18O Values Research Articles

The Spatiotemporal Variability of Snowpack and Snowmelt Water 18O and 2H Isotopes in a Subarctic Catchment

AbstractThis study provides a detailed characterization of spatiotemporal variations of stable water 18O and 2H isotopes in both snowpack and meltwater in a subarctic catchment. We performed extensive sampling and analysis of snowpack and meltwater isotopic compositions at 11 locations in 2019 and 2020 across three different landscape features: (a) forest hillslope, (b) mixed forest, and (c) open mires. The vertical isotope profiles in the snowpack's layered stratigraphy presented a consistent pattern in all locations before snowmelt, and isotope profiles homogenized during the peak melt period; represented by a 1–2‰ higher 18O value than prior to melting. Our data indicated that the liquid‐ice fractionation was the prime reason that caused the depletion of heavy isotopes in initial meltwater samples prior to the peak melt period. The liquid‐ice fractionation was influenced by snowmelt rate, with higher fractionation during slow melt. The kinetic liquid‐ice fractionation was evident only in close examination of meltwater lc‐excess values, not 18O values alone. Meltwater was isotopically heavier and more variable than the depth‐integrated snowpack; the weighted mean of meltwater isotope values was higher by 0.62–1.33‰ 18O than the weighted mean of snowpack isotope values in forest hillslope and mixed forest areas, and 1.51–6.37‰ 18O in open mires. Our results reveal close to 3.1‰ 18O disparity between the meltwater and depth‐integrated snowpack isotope values prior to the peak melt period, suggesting that proper characterization of meltwater 18O and 2H values is vital for tracer‐based ecohydrological studies and models.

Determinação de água exógena em suco de uva através da razão isotópica do 18O/16O

Abstract The consumption of grape juice has been growing significantly, so its quality is becoming an issue of great importance, both for the consumer and for the industry. However, identifying adulteration in juice is a great challenge and requires a reliable analytical process. The isotope ratio (18O/16O) is an important tool to determine the addition of exogenous water in beverages, however, there is no official method for juice in Brazil. This study aimed to develop and validate a method for detecting exogenous water in grape juice through isotopic analysis of 18O/16O. The development and validation of the analytical method were performed using Isotope Ratio Mass Spectrometry (IRMS). The effect of temperature and evaporation of δ18O in experimental juices was evaluated, and reference values were found for juices based on the δ 18O of musts. The influence of the juice industrial production process on 18O values was verified, and commercial juices were evaluated in relation to the values of reference regarding the addition of water. The temperature and evaporation parameters did not influence the results of the 18O of the juice, as they presented differences lower than the method uncertainty. The heat exchanger system did not influence the proposed method. The reference values for juice can come from the musts, without affecting the interpretation of the final results. Of the thirty real juices analyzed, nine had exogenous water, three proved to be reconstituted juices and eighteen were considered to have no exogenous water. The method proposed and validated in this study presented values for the limit of detection (LOD) of 0.24‰, the limit of quantification (LOQ) of 0.97‰ and measurement uncertainty of 0.71‰, proving to be effective for the detection of exogenous water in grape juice, through of the analysis of the isotopic ratio of 18O/16O by IRMS.

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

Detecting hydrologic distinctions among Andean lakes using clumped and triple oxygen isotopes

Oxygen isotope distributions from lacustrine carbonates provide insights into climate and hydrological change, but it is difficult to isolate the influences of catchment precipitation δ18O, water temperature, and evaporation on lacustrine carbonate δ18O values. Recent work shows the potential for using a combination of clumped (Δ47) and triple oxygen isotope (Δ′17O) measurements to identify the roles of temperature and evaporation on carbonate δ18O values in lakes, allowing precipitation δ18O values to be inferred and facilitating paleoclimate reconstructions. However, modern calibration of this approach has been mostly limited to arid regions with a high ratio of evaporative losses over inputs (XE) and low relative humidity (h<0.7). Developing this tool for paleoclimate and paleoelevation reconstructions requires expanding the modern calibrations to a greater range of climatic and hydrologic conditions. We sampled four lakes in different hydrologic states under a single, high humidity climate regime (h=0.7–0.9) in the Lake Junín region of central Peru. Clumped isotope temperatures from lake carbonates reflect water temperatures during carbonate formation. Lake hydrology is the main control on the Δ′17O values of carbonates and waters: Δ′17O values are lowest in the larger lakes with higher XE when compared to smaller, headwater lakes where evaporation is minimal and Δ′17O is indistinguishable from that of precipitation. Reconstructed unevaporated catchment precipitation δ′18O (δ′18Orucp) values from lake waters rely on accurate characterization of λlake, the triple oxygen isotope evaporation slope. We explore the influence of humidity on λlake using both new observations and modeled data. Accounting for local humidity improves λlake estimates, which allows for more accurate reconstructions of δ′18Orucp. We generate a δ′18Orucp value of −15.2±2.1‰ from modern carbonates and waters (n=15) in the Lake Junín region, which is similar to amount weighted mean annual precipitation −14.1 (±2.2‰). This study illustrates that (1) Δ′17O can be used to differentiate between lakes with differing XE in humid climates, (2) lake carbonate Δ′17O and δ18O values can be used to evaluate the influence of evaporation on lake water δ18O values in a range of climates, and (3) modeling λlake under appropriate humidity conditions improves δ′18Orucp estimates from lake carbonate Δ′17O.

Геохимическая активность снега и послойная изменчивость изотопного состава кислорода (δ18О) в снежной толще в условиях разной запыленности приземной атмосферы

The layered distribution of the isotopic composition (18O) in the snow mass under conditions of different dust pollution of the near-surface atmosphere was studied on the territory of two scientific test sites of the IAO SB RAS: the Fonovaya observatory and the suburban BEK test site (Tomsk). Interlayer differences in isotopic characteristics and the activity of snow chemical reactions were evaluated in conjunction with the analysis of the dispersed composition of the precipitated aerosol substance, the radiation transparency of snow in the UV range, and taking into account reverse trajectories of air mass transfer. Interlayer fluctuations in 18O values were established, the variability of which increased in layers confined to the thermal diffusion geochemical barrier. We suggested that due to the geochemical activity of snow and its ultraviolet transparency, as well as the presence of iron-containing dust-aerosol particles in the snow mass, conditions arose that initiated photoactivated snow-chemical reactions. Their occurrence may be accompanied by free radical oxidation of the precipitated aerosol matter and the formation of stable photoreaction products, which may be evidenced by the established post-sedimentary interlayer differences in the isotope stratification of the snow mass.

Using Stable Isotopes To Identify Spatial-Temporal control on Groundwater Recharge Between Lower Zab and Tigris River South of Al-Shirqat City-Iraq.

Stable hydrogen and oxygen isotopes were used as natural tracers to identify spatial-temporal control on groundwater wells recharge and basic physico-chemical parameters between lower Zab and Tigris river South of AlShirqat city-Iraq. the search aimed to study the relationships in isotope compositions to evaluate the source of groundwater recharge. Seven wells water samples were analyzed for stable isotopes for two periods, (dry and wet), 2021. There is a special and temporal variations in the distribution of δD and δ 18O values in the studied area, the δD values are distributed from -39.4 to -16.2 ‰, and from -42.2 to -18.14 ‰ in dry and wet periods, respectively, while the δ 18O values are distributed from -7 to -2.83 ‰, and from -7.26 to -3.08 ‰ in dry and wet periods, respectively. The data suggest that the groundwater is sourced mainly from local meteoric water line of Iraq (LMWL) with some interaction between lower Zab and Tigris river.

Oxygen Ablation during Atmospheric Entry: Its Influence on the Isotopic Composition of Micrometeorites

Micrometeorites (MMs) offer glimpses of the diverse nature of parent bodies that accreted during the first few million years after the formation of the proto-Sun. The present work explores this by evaluating the ablation of oxygen from MMs during atmospheric entry, and the resulting effect on the oxygen isotopic composition. A Chemical ABlation MODel (CABMOD) combined with the measured oxygen isotope composition of MMs, shows that at temperatures below 2000 K a relatively small percentage (∼0%–5%) of oxygen ablates; the temperature is nevertheless sufficient to induce diffusion among the different silicate phases of MMs. The large δ 18O composition found within different MM types with low oxygen ablation indicates that exchange with atmospheric oxygen is insignificant during entry. Therefore, to explain the large δ 18O values existing in heated MMs, where oxygen ablation is less than a few percent, we propose that these particles are from distinct C-type asteroids that have undergone nebular gas exchange and/or aqueously altered in their parent bodies. This is supported by the evidence from unmelted MMs that have not exchanged oxygen during atmospheric entry or undergone ablation, but have large δ 18O values. However, the oxygen isotope composition of different types of cosmic spherules does not appear to vary systematically with temperature and could be due to the heterogeneity of their precursors. This investigation overall provides insights into the oxygen ablation of the particles during atmospheric entry, oxygen isotopic alteration, and the reservoirs of the diverse extraterrestrial objects that prevailed in the early solar system.

Use of isotopes in examining precipitation patterns in north-central Ukraine

ABSTRACT North-central Ukraine is vulnerable to temperature increases and precipitation pattern changes associated with climate change. With water management becoming increasingly important, information on current water sources and moisture recycling is critically needed. Isotope ratios of oxygen (δ 18O) and hydrogen (δ 2H) in precipitation are sensitive to these variables and allow comparisons across the region. The δ 2H and δ 18O values from collected precipitation in Kyiv and Cherkasy in 2020 and published 3H data for Kyiv from the year 2000 show an influence of the North Atlantic Oscillation (NAO) and provide information about processes affecting precipitation along the storm trajectory. The δ 18O values also show a correlation with temperature, indicating that precipitation patterns may be affected by the rising temperatures in the region, as predicted by recent regional studies using Representative Concentration Pathway scenarios and the global climate model GFDL-ESM2M. When compared to backtracked storm trajectory and NAO data, clear relationships emerged between water isotope ratios, storm paths, and likely moisture recycling. Overall, δ 2H, δ 18O, 3H, and backtracked storm trajectory data provide more regional and local information on water vapour processes, improving climate-change-driven precipitation forecasts in Ukraine.

Происхождение цементолитов в верхнесилурийских лагунных отложениях Северного Урала

The Upper Silurian proximal lagoon deposits, widely developed in the Ilych River basin, were previously studied in detail. One of the surprising fabrics in them is large (up to 1.0 m in diameter) areas with zonal cements (cementstones), there are different points of view on their origin. The samples of these cementstones investigated by microscopic and isotopic methods, have a complex morphology characterized by horizontal and vertical element alterations. This internal texture is conditioned by centripetal zonal radial-fibrous calcite growth with thin layers of fine-grained dolomites. Most of the proposed interpretations (recrystallized stromatoporoids, stromatactis fabric, or methane spring cannels) were rejected because one or more cementstone features contradicted them. The paleokarst interpretation at least has no contradictions in all three characteristics considered: morphological, lithological, and geochemical. The 13C values of cementstones (and the host rocks at the boundary with them) vary within 0.9–1.95 ‰ (PDB), while the 18O values have narrower variations (25.51–25.88 ‰ SMOW in one case and 25.11–25.48 ‰ SMOW in the other case). In addition, these 18O values are higher than those in the host rocks.

Hydrogeochemical Characteristics of the Haiyuan-Liupanshan Seismic Belt at the Northeastern Edge of the Tibet Plateau

The hydrogeochemical characteristics and groundwater recharge environments along the deep-cut Haiyuan-Liupanshan fault zone (HLFZ) were investigated by major ion and isotopic compositions (δ18O and δD) of the water samples collected at 14 sites from 2016 to 2017. The Schukalev classification method, fuzzy membership function, the proportion coefficients of major ions and principal component analysis (PCA) were adopted to analysis the hydrogeochemistry, water quality, origins and controlling factors of groundwater. In terms of chemical types, the sites along HLFZ can be divided into two groups. Specifically, the Group 1 is in the north and west part of the HLFZ and the water samples are characterized by higher salinity and enriched in Na+ and SO42-, reflecting the control of evaporate dissolution in cretaceous and tertiary aquifers, reverse ionic exchange, stronger water-rock reaction and deep fluids. The higher concentrations of Ca2+ + Mg2+ and HCO3- were found in Group 2, which is located in the southeast of the HLFZ and may be attributed to carbonate weathering and the recharge of karst fissure water from ordovician dolomite and limestone. Contamination of groundwater in HLFZ is severe, with 78.6% of the sites classified as grade V, which means they cannot be used for drinking water or agriculture. The primary contaminants found in Group 1 are TDS, Na+, Cl- and SO42- and the exceedance in NO3-and pH value affect water quality in the Group 2. The 18O and δD values of groundwater in HLFZ indicated that meteoric water contributed dominantly to the groundwater and it was influenced by the water cycle and water-rock reaction. Furthermore, tectonic movement, seismicity, and the level of deformation along different segments of HLFZ are important factors in the migration of deep to shallow groundwater, and water-rock reactions during groundwater migration, which results in differences in chemical composition of the groundwater between Group 1 and Group 2. Most of the sites with higher TDS in HLFZ fall on the a higher stress state region (represented by a low b value&lt;0.75), which reflected a possible evidence of seismic activity affected the hydrogeochemistry of groundwater.

Flow Path of the Carbonate Geothermal Water in Xiong’an New Area, North China: Constraints From 14C Dating and H-O Isotopes

Studying the flow path of geothermal water in geothermal fields is an important basis for the scientific development and management of geothermal resources. However, due to the influence of engineering volume, economic benefits and demand, it is very difficult to fully grasp the flow path of deep geothermal water in large areas. The use of hydrogeochemical tracers to determine the flow path of geothermal water is a scientific and effective research method. In order to accurately describe the flow path of carbonate geothermal water in the Xiong’an New Area and its surrounding areas, this study systematically analyzed the 14C, 18O, and 2H data of carbonate and Cenozoic sandstone geothermal water, Quaternary groundwater, as well as mountain spring water of the study area. Based on these results, we can conclude that 1) The 14C, d, and 18O values are favourable clues for indicating the circulating runoff conditions and runoff paths of geothermal water. 2) The salinity of the Xushui-Wenan and Lilan transfer zone are &amp;lt;3 g/l, the 14C values are lower than 25000 years, the d value is higher, and the phenomenon of “18O drift” is weak, all these indicating the dominant flow path of carbonate geothermal water, featured by relative lower temperature. 3) The salinity of karst geothermal water in the southwest of Gaoyang low uplift, Rongcheng uplift and Niutuozhen uplift is &amp;gt; 3 g/l, the 14C values are higher than 40,000 years, the d value is lower, and the phenomenon of “18O drift” is obvious, all these indicating that the tectonic sites are the convergence areas of regional karst geothermal water, featured by relative high temperature. 4) The hydrochemical indicators combined with previous carbonate groundwater flow field indicate that the recharge of carbonate geothermal water in the Xiong’an New Area may not only drive from the western Taihang Mountains, but also along the Xushui-Wenan transfer zone and the Lilan fault, with the recharge of carbonate groundwater from the Cangxian uplift from east to west. By further identifying and defining the dominant flow path and supply direction of carbonate geothermal water in the Xiong’an New Area and surrounding areas, it provides strong support for the scientific development of regional carbonate geothermal water.

The role of thrust and strike-slip faults in controlling regional-scale paleofluid circulation in fold-and-thrust belts: Insights from the Jura Mountains (eastern France)

We combine structural and microstructural data with stable and clumped isotopes of syntectonic calcite veins or slickenfibers of five thrust and four strike-slip faults to characterize the paleofluid circulation in the Jura fold-and-thrust belt, eastern France. Syn-tectonic fluid circulation occurred along high permeability networks of breccias, foliated fault rocks, and discrete fault surfaces. At the regional scale, fluid circulation was dominated by cold meteoric fluids that infiltrated downward along both thrust and strike-slip faults, with various degrees of interaction with the carbonate host rocks. Fault-related mineralizations precipitated from fluids with δ⁠18O values between −0.8‰ and − 7.8‰ (V-SMOW) at temperatures between 8 °C and 54 °C. The δ⁠18O values of the paleofluids partly overlap those of modern meteoric waters of the region. The calcite mineralizations yielding the highest calculated δ⁠18O paleofluid values are also the warmest ones and those with the heaviest carbon isotope signal, indicating strong host rock buffering and fluid heating at depth. A contribution of deep fluids from Permo-Triassic rocks cannot be excluded, but not likely. This could be related to the presence of Middle Jurassic Opalinus Clay Formation, which acted as a regional low-permeability barrier in the sedimentary succession. This can create two different fluid circulation systems characterized by warm and partly basement-derived fluids and by cold meteoric fluids, respectively, below and above the Middle Jurassic Opalinus Clay Formation. Results from this study can be used for modeling fluid circulation at the regional scale in carbonate-dominant foreland fold-and-thrust belts elsewhere in the world.

Stable oxygen and hydrogen isotope ratios of the aufeis of the Viluy River valley

The object of the study is the isotope composition of three aufeis (icing) in the Viluy River basin. Two of the three tested icing were located in the wide valleys of the streams-tributaries of the Viluy River, one on the flat bottom of the thermosuffusion sinkholes. The areas of studied icings did not exceed 30 sq. m., their thickness ranges from 45 to 100 cm. Stratification is recorded in the icings. The co-isotope diagram &amp;#948;2H-&amp;#948;18O shows that icing ice was formed from spring water and generally is isotopically “lighter” compared to the water of Kysyl-Yurekh stream and Viluy River. The isotope composition of the icing ice varies in a very narrow range: a) for icing 1 &amp;#948;18O values vary from –19.3 to –20.9‰, &amp;#948;2H values vary from –156.5 to –162.9‰; b) for icing 2 &amp;#948;18O values vary from –19.7 to –22.4‰, &amp;#948;2H values vary from –153.2 to –173.1‰; c) for icing 3 &amp;#948;18O values vary from –19.8 to –22.7‰, &amp;#948;2H values vary from –162.9 to –181.3‰. The similarity of the isotope profiles of icing 2 on Viluy and icing IB93-5 on Baylot Island and isotope profiles of icing 3 on Viluy and icing F192-6 on Baylot Island was noted, however, the scale of isotopic variations for icings on Baylot Island are 5-6 times greater than that of Viluy icings.

Speleothem records of monsoon interannual-interdecadal variability through the Holocene

Modern observations show considerable interannual to interdecadal variability in monsoon precipitation. However, there are few reconstructions of variability at this timescale through the Holocene, and there is therefore less understanding of how changes in external forcing might have affected monsoon variability in the past. Here, we reconstruct the evolution of the amplitude of interannual to interdecadal variability (IADV) in the East Asian, Indian and South American monsoon regions through the Holocene using a global network of high-resolution speleothem oxygen isotope (δ 18O) records. We reconstruct changes in IADV for individual speleothem records using the standard deviation of δ 18O values in sliding time windows after correcting for the influence of confounding factors such as variable sampling resolution, growth rates and mean climate. We then create composites of IADV changes for each monsoon region. We show that there is an overall increase in δ 18O IADV in the Indian monsoon region through the Holocene, with an abrupt change to present-day variability at ∼2 ka. In the East Asian monsoon, there is an overall decrease in δ 18O IADV through the Holocene, with an abrupt shift also seen at ∼2 ka. The South American monsoon is characterised by large multi-centennial shifts in δ 18O IADV through the early and mid-Holocene, although there is no overall change in variability across the Holocene. Our regional IADV reconstructions are broadly reproduced by transient climate-model simulations of the last 6 000 years. These analyses indicate that there is no straightforward link between IADV and changes in mean precipitation, or between IADV and orbital forcing, at a regional scale.

Spatial distributions of oxygen and hydrogen isotopes in multi-level groundwater across South Korea: A case study of mountainous regions

This study presents the spatial distributions of stable isotopes for groundwater according to well depth and spring water across South Korea, using an interpolation model to provide baseline information for hydrological studies. In total, 888 groundwater and 108 spring water samples were collected across South Korea; their oxygen and hydrogen isotopic compositions (δ18O and δ2H) were analyzed. δ18O and δ2H values biased toward the summer local meteoric water line and low d-excess values indicate that summer precipitation is important for groundwater recharge. The δ18O and δ2H values for groundwater and spring water decrease progressively from the southwest to the northeast on the Korean Peninsula. Based on eight hydrological regions, the average δ18O values of groundwater and spring water are negatively correlated with latitude, but they are positively correlated with temperature. This result indicates that the spatial distributions of groundwater isotopic values in South Korea are significantly influenced by latitude and altitude effects associated with the movement of the North Pacific air mass in summer. Spring waters showed a negative correlation between δ18O and d-excess, with more depleted 18O values than groundwater, indicating that local recharge and flow within mountainous areas is dominant. Considering that the correlation in multi-level groundwater located in northern regions is similar to that of spring water, the contribution of regional groundwater flow, which is recharged in mountainous areas, is considered to be higher in the northern regions. The spatial distribution of δ18O in groundwater gradually approached the spatial distribution of spring water with increasing well depth, indicating that the contribution of regional groundwater flow may be greater in deep groundwater. Our results provide estimates for data-poor regions, supporting the investigation of links between groundwater and other hydrological factors.

Sediment hosted stratiform barite – (Cu-Zn-Pb) deposits in the southwest Mahabad, Iran; implications for geology, ore textural, compositional, and S-O isotopes geochemistry

The southwestern part of Mahabad town in the northwestern part of the Sanandaj-Sirjan metamorphic zone (SSZ) of Iran hosts seven barite-base metal deposits. They have occurred within the Precambrian-aged metasedimentary succession including black color fine-grained shale, slate, and phyllite with minor calcareous intercalation. This investigation is focused on three main ore deposits including Meraneh, Sorkhab, and Shekarbeig. The mineralized units and host rocks have been metamorphosed to lower greenschist facies in the Post-Cretaceous.Five different stages of mineralization were distinguished based on the field observations, mineralogical and textural relationships, morphology of the orebodies, and mineral chemistry studies. The followings are the stages of evolution: (1) precipitation of framboidal, colloform, and monomineralic pyrite bands and fine-grained barite (2) stratiform accumulation of barite with sulfide and un-mineralized sediment strata (3) stockwork mineralization and associated alteration (4) formation of discrete vent complex associated with massive sulfides and barite in replacement zone, and (5) post-mineralization deformation and shearing process, contemporaneous with regional metamorphism.Pyrite, chalcopyrite, sphalerite, and galena are the major sulfide minerals, in order of abundance, found in the studied deposits, accompanied by the minor amounts of tetrahedrite and covellite. The stratiform, massive and stockwork ores are indicative of the main ore-forming event and are volumetrically the most important facies. The electron probe micro-analyzer (EPMA) data of sulfide minerals indicates a distinct variation in trace element concentrations during the ore formation. Besides, this study focuses on distributions of δ 34S value in sulfide minerals, as well as δ 34S and δ 18O value of barite mineralization in stratiform, stratabound, and stockwork ore zones. The paragenetic relationships, mineral chemistry and isotopic study of minerals reveal that the stages 1 and 2 can be considered as the pre-date hydrothermal input of the stage 3 in all the three ore deposits. In addition, the mineralization event during stage 1 of the ore formation was found out to have occurred in a low temperature environment within the unconsolidated sediments, instantly under the sea floor. During stage 2, the stratiform ore has been deposited due to the diagenetic processes. The up-flow exhalative hydrothermal fluids resulted in the thermal alteration of the organic-rich host rock during stage 3, and formation of the massive mineralized bodies in stage 4. Finally, the lower greenschist facies metamorphism affected both the ore and host rocks during stage 5.On the basis of mineral chemistry inspections, all types of pyrites have high Ni and low Co contents and great majority of them show the Co:Ni ratios of lower than 1. Stratiform pyrites were fine-grained and enriched in As, Au, and Co, in contrast to hydrothermally pyrites. Ni, Pb, Zn, Bi, Hg, and Cu were mostly concentrated in coarse-grained hydrothermally pyrits. Also, the temperature and sulfur fugacity increased from stratiform stage to hydrothermal stage. The Se content of chalcopyrite as well as Bi and Ag contents of Galena increased from feeder to massive and stratiform ore. Sphalerite was generally iron-poor and its Fe content decreases from feeder to massive and stratiform ore. The Co/Ni ratio of pyrite and Zn/Cd ratio of sphalerite can be used to discriminate the VMS, magmatic or SEDEX origins for ore deposits. The Zn/Cd ratio of the sphalerites and Co/Ni ratio of pyrites provided the evidence for SEDEX style mineralization in the studied deposits.Barites with various textures and morphologies show overlapped distributions of δ34S and δ18O values from the stages 2, 3, and 4, range from + 34.1 to + 41.3‰ and + 10.2 to + 12.6‰, respectively. The d34S versus d18O patterns for the stratiform barite resemble the patterns that indicate sulfate is consumed by AOM. Sulfides have different isotopic compositions: stratiform with markedly more positive δ 34S values of + 28‰ to + 33‰; stockwork with δ 34S values of + 8‰ to + 26‰; and massive pyrite with δ 34S between + 8‰ and + 26‰. We suggest that the isotopic relationships (δ34S pyrite ≈ δ34S barite) in the stratiform ore zones may be related to anaerobic oxidation of methane coupled to sulfate reduction (AOM-SR), which has been developed during open system diagenesis. Textural and isotopic evidence indicates that the stockwork and massive ores has grown by thermochemical sulfate reduction (TSR) and reductively dissolving barite. On the other hand, the trend between d18O and δ34S suggest that the growth of the stockwork and massive barite is related to fluid seep on modern continental margins. Textural evidence documented during the different mineralization stages together with concentration and the distribution pattern of trace elements and isotopic investigation in the stratiform, massive, and stockwork ore zones signify that the SEDEX-type mineralization has been occurred in this district.

The triple oxygen isotope composition of phytoliths, a new proxy of atmospheric relative humidity: controls of soil water isotope composition, temperature, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration and relative humidity

Abstract. Continental atmospheric relative humidity is a major climate parameter whose variability is poorly understood by global climate models. Models' improvement relies on model–data comparisons for past periods. However, there are no truly quantitative indicators of relative humidity for the pre-instrumental period. Previous studies highlighted a quantitative relationship between the triple oxygen isotope composition of phytoliths, particularly the 17O excess of phytoliths, and atmospheric relative humidity. Here, as part of a series of calibrations, we examine the respective controls of soil water isotope composition, temperature, CO2 concentration and relative humidity on phytolith 17O excess. For that purpose, the grass species Festuca arundinacea was grown in growth chambers where these parameters were varying. The setup was designed to control the evolution of the triple oxygen isotope composition of phytoliths and all the water compartments of the soil–plant–atmosphere continuum. Different analytical techniques (cavity ring-down spectroscopy and isotope ratio mass spectrometry) were used to analyze water and silica. An inter-laboratory comparison allowed to strengthen the isotope data matching. Water and phytolith isotope compositions were compared to previous datasets obtained from growth chamber and natural tropical sites. The results show that the δ′18O value of the source water governs the starting point from which the triple oxygen isotope composition of leaf water, phytolith-forming water and phytoliths evolves. However, since the 17O excess varies little in the growth chamber and natural source waters, this has no impact on the strong relative humidity dependency of the 17O excess of phytoliths, demonstrated for the 40 %–80% relative humidity range. This relative humidity dependency is not impacted by changes in air temperature or CO2 concentration either. A relative humidity proxy equation is proposed. Each per meg of change in phytolith 17O excess reflects a change in atmospheric relative humidity of ca. 0.2 %. The ±15 per meg reproducibility on the measurement of phytolith 17O excess corresponds to a ±3.6 % precision on the reconstructed relative humidity. The low sensitivity of phytolith 17O excess to climate parameters other than relative humidity makes it particularly suitable for quantitative reconstructions of continental relative humidity changes in the past.

Preparation of high-precision CO2 with known triple oxygen isotope for oxygen isotope analysis

ABSTRACT The objective of this work is to propose a more effective way to prepare an in-house CO2 with known triple oxygen isotope compositions. The major experimental steps include: (1) the O2 is combusted to CO2 on a graphite rod at 750 °C with Pt-catalyst for 3–4 min; and (2) converted CO2 is subsequently purified by two cryogenic traps. The results show high reproducibility of δ 13C and δ 18O values of the converted CO2 within 0.010–0.020 ‰ and 0.006–0.010 ‰ (1σ, SD), and the identical δ 18O value within error with that of the original O2. Additionally, we have measured the triple oxygen isotope compositions of converted CO2 using an O2–CO2 Pt-catalyzed oxygen-isotope equilibration method. The measured δ 17O values of CO2 show high reproducibility within 0.006 ‰ (1σ, SD), and are identical within error with the original O2 as well. Notably, our experiments also found that the O2 with heavier oxygen isotope ratios (δ 18O > 40 ‰, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O2 to CO and CO to CO2, may explain the observed lower 17O/16O and 18O/16O ratios of the converted CO2 relative to the original O2.

Hydrochemistry and environmental isotopes (18O, 2H, 3H, 3He/4He) of groundwater and floodwater in the great area of Hurghada, Eastern Desert of Egypt

Porous and fractured aquifers exist in the area of Hurghada, Eastern Desert of Egypt, whose recharge processes through the common flash floods are not identified. Hydrochemical parameters, stable isotopes 18O, 2H and tritium in floodwater and groundwater were applied in the area subject to study. Additionally, He isotopes were investigated in the deep wells in the faulted zone at the Abu Shaar Plateau. 3H activity in all sampled points lies below the detection limit excluding a recent recharge component in groundwater. However, the hydrochemical ratios and the stable isotope signature confirm that the shallow wells and springs (Red Sea Hills group) are being recharged from modern precipitation. The hydrochemical parameters of the deep wells at the Abu Shaar Plateau (coastal plain group) confirm another origin for the ions rather than the modern precipitation. Together with the 18O and 2H values, the Br/Cl ratio of this group confirms the absence of seawater intrusion component and the role of the fault as a hydraulic barrier. These 18O and 2H values deviate from the GMWL confirming an evaporation effect and colder infiltration conditions and reveal strongly a possible mixing with the Nubian Sandstone in the region. The 3He/4He ratio confirms a mantle contribution of 2% from the total He components.

Seasonality of precipitation recorded in a modern (1907–2008) annually laminated stalagmite from central China

Seasonality of precipitation in the Asian monsoon region has significant impacts on social and economic development. Here, we analyzed a seasonally resolved δ18O series of an annually laminated stalagmite from Xianglong Cave to assess its potential as a proxy for seasonal precipitation. The δ18O values reveal fabric-correlated annual cycles, with lower δ18O values occurring in the white porous layer (WPL) during summer monsoon (SM) season, whereas higher values occurring in the dark compacted layer (DCL) during non-summer monsoon (NSM) season. We calculated the seasonal amplitude of δ18O (∆18O) using the highest value minus the lowest value in an annual cycle. Comparisons suggest that the ∆18O series can record precipitation seasonality, with lower ∆18O values corresponding to increased SM/NSM rainfall ratios and higher values corresponding to reduced SM/NSM rainfall ratios. Our reconstruction suggests increased precipitation seasonality contrast (i.e., increasing SM/NSM rainfall ratio with more SM rainfall and/or less NSM rainfall) during 1914–1919, 1935–1942, 1958–1962, 1979–1985, and 1999–2005 (A.D.), with a probably 27-year cycle. The seasonality of precipitation in central China correlates well with the Pacific Decadal Oscillation (PDO) on a decadal scale. Increased SM/NSM rainfall ratio was observed during the warm phase of PDO, and decreased SM/NSM rainfall ratio was observed during the cold phase of PDO.