Heterogeneous Distribution Of Water Research Articles

Effect of moisture change on water retention behavior of unsaturated silty soil under loading–unloading conditions

Earthen embankments either natural or constructed artificially often comprise of unsaturated soils being considered stronger in terms of compressibility and permeability. However, the internal nomenclature of unsaturated soils due to the presence of air, water, and soil particles makes it more complex while such soils interact with moisture under the circumstances of applied stress history during the earthen structure’s life span. To investigate this behavior, this study is designed to understand the soil–water interaction and quantify the retention behavior during loading and unloading conditions. To serve this idea, custom-designed static compaction tests were carried out under un-drained water and drained air conditions at the applied stress history. The results show application of loading and unloading cycles impact water retention behavior of soil with varying soil water contents. During the initial stages of the loading process, suction increases with decreasing void ratio due to the heterogeneous distribution of water in the soil. However, there is a unique increasing trend in suction at the reloading or wetting phases of the water retention curve for all moisture contents. To examine the impact on the void ratio, the experimental data have been compared with the selected model incorporating suction, void ratio, and degree of saturation for prediction of soil water retention behaviors. The model prediction deviates from the experimental data and shifts away from the model prediction indicating that the loading–unloading sequence coupled with the variation in moisture does affect the soil behavior.

Sound Velocities of the Hydrous Iron‐Rich HH1‐Phase: Implications for Lower Mantle Seismic Heterogeneities

AbstractWe investigated the compressional and shear velocities, VP and VS, of the HH1‐phase by combining the inelastic x‐ray scattering and x‐ray diffraction experiments. In the pressure range of 64.7–79.6 GPa and at room temperature, the VP and VS were measured to be 9.66–11.05 and 4.9–6.4 km·s⁻1, respectively. We employed a simplified model to quantitatively discuss the sound velocity differences between hydrous and anhydrous phase assemblages in the mid‐lower mantle, revealing that the hydrous assemblage exhibits increased VS and a reduced VP/VS ratio compared to its anhydrous counterpart. This suggests formation of seismic scatterers in the mid‐lower mantle exhibiting high VS anomalies may be related to the heterogeneous distribution of water. Moreover, the interpretation of a large VP/VS ratio as indicating the presence of water in the upper mantle and crust may not be applicable for detecting water in the lower mantle.

Heterogeneous water distribution in between peridotite xenoliths from Kaapvaal Craton kimberlites: Constraints on diamond barren nature of kimberlites

Nominally anhydrous mantle minerals (olivine, pyroxenes, garnets, etc.) in 11 peridotite xenoliths from four different uneconomic and economic Kaapvaal Craton kimberlite pipes (Matsoku, Thaba Putsoa, Pipe 200 and Bultfontein) have been investigated using Fourier transform infrared spectroscopy (FTIR). All xenoliths contain accessories of garnet, diopside, chromite, and phlogopite. High orthopyroxene content (>30 mol vol.%) in most xenoliths from all kimberlites and its interconnected channel-like nature hint towards hydrous siliceous fluid metasomatism. Peridotite xenoliths from uneconomic kimberlites show development of phlogopite and clinopyroxene (± chromite) forming veins and in garnet rims suggesting metasomatism by alkaline silico-carbonatite (possibly kimberlite-related) melt. The xenoliths contain significant H2O in olivine (17–62 ppm), orthopyroxene (21–230 ppm), and clinopyroxene (87–833 ppm), whereas garnets are dry and only show IR absorbance bands at > 3,670 cm−1 for contamination of hydrous minerals. Compared to the economic kimberlites in the Kaapvaal Craton, the uneconomic kimberlite xenoliths from this study have lower orthopyroxene and olivine H2O content. In the xenoliths affected by garnet breakdown metasomatism, the H2O content of orthopyroxene and olivine is higher and lower, respectively. The structural hydroxyl distribution profile across olivine and higher inter-mineral water partition coefficient, suggest diffusion of hydrogen and possible re-equilibration. Statistical analysis of the olivine spectra suggests that hydrogen bands at 3540, 3624, 3638, and 3672 cm−1 are a good discriminant of economic and uneconomic kimberlites and in literature, they are associated with metasomatism, weathering-associated processes, high water activity, and oxygen fugacity. The lower water concentration in xenoliths from uneconomic kimberlite from the margin of the craton than the economic kimberlites from the interior of the Kaapvaal Craton and identified metasomatism hints towards dehydration of xenoliths by water-poor and CO2-rich melts in tectonized cross-lithospheric zones causing diamond resorption and may be responsible for the diamond-poor nature of uneconomic kimberlites in northern Lesotho.

Hydrogen Diffusion in the Lower Mantle Revealed by Machine Learning Potentials

AbstractHydrogen may be incorporated into nominally anhydrous minerals including bridgmanite and post‐perovskite as defects, making the Earth's deep mantle a potentially significant water reservoir. The diffusion of hydrogen and its contribution to the electrical conductivity in the lower mantle are rarely explored and remain largely unconstrained. Here we calculate hydrogen diffusivity in hydrous bridgmanite and post‐perovskite, using molecular dynamics simulations driven by machine learning potentials of ab initio quality. Our findings reveal that hydrogen diffusivity significantly increases with increasing temperature and decreasing pressure, and is considerably sensitive to hydrogen incorporation mechanism. Among the four defect mechanisms examined, (Mg + 2H)Si and (Al + H)Si show similar patterns and yield the highest hydrogen diffusivity. Hydrogen diffusion is generally faster in post‐perovskite than in bridgmanite, and these two phases exhibit distinct diffusion anisotropies. Overall, hydrogen diffusion is slow on geological time scales and may result in heterogeneous water distribution in the lower mantle. Additionally, the proton conductivity of bridgmanite for (Mg + 2H)Si and (Al + H)Si defects aligns with the same order of magnitude of lower mantle conductivity, suggesting that the water distribution in the lower mantle may be inferred by examining the heterogeneity of electrical conductivity.

Improving Water Management and Reactant Distribution in PEM Fuel Cells Via Flow Fields with Biomimetic Auxiliary Channels

The bipolar plate, a component of the polymer electrolyte membrane (PEM) fuel cell is responsible for reactant delivery, product removal, and mechanical stability of PEM fuel cell stacks. Bipolar plates also account for 70-90% of the weight and volume, and 18-28% of the production cost of stacks (1). Improving the function of the flow fields embedded in the bipolar plates can significantly impact the energy density of PEM fuel cells by improving liquid water management and reactant distribution. Previous works show that water preferentially accumulates under the lands of flow fields in the gas diffusion layer (GDL) for various GDL materials, creating a heterogeneous distribution of water and reactants, thereby increasing cathode mass transport overpotential(2–4). Biomimetic channel architectures have been shown to enhance preferential water flow; however, these designs have not been tailored to control water accumulation for improved reactant distribution (5,6). Targeting areas of known water accumulation such as the under-land regions of GDLs, could have a profound impact on reducing mass transport losses and improving reactant homogeneity, thereby improving the power density and efficiency of the PEM fuel cell.In this work, biomimetic auxiliary channels were laser-cut into the lands of a parallel PEM fuel cell flow field to enhance the liquid water removal and reactant distribution in the under-land region of the GDL. Constant-current electrochemical testing and electrochemical impedance spectroscopy revealed a 29% increase in peak power density resulting from a 54% decrease in oxygen mass transport overpotential using the biomimetic flow field (BFF) compared to a baseline trapezoidal flow field (TFF). Operando synchrotron X-ray radiography revealed reduced GDL water accumulation when using the BFF compared to the TFF. Water accumulation under the BFF flow fields was more homogenous especially near the catalyst layer (CL) – GDL interface, indicating enhanced reactant distribution near the CL reaction sites. Therefore, the reduced mass transport overpotential and corresponding power density increase were attributed to enhanced liquid water removal and reactant distribution due to the biomimetic auxiliary channels. These results demonstrate that significant performance enhancements can be realized by embedding alternate pathways for air and water in the lands of flow field components. Ultimately, this work can be used to further optimize the design of bipolar plates for more efficient stacks and accelerate the commercialization of PEM fuel cells. Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020).N. Ge et al., Electrochim Acta, 328, 135001 (2019).D. Muirhead et al., Int J Hydrogen Energy, 42, 29472–29483 (2017).S. Chevalier et al., J Electrochem Soc, 164, F107–F114 (2017)N. Guo, M. C. Leu, and U. O. Koylu, Int J Hydrogen Energy, 39, 21185–21195 (2014).S. Feng et al., Science, 373, 1344–1348 (2021).

Plant growth‐promoting rhizobacteria mediate soil hydro‐physical properties: An investigation with Bacillus subtilis and its mutants

AbstractPlant growth‐promoting rhizobacteria and other soil bacteria have the potential to improve soil hydro‐physical properties and processes through the production of extracellular polymeric substances (EPS). However, the mechanisms by which EPS mediates changes in soil properties and processes remain incompletely understood, partly due to variations in EPS composition produced under different environmental conditions. In this study, we investigated the influence of different bacterial traits on intrinsic soil properties and processes of evaporation and infiltration using sand treated with the wild‐type Bacillus subtilis variant (UD1022) and its two mutant variants, – and srf. The – mutant suppresses EPS production through alterations in the eps and tasA genes, while the srf mutant lacks the gene for surfactin production. Experimental results confirmed that the solution viscosity of the – mutant was the lowest and the solution surface tension of the srf mutant was the highest among the three tested bacteria strains. The distinct intrinsic properties of EPS produced by these bacterial strains resulted in varied hydro‐physical responses in the treated sand. Key influences included modifications in wettability, hydraulic decoupling (or mixed wettability), and aggregation, which collectively led to reduced evaporation rates and heterogeneous water distribution during infiltration in the bacteria‐treated sands. Our findings advance the understanding of the role bacterial EPS play in vadose zone hydrology and offer insights for the development of sustainable strategies for increasing water retention, supporting crop production in arid regions, and facilitating land restoration.

Cracks and root channels promote both static and dynamic vertical hydrological connectivity in the Yellow River Delta

Vertical hydrological connectivity generally related heterogeneity of soil water and nutrient and the sustainability of vegetation restoration. Both the static and dynamic connectivity of soil have been studied for years, the relationship between them remains unclear, especially for coastal wetlands that greatly influenced by hydrological processes. In this study, static connectivity was defined as water flow paths and quantified by dye tracer experiment, whereas dynamic connectivity refers to the process of water movement and solute transport and described by solute penetration. Relationships between them were analyzed through the nonlinear fitting. Results showed that: 1) static connectivity was construed mainly by cracks in the upper soil layer and by root channels in the deeper soil, and these macropores led to heterogeneous distribution of water and solutes; 2) dynamic connectivity differed between soil columns, and non-equilibrium flow characterized by high infiltration rate and concentration in the initial phase was observed in soil with cracks and root channels; and 3) the static connectivity had significant effects on water movement while had no effects on solute transport. Infiltration rate decreased as dye coverage, fractal dimension, and the number of water pathway logistically increases. These findings highlight the importance of cracks and root channels on vertical hydrological connectivity in soil of S. salsa community, and suggest linking the static structure of water flow paths with soil water dynamic and heterogeneity to understand soil functions.

Hydration and Dehydration in Earth's Interior

Hydrogen and deuterium isotopic evidence indicates that the source of terrestrial water was mostly meteorites, with additional influx from nebula gas during accretion. There are two Earth models, with large (7–12 ocean masses) and small (1–4 ocean masses) water budgets that can explain the geochemical, cosmochemical, and geological observations. Geophysical and mineral physics data indicate that the upper and lower mantles are generally dry, whereas the mantle transition zone is wetter, with heterogeneous water distribution. Subducting slabs are a source of water influx, and there are three major sites of deep dehydration: the base of the upper mantle, and the top and bottom of the lower mantle in addition to slabs in the shallow upper mantle. Hydrated regions surround these dehydration sites. The core may be a hidden reservoir of hydrogen under the large water budget model. ▪ Earth is a water planet. Where and when was water delivered, and how much? How does water circulate in Earth? This review looks at the current answers to these fundamental questions.

Controlled heterogeneous water distribution and evaporation towards enhanced photothermal water-electricity-hydrogen production

Abstract The ability to control heterogeneous water distribution and evaporation could address low vapor generation issues which has great implications for distillation and energy systems efficiency. Herein, we devise an efficient solar-driven water-electricity-hydrogen generation system by spatially controlling water diffusion and evaporation of 3D hydrogel evaporators. Specifically, through template-assisted regulation of the interfacial structures of the hydrogel evaporator, the relationship between the macroscale liquid-vapor area and the water pumping pathway was studied. The hybrid wettability and distinct water distribution strategy achieved via selective hydrophobic-hydrophilic modification enhance the photothermal efficiency by 207% compared with the flat hydrophilic evaporator. Finally, the tailored hydrogels for contrasting evaporative cooling and solar absorption heating are integrated with Bi2Te3-based thermoelectric generator (TEG) to efficiently convert waste heat into electricity and drive electrochemical water splitting under outdoor sunny/cloudy conditions. The prototype demonstrates evaporation of 1.42 kg m−2 h−1, power output of 4.8 W/m2, and hydrogen evolution of 0.3 mmol/h. This work could pave the development of highly integrated hybrid systems to deliver three crucial water, energy and fuel commodities for global sustainability.

On the Use of an IoT Integrated System for Water Quality Monitoring and Management in Wastewater Treatment Plants

The deteriorating water environment demands new approaches and technologies to achieve sustainable and smart management of urban water systems. Wireless sensor networks represent a promising technology for water quality monitoring and management. The use of wireless sensor networks facilitates the improvement of current centralized systems and traditional manual methods, leading to decentralized smart water quality monitoring systems adaptable to the dynamic and heterogeneous water distribution infrastructure of cities. However, there is a need for a low-cost wireless sensor node solution on the market that enables a cost-effective deployment of this new generation of systems. This paper presents the integration to a wireless sensor network and a preliminary validation in a wastewater treatment plant scenario of a low-cost water quality monitoring device in the close-to-market stage. This device consists of a nitrate and nitrite analyzer based on a novel ion chromatography detection method. The analytical device is integrated using an Internet of Things software platform and tested under real conditions. By doing so, a decentralized smart water quality monitoring system that is conceived and developed for water quality monitoring and management is accomplished. In the presented scenario, such a system allows online near-real-time communication with several devices deployed in multiple water treatment plants and provides preventive and data analytics mechanisms to support decision making. The results obtained comparing laboratory and device measured data demonstrate the reliability of the system and the analytical method implemented in the device.

Characterisation of moisture migration of shiitake mushroom (Lentinula edodes) during storage and its relationship to quality deterioration

SummaryWater is a critical factor influencing the quality of mushrooms. This paper investigated the moisture migration of shiitake mushroom during storage using low‐field nuclear magnetic resonance (LF‐NMR) and magnetic resonance imaging (MRI) and its relationship to quality deterioration. Three water components assigned as water in different cell compartments of cell wall, cytoplasm and vacuole were observed in shiitake mushroom matrix. As the prolonging of storage time, the right shift of immobilised water and left shift of free water led to the merge of these two peaks at the end of storage. The increase in peak area of water in cytoplasm and decrease in the peak area of water in vacuole indicated evident moisture migration from vacuole to cytoplasm. MRI images showed heterogeneous water distribution in shiitake mushroom, and the water migrated from centre to surface, then evaporated to the environment. Besides, the moisture migration might be related to the weight loss and textural softening of shiitake mushroom.

Metallic iron limits silicate hydration in Earth’s transition zone

The Earth's mantle transition zone (MTZ) is often considered an internal reservoir for water because its major minerals wadsleyite and ringwoodite can store several oceans of structural water. Whether it is a hydrous layer or an empty reservoir is still under debate. Previous studies suggested the MTZ may be saturated with iron metal. Here we show that metallic iron reacts with hydrous wadsleyite under the pressure and temperature conditions of the MTZ to form iron hydride or molecular hydrogen and silicate with less than tens of parts per million (ppm) water, implying that water enrichment is incompatible with iron saturation in the MTZ. With the current estimate of water flux to the MTZ, the iron metal preserved from early Earth could transform a significant fraction of subducted water into reduced hydrogen species, thus limiting the hydration of silicates in the bulk MTZ. Meanwhile, the MTZ would become gradually oxidized and metal depleted. As a result, water-rich region can still exist near modern active slabs where iron metal was consumed by reaction with subducted water. Heterogeneous water distribution resolves the apparent contradiction between the extreme water enrichment indicated by the occurrence of hydrous ringwoodite and ice VII in superdeep diamonds and the relatively low water content in bulk MTZ silicates inferred from electrical conductivity studies.

Effect of microstructure on hydric strain in clay rock: A quantitative comparison

This paper presents a new method able to compare quantitatively strains and microstructure of a clay material. This method was applied to a Tournemire clay rock sample subjected to cyclic hydric loading in laboratory conditions. Local strains of a centimeter-size Tournemire clay rock sample were quantified by digital image correlation (DIC) on a field of view of 5.5 × 4.1 mm2 at the resolution of 2 μm.pixel−1, at a temperature of 22 °C and between 98 and 33% of relative humidity. At the end of the hydric loading, at dry state, the microstructure of the same field of view was mapped by an extended mosaic of scanning electron microscopy images at the resolution of 0.625 μm.pixel−1 and superimposed to the reference images used for DIC. Two microstructural parameters: the mean area and the area fraction of rigid clasts and clay matrix, were quantified by image analysis to be directly superimposed to local strain values. Speckle artefacts partly due to polished surfaces of clasts were filtered in the comparison between strains and microstructure. Strains concentrated in parts of the clay matrix, and at the interface between matrix and several quartz clasts which showed a slight detachment from the matrix. Constant clay and clast area fractions and sizes corresponded to very variable strain values at the microstructure scale. The relationship between strain values, mineral size and area fractions was not linear. Micro-mechanisms of deformation were therefore very complex at the scale of the experiment. On a very large field of view, very different microstructure behaviors were averaged which avoided any simple relationship between microstructure and strains. Heterogeneous water distribution and non-local microstructural control factors were suspected.

Testing the genetic relationship between fluid alteration and brecciation in CM chondrites

AbstractBoriskino is a poorly studied CM chondrite with numerous millimeter‐ to centimeter‐scale clasts exhibiting sharp boundaries. Clast textures and mineralogies attest to diverse geological histories with various degrees of aqueous alteration. We conducted a petrographic, chemical, and isotopic study on each clast type of the breccia to investigate if there exists a genetic link between brecciation and aqueous alteration, and to determine the controlling parameter of the extent of alteration. Boriskino is dominated by CM2 clasts for which no specific petrographic type could be assigned based on the chemical compositions and modal abundances of constituents. One clast stands out and is identified as a CM1 lithology, owing to its lack of anhydrous silicates and its overall abundance of dolomite‐like carbonates and acicular iron sulfides. We observe that alteration phases near clast boundaries exhibit foliation features, suggesting that brecciation postdated aqueous alteration. We measured the O‐isotopic composition of Ca‐carbonates and dolomite‐like carbonates to determine their precipitation temperatures following the methodology of Verdier‐Paoletti et al. (2017). Both types of carbonates yield similar ranges of precipitation temperatures independent of clast lithology, ranging from −13.9 ± 22.4 (2σ) to 166.5 ± 47.3 °C, precluding that temperature alone accounts for the differences between the CM1 and CM2 lithologies. Instead, we suggest that initial water/rock ratios of 0.75 and 0.61 for the CM1 and CM2 clasts, respectively, might control the extent of aqueous alteration. Based on these estimates, we suggest that Boriskino clasts originated from a single parent body with heterogeneous distribution of water either due to local differences in the material permeability or in the initial content of ice available. These conditions would have produced microenvironments with differing geochemical conditions thus leading to a range of degrees of aqueous alteration.

Heterogeneous distribution of water in the mantle transition zone inferred from wavefield imaging

The amount of water in the Earth's deep mantle is critical for the evolution of the Earth. Mineral physics studies revealed that the mantle transition zone can store several times the volume of water in an ocean. However, the actual water distribution in the transition zone remains enigmatic. We used the highest resolution images produced of scatterers in the North-American transition zone derived from teleseismic data recorded by the Earthscope Transportable Array. We find that the transition zone is filled with previously unrecognized small-scale heterogeneities that produce pervasive, negative polarity signals. Simulations demonstrated the images can be explained by low-velocity bodies shaped as distributed blobs or near vertical structures. We suggest these low-velocity bodies may be heterogeneously distributed, water-enriched subducted harzburgites produced through long-term accumulation.

Water in the Earth’s Interior: Distribution and Origin

The concentration and distribution of water in the Earth has influenced its evolution throughout its history. Even at the trace levels contained in the planet’s deep interior (mantle and core), water affects Earth’s thermal, deformational, melting, electrical and seismic properties, that control differentiation, plate tectonics and volcanism. These in turn influenced the development of Earth’s atmosphere, oceans, and life. In addition to the ubiquitous presence of water in the hydrosphere, most of Earth’s “water” actually occurs as trace amounts of hydrogen incorporated in the rock-forming silicate minerals that constitute the planet’s crust and mantle, and may also be stored in the metallic core. The heterogeneous distribution of water in the Earth is the result of early planetary differentiation into crust, mantle and core, followed by remixing of lithosphere into the mantle after plate-tectonics started. The Earth’s total water content is estimated at $18_{-15}^{+81}$ times the equivalent mass of the oceans (or a concentration of $3900_{-3300}^{+32700}~\mbox{ppm}$ weight H2O). Uncertainties in this estimate arise primarily from the less-well-known concentrations for the lower mantle and core, since samples for water analyses are only available from the crust, the upper mantle and very rarely from the mantle transition zone (410–670 km depth). For the lower mantle (670–2900 km) and core (2900–4500 km), the estimates rely on laboratory experiments and indirect geophysical techniques (electrical conductivity and seismology). The Earth’s accretion likely started relatively dry because it mainly acquired material from the inner part of the proto-planetary disk, where temperatures were too high for the formation and accretion of water ice. Combined evidence from several radionuclide systems (Pd-Ag, Mn-Cr, Rb-Sr, U-Pb) suggests that water was not incorporated in the Earth in significant quantities until the planet had grown to $\sim60\mbox{--}90\%$ of its current size, while core formation was still on-going. Dynamic models of planet formation provide additional evidence for water delivery to the Earth during the same period by water-rich planetesimals originating from the asteroid belt and possibly beyond. This early delivered water may have been partly lost during giant impacts, including the Moon forming event: magma oceans can form in their aftermath, degas and be followed by atmospheric loss. More water may have been delivered and/or lost after core formation during late accretion of extraterrestrial material (“late-veneer”). Stable isotopes of hydrogen, carbon, nitrogen and some noble gases in Earth’s materials show similar compositions to those in carbonaceous chondrites, implying a common origin for their water, and only allowing for minor water inputs from comets.

Effect of Applying Sewage Effluent with Subsurface Drip Irrigation on Soil Enzyme Activities during the Maize Growing Season

AbstractSubsurface drip irrigation is an appropriate method when using sewage effluent for crop irrigation, but its resultant heterogeneous distribution of water and nutrients in the soil may affect enzyme activities (EAs). Field experiments were designed, with three lateral depths at 0, 15, and 30 cm beneath the soil surface and three irrigation levels of 70, 100, and 130% of evapotranspiration, to investigate the effects of lateral depth, irrigation level, and water quality on the EAs of alkaline phosphatase, urease, and invertase in soil. Over 2 years, a greater lateral depth noticeably enhanced EAs in deeper soils, while EAs at a shallow lateral depth were higher in topsoil. Compared to lateral depth, the effects of irrigation level on EAs were unstable in both years. The correlations between urease activities and NO3‐N content indicated that the character of urease activities in soil N cycling was initially facilitating N mineralization and was subsequently converted to facilitate N uptake and immobilization during the maize growing seasons. Additionally, the EAs with both sewage effluent and groundwater irrigation at harvest, were generally higher than EAs measured prior to sowing. Furthermore, the sewage effluent irrigation imposed no negative effects on nutrient exchange and ecosystem functions in the soil. Our study recommends subsurface drip irrigation as a promising method for applying sewage effluent. Copyright © 2017 John Wiley & Sons, Ltd.

Origins of water content variations in the suboceanic upper mantle: Insight from Southwest Indian Ridge abyssal peridotites

AbstractTo investigate the origin of heterogeneous water distribution in the suboceanic lithospheric mantle, we performed a detailed petrological and geochemical analysis of abyssal peridotites collected from two localities (53°E and 63.5°E) on the Southwest Indian Ridge. These serpentinized peridotites display primary olivine‐orthopyroxene‐clinopyroxene‐spinel assemblage and record equilibrium temperature of 1150–1200°C and around 1000°C for the 53°E and 63.5°E locations, respectively. The rocks were thus equilibrated in the spinel stability field prior to their exhumation to the seafloor. Our FTIR analyses show variable water contents in orthopyroxene ranging from 24 to 262 wt ppm H2O. Orthopyroxene in the 63.5°E peridotites is characterized by homogeneous and high water content (>200 ppm), whereas orthopyroxene in the 53°E peridotites displays a wider range of water contents (24–246 ppm). We first demonstrate that differences in equilibrium conditions (i.e., pressure and temperature) and mineral chemistry and serpentinization cannot explain the water content variations. Melting modeling show that a fractional melting in both garnet and spinel stability fields is needed to explain the MREE and HREE concentrations in clinopyroxene. Enrichment in LREE, high water contents, and high H2O/Ce, however, require a postmelting rehydration event such as metasomatism. Based on petrographic evidence and investigation of chemical heterogeneities at segment/dredge scale, we suggest that this event involves a metasomatic agent enriched in water and incompatible elements. We infer that the small‐scale heterogeneities in water and trace elements may result either from successive infiltration of various amounts of melt/fluids as described in the formation of oceanic core complex or from spatial heterogeneities of melt infiltration as observed in peridotite massifs.

Heterogeneous distribution of water in the mantle beneath the central Siberian Craton: Implications from the Udachnaya Kimberlite Pipe

The paper presents new petrographic, major element and Fourier transform infrared (FTIR) spectroscopy data and PT-estimates of whole-rock samples and minerals of a collection of 19 relatively fresh peridotite xenoliths from the Udachnaya kimberlite pipe, which were recovered from its deeper levels. The xenoliths are non-deformed (granular), medium-deformed and highly deformed (porphyroclastic, mosaic-porphyroclastic, mylonitic) lherzolites, harzburgite and dunite. The lherzolites yielded equilibration temperatures (T) and pressures (P) ranging from 913 to 1324°C and from 4.6 to 6.3GPa, respectively. The non-deformed and medium-deformed peridotites match the 35mW/m2 conductive continental geotherm, whereas the highly deformed varieties match the 45mW/m2 geotherm. The content of water spans 2±1–95±52ppm in olivine, 1±0.5–61±9ppm in orthopyroxene, and 7±2–71±30ppm in clinopyroxene. The amount of water in garnets is negligible. Based on the modal proportions of mineral phases in the xenoliths, the water contents in peridotites were estimated to vary over a wide range from <1 to 64ppm. The amount of water in the mantle xenoliths is well correlated with the deformation degree: highly deformed peridotites show highest water contents (64ppm) and those medium-deformed and non-deformed contain ca. 1ppm of H2O. The high water contents in the deformed peridotites could be linked to metasomatism of relatively dry diamondiferous cratonic roots by hydrous and carbonatitic agents (fluids/melts), which may cause hydration and carbonation of peridotite and oxidation and dissolution of diamonds. The heterogeneous distribution of water in the cratonic mantle beneath the Udachnaya pipe is consistent with the models of mantle plume or veined mantle structures proposed based on a trace element study of similar xenolithic suits. Mantle metasomatism beneath the Siberian Craton and its triggered kimberlite magmatism could be induced by mantle enrichment in volatiles (H2O, CO2) supplied by numerous subduction zones which surrounded the Siberian continent in Neoproterozoic-Cambrian time.

Growing Out of Stress: The Role of Cell- and Organ-Scale Growth Control in Plant Water-Stress Responses.

Water is the most limiting resource on land for plant growth, and its uptake by plants is affected by many abiotic stresses, such as salinity, cold, heat, and drought. While much research has focused on exploring the molecular mechanisms underlying the cellular signaling events governing water-stress responses, it is also important to consider the role organismal structure plays as a context for such responses. The regulation of growth in plants occurs at two spatial scales: the cell and the organ. In this review, we focus on how the regulation of growth at these different spatial scales enables plants to acclimate to water-deficit stress. The cell wall is discussed with respect to how the physical properties of this structure affect water loss and how regulatory mechanisms that affect wall extensibility maintain growth under water deficit. At a higher spatial scale, the architecture of the root system represents a highly dynamic physical network that facilitates access of the plant to a heterogeneous distribution of water in soil. We discuss the role differential growth plays in shaping the structure of this system and the physiological implications of such changes.