Uppermost Layer Research Articles

Roles of Epithelial and Mesenchymal TRP Channels in Mediating Inflammatory Fibrosis.

The maintenance of normal vision is dependent on preserving corneal transparency. For this to occur, this tissue must remain avascular and its stromal architecture needs to be retained. Epithelial transparency is maintained provided the uppermost stratified layers of this tissue are composed of terminally differentiated non-keratinizing cells. In addition, it is essential that the underlying stromal connective tissue remains avascular and scar-free. Keratocytes are the source of fibroblasts that are interspersed within the collagenous framework and the extracellular matrix. In addition, there are sensory nerve fibers whose lineage is possibly either neural crest or mesenchymal. Corneal wound healing studies have been undertaken to delineate the underlying pathogenic responses that result in the development of opacification following chemical injury. An alkali burn is one type of injury that can result in severe and long- lasting losses in ocular transparency. During the subsequent wound healing process, numerous different proinflammatory cytokines and proteolytic enzymes undergo upregulation. Such increases in their expression levels induce maladaptive expression of sustained stromal inflammatory fibrosis, neovascularization, and losses in the smooth optical properties of the corneal outer surface. It is becoming apparent that different transient receptor potential channel (TRP) isoforms are important players in mediating these different events underlying the wound healing process since injury upregulates both their expression levels and functional involvement. In this review, we focus on the involvement of TRPV1, TRPA1 and TRPV4 in mediating some of the responses that underlie the control of anterior ocular tissue homeostasis under normal and pathological conditions. They are expressed on both different cell types throughout this tissue and also on corneal sensory nerve endings. Their roles have been extensively studied as sensors and transducers of environmental stimuli resulting from exposure to intrinsic modulators and extrinsic ligands. These triggers include alteration of the ambient temperature and mechanical stress, etc., that can induce pathophysiological responses underlying losses in tissue transparency activated by wound healing in mice losses in tissue transparency. In this article, experimental findings are reviewed about the role of injury-induced TRP channel activation in mediating inflammatory fibrotic responses during wound healing in mice.

SARS-CoV-2 might transmit through the skin while the skin barrier function could be the mediator

During thecoronavirus disease 2019 (COVID-19) pandemic, it were reported that COVID-19 patients could have cutaneous symptoms, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was observed on the skin of COVID-19 patients, which indicated that the skin is one target of SARS-CoV-2. Meanwhile, reports about SARS-CoV-2 transmission through food cold-chain overpacks emerged. With the fact that SARS-CoV-2 could survive on the skin for more than 9 h, the skin could be implicated in SARS CoV-2 transmission. Angiotensin-converting enzyme 2 (ACE2), a critical membrane protein for SARS-CoV-2 that enters a host cell, was recognized to be associated with the risk of SARS-CoV-2 infection. Therefore, tissues that express ACE2 might have the potential to be infected by and transmit SARS-CoV-2. The skin is one such tissue that expresses ACE2. However, unlike the lung that expresses ACE2 on the upper-most epithelial layer, the skin is composed of different layers of cells that function as a barrier, and cells under the top epidermal layer express ACE2. Since the skin barrier is the first line of protection, the typical position of ACE2-expressing cells in the skin implies that the skin barrier function could be the mediator of SARS-CoV-2. In our study, we found that ACE2 could be expressed in the skin, and its expression level is increased in psoriasis, an inflammatory disease of the skin with barrier dysfunction. Additionally, by applying the SARS-CoV-2 pseudovirus on mouse models with or without deteriorated skin barrier, we found that the SARS-CoV-2 pseudovirus could infect the skin and lungs of mouse models, and when the skin barrier was impaired, more SARS-CoV-2-infected cells could be found. Thus, we hypothesized that a deteriorated condition of the skin barrier might increase the risk of SARS-CoV-2 infection through the skin.

Problems Threatening Sustainability in Siwa Oasis and Recommendations for Understanding the Sources of Water Quality Deterioration

Siwa Oasis has been chosen as the location for the current investigations. Siwa Oasis is an isolated closed depression located in Egypt’s Western desert. It is surrounded by the Mediterranean Sea to the north (about 330 km), to the west by the Libya-Egypt border (70 km) and Cairo to the east (560 km). There are three major activities in Siwa Oasis: that are represented by agriculture (palm tree, olive, fruits and vegetables), industry, (e.g. mineral water bottling and olive oil extraction), and tourism (medical treatment, safaris). The climate of the Western Desert, particularly in Siwa, is generally torrid and arid. The Siwa depression is occupied by Quaternary deposits (aeolian deposits and lakes), Middle Miocene, Upper Cretaceous (sandstone), and Precambrian (basement complex). The groundwater system in Siwa Oasis hastwo main productive aquifers: a Miocene aquifer (fractured limestone) and a Lower Cretaceous aquifer (Nubian Sandstone). Besides, the Quaternary (clay and sand) uppermost layer is water-bearing because of waterlogging. Siwa Oasis is suffering from waterlogging, increasing soil salinity, and deterioration of water quality in the aquifers. This review includes the problems in Siwa Oasis and recommendations for understanding hydrogeological situations and sources of water quality deterioration to avoid waterlogging and soil salinization through integration of flow modeling, geochemistry and isotopic tracers.

Seasonal sedimentation in saline Lake Shira (Siberia, Russia) and meromixis: implications for regional paleoclimate reconstructions

Abstract. Detailed studies of processes of sediment record formation are necessary for accurate sediment-derived paleo-environmental reconstructions. We conducted the multi-year seasonal sediment evolution of sediment fluxes of chemical elements, organic and inorganic carbon, total nitrogen, and photosynthetic pigments for a period from 2012 to 2017. In 2013, 2016, 2017, and 2018, we estimated the contents of photosynthetic pigments in the uppermost sediment layers frozen in situ with a freeze-corer. In 2015 and 2016, a rare event of transition from meromixis (i.e. long-term hypolimnetic anoxia) to holomixis was observed, which was accompanied by the temporary disappearance of hydrogen sulfide from the water column in spring and a decrease in hydrogen sulfide in other seasons compared to the meromictic state. We have demonstrated that okenone and Mo in the Lake Shira sediments reflect the presence of hydrogen sulfide in the water column. However, the okenone showed smoothened multi-year dynamics without a pronounced seasonal one. Therefore, the okenone can be a proxy of sulphidic conditions in photic zone and weakly depend on seasons whereas Mo can be used as an indicator of winter periods when analyzed in cores with annual resolution. Sedimentation fluxes of other substances showed typical seasonal dynamics with a minimum in winter and a maximum in late summer and autumn. All chemical elements in the sedimentation flow can be roughly divided into those associated with organic matter and terrigenous-chemogenous. The components of the second group showed a pronounced peak of sedimentation in autumn 2012 and summer 2017 presumably due to the increased amount of precipitation at that time. This demonstrates the relationship between the terrigenous components and the climate humidity for this lake. Besides, it reflects the irregularity of annual varves composition.

FOUNDATION CHARACTERIZATION IN IKATE AREA SOUTHWESTERN NIGERIA USING ELECTRICAL RESISTIVITY TOMOGRAPHY AND CONE PENETRATION TEST

The establishments of the nexus between the underlying geology and engineering properties are fundamentals to the safe, economic and serviceable designs of civil engineering structures. Cone Penetration Test (CPT) and Electrical Resistivity Tomography (ERT) are critical tools in foundation parameterization especially within Quaternary sediments serving as foundation of engineering structures. Both techniques were used to obtained point data and lateral continuity of geologic units within Ikate Area of Lagos Metropolis for foundation parameterization. Measurements which comprising 4 profiles of 2D resistivity imaging using the Wenner electrode configuration; 1 borehole and 12 cone penetration tests (CPT) were taken with Pasi Terrameter, percussion rig and the 10.0 tons penetrometer respectively. The ERT results interpreted using Dipro software were presented in Pseudo-sections while the cone penetration test results analysed with Microsoft Excel were represented as resistance curves. Interpretation from the two methods integrated with the borehole results reveals the presence clay, peat and sand of varying properties. The uppermost layer consists of medium dense sand followed by clay/peat of very low resistivity (< 3.5 ohm-meter) covering about 6. 0 – 8.0m in depth and terminating in another layer of sand (8.0 – 15.0m). The last sandy layer with cone resistance range between 30 – 120kg/cm2 is considered a suitable layer upon which deep foundation may be founded. Shallow foundation capacity estimates at depths 0.2 – 4.0m derived from direct CPT data using three different computation techniques gives value range from 1.7 – 49.4kg/cm2, 0.7 – 15.2kg/cm2 and 0.4 – 12.6kg/cm2 respectively. Deep foundation for skyscrapers within the area are advised to be founded within the competent layer encountered beyond 10.m depth.

Phosphorus speciation and distribution in a variable‐charge Oxisol under no‐till amended with lime and/or phosphogypsum for 18 years

AbstractLong‐term management with lime and/or phosphogypsum (PG) can change phosphorus (P) forms across the soil profile. In this study, we used synchrotron‐based spectroscopy and sequential chemical fractionation to investigate P chemical species after long‐term (18 years) application of amendments in a subtropical Oxisol. The availability of nutrients increased with the combined use of lime and PG and a stratification of attributes was identified due to long‐term broadcast applications. X‐ray absorption near edge structure (XANES) spectra profiles revealed the predominance of P bounded to haematite (Hm) (48% on average) and also P bound to kaolinite (32% on average) species. Low proportions (16%) of calcium‐phosphates in the uppermost soil layer (0–5 cm) were found in the treatment that received high calcium (Ca) inputs by lime and PG broadcast. Few correlations were identified between the proportions of P species obtained by XANES and P fractions operationally defined by sequential chemical fractionation (SF). Our results suggest that P‐species bound to kaolinite can store stable P forms, which correlated (p < 0.05) with the residual P fractions obtained by SF, highlighting the importance of kaolinite as a legacy P store in Oxisols.Highlights Lime and phosphogypsum broadcast under no‐till improve soil fertility and P availability. Labile and moderately labile P fractions were the only ones influenced by lime and/or phosphogypsum. Proportions among P bounded to Fe‐ and Al‐(hydr)oxides with different structural may be affected by long‐term Al‐suppressors. P‐species bounded to kaolinite may store stable P forms in Oxisols.

The Epidermis: Redox Governor of Health and Diseases.

A functional epithelial barrier necessitates protection against dehydration, and ichthyoses are caused by defects in maintaining the permeability barrier in the stratum corneum (SC), the uppermost protective layer composed of dead cells and secretory materials from the living layer stratum granulosum (SG). We have found that loricrin (LOR) is an essential effector of cornification that occurs in the uppermost layer of SG (SG1). LOR promotes the maturation of corneocytes and extracellular adhesion structure through organizing disulfide cross-linkages, albeit being dispensable for the SC permeability barrier. This review takes psoriasis and AD as the prototype of impaired cornification. Despite exhibiting immunological traits that oppose each other, both conditions share the epidermal differentiation complex as a susceptible locus. We also review recent mechanistic insights on skin diseases, focusing on the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/NFE2-related factor 2 signaling pathway, as they coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of thiol-mediated crosstalk between keratinocytes and leukocytes in the epidermis that was put forward earlier.

Changes in soil organic matter fractions induced by cropland and pasture expansion in Brazil's new agricultural frontier

Recently, the so-called Matopiba region (northeastern Brazil) has experienced an accelerated agricultural expansion, with large areas of native vegetation (NV: Cerrado biome) converted to extensive pasture (PA) and cropland under no-tillage (CL). However, because soils from this region contain a large amount of sand (> 60%) and a high susceptibility to erosion, concerns have been raised about the impacts of land-use change (LUC) on soil organic matter (SOM) dynamics. Therefore, we assessed the magnitude that agricultural expansion affects SOM fractions in the most common LUC scenarios observed in the Matopiba region. Soil samples were collected to a depth of 1-m in three adjacent sites (i.e., NV, PA, and CL) located in a representative agricultural area of the region. Soil organic matter was physically fractioned into particulate organic matter (POM) and mineral-associated organic matter (MAOM); and carbon (C) and nitrogen (N) were determined in SOM fractions, in addition to in bulk soil samples. Additionally, the C management index (CMI) was used as a proxy to infer soil health changes. The conversion from NV to PA decreased C (by ~28 Mg ha−1 at 0–100 cm) and N (by ~0.5 Mg ha−1 at 0–50 cm) stocks at an annual loss rate of ~1.3 and 0.02 Mg ha−1, respectively. Carbon loss occurred in both POM and MAOM fractions, which were lower in ~36% and 34%, respectively, compared with NV (0–100 cm). This C depletion resulted in the smallest CMI value (75%) in the 0–30 cm soil layer in PA. The conversion from NV to CL had no effect on total C and N stocks (0–100 cm), but impacted C dynamics in SOM fractions. A lower value was observed for MAOM-C (~22%) in the 30–70 cm layer compared to NV, but the C accrual in the POM fraction (~24%) in the uppermost soil layers (0–30 cm) offset MAOM-C loss. This increase in the POM stocks enhanced the CMI, which was 37% higher than NV for the 0–30 cm layer. Our results revealed that PA expansion in the Matopiba region, besides declining C and N levels, reduced soil health as indicated by the low CMI values. On the other hand, land conversion from NV to CL did not impact C and N stocks and increased CMI. However, we advocated that agriculture expansion over NV areas is not a sensible option to promote the region's sustainable development. It should be prioritized on degraded PA areas and be based on best management practices as a strategy to recarbonize PA soils and restore soil health. This is paramount to mitigate climate change and increase sustainable food production in the Matopiba region over time.

Dike Propagation During Global Contraction: Making Sense of Conflicting Stress Histories on Mercury

Thrust fault-related landforms, smooth plains units, and impact craters and basins have all been observed on the surface of Mercury. While tectonic landforms point to a long-lived history of global cooling and contraction, smooth plains units have been inferred to represent more punctuated periods of effusive volcanism. The timings of these processes are inferred through impact cratering records to have overlapped, yet the stress regimes implied by the processes are contradictory. Effusive volcanism on Mercury is believed to have produced flood basalts through dikes, the propagation of which is dependent on being able to open and fill vertical tensile cracks when horizontal stresses are small. On the contrary, thrust faults propagate when at least one horizontal stress is very large relative to the vertical compressive stress. We made sense of conflicting stress regimes through modeling with frictional faulting theory and Earth analogue work. Frictional faulting theory equations predict that the minimum and maximum principal stresses have a predictable relationship when thrust faulting is observed. The Griffith Criterion and Kirsch equations similarly predict a relationship between these stresses when tensile fractures are observed. Together, both sets of equations limit the range of stresses possible when dikes and thrusts are observed and permitted us to calculate deviatoric stresses for regions of Earth and Mercury. Deviatoric stress was applied to test a physical model for dike propagation distance in the horizontally compressive stress regime of the Columbia River Flood Basalt Province, an Earth analogue for Borealis Planitia, the northern smooth plains, of Mercury. By confirming that dike propagation distances from sources observed in the province can be generated with the physical model, we confidently apply the model to confirm that dikes on Mercury can propagate in a horizontally compressive stress regime and calculate the depth to the source for the plains materials. Results imply that dikes could travel from ∼89 km depth to bring material from deep within the lithosphere to the surface, and that Mercury’s lithosphere is mechanically layered, with only the uppermost layer being weak.

Dynamic triggering mechanism of the Pusa mining-induced landslide in Nayong County, Guizhou Province, China

Catastrophic landslides have occurred frequently in the karst areas of Southwestern China for these years, which makes it urgently necessary to reveal their triggering mechanisms. The universal distinct element code (UDEC) was used to simulate whole response of the Pusa landslide during its underlying coal-seam mining. The results are as follows. First, under the given pre-conditions, when coal seams beneath the original slope were mined from bottom to top, caving zone, fracture zone, and deformation zone overlying the goaf gradually expanded; and as the uppermost layer was mined, the deformation, which was apparently characterized by subsidence and clockwise rotation, overwhelmed the slope. Second, under action of the heavy rainfall, the deformed slope, which was affected by the goaf, behaved further progressive deformation characterized by subsidence and clockwise rotation as a whole. Third, with continuous action of near stoping blasting vibrations, the more-deformed slope, which had been influenced by the goaf and the heavy rainfall, behaved continuous progressive deformation, critical failure, shattering, ejection, debris flow, and accumulation. The deformation exhibited significant subsidence, clockwise rotation, and collapse. These responses were verified by the field reconnaissance. It is the first time to explore dynamic triggering mechanism of the landslide triggered by the vibrations.

Ultrastructural Analysis of Rehydrated Human Donor Corneas After Air-Drying and Dissection by Femtosecond Laser.

Purpose: To evaluate the efficiency of femtosecond laser (FSL) incision of rehydrated human donor corneas after air-drying and its effects on corneal structure.Methods: We compared the rehydrated and fresh-preserved corneas by microscopy following Victus-Tecnolas FSL treatment for straight-edge anterior lamellar keratoplasty (ALK). The corneas were dehydrated at room temperature under a laminar-flow hood.Results: To obtain the horizontal cut in rehydrated corneas, we increased the FSL pulse energy to 1.2 μJ from 0.80 μJ applied for the fresh corneas and obtained a clear-cut separation of the lamellar lenticule cap from the corneal bed. Light microscopy showed regular arrangement of stromal collagen lamellae, with spaces in between the fibers in the corneal stroma in the fresh and the rehydrated corneas, but the uppermost epithelial layers in the rehydrated corneas were lost. Transmission electron microscopy (TEM) revealed no signs of thermal or mechanical damage to the corneal structure. The epithelial basal membrane and Bowman's layer maintained their integrity. The epithelial basal layer and cells were separated by large spaces due to junction alteration in the rehydrated corneas. There were gaps between the lamellar layers in the stroma, especially in the rehydrated corneas. Keratocytes displayed normal structure in the fresh corneas but were devoid of microorganules in the rehydrated corneas. Minor irregularities were observed in the vertical incision and the horizontal stroma appeared smooth on scanning electron microscopy.Conclusion: The corneal stroma of rehydrated corneas maintained morphology and integrity, while corneal cellular components were generally altered. When corneas are intended for FSL-assisted ALK, effective stromal bed incision is best achieved at a laser power higher than that currently adopted for fresh corneas.

Does forest conversion to tree plantations affect properties of subsoil horizons? Findings from mainland Southeast Asia (Lao PDR, Yunnan-China)

While forest conversion to tree plantations in northern Laos is ongoing since the 1990s, its impact on soil properties is yet to be assessed. Our objectives were (i) to assess changes in soil properties, including subsoil horizons down to 160 cm, in <14-year-old teak and 21-year-old rubber tree plantations compared to forest soils, in Luang Namtha province, Laos; (ii) review the recently published studies on the impact of tree plantations in neighboring Xishuangbanna, China; and (iii) to provide, based on (i) and (ii) broad recommendations for sustainable soil management in areas of northern Laos converted to tree plantations.We analyzed selected chemical and physical properties of soil collected at 6 depths, from surface to a depth of 160 cm, along hillslopes, at the locations of 4 paired sites. All layers (0–160 cm) were very acidic pH (≤ 4.3) and depleted in exchangeable cations. Compared to their levels in the surface layer (0–10 cm), organic carbon content (21 g kg−1) and specific pore volume (0.68 cm3 g−1) decreased by 62% and 44%, respectively at 40 cm, and by 81% and 53%, respectively at 110 cm. Forest conversion to tree plantations induced a decrease in pore volume and carbon content in the topsoil, but the subsoil remained unaffected. In rubber tree plantations, the nitrogen content dropped in all layers, including subsoil. In teak tree plantations, pH and phosphorus content increased in the deepest layers. Studies from Xishuangbanna reported comparable degradations, also limited to the upper layers, following conversion to rubber tree plantations. Some isolated studies mentioned some apparent improvements of soil properties, related to textural differences.Overall, the only significant subsoil degradation consisted in N depletion (0–160 cm) under rubber plantations. Even though the impact of forest conversion on soil properties, up to two decades following tree plantation, appeared limited to the uppermost soil layers, the observed alteration of soil porosity may have an impact on runoff and erosion, inducing irreversible degradation of soil functions and productive potential. The subtle nature of such changes hampers adequate perception of their actual importance by farmers and stakeholders who likely have the false impression that soils are unaffected by forest conversion to tree plantations. Consequently, an enforcement of soil conservation practices is recommended when establishing commercial tree plantations on the naturally nutrient-depleted and low porosity Acrisols of this region.

Soil Water Stable Isotopes Reveal Surface Soil Evaporation Loss Dynamics in a Subtropical Forest Plantation

Line-conditioned excess (lc-excess), the deviation of the relationship between δD and δ18O in soil water from that of precipitation, is often used to indicate soil evaporation loss, but the conditions of using lc-excess under the influences of precipitation infiltration or percolation had not been identified. The interaction effects of climate, soil and vegetation on soil evaporation in forests are not well known. We collected soil water at 0–5, 15–20 and 40–45 cm depths and event-based precipitation from 2011 to 2015 in a subtropical forest plantation and calculated the lc-excess. Precipitation on the sampling day and percolation of upper soil water with low lc-excess affected the capacity of the lc-excess to indicate the soil evaporation fractionation signals. Lc-excess of soil water at 0–5 cm depth indicated a reliable soil evaporation loss estimate over 30 days prior to the sampling day. Soil evaporation loss was dominated by the cumulative soil temperature (Tss) during drought periods and was dominated by the relative soil water content (RSWC) during non-drought periods. High Tss decreased soil evaporation loss by increasing transpiration and relative humidity. Our results emphasize the importance of sampling the upper-most soil layer when there is no rain and vegetation during drought periods in forests when studying soil evaporation loss dynamics.

Do epidermal keratinocytes have sensory and information processing systems?

It was long considered that the role of epidermal keratinocytes is solely to construct a water-impermeable protective membrane, the stratum corneum, at the uppermost layer of the skin. However, in the last two decades, it has been found that keratinocytes contain multiple sensory systems that detect environmental changes, including mechanical stimuli, sound, visible radiation, electric fields, magnetic fields, temperature and chemical stimuli, and also a variety of receptor molecules associated with olfactory or taste sensation. Moreover, neurotransmitters and their receptors that play crucial roles in the brain are functionally expressed in keratinocytes. Recent studies have demonstrated that excitation of keratinocytes can induce sensory perception in the brain. Here, we review the sensory and information processing capabilities of keratinocytes. We discuss the possibility that epidermal keratinocytes might represent the earliest stage in the development of the brain during the evolution of vertebrates.

Study of UV ageing effects in modern artists’ paints with MeV-SIMS

In the present work, alkyd and acrylic self-made paints containing synthetic organic pigments (SOPs) of different chemical classes (phthalocyanine, quinacridone, and diketopyrrolo-pyrrole) were analysed by Secondary Ion Mass Spectrometry with MeV primary ions (MeV-SIMS) to study the chemical changes that occur due to accelerated UV ageing. MeV-SIMS is an emerging accelerator-based, surface-sensitive mass spectrometry technique that can provide information about the chemical composition in the uppermost layers of materials. Two-component mock-up samples were prepared and aged for two and four months, to mimic environmental ageing over periods of one and two years. The obtained results show that the studied SOPs are stable under the accelerated ageing conditions used in this study and that they can be easily identified in aged paints, while the binder components undergo structural changes due to the photodegradation processes. The kinetics of binder degradation were found to be dependant on the pigment present in the paint, with phthalocyanines having the highest photostabilizing effect amongst the pigments studied. In addition, the acrylic binder exhibited slightly higher stability to UV ageing than the alkyd medium. This study allowed the identification of SOPs and binders in the selected contemporary artworks, which date from different periods and belong to both outdoor and indoor collections.

Exciton–polaritons in GaAs-based slab waveguide photonic crystals

We report the observation of bandgaps for low loss exciton–polaritons propagating outside the light cone in GaAs-based planar waveguides patterned into two-dimensional photonic crystals. By etching square lattice arrays of shallow holes into the uppermost layer of our structure, we open gaps on the order of 10 meV in the photonic mode dispersion, whose size and light–matter composition can be tuned by proximity to the strongly coupled exciton resonance. We demonstrate gaps ranging from almost fully photonic to highly excitonic. Opening a gap in the exciton-dominated part of the polariton spectrum is a promising first step toward the realization of quantum-Hall-like states arising from topologically nontrivial hybridization of excitons and photons.

On the Evolution and Fate of Sediment Diapirs in Subduction Zones

AbstractAt subduction zones, significant volumes of sediments and other crustal material are carried on top of the downgoing plate past the trench and into the mantle. This represents the dominant process by which material from the Earth's surface is recycled to the interior. However, the fate of these recycled materials is uncertain. Subducted material may be carried with the slab into the deep mantle, or it may form diapirs that ascend into the hotter portions of the mantle wedge, where they can melt and/or be relaminated to the base of the arc crust. While this material can be a mixture (or “mélange”) of sediments, oceanic crust and mantle rocks, here we focus on the dynamics of the uppermost layer of sediments on the downgoing slab. We modified a thermodynamic model to accurately predict the equilibrium mineral assemblage, melting behavior, and density of a range of subducted sediment compositions at pressure and temperature conditions relevant to subduction zones. Using this thermodynamic model, we constructed a coupled dynamic model of sediment diapirs and identified the primary parameters that control diapir behavior: sediment thickness and composition, and the thermal state of the subduction zone. Relamination of ascending diapirs is favored by greater sediment thicknesses, more felsic compositions, and warmer thermal conditions. By contrast, diapirism is suppressed in colder arcs, or where subducted sediment layers are thin or more mafic. Applying this model to modern subduction zones suggests that multiple processes are active today, with relamination occurring in a significant subset of modern arcs.

Improving Constraints on Planetary Interiors With PPs Receiver Functions.

Seismological constraints obtained from receiver function (RF) analysis provide important information about the crust and mantle structure. Here, we explore the utility of the free‐surface multiple of the P‐wave (PP) and the corresponding conversions in RF analysis. Using earthquake records, we demonstrate the efficacy of PPs‐RFs before illustrating how they become especially useful when limited data is available in typical planetary missions. Using a transdimensional hierarchical Bayesian deconvolution approach, we compute robust P‐to‐S (Ps)‐ and PPs‐RFs with InSight recordings of five marsquakes. Our Ps‐RF results verify the direct Ps converted phases reported by previous RF analyses with increased coherence and reveal other phases including the primary multiple reverberating within the uppermost layer of the Martian crust. Unlike the Ps‐RFs, our PPs‐RFs lack an arrival at 7.2 s lag time. Whereas Ps‐RFs on Mars could be equally well fit by a two‐ or three‐layer crust, synthetic modeling shows that the disappearance of the 7.2 s phase requires a three‐layer crust, and is highly sensitive to velocity and thickness of intra‐crustal layers. We show that a three‐layer crust is also preferred by S‐to‐P (Sp)‐RFs. While the deepest interface of the three‐layer crust represents the crust‐mantle interface beneath the InSight landing site, the other two interfaces at shallower depths could represent a sharp transition between either fractured and unfractured materials or thick basaltic flows and pre‐existing crustal materials. PPs‐RFs can provide complementary constraints and maximize the extraction of information about crustal structure in data‐constrained circumstances such as planetary missions.

The role of sublimation as a driver of climate signals in the water isotope content of surface snow: laboratory and field experimental results

Abstract. Ice core water isotope records from Greenland and Antarctica are a valuable proxy for paleoclimate reconstruction, yet the processes influencing the climate signal stored in the isotopic composition of the snow are being challenged and revisited. Apart from precipitation input, post-depositional processes such as wind-driven redistribution and vapor–snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal subsequently stored in the ice. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor–snow exchange is an important driving mechanism. Here we investigate how vapor–snow exchange processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under forced sublimation show an increase in snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer due to sublimation, with an attenuated signal down to 3 cm snow depth over the course of 4–6 d. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Our observations confirm that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 d field experiments at the East Greenland Ice Core Project site (northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation contribute to the climate signal recorded in the water isotopes in surface snow, in both laboratory and field settings. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such, particularly in regions of low accumulation.

Soil suction and temperature measurements in a heavy haul railway formation

Transportation foundations around the world exist predominantly in an unsaturated state. Support for the adoption of unsaturated soil mechanics in routine geotechnical engineering is ever-increasing. However, the measurement and characterization of soil suction is a potentially significant barrier thereto. To this end, the efficacy of various measurement techniques was investigated, with the aim to characterize the temporal variation in soil suction and temperature within the formation layers of a heavy haul railway formation. Tensiometers, fixed-matrix soil-water matric potential sensors and capacitance-type volumetric water content sensors were installed within the formation layers of a railway track and monitored for a period of 18 months. The average suction measured over the observational period was 25.6, 12.7, 3.5 and 4.2 kPa for the special subballast, subballast and two subgrade layers respectively. Suctions reached a minimum of ≈0 kPa at the end of the rainfall season across all layers and reached a maximum, ranging between 10 and 60 kPa across all layers at the end of the dry season. Soil temperatures for the observational period varied between 10 and 22 °C and displayed seasonality in-phase with the monitored air temperatures. The special subballast layer (uppermost layer) showed the greatest variation in both suction and temperature and is the layer which experienced the greatest stress changes as a result of seasonal variations in rainfall and air temperature.