δD Values Research Articles

The Absolute Age and Origin of the Giant Gypsum Geode of Pulpí (Almería, SE Spain)

Subaqueous gypsum (CaSO4·2H2O) crystals are relatively common in epithermal systems where sulfide ore deposits are present. The Giant Geode of Pulpí (Almería, SE Spain) hosts some of the largest (up to 2 m in length) subaqueous gypsum crystals discovered to date. Here, we present the first U-series ages of its crystals and reconstruct the oxygen and hydrogen isotopic composition (δ18O and δ2H) of the Pulpí paleo-aquifer from which the crystals formed by using stable isotopes of gypsum hydration water. We successfully dated the onset of gypsum precipitation in the Geode at 164 ± 15 ka. However, the extremely low U concentration (11 ppb) and relatively high detrital Th content (230Th/232Th 3.2) hinder accurate dating other gypsum samples. The δ18O and δD values of the paleo-aquifer during the growth of the crystals aligned with the local meteoric water line, suggesting that the sulfate-enriched mother solution consisted of meteoric water that recharged the aquifer during that period. The mean isotopic composition of the Pulpí paleo-aquifer (δ18O = −6.5 ± 0.1‰ and δ2H = −42.3 ± 0.5‰) during the formation of the crystals was similar to the current groundwater in this area (δ18O = −6.1 ± 0.8‰, δ2H = −42 ± 6‰). The isotopic differences observed in samples collected from distinct locations and in individual crystals were probably related to changes in the isotopic composition of the aquifer, as a consequence of varying climate that impacted on the isotopic composition of rainwater during thousands of years in this region. Our results indicated that subaqueous selenite crystals may be useful for paleo-hydrological reconstructions. However, improving the current analytical techniques for dating gypsum with low U concentrations will be essential to obtain accurate and reliable records from Quaternary gypsum cave crystals in the future.

Characterization of spatiotemporal patterns of soil water stable isotopes at an agricultural field

Spatiotemporal variations in soil water content (SWC) and soil water stable isotopic compositions (SWSIC; 2H/1H (δD) and 18O/16O (δ18O)) provide critical information on elucidating land surface processes across scales. Meanwhile, little is known about the spatiotemporal characteristics of SWSIC and its driving factors. Therefore, it's necessary to improve tracer techniques of SWSIC by interpreting their spatiotemporal variability patterns as well as the correlations with other factors such as texture, soil depth and vegetation. To this end, the spatiotemporal variations in SWC and SWSIC along with their controlling factors were jointly investigated based on seven field campaigns over roughly a two-year period at an agricultural field in North China Plain. Two transects, vegetated and bared, were considered. The results of vegetated transect showed that both SWC and SWSIC exhibited considerable spatiotemporal variabilities at the field scale of ~100 m, with SWSIC displaying more complex patterns. Overall, the spatial variations in SWSIC were larger in wet seasons than in dry seasons, which decreased with increasing soil depth, largely due to less impacts of precipitation inputs and soil evaporation on SWSIC dynamics at deeper depths. The temporal stability analysis (TSA) showed that there existed temporal persistence of the spatial structure of SWSIC, particularly at deeper soil depths. Moreover, the SWSIC data in our study showed that the effect of vegetation on the SWSIC dynamics was noticeable with shading effects, root distribution and water uptake, which caused much lesser degrees of soil evaporation at the vegetated transect. What's more, the representative sites for monitoring spatial average δD values were identified, demonstrating the viability of using the TSA method to estimate the spatial average SWSIC values at field scales. These findings can improve the interpretation of SWSIC data for practical applications.

Asynchronous variations of East Asian summer monsoon, vegetation and soil formation at Yulin (North China) in the Holocene

ABSTRACTIn the East Asian monsoon region, Chinese speleothem δ18O records exhibit a maximum monsoon strength during the early Holocene. However, other proxy data from lakes or loess, interpreted as monsoon rainfall, show a mid‐Holocene monsoon optimum. This discrepancy may come from specific climate interpretation of different proxies. Here we report multiproxy records from a single loess–palaeosol sequence at Yulin in the monsoon marginal northern China, based on an independent and high‐precision chronology. Our long‐chain n‐alkane δD values, together with related biomarker proxies including the average chain length and concentration of long‐chain n‐alkanes, reveal a weakening trend in monsoon strength and less woody vegetation since ~6 ka. However, other soil formation‐related proxies, such as magnetic susceptibility, grain‐size distribution and total organic carbon, show a decreasing trend since 4–3 ka. We find that monsoon and vegetation are controlled by insolation variation, while soil formation is more related to temperature and humidity changes. Our multiple proxy comparison reveals different controlling mechanisms leading to different interpretations in monsoon, vegetation and soil formation reconstructions. This finding suggests that previous debates on Holocene monsoon changes in East Asia probably stem from the specific proxy interpretation.

Isotope Geochemistry of the Shenshuitan Gold Deposit within the Wulonggou Gold Field in the Eastern Kunlun Orogen, Northwest China: Implications for Metallogeny

The Shenshuitan gold deposit is located within the Eastern Kunlun Orogen in northwest China. The gold mineralization here occurs primarily within the ductile fault XI. The sulfide mineral assemblage is dominated by pyrite and arsenopyrite, with minor pyrrhotite, chalcopyrite, galena, and sphalerite. Host rocks predominantly consist of Ordovician silicic slate and late Silurian granites, and their alterations include silicification and sericitization. The measured δD and δ18O values of quartz and sericite range from −113.9‰ to −93.1‰ and from 4.6‰ to 12.0‰, respectively. Bulk and in situ δ34S values of sulfides range from −7.3‰ to +9.6‰ and from −3.92‰ to 11.04‰, respectively. Lead isotope compositions of sulfides show 206Pb/204Pb ratios from 18.071 to 19.341, 207Pb/204Pb ratios from 15.530 to 15.67, and 208Pb/204Pb ratios from 37.908 to 38.702. Collectively, the isotope (H, O, S, and Pb) geochemistry suggests that the ore-forming fluids were of a metamorphic origin mixed with meteoric water and that the sulfur and lead were sourced from a mixture of host rocks and original ore-forming metamorphic fluids. Lastly, this deposit can be classified as an orogenic gold deposit associated with the final collision between the Bayan Har–Songpanganzi Terrane and the Eastern Kunlun Orogen during the Later Triassic.

Mapping of β-lactoglobulin − mucin interactions in an in vitro astringency model: Phase compatibility, adsorption mechanism and thermodynamic analysis

This study investigates the astringency-related interfacial behaviour, mechanistic parameters, and interaction mechanisms of a typical milk protein, β-lactoglobulin (β-LG), with mucin acting as model salivary protein. For a series of β-LG – mucin compositions, the most intense phase separation is observed for a 75:25 w/w mixture of mucin and β-LG at pH 3. QCM-D shows that, at pH 3, β-LG adsorption on a mucinous interface yields a heavily-hydrated viscoelastic layer with increased energy dissipation [ΔD ≤ 9.92 ± 0.01 ( × 10−6], thickness (Δt = 25.51 ± 0.01 nm), and wet mass values (Δm = 2623.30 ± 1.27 ng cm−2). At pH 7, β-LG (Δm = 855.86 ± 0.45 ng cm−2) forms highly-ordered (more rigid), relatively less dissipative, but thinner interfacial layer, as indicated by the decreased Δt (7.13 ± 0.01 nm) and ΔD values [≤ 2.52 ± 0.01 ( × 10−6)]. Furthermore, ΔD vs.Δf plots point to the existence of greater conformational and molecular reordering upon progressive coupling of β-LG at pH 3, as compared to pH 7. β-LG exhibits a two-step binding with mucin at pH 3; whilst a single-step (low affinity) mechanism exists at pH 7, as elucidated by fluorimetry. Thermodynamic analysis suggests two macromolecular populations interact spontaneously (ΔG < 0) regardless of pH. Interestingly, ΔS values are substantially greater at pH 3 (≥182.76–292.30 J K−1M−1), in comparison with pH 7 (≤17.07 J K−1M−1); suggesting that entropy-driven flocculation of β-LG and mucin arise from well-defined electrostatic and/or hydrophobic forces. The above results highlight the inherent complexity of pH-induced β-LG – mucin interactions, and the resulting complexity of the physicochemical basis of astringency.

Stable isotopic variations (δD and δ18O) in a mountainous river with rapidly changing altitude: Insight into the hydrological processes and rainout in the basin

AbstractHydrological processes play an important role in stable isotopic compositional variations of the river water. The present study includes spatial distributions of stable hydrogen and oxygen isotopes (δD and δ18O) of a Himalayan River (the Teesta) to trace various hydrological processes and their associated roles on isotopic fractionation of river water. The δ18O compositions of the water samples varies between −12.2‰ and −5.4‰ (mean: −8.01‰ ± 1.81‰) and that of δD between −95.1‰ and −38.5‰ (mean: −57.6‰ ± 15.6‰). The observed compositional variation in δ18O, δD and d values of river water is mainly governed through snowmelt input, evaporation, and recycled moisture contribution. The variation of δ18O and δD values point towards an early melting of snow in the basin and a significant contribution of snowmelt to the river water. The orographic induced precipitation front appears to control the hydrological regimes in a distinct manner as reflected in the trend between d values and elevation. The rain shadow affected northern reaches of the basin are characterized with dry &amp; arid climate triggering evaporation whereas, the windward southern side witness temperature influenced evaporation. The study suggests that the differential degree of recycled moisture contribution to the local precipitation is also a key component in bringing the stable isotopic variation in the river water. This varied magnitude of moisture recycling could result from uneven distribution of evapotranspiration and surface water evaporation. Results found that a rapid change in the altitude of a river basin can give rise to different hydrometeorological conditions, thereby resulting in simultaneous operation of almost all the major hydrological processes and a complex isotopic compositional variation in the river water. Also, the rainout percentage in the Teesta basin is found to be higher owing to this rapid rate of elevation increase.

Origin of Li brine-type deposits in the Cretaceous gypsum-bearing formation of the Jitai Basin, South China: Constraints from geochemistry and H, O, Li, B, and Sr isotopes

Li brine-type deposits have recently been discovered in the Upper Cretaceous gypsum-bearing formation of the Jitai Basin, South China. The source and enrichment mechanism of Li in brines, however, are still unclear. To define the origin of lithium and evaluate the water-rock interaction process, this work presents chemical and multi-isotope data for Li-rich brines from the Jitai Basin. Seven brine samples collected from Meigang boreholes contain high salinities of 190–339 g/L, lithium concentrations of 60.6–106.0 mg/L, and low magnesium/lithium ratios of ∼11. The good correlation between δD and δ18O values suggests that the primary brine has been diluted by meteoric water, while contributions from halite dissolution or secondary brines having dissolved solid halite are also indicated by the high Na/Cl (0.58–0.63) and Cl/Br (average of ∼26987) mass ratios, the Na deficit and Ca excess, and the fact that high-salinity brines have lower δD, δ18O and δ34SSO4 values. Among the chemical geothermometers commonly used in the literature, only the SiO2-chalcedony, Na/K/Ca and K/Mg thermometric relationships give concordant temperature values of 120 ± 15 °C for the deep reservoir of these brines, suggesting that the latter are not in full chemical equilibrium with the reservoir rocks (excess of sodium due to halite dissolution), but this temperature can be considered as representative of their deep reservoir. Moreover, most of the chemical geothermometers yield close temperature values of 115 ± 15 °C for the deep reservoir of three neighboring dilute thermal waters. The homogeneous 87Sr/86Sr ratios (0.713865–0.713915) and δ11B (+1.8‰–+3.4‰) and δ7Li (+13.1‰–+14.2‰) values show a close affinity to the continental crust, possibly implying a fluid signature involving the interactions between clastic host rocks and brines. X-ray diffraction and scanning electron microscopy analyses and Li contents of reservoir rocks reveal the presence of dominant lithian muscovites of clastic origin, probably originating from weathering of Li-enriched igneous rocks, which contribute to most of the lithium input in the hydrologic system of the basin. Thus, it is proposed that lithium enrichment in brines from the Upper Cretaceous gypsum-bearing clastic aquifers of the Jitai Basin was generated by water-rock interactions involving lithian muscovites.

Genesis and magmatic-hydrothermal evolution of the Shapoling Mo deposit, East Qinling, China: Insights from geochronology, petrogenesis and fluid evolution

The Shapoling deposit, located in Xiong'ershan area, East Qinling, China, is characterized by a magmatic-hydrothermal Mo vein system. We present whole-rock geochemical, zircon U-Pb-Hf-O isotopic, quartz H-O isotopic and fluid inclusion data for the Shapoling deposit. We use these data to investigate the petrogenesis of granitoids associated with Mo mineralization and the processes of magmatic-hydrothermal evolution that formed the Mo deposit. The granitoids from the Shapoling deposit are metaluminous, alkalic to calc-alkalic, shoshonitic to high-K series, and belong to highly fractionated I-type granitoids. These granitoids are strongly enriched in light rare earths (LREEs) and large ion lithophile elements (LILE), but depleted in heavy rare earths (HREEs) with negative europium anomalies and high field-strength elements (HFSE), mostly plotting in the range of the Taihua Group rocks. Most of the Shapoling granitoids show relatively lower Sr/Y and (La/Yb)N than the typical adakitic rocks, showing that the parental magmas were generated under lower pressure. Therefore, the Shapoling granitoids were generated at thin crustal levels by lithospheric thinning process linked to the tectonic transition from compression to extension. Zircon U-Pb ages of the Shapoling granitoids range from 132.9 ± 1.3 Ma to 126.5 ± 0.7 Ma. The εHf(t) values and δ18Ozircon values show a variation trend from −19.1 to −8.0 and 5.33‰ to 6.30‰, which are consistent with Hf-O isotopic features of mixing of the partially melted Taihua Group with mantle-derived components. FIluid inclusion microthermometry results suggest that the hydrothermal fluids forming the Shapoling Mo deposit changed from early moderate- to low-salinity CO2-rich fluids in the H2O-NaCl-CO2 system, to late H2O-NaCl low-salinity fluids. The corresponding quartzs have δD values varying from −93.3‰ to −78.2‰ and δ18O values from −5.14‰ to 0.92‰, indicating a dominant magmatic source but were diluted by meteoric water in the late stage. Fluid boiling is the key factor that controlling the precipitation of molybdenite. Our study provides insights into the formation of Mo system associated with a prolonged and active magmatic system, upwelling of hot asthenosphere and intense mantle-crust interaction. The prolonged magmatic system is steadily replenished by mantle-derived materials in the magma chamber, which feed the hydrothermal systems and govern the formation of the Shapoling Mo deposit.

Characterization of Physicochemical Properties of Chitosan Coconut Crabs Shells (Birgus latro)

The coconut crab, or in the language of North Maluku called coconut crab, is one of the biological resources with high economic value. People consume coconut crab dishes that have a flavor similar to lobster. The utilization of coconut crab shells has not been done. At the same time, this study aims to isolate and characterize chitosan coconut crab shells by deacetylation method using different concentrations of NaOH and different heating times. The results of the best chitosan synthesis with a variation of 15% NaOH concentration, 120 minutes of heating included the characterization of FTIR spectrum DD values (89.15%) so that there was an increase in crystallinity in each peak spectrum of 3448 cm-1 area that binds hydrogen bonds (O-H). Likewise, for molecular weight (368 kDa), the morphology of chitosan CC is shown using SEM, which shows the similarity of the structure of the microfibrils structure. In comparison, the XRD pattern shows distinctive characteristics of peak crystallinity. Likewise, the quality of water content, ash, protein, fat, color of chitosan CC is under the standards of Protan Biopolymer. Chitosan CC micrograph has the same shape of microfibril structure due to the heating process. While the average crystal peak is 19.2-29.4 O, the best treatment recommended in this study is the deacetylation process using a 10% NaOH concentration with a heating time of 120 minutes. Thus chitosan, which has the best characterization value, is used as a polymer that can be used in the food sector.

Catchment-scale impacts of shallow landslides on stream water chemistry

Catchment water quality plays an important role in ecosystem and water resource management in mountainous areas. Shallow landslides triggered by earthquakes or heavy rainfall can cause a sudden and long-term deterioration in stream water quality by releasing contaminants into streams. Although many studies have been undertaken on the relationship between a single landslide and the water chemistry of a nearby river, little is known about the impact of densely distributed shallow landslides on stream water chemistry at the catchment scale. To this end, this study determined the major ion concentrations and isotopic compositions of stream water along with the shallow landslide area/catchment area ratio (LCR) in 37 headwater subcatchments in the southern part of Hokkaido, Japan, where an earthquake caused more than 6000 shallow landslides on September 6, 2018. In subcatchments with a high LCR, stream water exhibited significantly higher Ca2+ and HCO3− concentrations, while there was no correlation between the LCR and concentrations of Na+ and Cl−. The δ18O and δD values of stream water plotted between the local meteoric water lines of summer and winter precipitation, indicating that they originated from meteoric water. Shallow landslides formed sliding surfaces, landslide deposits, and landslide-dammed lakes, which enhanced the interaction between the surface soil and stream water, leading to Ca–HCO3 type water. The results showed that shallow-landslide-driven changes in stream water quality could be linearly approximated by the fraction of the landslide area at the catchment scale, which is a more versatile approach than the local framework of a single landslide and a nearby stream. In future research, these findings could be combined with a slope stability model and the background climatic, geological, topographical, and water quality conditions of a watershed to evaluate water pollution triggered by shallow landslides at the catchment scale.

Volume Dependence of Hydrogen Diffusion for Sorption and Desorption Processes in Cylindrical-Shaped Polymers.

In the actual application of gas transport properties under high pressure, the important factors are sample size dependence and permeation efficiency, related to gas sorption. With a modified volumetric analysis technique, we firstly measured the overall diffusion properties and equilibrium times for reaching the saturation of hydrogen content in both hydrogen sorption and desorption processes. The measured parameters of total uptake (C∞), total desorbed content (C0), diffusion coefficient in sorption (Ds), diffusion coefficient in desorption (Dd), sorption equilibrium time (ts) and desorption equilibrium time (td) of hydrogen in two polymers were determined relative to the diameter and thickness of the cylindrical-shaped polymers in the two processes. C∞ and C0 did not demonstrate an appreciable volume dependence for all polymers. The identical values of C∞ and C0 indicate the reversibility between sorption and desorption, which is interpreted by the occurrence of physisorption by sorbed hydrogen molecules. However, the measured diffusivity of the polymers was found to be increased with increasing thickness above 5 mm. Moreover, the larger Dd values measured in the desorption process compared to Ds may be attributed to an increased amorphous phase and volume swelling caused by increased hydrogen voids and polymer chain scission after decompression. The ts and td were found to be linearly proportional to the square of the thickness above an aspect ratio of 3.7, which was consistent with the numerical simulations based on the solution of Fick’s law. This finding could be used to predict the ts in a polymer without any measurement, depending on the sample size.

Radioactive and stable isotopes reveal variations in nearshore submarine groundwater discharge composition and magnitude across low inflow northwestern Gulf of Mexico estuaries

To determine how submarine groundwater discharge (SGD) magnitudes and composition (fresh or saline/recirculated) vary in nearshore low inflow estuaries across ⁓125 km of a semiarid coastline, this study assessed three south Texas estuaries, using radon [222Rn], radium [226Ra and 224Ra], and water isotopes [δ18O and δD]. Mass balance models of time-series 222Rn, found to be representative of total SGD in this study, revealed much higher SGD inputs to the Nueces Estuary (average [x̅] Nueces, Corpus Christi and Oso Bays: 120, 83, and 44 cm·d−1, respectively), attributed to anthropogenically-disturbed substrates and potentially surfacing growth-faults. The lowest 222Rn-derived SGD occurred in the Upper Laguna Madre Estuary (x̅: Upper Laguna Madre and Baffin Bay: 21 and 18 cm·d−1, respectively), explained by the drier climate, lower anthropogenic disturbance, and neighboring groundwater cone of depression. Aransas Bay in the Mission Aransas Estuary received greater average annual precipitation but exhibited low total SGD rates (x̅: 23 cm·d−1). Seasonally, average 222Rn-derived SGD rates increased following Hurricane Harvey (43 cm·d−1 in spring to 64 cm·d−1 in summer). In the Nueces Estuary, the overall 222Rn-derived SGDs were substantially higher than SGDs from 224Ra and 226Ra. The closer agreement between 224Ra and 222Rn-derived SGD and larger 224Ra rates in the Upper Laguna Madre Estuary, Aransas Bay and Oso Bay indicate that saline/recirculated SGD contributions were significant. Values of δ18O and δD confirm these types of inputs, with effects of evaporation/salinization more pronounced where recirculation was predominant and the opposite where terrestrial/222Rn-derived SGD inputs dominate. 226Ra-derived SGDs were lower than the 224Ra due to different behavior of the two isotopes while released into water following transport through saline and fine-grained estuarine sediments or due to wind-driven disturbances.

Stable isotope compositions of surface water in Mexico between 22–26 °N

We study the δ18O, δD, and d-excess values of 205 surface water samples collected in a wet and a dry season from the west to the east coast of Mexico between 22 and 26 °N to understand the controlling factors of isotopic patterns and lapse rates. The samples include lake, pond, river, spring, and tap waters. The δ18O (δD) values range from −13.2‰ (−97.2‰) to +20.3‰ (+74.0‰), and decrease from both coasts to higher elevations in the mountains adjacent to the coasts. The lake and pond waters have the largest stable isotopic variations and gentlest surface water slopes (<5.5) in both seasons, suggesting surface evaporation. Our moisture back trajectory analysis indicates that the strongest evaporation occurs in the Mexican Plateau, where dry season moisture from the east and west mix, and up to 17% of the moisture in the wet season precipitation is recycled. The river waters in the dry season and the spring waters in both seasons also have gentle surface water slopes (∼6.6), suggesting some degree of evaporation. On the Sierra Madre Occidental, the δ18O isotopic lapse rate of river and spring water is generally low, −1.3‰/km in the wet season and −1.8‰/km in the dry season, most likely because of sub-cloud evaporation of rain at high elevation. Our results highlight that isotopic lapse rates vary greatly because of changes in local climate conditions, and these changes are not necessarily contemporaneous at high and low elevations. Therefore, evaporation of ground and river water in the geologic past should be considered in stable isotope-based paleoclimate reconstructions, and a range of isotopic lapse rates should be used in stable isotope paleoaltimetry.

Determination of the initial hydrogen isotopic composition of the solar system

The initial isotopic composition of water in the Solar System is of paramount importance to understanding the origin of water on planetary bodies but remains unknown, despite numerous studies1–5. Here we use the isotopic composition of hydrogen in calcium–aluminium-rich inclusions (CAIs) from primitive meteorites, the oldest Solar System rocks, to establish the hydrogen isotopic composition of water at the onset of Solar System formation. We report the hydrogen isotopic composition of nominally anhydrous minerals from CAI fragments trapped in a once-melted host CAI. Primary minerals have extremely low D/H ratios, with δD values down to −850‰, recording the trapping of nebular hydrogen. Minerals rich in oxidised iron formed before the capture of the fragments record the existence of a nebular gas reservoir with an oxygen fugacity substantially above the solar value and a D/H ratio within 20% of that of the Earth’s oceans. Hydrogen isotopes also correlate with oxygen and nitrogen isotopes, indicating that planetary reservoirs of volatile elements formed within the first 2 × 105 years of the Solar System, during the main CAI formation epoch. We propose that the isotopic composition of inner Solar System water was established during the collapse of the protosolar cloud core owing to a massive admixture of interstellar water. The hydrogen isotopic composition of the oldest Solar System rocks demonstrates that a gaseous reservoir of terrestrial isotopic composition existed as early as the onset of Solar System formation and coexisted with the solar gas.

Hydrogen sorption and desorption properties in rubbery polymer

We firstly characterized the sorption and desorption properties of hydrogen gas dissolved in rubbery polymer by utilizing a newly developed volumetric analysis technique. This method was applied to spherical-shaped sealing rubber, such as ethylene propylene diene monomer. The total sorption uptake (C∞), total desorbed content (C0), sorption diffusion coefficient (Ds) and desorption diffusion coefficient (Dd) of hydrogen in rubber are quantified as a function of diameter in both adsorption and desorption processes. No diameter dependence is observed for C∞ and C0, whereas Ds and Dd is diameter-dependent. The reversibility between C∞ and C0 observed in the process of adsorption and desorption implies the occurrence of physisorption rather than chemisorption by introducing hydrogen molecules. However, the difference between the Ds and Dd values may be ascribed to two different processes. Time to reach equilibrium in both sorption and desorption processes is found to be linearly proportional to the square of sample radius.

Substantial peak size effect on compound-specific δD values analyzed on isotope ratio mass spectrometry

Lipid compound-specific hydrogen isotopes (δD) have been widely applied in studies of biogeochemistry and paleoclimatology. δD values of lipid homologues with different chain lengths from a single analysis are often utilized together in order to make full use of the δD information. However, this approach could be potentially impacted by the large analytical error due to the inappropriate amount injected for some homologues. Here, we systematically investigate compound-specific δD deviations with varying contents injected on the isotope ratio mass spectrometry, expressed as amplitudes, using both lab working standards and natural samples. The n-alkane δD values of lab working standards (mixed C21, C25, C27, C29, C31, and C33) could vary by 40‰ to 70‰ when the amplitudes of n-alkanes change from 0.5 V to 10 V. For natural samples (27 n-alkane and 77 fatty acid samples), we have made repeated analyses of the same samples with different homologues targeted for the optimum range. The measured δD values are higher by 20‰ to 40‰ with the amplitudes lower than the optimum range, and lower by 10‰ to 20‰ with higher amplitudes. All the results consistently show higher δD values with decreasing amplitudes, and larger deviations occurring in low amplitude range, implying that special caution should be taken with the δD values measured at low amplitude range. We have attempted amplitude-based correction of lipid δD values, however, this approach should be cautious owing to their large residual errors. Hence, δD values of different homologues in the same samples have to be measured in separate analysis if they could not fall within the optimum range at the same time.

The role of cave ventilation in the triple oxygen and hydrogen isotope composition of condensation waters in Altamira Cave, northern Spain

In cave environments, water vapor condensation occurs naturally when warmer/wet air masses flow close to colder cave surfaces. Artificial microclimate perturbations in show caves can enhance this process, leading to potential deterioration of rock art and degradation of speleothems. Here we investigate the triple oxygen and hydrogen isotopic compositions of condensation water in Altamira Cave (Cantabria, northern Spain) to evaluate the potential of stable isotopes in the study of condensation mechanisms in caves. We assess the role of cave ventilation in the spatiotemporal isotopic variability of condensation water in Altamira Cave. To this end, water drops that condense naturally on artificial supports in different parts of the cave were collected for 7 years and their isotopic compositions (δ17O, δ18O, δD and derived parameters 17O-excess and d-excess) were compared to those of droplets with no apparent dripping taken from the cave ceiling (i.e. presumably condensation water) and fast dripping points (i.e. infiltration water) during the same period. Condensation waters in the outmost cave sectors, closer to the entrance, show higher δ17O, δ18O and δD values during the cave ventilation period (June to October) compared to the rest of the year. This seasonal pattern can be explained by changes in the contributions of two moisture sources for condensation: advection of allochthonous water vapor from outside during the cave ventilation period and recycling of autochthonous vapor generated from cave dripwater during the stagnation period. In contrast, the isotopic values of condensation waters in the inner cave sectors are similar to those of infiltration water, with insignificant seasonal variability. This suggests that water condensation in the inner cave sectors is sourced by autochthonous vapor, with no significant contributions of external moisture, even during the cave ventilation period. We conclude that allochthonous water vapor condenses preferentially in the Entrance Hall and does not affect significantly the rest of the cave. These results are relevant for the management of Altamira Cave and for future investigations on condensation mechanisms in cavities elsewhere.

Equilibrium and kinetic controls on molecular hydrogen abundance and hydrogen isotope fractionation in hydrothermal fluids

Molecular hydrogen (H2) is among the main components in hydrothermal fluids and exerts a major role in geochemical and biological processes. Nevertheless, the understanding and quantification of factors controlling H2 abundance and isotope composition remain uncertain. Sub-aerial hydrothermal systems provide a unique opportunity to study sources and reactions of H2. Here, we present hydrogen fugacity (fH2) and δD values of H2 and H2O in hydrothermal fluids from such systems worldwide (Greece, Iceland, Kenya and New Zealand), representative of mid-ocean ridge and arc systems and sourced by seawater and meteoric water. The hydrothermal fluid temperatures are 226-359°C, and the fH2, δD-H2 and δD-H2O values are 0.002-3.3 bar, -646 to -391‰ and -94.1 to +11.3‰, respectively. Comparison of measured data with geochemical modeling reveals that H2 is predominantly sourced from the reduction of H2O, enabled through the oxidation of aqueous Fe+II to Fe+III and precipitation of Fe+III-bearing hydrothermal minerals (e.g., epidote). We argue that fH2 in hydrothermal fluids is controlled by metastable mineral-fluid and fluid-fluid equilibria upon progressive rock alteration and depend on temperature, rock-to-water ratio (r/w), source water composition and volcanic gas input. Consequently, fH2 in these systems is not fixed by a sole redox buffer. Our data demonstrate that δD-H2 values of reservoir fluids at depth are controlled by the δD value of the source water and the equilibrium isotope fractionation characteristic of the hydrothermal reservoir temperatures. Attainment of isotopic equilibrium at reservoir conditions is supported by fast isotopic equilibration times at T > 200°C, on the order of minutes to few hours, relative to hydrothermal fluid residence times within the reservoirs of years to decades or even longer. During its ascent to the surface, the isotopic composition of H2 can be modified due to isotopic re-equilibration with H2O. The extent of re-equilibration depends on the interplay between fluid flow velocity, cooling rate and kinetics of D-H exchange between H2 and H2O. For fast flowing well discharges (∼0.1 to >10 m/s), negligible changes occur, whereas for slowly flowing (<0.06 m/s) fumaroles, complete re-equilibration at surface temperatures (∼100°C) is sometimes observed. Based on the extent of hydrogen isotope disequilibrium relative to reservoir conditions, fluid reservoir-to-surface travel times are estimated to range from few minutes to <3 hrs for well fluids and few hours to days for fumarolic vapor.

Clinical Value of Coagulation Index Changes in Early Diagnosis and Nursing Intervention for PICC-Related Venous Thrombosis in Tumor Patients.

Purpose To explore the clinical value of coagulation index changes in early diagnosis and nursing intervention for PICC-related venous thrombosis in tumor patients. Patients and Methods. A total of 170 tumor patients hospitalized for the first time with catheterization were enrolled from February 2018 to June 2022. According to the diagnostic criteria of venous thromboembolism, high-risk patients with venous thrombosis within 13 days after catheterization were enrolled in the observation group, and those without thromboembolism were enrolled in the control group. Venous blood was taken from all patients on days 1, 5, 9, and 13 after catheterization to measure the change trend of coagulation indexes of patients and to compare the difference of coagulation indexes between the observation group and the control group. Results PT values of all patients were within the normal reference range at days 1, 5, 9, and 13 after catheterization. Compared with the control group, the observation group was significantly reduced on days 5, 9, and 13 after catheterization (P < 0.05), and continued to decrease with the prolonging of time(P < 0.05). After catheterization, the values of all patients at each time point were lower than the normal reference range. Compared with the control group, the values of tumor patients in the observation group were significantly decreased on days 5, 9, and 13 (P < 0.05) and continued to decrease at each time point (P < 0.05). DD values in the observation group were all higher than the normal reference range on days 1, 5, 9, and 13 after catheterization. Compared with the control group, DD values in the observation group were significantly higher on days 1, 5, 9, and 13 after catheterization (P < 0.05). Conclusion PT and APTT continued to decrease after catheterization, and DD kept fluctuating at a high level, highly suggesting the possibility of venous thrombosis. The nursing staff should keep high vigilance and give appropriate nursing intervention.

Values of δD and δ18O and concentrations of 3H and 14C of deep groundwater in Djibouti

Values of δD and δ¹⁸O and concentrations of ³H and ¹⁴C of deep groundwater in Djibouti