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We introduce a new isotope chronological model in which the natural mass-dependent isotopic fractionation effects of the radioactive (“parent”) and radiogenic (“daughter”) elements are systematically and rigorously considered. Using this model, we show that internally-normalized radiogenic isotopic ratios, commonly determined for daughter elements such as Sr, Nd, Cr, Ni, Hf, W, and Os, are dependent on the extent of natural isotopic fractionation of the daughter and parent elements at the time of system closure. This dependence indicates that (1) in two samples derived from the same isotopically homogeneous source at the same time and with identical radiogenic ingrowth over time, the present-day internally-normalized radiogenic isotope ratios would be different if they were initially fractionated to different degrees, and (2) if different internally-normalized radiogenic isotopic ratios are observed for two co-genetic objects, the difference between them would include contributions from both radiogenic ingrowth and natural isotopic fractionation. Consequently, the isochron dating equations employed in traditional chronological studies will yield inaccurate results when significant natural isotopic fractionation is present among the studied samples. Modified isochron equations that can be used to retrieve correct chronological information from isotopically-fractionated samples are presented. These theoretical considerations are applied to the 87Rb–87Sr, 147Sm–143Nd, and 146Sm–142Nd isotope systems of calcium–aluminium-rich inclusions (CAIs), a set of samples that have undergone significant natural Sr, Nd, and Sm isotope fractionation during their formation. The large natural Sr isotope fractionation (up to ca. 5.3 ‰ for 88Sr/86Sr) in fine-grained CAIs can generate analytically well-resolvable biases (>120 ppm) in the internally-normalized 87Sr/86Sr ratios and lead to significant scatters of their 87Rb–87Sr isochron (in conjunction with scatters induced by open-system disturbances). The 87Rb–87Sr systems of coarse-grained CAIs, on the contrary, are essentially not affected by natural Sr isotopic fractionation due to their much subdued fractionation degrees, resulting in a more robust isochron. Similarly, the large natural Nd (up to ca. 4.0 ‰ for 146Nd/144Nd) and Sm (up to ca. 7.1 ‰ for 152Sm/148Sm) isotopic fractionation in fine-grained CAIs can induce significant scatters of the 147Sm–143Nd isochron if the natural fractionation followed the kinetic or power law, and 146Sm–142Nd isochron if the natural fractionation followed the equilibrium, Rayleigh, or power law. This implies that when studying radioactive isotope systems in objects whose daughter and parent elements can undergo significant isotope fractionation in nature, accompanying stable isotope analyses are necessary for accurate chronological interpretations.

As a potential renewable and clean energy source, the distribution and exploration prospects of natural hydrogen have garnered widespread attention. However, the limitations in understanding the formation mechanisms and accumulation patterns of underground natural hydrogen have significantly constrained its efficient exploration and utilization. This study reports H2 content and isotopes in natural gas from deep formations in sedimentary basins through geochemical analysis of 58 conventional gas samples from the Sinian to Triassic strata in the central Sichuan Basin. We discovered that H2 content in deep natural gas in central Sichuan generally exceeds 0.1%, with a maximum of 1.6%, and hydrogen isotopes ( δ 2 H H 2 ) range from −850‰ to −586‰. Analysis of the geological conditions, hydrogen generation mechanisms, and isotope fractionation characteristics in the study area confirms that microbial fermentation or in-situ organic matter cracking are not effective pathways for deep H2 generation. Combined with helium content and isotope analysis of the natural gas, it is inferred that the volcanic basement in the central Sichuan area is the potential source rock for natural H2 in the Sinian to Triassic strata. Specifically, H2 originates from the radiolysis of water and hydrothermal reactions of Fe(II) in the basement granite. Additionally, a diffusion fractionation model reveals significant isotope fractionation during the migration and accumulation of deep H2 into sedimentary reservoirs, which lead to anomalously light δ 2 H H 2 in deep natural gas in central Sichuan. This indicates that the underground natural hydrogen accumulation is in a long-term dynamic process, with simultaneous H2 accumulation and dissipation in the gas reservoirs. This research not only elucidates the formation mechanism of deep H2 but also provides insights for the resource potential of natural hydrogen in sedimentary basins. [ABSTRACT FROM AUTHOR]

The large molybdenum (Mo) isotope fractionation from seawater is caused by the adsorption of Mo on manganese oxides. However, the effects of the manganese oxide mineralogy (crystal structure) and surface Mo coverage on Mo isotope fractionation have not been investigated. In this study, the isotope fractionation of Mo by adsorption on synthetic todorokite, birnessite, and δMnO2 was investigated under a wide range of surface Mo coverages. The Mo isotope fractionation changed from Δ98/95Mo = 2.18 ± 0.05‰ to 2.61 ± 0.06‰ for todorokite; from 1.25 ± 0.05‰ to 2.10 ± 0.05‰ for birnessite; and from 2.19 ± 0.07‰ to 2.73 ± 0.08‰ for δMnO2. The Mo isotope fractionations of the three manganese oxides were negatively correlated with surface coverage normalized to the specific surface area. The independence of the obtained correlation of the manganese oxide species indicates that the Mo isotope fractionation depends on the surface coverage but not on the mineralogy of the manganese oxides. The experimentally observed Mo isotope fractionation (<2.7‰) in manganese oxides generally underestimates the isotope fractionation in natural ferromanganese oxides (~3‰). According to the dependency of the Mo isotope fractionation on the surface coverage, the underestimation relative to previous experimental studies can be attributed to the lower Mo surface coverage of natural ferromanganese oxides. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top‐canopy twigs and breast‐height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra‐seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C‐enriched C‐1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water‐soluble carbohydrates, possibly caused by discrimination against 18O during O2‐based diterpene oxidation and 35%–50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within‐tree and among‐tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long‐term proxy for physiological and environmental changes. Summary Statement: We studied the poorly understood intra‐seasonal dynamics of resin δ13C and δ18O. We found that resin δ13C was c. 2‰ lower than sucrose δ13C, while resin δ18O was c. 20‰ higher than xylem water δ18O in mature Pinus sylvestris. Both resin δ13C and δ18O recorded a signal of soil water potential. [ABSTRACT FROM AUTHOR]

• A two-stage condensation process governs the behavior of Cd/Pb during coal combustion. • The distribution of Cd isotopes is significantly influenced by the particle size. • The power plant exerts a significant impact on remote regions in the downwind directions. • The vertical variation in soil Pb respond to the historical evolution of dust removal. Coal power plants annually generate quantities of byproducts that release environmentally hazardous heavy metals like Cd and Pb. Understanding the behavior and spatiotemporal impacts on soils of these releases is crucial for pollution control. This study investigated the concentrations and isotope ratios of Cd/Pb in combustion byproducts, depositions and soils collected from a coal-fired power plant or its surrounding area. The pulverized fuel ash (PFA) and desulfurized gypsum (DG) exhibited heavier Cd isotopes with Δ114Cd values of 0.304‰ and 0.269‰, respectively, while bottom ash (BA) showed lighter Cd isotopes (Δ114Cd BA-coal = –0.078‰), compared to feed coal. We proposed a two-stage condensation process that governs the distribution of Cd/Pb, including accumulation on PFA and DG within electrostatic precipitators and desulfurization unit, as well as condensation onto fine particles upon release from the stack. Emissions from combustion and large-scale transport make a significant contribution to deposition, while the dispersion of Cd/Pb in deposition is primarily influenced by the prevailing wind patterns. However, the distribution of Cd/Pb in soils not only exhibit predominant wind control but is also potentially influenced by the resuspension of long-term storage byproducts. The power plant significantly contributes to soil in the NW–N–NE directions, even at a considerable distance (66%–79%), demonstrating its pervasive impact on remote regions along these orientations. Additionally, based on the vertical behavior in the profile, we have identified that Cd tends to migrate downward through leaching, while variations in Pb respond to the historical progression of dust removal. [Display omitted] [ABSTRACT FROM AUTHOR]

The magnitude and spatial variability of CO2 surface emissions and processes involving CO2 released to the atmosphere from the soils are relevant issues in the context of climate change. This work evaluated CO2 fluxes and 13C/12C ratio of vegetation, organic matter, and soil gases from no disturbed soils of Chaco Pampean Plain (Argentina) with different soil properties and environmental conditions (PL and PA units). Soil organic decomposition from individual layers was accompanied by δ13C of total organic carbon (δ13C-TOC) values more enriched to depth. δ13C-TOC values in the upper soil profile ~ ca. 0–15 cm were like the plant community of this area (~−33 to −29 ‰) while δ13C-TOC varied stronger bellow horizon A, till ~ −24‰. Both δ13C-TOC and soil δ13C-CO2 were similar (~ −24 to 26 ‰) at deeper horizons (~ 50–60 cm). Toward the superficial layers, δ13C-TOC and δ13C-CO2 showed more differences (till ~ 4 ‰), due influence of the diffusion process. Horizon A layer (~ 0–20 cm) from both PL and PA units contained the most enriched δ13C-CO2 values (~ −15–17 ‰) because atmospheric CO2 permeated the soil air. A simple two-component mixing model between sources (atmospheric δ13C-CO2 and soil CO2) confirmed that process. Isotopically, CO2 fluxes reflected the biodegradation of C3 plants (source), diffusive transport, and CO2 exchange (atmosphere/soil). Soil moisture content appeared as a determining factor in the diffusion process and the magnitude of CO2 surface emissions (12–60 g·m−2·d−1). That condition was confirmed by CO2 diffusion coefficients estimated by air-filled porosity parameters and soil radon gradient model. [ABSTRACT FROM AUTHOR]

Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions. Plain Language Summary: Carbon dioxide is emitted into the atmosphere when sedimentary rocks containing ancient organic carbon are exposed to oxygen. This process, referred to as oxidative weathering, is an important part of the global carbon cycle that may play a vital role in climate change over geological timescales. In this study, we have investigated whether it is possible to use the isotope composition of rhenium metal as a proxy for this oxidation process since rhenium is liberated from rocks alongside organic carbon. Our findings show that the rhenium removed from rocks during weathering has an isotopic fingerprint that is linked to the degree of weathering—and thus presumably to the extent of carbon oxidation. There are several important features of rhenium isotope behavior that are still underconstrained, not least where Re resides in organic rich rocks, but our findings nonetheless advance an emerging approach to reconstructing the ancient carbon cycle. Key Points: Oxidative weathering removes isotopically heavy rhenium from organic‐rich sedimentary rocksThe isotopic composition of weathered rhenium changes with weathering intensityRhenium isotopes may trace variations in oxidative weathering intensity, and hence, oxidative CO2 emission fluxes in the Earth's ancient past [ABSTRACT FROM AUTHOR]

The Yan'an gas field in the Ordos Basin is a typical deep coalbed methane field with tremendous resource potential. Evaluation methods for gas content in deep coal seams are urgently required to be established. This study is aimed at quantitatively analyzing the gas content of coalbed methane in deep coalbed methane reservoirs and revealing its influencing factors. With the coal rock samples of typical deep coalbed methane wells in the Yan'an gas field of the Ordos Basin as the research objects, the gas-bearing characteristics of deep coal rocks were analyzed, and the main controlling factors of gas-bearing properties were explored. The research results indicate that (1) the deep coal seams in the Yan'an gas field have a considerable thickness, a high total organic carbon content, and the potential of pyrolysis hydrocarbon generation is generally elevated, presenting excellent hydrocarbon generation potential. (2) Various types of pores and fractures in the deep coal rocks of the Yan'an gas field are well-developed, providing a favorable preservation space and migration channel for deep coalbed methane. (3) The total gas content of on-site analysis of deep coalbed methane in the Yan'an gas field is relatively high, mainly existing in the form of free gas, and has significant exploration and development potential. (4) The gas content of deep coal rocks in the Yan'an gas field is jointly controlled by multiple factors such as the total organic carbon content, minerals, and pore structure. In conclusion, the deep coal seams in the Yan'an gas field have favorable reservoir-forming conditions and great exploration and development potential. [ABSTRACT FROM AUTHOR]

Excessive dense nonaqueous phase liquids (DNAPLs) in subsurface aquifers posed a threat to human health and sustainable development of groundwater resources. Accurately identifying the sources of DNAPLs is crucial for groundwater remediation and prevention efforts. In the previous studies, significant advances were made in using isotope techniques for identifying DNAPLs in groundwater. In this paper, we provide a comprehensive overview of the commonly used isotopic tools applied to source identification. This overview will outline the advantages and limitations of the isotope technique and describe the needs for future research. Isotope tracing techniques are based on the unique isotopic characteristics of DNAPLs from different sources, enabling the identification and differentiation of DNAPL sources. The δ13C and δ37Cl values are most commonly used for identifying DNAPLs in groundwater. In field applications, however, the differences in isotopic characteristics from diverse sources can be weakened after undergoing a series of human and natural factors, which can affect the accuracy of source identification. To improve the accuracy of DNAPL source identification, a dual-isotope tracing approach seems the best available solution. Nonetheless, in the face of complex polluted environments, the dual-isotope method seems stretched. Therefore, further researches remain to be carried out to accurately and efficiently assess the sources of DNAPLs in groundwater and their individual contributions. This is a prerequisite for groundwater resource conservation and remediation efforts. [ABSTRACT FROM AUTHOR]

The study of mixed natural gas can clarify the specific sources of natural gas accumulation and provide the basis for the exploitation of natural gas resources. Analysis of gas compositions and carbon isotopic ratios of different components of mixed natural gas shows that the carbon isotopic fractionation of methane and ethane from different sources has a small difference after mixing. This conclusion is derived from the experimental data in Table 1, 0.88 is the average of all Ro values. Well DN8 and DN9 produced light oil with a density between 0.75 and 0.82 g/cm3 and viscosity between 1.63 and 3.3 MPa. Generally, in the high maturity stage of organic matter, the carbon isotopic fractionation values of methane and ethane of natural gas from a single source should display a difference of at least 4.0% to 5.0%. The δ13C value of methane and ethane in well DN8 are only 1.6%. It is considered that the mixing of natural gas from different sources causes this phenomenon. [ABSTRACT FROM AUTHOR]

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Nitrogen isotope analyses of amino acids (δ15N‐AA) are being increasingly used to decipher trophic dynamics. Interpretation of δ15N‐AA in consumers relies on the assumption that consumer physiological status and nutritional status of prey have negligible influences on the trophic discrimination factor (TDF), hence a constant TDF value is used in trophic position (TP) equations. Recent experiments have shown that this is not always the case and there is also a need to validate derived TP estimates in the field. We take advantage of the uniquely long time series of environmental monitoring data and archived (frozen) samples from the species‐poor Baltic Sea. We analyzed δ15N‐AA in similar sized individuals of cod and in its prey herring from four decades, 1980–2018; including time periods where dramatic reduction in condition status of cod has occurred. We expected that TDF in trophic AAs would increase during periods of poor cod condition, resulting in inflated TP estimates. We found that calculated TP and empirical estimates of TDF (difference in δ15N in trophic AAs between cod and herring) for cod increased in recent decades and that this was linked to condition status, herring (prey) lipid content and the hypoxic state of the ecosystem. Statistically adjusting TP for condition and prey lipid content as well as environmental stress (hypoxia) resulted in lower cod TP which better resembled the observed decrease in herring TP in recent decades. TP calculated from stomach analysis data in cod individuals over the same period showed no trend over time and confirmed that adjusted TP estimates mirror the real dietary TP better than unadjusted. By simultaneously measuring condition/nutritional status in both predator and prey it is possible to adjust for them as confounding variables and decipher actual consumer TP, partly overcoming the issues of unknown and variable TDF‐values. Our study also highlights the importance of including environmental stressors (here hypoxia) when interpreting TP and reconstructing food webs. [ABSTRACT FROM AUTHOR]

Abstract Oxidative weathering of organic carbon in sedimentary rocks is a major source of CO2 to the atmosphere over geological timescales, but the size of this emission pathway in Earth's past has not been directly quantified due to a lack of available proxy approaches. We have measured the rhenium isotope composition of organic‐rich rocks sampled from unweathered drill cores and weathered outcrops in south Texas, whose stratigraphic successions can be tightly correlated. Oxidative weathering of more than 90% of the organic carbon and ∼85% of the rhenium is accompanied by a shift to lower rhenium isotope compositions in the weathered outcrops. The calculated isotope composition of rhenium weathered from the initial bedrock for individual samples varies systematically by ∼0.7‰ with different fractions of rhenium loss. This variation can be empirically modeled with isotope fractionation factors of α = 1.0002–1.0008. Our results indicate that the isotope composition of rhenium delivered to the oceans can be altered by weathering intensity of rock organic matter and that the rhenium isotope composition of seawater is sensitive to past oxidative weathering and associated CO2 emissions.

Isotope technology is an ideal tool for tracing the sources of certain pollutants or providing insights into environmental processes. In recent years, the advent of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has enabled the precise measurement of various metal stable isotopes. Due to the presence of ''fingerprint'' properties in various environmental samples, metal stable isotopes have been applied to distinguish the source of contaminants effectively and further understand the corresponding environmental processes. The environmental fate of metal elements is strongly controlled by adsorption, an essential process for the distribution of elements between the dissolved and particulate phases. The adsorption of metal elements on mineral and organic surfaces significantly affects their biogeochemical cycles in the environment. Therefore, it is crucial to elucidate the fractionation characteristics of stable metal isotopes during the adsorption process. In this review, three typical transitional metal elements were selected, considering Mo as the representative of anionic species and Fe and Zn as the representative of cationic species. For Mo, the heavier Mo isotope is preferentially adsorbed in the solution phase, pH has a more significant influence on isotope fractionation, and temperature and ionic strength are relatively insensitive. Differences in coordination environments between dissolved and adsorbed Mo during adsorption, i.e., attachment mode (inner- or outer-sphere) or molecular symmetry (e.g., coordination number and magnitude of distortion), are likely responsible for isotopic fractionation. For Fe, The study of equilibrium/kinetic Fe isotopic fractionation in aqueous Fe(II)-mineral is not simple. The interaction between aqueous Fe(II) and Fe (hydroxyl) oxides is complex and dynamic. The isotope effect is due to coupled electron and atom exchange between adsorbed Fe(II), aqueous Fe(II), and reactive Fe(III) on the surface of Fe (hydroxyl) oxide. For Zn, the heavier Fe isotope preferentially adsorbs on the solid phase, and pH and ionic strength are essential influencing factors. The difference in coordination environment may be the cause of isotope fractionation.

The Yan’an gas field in the Ordos Basin is a typical deep coalbed methane field with tremendous resource potential. Evaluation methods for gas content in deep coal seams are urgently required to be established. This study is aimed at quantitatively analyzing the gas content of coalbed methane in deep coalbed methane reservoirs and revealing its influencing factors. With the coal rock samples of typical deep coalbed methane wells in the Yan’an gas field of the Ordos Basin as the research objects, the gas-bearing characteristics of deep coal rocks were analyzed, and the main controlling factors of gas-bearing properties were explored. The research results indicate that (1) the deep coal seams in the Yan’an gas field have a considerable thickness, a high total organic carbon content, and the potential of pyrolysis hydrocarbon generation is generally elevated, presenting excellent hydrocarbon generation potential. (2) Various types of pores and fractures in the deep coal rocks of the Yan’an gas field are well-developed, providing a favorable preservation space and migration channel for deep coalbed methane. (3) The total gas content of on-site analysis of deep coalbed methane in the Yan’an gas field is relatively high, mainly existing in the form of free gas, and has significant exploration and development potential. (4) The gas content of deep coal rocks in the Yan’an gas field is jointly controlled by multiple factors such as the total organic carbon content, minerals, and pore structure. In conclusion, the deep coal seams in the Yan’an gas field have favorable reservoir-forming conditions and great exploration and development potential.

Potassium (K) isotopic compositions for a suite of crustal rocks (plutonic unit, sheeted dike complex, and volcanic sequence) in the Troodos ophiolite, Cyprus, were determined to investigate fluid-transport processes during subduction inception. The gabbros and plagiogranites in the plutonic unit have restricted K isotopic compositions (0.01–0.20 ‰ and −0.17 to 0.02 ‰, respectively), whereas diabases in the sheeted dike complex have variable δ41K values from −0.24 to 1.13 ‰. The δ41K values of the volcanic sequence range from −0.26 to −0.07 ‰ in the lower pillow lavas, and from −0.71 to 0.34 ‰ in the upper pillow lavas. These δ41K values are clearly distinct from those of subducting sediments and altered oceanic crust, ruling out direct crustal input as the cause of the unusually heavy K isotopic compositions. Rather, the high K/Th, K/U, and Sr/Th ratios of the investigated samples, together with binary mixing modelling, reveal that the anomalously heavy K isotopic compositions in Troodos rocks are attributed to the influx of fluids during subduction inception. Notably, the δ41K values in the crustal rocks of the Troodos ophiolite are more variable and extend to higher values than those of arc-front and rear-arc lavas of the Izu arc and arc lavas of Martinique in the Lesser Antilles, indicating continuous K isotope fractionation during slab dehydration. Thus, the heavy K isotopic compositions of the Troodos ophiolite reflect K isotope fractionation during dehydration of a shallow slab within a newly formed subduction system, where heavy K isotopes preferentially enter into the aqueous fluids. Later, progressive breakdown of K-bearing phases at deeper levels results in isotopically lighter hydrous melts, which can be delivered to the arc. [ABSTRACT FROM AUTHOR]

Marine carbonates record geochemical information on the state of Earth's surface environment in the geological past, but recrystallization during burial can make the records difficult to interpret. Here, we report shore to basin gradients in δ44Ca values in matrix limestone and burrow dolomite across a sequence of Late Ordovician (Katian Stage) burrow-mottled carbonates in the Williston Basin, an intracratonic epeiric marine basin in North America. Both gradients are interpreted to have diagenetic origins. The gradient in limestone δ44Ca values developed in a bathymetrically controlled sediment- to fluid-buffered diagenetic system operating between the center and the edges of the basin. Two dolomitizing events formed the gradient in dolomite δ44Ca values. The sediment-buffered end of the limestone gradient preserves the δ44Ca value of the original carbonate mud (∼–1.28 ± 0.10 ‰). The fluid-buffered end of the gradient conserves the δ44Ca value of contemporaneous seawater (–0.47 ± 0.10 ‰), because: (1) pore water exchange drivers operated with greater variety and intensity in shallow water settings, (2) shallow nearshore deposits exchanged more Ca with seawater during recrystallization to diagenetic calcite than deeper offshore deposits, and (3) diagenetic calcite formed with negligible fractionation under equilibrium conditions. The gradient conserves the local value of Δ sed (–0.81 ± 0.20 ‰) despite its diagenetic origin, and the magnitude of Δ sed is consistent with primary calcite precipitation in a 'calcite sea'. Field assessment of the equilibrium Ca isotope fractionation factor between calcite and dolomite of –0.41 ± 0.17 ‰ at ambient temperature is applied to correct basin-centered dolomite for fractionation, yielding –1.62 ± 0.27 ‰, which is very different from the –0.25 ± 0.07 ‰ value of Ca in evaporatively concentrated seawater from which the dolomite originally formed. Applying the same fractionation factor to correct literature data on early diagenetic dolomite in the Great Basin, North America, yields –0.69 ± 0.22 ‰ for the δ44Ca value of seawater, which is ∼0.2 ‰ lower than 'normal marine' waters in stratigraphically equivalent deposits in the Willison Basin, and 0.44 ‰ lower than evaporatively concentrated seawater during a brief period of basin restriction and anhydrite deposition. The nearly 0.5 ‰ variation in the δ44Ca value of Katian seawater falls within the range of scatter in the brachiopod reconstruction of seawater Ca isotopes. Here, we propose that the true ocean record of secular change lies towards the bottom of the range of scatter, and that the higher values in the record reflect local Ca cycling and circulation restriction in epeiric seas. Epeiric seas cultivate the fluid-buffered diagenetic conditions required to promote Ca isotope exchange between reactive carbonate sediments and seawater through carbonate mineral dissolution/recrystallization, crystal coarsening by way of Ostwald ripening, and replacive dolomitization. It is not the apportioning of kinetically fractionated aragonite and calcite in the carbonate deposition flux that drove secular changes in global value of Δ sed between 'calcite' and 'aragonite' seas, but rather the replacement of kinetic fractionations with equilibrium fractionations during fluid-buffered diagenesis with seawater. [ABSTRACT FROM AUTHOR]

Isotope technology is widely used in geochemical mechanisms analysis; however, studies on the origin of pit lake water by isotopes in coal concentration areas in grassland are rare. In this study, 20 groups of water samples were collected, which were subjected to chemical analysis to determine the hydrogeochemical characteristics of pit lake water. The mechanisms of pit lake water formation and recharge–evaporation were ascertained through principal component analysis and the Rayleigh fractionation model. The results indicate that the phreatic water is least affected by evaporation, followed by confined water, surface water and pit lake water. The ionic composition of surface water, phreatic water and most of the confined water is mainly affected by leaching, some confined water can be recharged by surface or phreatic water; while the ionic composition of pit lake water is dominantly affected by evaporation (69.4 %) and is less affected by groundwater recharge (17.1 %) and human activities (11.5 %). The pit lake water is recharged by precipitation, phreatic water and the lateral runoff of confined water; however, the proportion of phreatic and confined water recharge is small. The evaporative loss of the pit lake water is 40–61 % of the initial water body. [ABSTRACT FROM AUTHOR]

Agricultural run‐off exposes recipient water bodies to nitrate (NO3−) pollution. Biological denitrification is a suitable method for removing NO3− in water resources that can be induced by the use of industrial organic liquid waste as an electron donor source. In light of this, batch and column laboratory experiments were performed to assess the potential of two industrial wine residues (lías and vínico) to induce biological denitrification of NO3− contaminated water from a constructed wetland and to evaluate the efficiency of these treatments using chemical and isotopic tools. In batch experiments (performed at a C/N ratio of 1.25), vínico was not efficient enough in removing N species, attenuating only 35% NO3− and was not used in column experiments. In similar experimental conditions, lías completely removed N species from water in both batch and column experiments. The calculated isotope fractionation (ε15NNO3 and ε18ONO3) was the same in both batch and column experiments biostimulated with lías and differed from those for vínico. The isotopic data confirmed that denitrification was the principal NO3− attenuation pathway in all the experiments. The isotopic fractionation can be later applied to field studies to quantify the efficiency of biologically enhanced denitrification. A numerical geochemical model that accounts for the changes in nitrate, nitrite concentration and isotopic composition due to the degradation of lías and vínico, including transport in the case of the column experiment, was performed to simulate the experimental results and can be up‐scaled in field treatments. Plain Language Summary: Groundwater nitrate pollution is a significant global concern resulting from excessive fertilizer use in agriculture. This pollution poses health risks to humans and ecosystems by contaminating drinking water supplies and aquatic ecosystems. Sustainable remediation of nitrate is necessary to safeguard human health and the environment. Successful field‐scale remediation requires laboratory feasibility studies to find the appropriate compounds to reduce nitrate (electron donors) and the best application measures to remove nitrate at a minimum cost. In our research, laboratory experiments were carried out using two industrial wine wastes as electron donors to evaluate their potential to remove nitrate from nitrate‐polluted water. Chemical, isotopic, and numerical modeling tools have been used to quantify the amount of nitrate removed. The results indicate that one product successfully removed nitrate and can be implemented in the field as a mitigation strategy, while the other was ineffective and cannot be used. The isotopic fractionation from the laboratory experiments and the numerical model would be subsequently applied in the field to quantify the efficiency of nitrate removal. Key Points: Wine industry residues induced nitrate attenuation in laboratory batch and column experimentsDenitrification efficiency varied with the wine residue type, showing ε15N between −16.5–−32.0‰ and ε18O between −12.1–−27.6‰A geochemical model describing the trends of the experimental results has been developed and can be used for field applications [ABSTRACT FROM AUTHOR]

The hydrogen isotope ratios (d2HAA values) of amino acids in all organisms are substantially fractionated relative to growth water. In addition, they exhibit large variations within microbial biomass, animals, and human tissues, hinting at rich biochemical information encoded in such signals. In lipids, such d2H variations are thought to primarily reflect NADPH metabolism. Analogous biochemical controls for amino acids remain largely unknown, but must be elucidated to inform the interpretation of these measurements. Here, we measured the d2H values of amino acids from five aerobic, heterotrophic microbes grown on different carbon substrates, as well as five Escherichia coli mutant organisms with perturbed NADPH metabolisms. We observed similar d2HAA patterns across all organisms and growth conditions, which-consistent with previous hypotheses-suggests a first-order control by biosynthetic pathways. Moreover, d2HAA values varied systematically with the catabolic pathways activated for substrate degradation, with variations explainable by the isotopic compositions of important cellular metabolites, including pyruvate and NADPH, during growth on each substrate. As such, amino acid d2H valuesmay be useful for interrogating organismal physiology and metabolism in the environment, provided we can further elucidate the mechanisms underpinning these signals. [ABSTRACT FROM AUTHOR]

In this study, we used an improved "diffusion cell" method to precisely determine the diffusion-driven kinetic isotope fractionation factors of the Li, K, Rb, Mg, Ca, Sr, and Ba cations in aqueous solutions under room temperature. The obtained isotope fractionation factors (±2σ errors) are, α 7/6Li = 0.996139 ± 0.000140, α 41/39K = 0.998572 ± 0.000072, α 87/85Rb = 0.999333 ± 0.000020, α 26/24Mg = 0.999877 ± 0.000010, α 44/42Ca = 0.999704 ± 0.000010, α 88/86Sr = 0.999781 ± 0.000014, α 138/135Ba = 0.999716 ± 0.000018. The results show that the charge of the cation and the ion-water bond length for the aquo ions are the two predominant factors affecting the mass dependence of isotope fractionation (β factor) during cation diffusion in aqueous solutions. Cations with higher charge numbers and shorter ion-water bond lengths exhibit less kinetic isotope fractionation during diffusion. Therefore, the isotope separation effect during diffusion (or β factor) in fluids is fundamentally controlled by the intensity of ion-water interaction. Weaker ion-water interaction (e.g., lower charge number, longer ion-water bond length) leads to less prominent hydrodynamic behavior for diffusing ions at the molecular level, thus more significant isotope fractionation in bulk solutions, and vice versa. Ions of larger radius would show stronger mass dependence of isotope fractionation (β factor), which can cancel the effect of decreasing relative isotope mass difference for heavier elements, thus kinetic isotope fractionation during diffusion in aqueous solutions remains prominent even for heavy elements such as Rb, Sr, and Ba. The diffusion-driven kinetic isotope fractionation factors measured in this study could provide a useful basis for interpreting specific natural isotopic variability of alkaline and alkaline-earth elements in supergene environments where chemical diffusion takes place. [ABSTRACT FROM AUTHOR]

The origin of the wide range of sulfur isotope compositions (i.e., δ34S) measured in arc rocks remains debated. While the observed δ34S variability has been attributed to slab-related fluids that flux the sub-arc mantle, others have argued that it primarily reflects crustal-derived processes by some combination of magmatic differentiation, country rock assimilation, and/or degassing. Here, we present new whole rock sulfur isotopes for the Late Cretaceous Bear Valley Intrusive Suite (BVIS) that represents a continuous arc crustal section in the southern Sierra Nevada Batholith, exposing lower crustal mafic cumulates and cogenetic mid-upper crustal tonalites. Our data reveal a range of δ34S-depleted values (–1.2 to − 5.1‰) for the BVIS with overlapping δ34S between mafic cumulates and tonalites. Complementary δ34S measurements of structurally concordant metasedimentary pendants indicate δ34S-depleted values (–11.5 to − 5.2‰) for deep metasedimentary rocks compared to δ34S-enriched values (+ 1.6 to + 6.4‰) for shallower ones. Quantitative mixing models suggest that assimilation of crustal-derived sulfur from metasedimentary rocks in the lower crust can account for the δ34S-depleted values in the BVIS, whereas assimilation of shallower ones is unlikely. Sulfur degassing modelling indicates that the range of δ34S-depleted values observed within mid-upper crustal tonalites can be reproduced by degassing ~60–80% of the initial melt sulfur at fO2 ≤ FMQ + 1 with initial H2O content of 10–12 wt%. Finally, the identical ranges of δ34S values within the tonalites and mafic cumulates argue for limited sulfur isotope fractionation related to magmatic sulfide immiscibility. Although assimilation, magma degassing and sulfide immiscibility are not mutually exclusive during crustal magmatic processes, field, thermal and geochemical evidence favor lower crustal-derived sulfur assimilation as the primary mechanism to explain the range of δ34S- depleted values within the mafic cumulates, which are ultimately inherited by the derivative tonalitic melts. Overall, this study emphasizes that deep crustal magmatic processes can severely influence the early δ34S evolution of arc magmas. [ABSTRACT FROM AUTHOR]

Nitrate pollution in groundwater has become a global concern. One of the most important issues in controlling the nitrate pollution of groundwater is to identify the pollution source quickly and accurately. In this review' we firstly summarized the isotopic background values of potential sources of nitrate pollution in groundwater in 17 provinces (cities' autonomous regions) and 29 study areas in China' which could provide the fundamental database for subsequent research. Secondly' we reviewed the research progress of nitrate isotopes combined with multiple tracers for tracing nitrate in groundwater' and discussed their applicable conditions' advantages' and disadvantages. We found that halides and microorganisms combined with nitrate isotopes could accurately trace the pollution sources of domestic sewage' excrement and agricultural activities. The combination of Δ17O and nitrate isotopes could effectively distinguish the source of atmospheric deposition of nitrate in groundwater. The combination of groundwater age and nitrate isotopes could further determine the time scale of nitrate pollution. In addition' we summarized the application cases and compared the characteristics of mass balance mixing model' IsoSource model' Bayesian isotope mixing model' and EMMTE model for quantitative identification of nitrate pollution in groundwater. For the complexity and concealment of groundwater pollution sources' the coupling of nitrate isotopes with other chemical and biological tracing methods' as well as the application of nitrate isotope quantitative models' are effective tools for reliably identifying groundwater nitrate sources and transformation processes. [ABSTRACT FROM AUTHOR]

The fluxes of metal cations and isotopes released by weathering of silicate rocks are crucial and a prerequisite for constraining geochemical fluxes to rivers and oceans. This study presents mineral and elemental compositions along with 87Sr/86Sr and δ88Sr data from a basaltic weathering regolith on Hainan Island, South China to elucidate Sr isotope fractionation and weathering fluxes. The 87Sr/86Sr ratios vary from 0.703936 to 0.706338 as a result of differential weathering of the minerals. δ88Sr values in the weathering regolith range from −0.29 to 0.37‰, with the majority of the weathering regolith having lower δ88Sr values than the parent rock. Sr is leached into the soil solution during plagioclase decomposition, while 86Sr is preferentially adsorbed on the surface of secondary minerals. As weathering progresses, smectite decomposes and kaolinite desorbs under weakly acidic conditions, releasing the previously adsorbed 86Sr into the soil solution. The differential weathering of kaolinite and smectite controls the δ88Sr values of the weathering regolith, with pH being an important determinant of isotope fractionation. Furthermore, Sr elemental fluxes (SrFlux) and Sr isotopic fluxes (δ88SrFlux) of this weathering regolith were calculated using a mass balance model, yielding mean values of 0.20 (mg cm−3 Myr−1) and 0.052 (‰ (mg cm−3 Myr−1)), respectively. The δ88SrFlux exhibits a nonlinear positive correlation with the Chemical Index of Alteration (CIA), indicating that enhanced weathering leads to significant stable Sr isotope fractionation at CIA values below 95%. Our research promotes the understanding of Sr recycling and the fractionation behavior of stable Sr isotopes during consecutive weathering. Plain Language Summary: The stable Sr isotopic composition is sensitive to continental weathering processes and offers insights into weathering mechanisms. However, the fractionation mechanism of stable Sr isotopes remains elusive. Significant stable Sr isotope fractionation was observed in a basaltic weathering regolith on Hainan Island, South China. Plagioclase decomposition releases Sr, with isotopically light Sr adsorbed onto the surfaces of secondary minerals during incipient weathering. Smectite decomposition and kaolinite desorption control the stable Sr isotopic composition of the weathering regolith during advanced weathering. The variable pH of the regolith is an important external control factor. We focus on modeling Sr isotopic fluxes and Sr elemental fluxes from weathering regolith. Our results show that within a certain range, an increase in weathering intensity leads to a nonlinear increase in weathering fluxes. The δ88Sr values of the loss component are consistent with those in silicate–dominated river catchments, suggesting that metal cations from the weathering of silicate rocks have a significant influence on the hydrochemical and isotopic composition of river waters in these catchments. Stable Sr isotope fractionation thus provides quantitative constraints on continental weathering fluxes. Key Points: Significant fractionation of stable Sr isotopes occurs with increasing weathering intensity at CIA values of less than 95%Secondary clay minerals control the variation in δ88Sr values in the weathering regolith, with 86Sr being preferentially adsorbed by kaoliniteThe model has been developed to simulate both Sr isotopic fluxes and Sr elemental fluxes from the weathering regolith [ABSTRACT FROM AUTHOR]