastre and the ampelecological characteristics data management. Results. The study highlighted differences in the ecological conditions of vineyards in the Odesa and Mykolayiv regions and within the Tairovo and Izmail territorial communities in the Odesa region, focusing on soil and microclimatic characteristics. Saccharomyces cerevisiae strains isolated in 2012 and 2013, years with varying weather conditions in temperature and precipitation, were primarily clustered by the year of isolation. Two notable exceptions included a strain isolated from the Isabela variety belonging to a hybrid group (direct producer, contrary to other varieties, which mainly represent Vitis vinifera or its hybrids with Vitis riparia, Vitis amurensis, Vitis berlandieri) and a strain isolated from the Odesa Black variety inoculated at the beginning of fermentation with a commercial strain of wine yeast. The 2013 isolates, collected under conditions of higher precipitation and lower temperature in the first half of the growing season, showed a more differentiated clustering pattern, with two strains isolated from the Sukholymansky White variety forming a distinct cluster, while the rest grouped together, irrespective of the region, formed of isolation. Conclusions. Phylogenetic analysis of 64 strains of Saccharomyces cerevisiae isolated from 36 technical grape varieties based on the ITS1_5.8S_ITS2 nucleotide sequence demonstrated that the year of isolation (reflecting agroclimatic factors) was the primary influence on sample clustering. These factors, as components of the ecological conditions of terroir, form the foundation for terroir identification.

Acceleration of Modeling Capability for GDI Spray by Machine-Learning Algorithms

Cold start causes a high amount of unburned hydrocarbon and particulate matter emissions in gasoline direct injection (GDI) engines. Therefore, it is necessary to understand the dynamics of spray during a cold start and develop a predictive model to form a better air-fuel mixture in the combustion chamber. In this study, an Artificial Neural Network (ANN) was designed to predict quantitative 3D liquid volume fraction, liquid penetration, and liquid width under different operating conditions. The model was trained with data derived from high-speed and Schlieren imaging experiments with a gasoline surrogate fuel, conducted in a constant volume spray vessel. A coolant circulator was used to simulate the low-temperature conditions (−7 °C) typical of cold starts. The results showed good agreement between machine learning predictions and experimental data, with an overall accuracy R2 of 0.99 for predicting liquid penetration and liquid width. In addition, the developed ANN model was able to predict detailed dynamics of spray plumes. This confirms the robustness of the ANN in predicting spray characteristics and offers a promising tool to enhance GDI engine technologies.

Regulating Li2S Deposition and Accelerating Conversion Kinetics through Intracavity ZnS toward Low-Temperature Lithium-Sulfur Batteries.

The uncontrolled deposition behavior and sluggish conversion kinetics of the discharging product (solid Li2S) severely deteriorate the electrochemical performance of lithium-sulfur (Li-S) batteries, especially under high S loading and low-temperature conditions. Herein, a multifunctional S cathode host consisting of ZnS nanoparticles (NPs) confined in hollow porous carbon spheres (ZnS@HPCS) is synthesized via a unique capillary force-driven melting-diffusion strategy. The porous carbon shell of ZnS@HPCS provides a space-confined reservoir for soluble polysulfides and solid Li2S, while the intracavity ZnS NPs trap polysulfides, induce Li2S inside deposition, and accelerate conversion kinetics. Thus, Li-S batteries with ZnS@HPCS-S cathodes exhibit excellent electrochemical performance at both room and low temperatures (-40 °C) and high reversible capacities under high S loading (5.2 mg cm-2). Furthermore, Li2S nucleation/deposition, in situ Raman, and theoretical analyses reveal the underlying mechanism. This work offers fundamental insights into regulating Li2S deposition and designing S hosts for high-performance Li-S batteries.

Crucial aspects for maintaining rAAV stability.

The storage of rAAV vectors for gene therapy applications is critical for ensuring a constant product quality and defined amount of medication at the time of administration. Therefore, we determined the influence of different storage conditions on the physicochemical and biological properties of rAAV8 and rAAV9 preparations. Particular attention was paid to short-term storage, which plays a crucial role in both the manufacturing process and in clinical applications. Additionally, we addressed the question, of viability of rAAV8 and rAAV9 when subjected to very low-temperature storage conditions (below -65°C) or lyophilization. To determine the impact on rAAV vectors, various analyses were used, including the quantification of capsid and genome titers, as well as biopotency assessments, which are pivotal determinants in characterizing vector behavior and efficacy. Our data showed that freeze/thaw cycles hardly affected the functionality of rAAV9-aGAL vectors. In contrast, prolonged storage at room temperature for several days, resulted in a discernible decrease in biopotency despite consistent capsid and genome titers. When the storage temperature was further increased, the rAAV8-aGAL decay accelerated. For example, a short-term exposure of + 40°C and more, led to a reduction in the physical viral titer and to an even faster decline in efficacy determined by biopotency. However, the addition of sucrose and sorbitol to the rAAV9-aGAL and rAAV9-GAA preparations reduced the temperature sensitivity of rAAV and improved its stability. Furthermore, exposure of rAAV9-aGAL to highly acidic conditions (pH 2.5) dramatically reduced its biopotency by 70% or more. Most interestingly, a long-term storage of rAAV9-aGAL and rAAV8-FVIII vectors over 12 and 36months, respectively, demonstrated exceptional stability at storage temperatures below -65°C. Also, lyophilization conserved functionality for at least 10months. Our data showed how to maintain rAAV biopotency levels over the time without substantial loss. Storage at very low temperatures (below -65°C) preserved its effectiveness over years. Overall, pH and temperature conditions during the manufacturing process, storage and clinical application are worth considering. Consistency in the rAAV capsid titer determination did not necessarily indicate the preservation of biopotency. In conclusion, our approach determined several options for maximizing rAAV stability.

A Measurement Device for the Normal Spectral Emissivity of Materials Under Low-Temperature and Vacuum Conditions

Based on parallel light, a device for measuring sample emissivity under vacuum and low temperature was established. In this paper, a new emissivity measurement formula was designed, which replaces the derivation of Kirchhoff’s law of thermal radiation. The device is designed with a light-weight blackbody, an improved cooling speed, and an improved PID temperature control system to achieve a good temperature stability, close to 1 mK. The device is capable of measuring within a wavelength range of 4 μm to 16 μm. The results of the uncertainty assessment show that the uncertainty of the normal emissivity is better than 1.6% in the range of 4 μm to 7 μm, and better than 0.6% in the range of 7 μm to 14 μm (k = 1) at 0 °C.

Analysis of factors influencing Y-ring sealing under ultra-high-pressure, high-temperature and low-temperature conditions

Abstract To study the factors affecting the sealing performance of a Y-shaped sealing ring at the stem of a 140-MPa cage throttle valve under -46°25C and 180°C operating conditions, uniaxial tensile tests were conducted on polytetrafluoroethylene (PTFE) and its modified materials. Finite element simulation software was then used to perform a simulation study of the Y-shaped sealing ring. The finite element simulation software was used to perform a sensitivity analysis on the five most critical parameters of the Y-shaped sealing ring and to perform dimensional optimization by using the multi-island genetic algorithm. The results show that compared with 25°C, under a 180°C condition, the contact stress at both ends of the sealing lip decreases when the valve stem moves upward . Under the condition of -46°C, the contact stress at the sealing lip increases when the valve stem goes down, the contact stress at both ends of the sealing lip decreases when the valve stem goes up; and the impact of the stem movement speed on the maximum value of the Y-shaped sealing ring contact stress is small.The design dimensions that have the greatest influence on the maximum von Mises stress and the maximum contact stress of the inner lip of the Y-seal during stem movement are the width and the tip height of the lip, respectively. The optimum values of the design variables are determined and the feasibility of the theoretical design is verified by testing.

Development of Low Temperature Lithium Ion Batteries

This article briefly introduces the history of the birth of lithium-ion batteries and discusses the necessity of studying how to make lithium-ion batteries work properly under low-temperature conditions. It also introduces the development of ternary materials, a common material for lithium-ion batteries, in the past two years, as well as the working conditions and performance advantages and disadvantages of ternary materials and another commonly used positive electrode material, lithium iron phosphate, in different environments. Finally, a comprehensive overview of the development path of lithium-ion positive electrode materials under low-temperature conditions is given.

Development of Idaea inquinata (Lepidoptera Geometridae) at different constant temperatures and relative humidities under controlled conditions

The rusty wave moth Idaea inquinata is an insect pest that infests dried herbs, above all when stored in warehouses. Infestations were historically localised, but the recent climatic change might increase the incidence of this pest in many areas of north Italy. The artificial regulation of the environmental conditions of warehouses is one of the most common techniques to control pests, often combined with thermal treatments just after the introduction of the stocks. The optimisation of the warehouse conditions, however, requires a deep knowledge on how the species react to variations in temperature and relative humidities. This information is to date missing for I. inquinata and this work aimed to fill this gap in knowledge. The life tables at 35% and 70% RH, and at different constant temperatures were obtained for the egg, larval, and pupal stages by combining datasets provided by 20 years of continuous rearing of this species. A second part of the study, instead, concerned the estimation of the parameters of the temperature-dependent development rate functions, laying the foundations for further formulations of mathematical models to be applied in decision support systems. Life tables showed that conditions of low relative humidities and low temperatures are a good compromise that slows down the development time of the preimaginal stages. The upper thermal limit for the development of this species, instead, is around 40 °C, a threshold that can be considered for further thermal treatments to disinfest warehouses before the introduction of pest-free stocks or as a controlling action in case of infestations.

On Thermoelastic Impact Modelling of Frozen Composite Target During Pre – Heated Projectile Penetration Starts of Motion

This study investigates a composite double-layer structure for improved thermal shock resistance. A modified Hugoniot elastic limit model is presented for the composite, followed by a 2D thermo-elastic impact simulation using commercial software. The simulation focuses on a composite material under initial extreme low temperature conditions with alternating metallic (Steel, Aluminum) and non-metallic layers (Kevlar 49, Graphite). The frozen target is subjected to pre- heated projectile. The objective is to optimize the composite's durability by strategically placing reinforcement particles within specific layers. The analysis explores the effect of different particle types (oil, water, Aluminum, Steel) and sizes (0.3mm, 0.5mm, 1mm) on the composite's stress response. It was found that aluminum and steel particles significantly reduce stress compared to fluid/gas particles, confirmed qualitatively by literature. Kevlar particles within the SiCp layer enhance its resistance, while Aluminum particles within the Kevlar layer offer weight reduction benefits. Moreover, for Kevlar, larger particles improve resistance, and vice versa for the SiCp case. Considering weight, a particle size of 0.5mm is chosen for both layers. Moreover, a finite element analysis of the optimized composite model subjected to thermoelastic impact loading demonstrates its superior performance compared to the non-reinforced composite. Specific layer combinations (SiCp with Kevlar particles, Graphite or Kevlar with Aluminum particles) show the most significant stress reduction. Finally, separate 3D ballistic analysis was performed for Tungsten having 600m/sec projectile into 5 layered target with thickness of 2.8mm each layer and appropriate interaction friction (SiCp - Steel 304 - Al 7075-T651 - Kevlar 49 - Graphite Crystalline) during penetration time of 0.006sec at 300K. The dynamic explicit transient analysis was confirmed with the predecessors' analytic calculations.

Varying Performance of Low-Cost Sensors During Seasonal Smog Events in Moravian-Silesian Region

Air pollution monitoring in industrial regions like Moravia-Silesia faces challenges due to complex environmental conditions. Low-cost sensors offer a promising, cost-effective alternative for supplementing data from regulatory-grade air quality monitoring stations. This study evaluates the accuracy and reliability of a prototype node containing low-cost sensors for carbon monoxide (CO) and particulate matter (PM), specifically tailored for the local conditions of the Moravian-Silesian Region during winter and spring periods. An analysis of the reference data observed during the winter evaluation period showed a strong positive correlation between PM, CO, and NO2 concentrations, attributable to common pollution sources under low ambient temperature conditions and increased local heating activity. The Sensirion SPS30 sensor exhibited high linearity during the winter period but showed a systematic positive bias in PM10 readings during Polish smog episodes, likely due to fine particles from domestic heating. Conversely, during Saharan dust storm episodes, the sensor showed a negative bias, underestimating PM10 levels due to the prevalence of coarse particles. Calibration adjustments, based on the PM1/PM10 ratio derived from Alphasense OPC-N3 data, were initially explored to reduce these biases. For the first time, this study quantifies the influence of particle size distribution on the SPS30 sensor’s response during smog episodes of varying origin, under the given local and seasonal conditions. In addition to sensor evaluation, we analyzed the potential use of data from the Copernicus Atmospheric Monitoring Service (CAMS) as an alternative to increasing sensor complexity. Our findings suggest that, with appropriate calibration, selected low-cost sensors can provide reliable data for monitoring air pollution episodes in the Moravian-Silesian Region and may also be used for future adjustments of CAMS model predictions.

Laboratory experiments of carbon mineralization potential of the main terrestrial basalt reservoirs in China

Against the background of realizing the goal of “carbon peaking and carbon neutrality”, using basaltic rocks for carbon mineralization is one of the most promising approaches to reduce the rise in atmospheric CO2 concentrations. This study conducted a series of experiments to assess carbon mineralization in nine basalt samples from the main terrestrial basalt reservoirs in China within CO2-H2O/brine-rock systems at low temperatures (≤35 °C). The results indicate that the secondary carbonates formed in the CO2-H2O/brine-basalt system are predominantly calcite rather than Mg-carbonate minerals at low temperatures (≤35 °C). Hence, at low temperatures (≤35 °C), basalt rich in Ca-bearing minerals promotes the formation of stable carbonate minerals more effectively than basalt containing Mg-bearing minerals. Furthermore, under conditions of low temperatures (≤35 °C) and pressures of approximately 3 MPa, the results suggest that alkaline olivine basalt, with a higher content of Ca-minerals and typical alkaline minerals (nepheline and Na-sanidine), exhibits the highest pH value and the highest amount of calcite. Hence, the alkaline minerals, nepheline and Na-sanidine, serve as pH buffers to increase the pH and promote the precipitation of calcite within CO2-H2O– basalt systems at low temperatures (≤35 °C). Among the nine evaluated basalts, basalt from the Shandong Linqu-Changle volcanic basin exhibits the highest rate of carbon mineralization at low temperatures (≤35 °C). Hence, Cenozoic alkaline olivine basalt from Shandong Linqu-Changle volcanic basin is one of the most promising basalt reservoirs in China for future in- situ carbonation. As for ex- situ carbonation, compared with olivine, diopside or Ca-plagioclase may be more appropriate for increasing ocean negative emissions.

Experimental study on the low-temperature preheating performance of positive-temperature-coefficient heating film in the prismatic power battery module

The performance of a power battery directly affects the thermal safety performance of the vehicle. Aiming at the improvement of thermal safety of lithium-ion batteries under low temperature condition, this study focuses on the effect of the positive-temperature-coefficient (PTC) heating film on the heating performance of batteries through experimental testing. First, the side and bottom of the cell were heated, and the heat transfer path and mode of the single cell were analyzed. The effects of different power densities and geometric positions on the heating effect were studied by testing the heating time and temperature consistency. Second, for the battery module, a low-temperature heating thermal management heat transfer model was built to analyze the heating mechanism of the heating film under different heating power densities. Finally, the results of these studies were synthesized to obtain the optimal heating power density. The results show that for the cell, the optimum power density of side heating and bottom heating is 0.5 W /cm2 and 0.4 W /cm2, respectively. The time required for side heating from −20 °C to 10 °C is 730 s lower than that of bottom heating, and the maximum temperature difference is 1.885 °C lower. For battery modules, a power density of 0.5 W/cm2 was appropriate for both bottom and side heating methods. Due to the existence of heat conduction between battery packs, the battery modules will be quickly and evenly preheated. Under the optimal power density, the time length for side heating from –20 °C to 10 °C was 1459 s, and the maximum temperature difference was 6.32 °C; bottom heating time required slightly more time (1783 s), and the maximum temperature difference was 6.221 °C. Side heating can be beneficial for the rapid preheating of the battery module. This study will contribute to improving the performance and safety of batteries in cold environments.

Efficient removal of nitrate and ammonium by strain Pseudomonas poae EH-E3 under acidic pH and low-temperature conditions

The combined effect of low temperature and an acidic environment may restrict the growth and metabolic activity of microorganisms involved in nitrogen removal. To overcome poor biological nitrogen removal efficiency during low-temperature treatment of acidic wastewater, a novel pure strain of Pseudomonas poae EH-E3 was successfully isolated and screened based on its strong heterotrophic nitrification and aerobic denitrification capacity. Strain EH-E3 could completely eliminate inorganic nitrogen sources of nitrate within 30h and ammonium within 20h at 15 °C and pH 5.0, with corresponding removal efficiencies for total nitrogen of 95.13% and 91.35%, respectively. Nitrogen balance testing indicated that strain EH-E3 removed 43.25% of ammonium, 45.72% of nitrate, and 51.20% of nitrite in the form of gaseous products. Enzyme activity assays revealed that the specific activities of ammonia monooxygenase, nitrate reductase, and nitrite reductase were 0.533, 0.956, and 0.011 U/mg proteins, respectively. These findings suggest that strain EH-E3 has strong potential for use in low-temperature treatment of acidic wastewater.

A Nonaxial-Type Swirling Cavitating Nozzle for Exploiting Natural Gas Hydrate

Summary Natural gas hydrates (NGHs) have garnered widespread attention in the new energy sector, owing to their efficient and clean combustion properties. NGHs are ice-like substances formed by methane and water under high-pressure and low-temperature conditions, abundantly deposited in seabeds and frozen soil of highlands on Earth. However, the rock shelves of NGH reservoirs are mostly fragile and sparsely colloidal. Traditional mechanical mining methods can easily cause rock-shelf collapses, leading to mining accidents. Long-term indoor experiments and pilot mining projects have shown that cavitating nozzles can provide a feasible solution to the problem of efficient mining of NGHs. To further improve the efficiency of cavitating nozzle mining for NGHs, we have optimized and designed a nonaxial-type swirling cavitating nozzle (NASCN) based on traditional swirling cavitating nozzles (SCNs). Both numerical simulations and indoor experiments have verified the higher mining performance of this nozzle. In the numerical simulation experiments, we analyzed the cavitation performance, erosion performance, and energy consumption characteristics of different cavitating nozzles using the mixture multiphase flow model and the renormalization group (RNG) k-ε turbulence model. In the indoor experiments, we utilized a jet erosion experimental device for NGHs to analyze the erosion effects of different cavitating nozzles on hydrate samples. The results of these experiments indicate that the NASCN reduces energy consumption by 12% compared with traditional nozzles when there is little difference in cavitation performance and erosion performance. Moreover, under similar energy consumption, the NASCN improves erosion efficiency by 35.2% compared with traditional nozzles. These results demonstrate that the NASCN has good application value in the mining engineering of NGHs.

Detection of matrix cracks in composite laminates using embedded fiber-optic distributed strain sensing

We used an optical frequency-domain reflectometry fiber Bragg grating (FBG) distributed strain measurement system to detect matrix cracks in carbon fiber-reinforced plastics. Load/unload tests were performed on cross-ply laminates under ambient-, high-, and low-temperature conditions using embedded 100mm gauge FBG sensors. We measured the strain distributed along the gauge and examined the crack initiation using optical microscopy and soft X-ray inspection. A peak appeared in the distributed strain corresponding to the occurrence of cracks. The strain distribution during crack initiation was calculated in each temperature range via finite element analysis and compared with the measurement results. We determined that the number and location of cracks can be determined by extracting the peaks from the distributed strain. However, the peaks in the distributed strain do not correspond to the occurrence of cracks that are close to each other, warranting a measurement method with a higher strain resolution.

Geochemical signatures of forearc serpentinites from oceanic to continental subduction

In subduction systems, the forearc (FA) serpentinized mantle plays a key role as a reservoir for fluid-mobile elements, especially those prone to early mobilisation from the slab. FA serpentinites therefore provide an indication of the fluid characteristics that have been steamed out of the slab, and allow better quantification of elemental recycling and fluid flow. FA serpentinites outcropping along the Indus Suture Zone are formed by hydration of mantle peridotites by fluids derived from the Indian slab, providing a geochemical record of fluid-rock interactions during the India-Eurasia convergence. Systematic trace and multi-isotope (Sr and Pb) analyses of serpentinites from three major sites, namely Shergol-Tingdo, Kargil and Tso Morari, along the Indus Suture Zone in Ladakh (NW Himalaya) show that these rocks record a major change in the origin of metasomatic agents, from oceanic to continental subduction. The Shergol-Tingdo and Kargil FA serpentinites, formed under low temperature and pressure conditions, are characterised by high B enrichment and As and Sb depletion, high alkali/U ratios and relatively unradiogenic Sr and Pb isotope ratios. These geochemical characteristics are identical to those reported for modern oceanic subduction zones (e.g., Mariana forearc) and are consistent with input by fluids derived from subducted oceanic crust. In contrast, FA serpentinites from the Tso Morari ultra-high pressure unit show enrichment in fluid mobile elements such as As, Sb and U, low alkali/U ratios and radiogenic Sr and Pb isotopic compositions. These features suggest a change in the metasomatizing agent with a strong influence from subducted continental material. Consistent with this scenario, the Sr-Pb isotopic composition of the Kargil FA serpentinites can be reproduced by mixing between an Indian MORB-depleted mantle source and fluids derived from dewatering of blueschist facies oceanic metasediments, whereas in the case of Tso Morari a fluid end-member derived from various eclogitic continental metasediments is required. We propose that the observed geochemical signature of the Indus Suture Zone FA serpentinites can be used to reconstruct the geochemical exchanges between the slab and the overlying mantle from intra-oceanic to continental subduction. This successful systematic approach could be applied to other collisional contexts

The effect of burning on the dissolution behaviour and silicon and oxygen isotope composition of phytolith silica

Theδ30Si andδ18O values of opal-A precipitated in plants (silica phytoliths) have been shown to be useful for paleoenvironmental reconstructions. Here, the effects of burning and partial dissolution of phytoliths on their isotopic compositions and dissolution behaviour were examined. Phytoliths were heated to 700 °C and then dissolution experiments were conducted in batch reactors under a range of pH (4–8) and temperature (4–19 °C) conditions. Heating caused a −2.6 ‰ shift in phytolithδ18O values. NMR results suggest that heating reduces the number of surface vicinal silanols, which likely results in the formation of strained SiOSi bonds which incorporate oxygen from18O-depleted hydroxyl groups. During dissolution, theδ18O of burned phytoliths increased by up to 3.5 ‰ (average 1.8 ‰) until 15–45 % saturation was reached, and then adsorption of silica on the surface of the solid began to reducethe δ18O value of solid silica despite a net dissolution. The maximum increase in δ18O during dissolution of burned phytoliths is 1.8 ‰ smaller than previously observed for unburned silica subjected to partial dissolution under the same conditions. Heating did not cause a significant change inδ30Si values, and partial dissolution of burned phytoliths caused a slight increase inδ30Si values that was smaller in magnitude than for unburned phytoliths. Dissolution of burned phytoliths progressed more slowly than dissolution of fresh phytoliths in low pH and temperature conditions, but was faster than the dissolution of fresh phytoliths when pH > 6 and temperature = 19 °C. We propose that because fewer hydrolysis sites exist on the surface of burned phytoliths that the isolated silanols that remain after heating are difficult to deprotonate at low pH resulting in slower dissolution. However, at higher pH the breakage of strained SiOSi bonds in burned phytoliths may explain their higher dissolution rate relative to fresh phytoliths. We recommend caution in using theδ18O values of soil phytoliths in paleoclimate reconstructions as they can be altered during both heating and partial dissolution. For phytolith assemblages collected from archaeological hearths or grasslands prone to wildfires, the shift towards lowerδ18O values caused by heating would result in overestimations of temperature using paleothermometer equations. Care must be taken to identify alteration by dissolution or burning, which may not always be visually evident.