Minor Isotope Research Articles

Molar mass measurement of a 28Si-enriched silicon crystal with high precision secondary ion mass spectrometry (SIMS)

Several highly-enriched 28Si crystals were produced to enable a better determination of the Avogadro constant through removing the uncertainty associated with the abundance determination of the minor isotopes 29Si and 30Si.

Geochemical Characteristics and Origin of Formation Water From the Upper Triassic Xujiahe Tight Sandstone in the Xiaoquan-Fenggu Structural Belt, Western Sichuan Depression, China

Formation water represents an important driving force and carrier for the migration and accumulation of oil and gas; thus, research on its origin is a hot spot in petroleum geology. The Upper Triassic Xujiahe Formation in the Xiaoquan-Fenggu Structural Belt in the western Sichuan Depression, China, has developed thick tight sandstone gas reservoirs. However, previous studies have provided different conclusions on the origin of the formation water in the Xujiahe tight sandstone reservoir. In this paper, the origin of the formation water in the Xujiahe Formation was determined based on the latest major and minor elemental concentration data, hydrogen and oxygen isotopes data of formation water, and carbon and oxygen isotope data of carbonate cements. The results show that the salinity of the formation water of the Xujiahe Formation in the study area is generally greater than 50 g/L. The water type is mainly the CaCl2 type, although a small proportion of NaHCO3 type water with high salinity is observed, which is related to hydrocarbon expulsion by overpressure. Moreover, the formation water in the sandstone of the Xujiahe Formation is obviously rich in Br, which is related to membrane infiltration, overpressured hydrocarbon expulsion of shale and diagenesis of organic matter. The composition of Cl− and Na+ ions in the formation water in the Xujiahe tight sandstone reservoir is consistent with the seawater evaporation curve, which deviates significantly from the freshwater evaporation curve. The hydrogen and oxygen isotopes of condensate water in the Xujiahe Formation tight sandstone are similar to those of atmospheric precipitation water, while the hydrogen and oxygen isotopes of the formation water in the Xujiahe Formation show that it is of seawater origin. Therefore, to use hydrogen and oxygen isotopes to determine the origin of formation water, condensate water must be accurately differentiated from formation water. Otherwise, if the condensate water is misjudged as formation water, then incorrect conclusions will be drawn, e.g., that the formation water of the Xujiahe Formation originated from fresh water. Affected by organic carbon, the carbon isotope Z value of the carbonate cements in the Xujiahe Formation is low (mainly distributed between 110 and 130). A Z value of less than 120 does not indicate that the ancient water bodies formed by cements were fresh water or mixed water bodies. However, Z values greater than 120 correspond to a formation temperature lower than 80 C, which indicates that carbonate cement was not affected by organic carbon; thus, the Z value can reflect the origin of ancient water bodies. The results of this study indicate that the formation water of the Xujiahe tight sandstone in the study area is of seawater origin. The determination of the origin of the formation water and seawater of the Xujiahe Formation provides strong evidence for the determination of the marine sedimentary environment of the Xujiahe Formation in the study area, and can provide scientific guidance for the search for high-quality reservoirs.

Measuring titanium isotope ratios in exoplanet atmospheres

Context. Measurements of relative isotope abundances can provide unique insights into the formation and evolution histories of celestial bodies, tracing various radiative, chemical, nuclear, and physical processes. In this regard, the five stable isotopes of titanium are particularly interesting. They are used to study the early history of the Solar System, and their different nucleosynthetic origins help constrain Galactic chemical models. Additionally, titanium’s minor isotopes are relatively abundant compared to those of other elements, making them more accessible for challenging observations, such as those of exoplanet atmospheres. Aims. We aim to assess the feasibility of performing titanium isotope measurements in exoplanet atmospheres. Specifically, we are interested in understanding whether processing techniques used for high-resolution spectroscopy, which remove continuum information about the planet spectrum, affect the derived isotope ratios. We also want to estimate the signal-to-noise requirements for future observations. Methods. We used an archival high-dispersion CARMENES spectrum of the M-dwarf GJ 1002 as a proxy for an exoplanet observed at very high signal-to-noise. Both a narrow (7045–7090 Å) and wide (7045–7500 Å) wavelength region were defined for which spectral retrievals were performed using petitRADTRANS models, resulting in isotope ratios and uncertainties. These retrievals were repeated on the spectrum with its continuum removed to mimic typical high-dispersion exoplanet observations. The CARMENES spectrum was subsequently degraded by adding varying levels of Gaussian noise to estimate the signal-to-noise requirements for future exoplanet atmospheric observations. Results. The relative abundances of all minor Ti isotopes are found to be slightly enhanced compared to terrestrial values. A loss of continuum information from broadband filtering of the stellar spectrum has little effect on the isotope ratios. For the wide wavelength range, a spectrum with a signal-to-noise of 5 is required to determine the isotope ratios with relative errors ≲10%. Super Jupiters at large angular separations from their host star are the most accessible exoplanets, requiring about an hour of observing time on 8-meter-class telescopes, and less than a minute of observing time with the future Extremely Large Telescope.

Multiple sulfur isotopes discriminate organoclastic and methane-based sulfate reduction by sub-seafloor pyrite formation

The marine sulfate inventory represents the largest standing pool of electron acceptors, which, via microbial sulfate reduction, is responsible for roughly half of the organic matter mineralization globally in marine sediments. In addition to the oxidation of buried organic matter, sulfate reduction can be coupled to the oxidation of methane migrating upward. Multiple sulfur isotope ratios were measured for porewater sulfate, sulfide, elemental sulfur and pyrite from core samples collected from continental shelf (19–96 m water depth) in the Baltic Sea and slope (1098 m water depth) in the Andaman Sea, in order to test if their isotope systematics can be used to trace the two different sulfate reduction processes. For shallow shelf sediments (<43 cm below seafloor), both δ34S and Δ33S values of porewater sulfate increased with increasing depth as a result of organoclastic sulfate reduction (OSR). However, the Δ33S values of both porewater sulfate and sulfide decreased as the δ34S values increased downcore at 43–73 cm depth where sulfate reduction was coupled to anaerobic oxidation of methane (AOM). Pyrite in shelf sediments yielded positive Δ33S values, reflecting Δ33S of porewater sulfide produced by OSR. In contrast, pyrite in slope sediments yielded negative Δ33S values as low as −0.15‰, as a result of mixing of sulfides derived from OSR and AOM. This is consistent with the slowly migrating sulfate–methane transition (SMT) in slope sediments inferred from sulfur and iron speciation, carbon isotope ratios of carbonates, and magnetic susceptibility data. A stable SMT, focusing AOM at roughly the same depth over the past few millennia, further provides favorable conditions for prolonged pyrite formation with the development of cubic crystals, while the sulfur isotope difference between bulk pyrite and macroscopic pyrite reflects the significance of OSR throughout the sediment column. We conclude that minor sulfur isotopes provide a unique proxy that can be applied to differentiate OSR and AOM and the origin of pyrite in diverse sediments and sedimentary rocks. This contribution highlights strong local diagenetic controls on pyrite formation and its multiple sulfur isotopic composition in various marine settings.

Geochemistry and Diagenetic Evidence of Middle-Late Permian Deposits, Northern Iran

This study provides a evaluation of the initial carbonate mineralogy, and diagenetic condition of the Ruteh Formation, a middle-late Permian carbonate sequence, in the Emarat section in Central Alborz, northern Iran. 200 samples were examined for petrographical contents and thirty-four samples were collected for geochemical analysis. The high Sr and Na contents, Sr/Na>1, and the presence of dolomites and dissolution fractures are indicative aragonite early mineralogy. The diagenetic process in the Ruteh Fm. are an indication of the marine, meteoric and burial diagenetic environments. The original carbonate texture in the Ruteh Fm. are Severely affected by diagenetic process. The data obtained from the values of the Major (Ca and Mg), minor (Sr, Na, Fe, and Mn), oxygen and carbone isotopes show the initial aragonite composition of the Ruteh Fm. deposited in a subtropical shallow water. An open diagenetic system was indicated by changes in the values of Sr / Ca and δ18O vs. Mn. The shallow burial diagenetic temperature of the Ruteh carbonate was approximate 28.6°C with the maximum diagenetic temperature of 53.4°C.

Neoarchean atmospheric chemistry and the preservation of S-MIF in sediments from the São Francisco Craton

Sulfur mass-independent fractionation (S-MIF) preserved in Archean sedimentary pyrite is interpreted to reflect atmospheric chemistry. Small ranges in Δ33S that expanded into larger fractionations leading up to the Great Oxygenation Event (GOE; 2.45–2.2 Ga) are disproportionately represented by sequences from the Kaapvaal and Pilbara Cratons. These patterns of S-MIF attenuation and enhancement may differ from the timing and magnitude of minor sulfur isotope fractionations reported from other cratons, thus obscuring local for global sulfur cycling dynamics. By expanding the Δ33S record to include the relatively underrepresented São Francisco Craton in Brazil, we suggest that marine biogeochemistry affected S-MIF preservation prior to the GOE. In an early Neoarchean sequence (2763–2730 Ma) from the Rio das Velhas Greenstone Belt, we propose that low δ13Corg (<−30‰) and dampened Δ33S (0.4‰ to −0.7‰) in banded iron formation reflect the marine diagenetic process of anaerobic methane oxidation. The overlying black shale (TOC up to 7.8%) with higher δ13Corg (−33.4‰ to −19.2‰) and expanded Δ33S (2.3‰ ± 0.8‰), recorded oxidative sulfur cycling that resulted in enhance preservation of S-MIF input from atmospheric sources of elemental sulfur. The sequence culminates in a metasandstone, where concomitant changes to more uniform δ13Corg (−30‰ to −25‰), potentially associated with the RuBisCO I enzyme, and near-zero Δ33S (−0.04‰ to 0.38‰) is mainly interpreted as evidence for local oxygen production. When placed in the context of other sequences worldwide, the Rio das Velhas helps differentiate the influences of global atmospheric chemistry and local marine diagenesis in Archean biogeochemical processes. Our data suggest that prokaryotic sulfur, iron, and methane cycles might have an underestimated role in pre-GOE sulfur minor isotope records.

Neutronics Analysis of the Stellarator-Type Fusion–Fission Hybrid Reactor Using Mesh Simplification

The stellarator plasma device has been widely studied as one of the candidate solutions paralleling the ITER project, and its coupling with a fission blanket can bring benefits promoting the development of fusion technology with stable energy production simultaneously. However, the neutronics optimization design for the stellarator-type Fusion-Fission Hybrid Reactor (FFHR) is extremely complex since the helical structure with a large amount of spline curved surfaces cannot be exactly described in most of the Monte Carlo simulation processes, and the preliminary design stage has also been a time-consuming and error-prone task with the requirements frequently changing. In this context, the mesh-oriented optimized method has been considered for the parametric modeling analysis in order to get the ideal structure without redundant topologic information, and the corresponding conversion process from computer-aided design (CAD) to Monte Carlo simulation has been fulfilled by the CAD-PSFO code. Moreover, the liquid type of thorium-uranium fuels has been selected as the solutes dissolve in the molten salt blanket with its multilayer structure, where the burnup feature and neutronics properties have been analyzed and explained with the help of the OMCB code. The stellarator-type FFHR has been designed as a compact multifunctional device that can incinerate plutonium and transmute the minor actinide isotopes with tritium self-sufficiency and the high-energy multiplication factor.

Primary mineralogy of Dalichai carbonate formation and separation of upper boundary with Lar formation based on geochemical studies in northeast of Semnan

The Dalichai Formation is the first rock unit of the Middle Jurassic in the Alborz sedimentary basin that has occurred in a marine environment. The boundary of the Dalichai formation with Shemshak Formation is erosional unconformable while it is concordant with Lar formation. Due to lithological similarity, the boundary of the Dalichai formation with the Lar formation is unclear. It is also very difficult to identify the primary carbonates mineralogy, due to the effects of diagenetic processes solely on the basis of petrographic studies. We studied a section of Sharaf mountain with a thickness of 1420m and 149 samples was studied. The study of the major and minor elements, the Oxygen and Carbon isotopes, and plotting of these values ​​against each other represents that the Dalichai formation have had original aragonite mineralogy, and the nonmarine diagenesis have had the highest impact on them. Plotting the Sr/Ca ratio versus Mn value, shows that these carbonates are affected in a semi-closed to open diagenetic system. Using Sr, Sr/Na, Sr/Ca, Oxygen and Carbon isotopes, the boundary of this formation with the Lar Formation is recognized in thickness of 1200m. The diagenetic environment temperature for this section limestones is 32.9oC.

SF6+: Stabilizing Transient Ions in Helium Nanodroplets.

There are myriad ions that are deemed too short-lived to be experimentally accessible. One of them is SF6+. It has never been observed, although not for lack of trying. We demonstrate that long-lived SF6+ can be formed by doping charged helium nanodroplets (HNDs) with sulfur hexafluoride; excess helium is then gently stripped from the doped HNDs by collisions with helium gas. The ion is identified by high-resolution mass spectrometry (resolution m/Δm = 15000), the close agreement between the expected and observed yield of ions that contain minor sulfur isotopes, and collision-induced dissociation in which mass-selected HenSF6+ ions collide with helium gas. Under optimized conditions, the yield of SF6+ exceeds that of SF5+. The procedure is versatile and suitable for stabilizing many other transient molecular ions.

Determination of minor isotope ratios of individual uranium particles by accelerator mass spectrometry.

The determination of uranium isotope ratios in uranium particle is an essential technique in the analysis of environmental samples for nuclear safeguards. At present, mass spectrometry has been widely used to measure isotope ratios of uranium particles. We developed a new analytical method for measuring minor isotope ratios of individual uranium particles directly. The technique includes single particle identification by energy dispersive X-ray spectrometer (EDX), transfer by scanning electron microscope (SEM) combined with micromanipulator and isotope ratios analysis with accelerator mass spectrometry (AMS). The minor isotope ratios of individual uranium particles with four isotopic abundances and different sizes from certified reference materials were measured by AMS. The results show that the relative error (RE, i.e., the deviation of measured value from the certified value) of 234 U/235 U and 234 U/236 U isotope ratios was 9.0% and 19.3%, respectively, and the relative standard deviation (RSD) was within 9.9% and 16%, respectively. The minimum particle determined was about 2 μm. The method was found to be an alternative analytical means for nuclear safeguards.

Isotope Effect in Thermal Conductivity of Polycrystalline CVD-Diamond: Experiment and Theory

We measured the thermal conductivity κ(T) of polycrystalline diamond with natural (natC) and isotopically enriched (12C content up to 99.96 at.%) compositions over a broad temperature T range, from 5 to 410 K. The high quality polycrystalline diamond wafers were produced by microwave plasma chemical vapor deposition in CH4-H2 mixtures. The thermal conductivity of 12C diamond along the wafer, as precisely determined using a steady-state longitudinal heat flow method, exceeds much that of the natC sample at T&gt;60 K. The enriched sample demonstrates the value of κ(298K)=25.1±0.5 W cm−1 K−1 that is higher than the ever reported conductivity of natural and synthetic single crystalline diamonds with natural isotopic composition. A phenomenological theoretical model based on the full version of Callaway theory of thermal conductivity is developed which provides a good approximation of the experimental data. The role of different resistive scattering processes, including due to minor isotope 13C atoms, defects, and grain boundaries, is estimated from the data analysis. The model predicts about a 37% increase of thermal conductivity for impurity and dislocation free polycrystalline chemical vapor deposition (CVD)-diamond with the 12C-enriched isotopic composition at room temperature.

Fractionation of the copper, oxygen and hydrogen isotopes between malachite and aqueous phase

Studies of the equilibrium isotope properties of stable isotopes of minerals have been initiated principally because of their application to the solution of geochemical problems. Therefore, we examined malachite, a common secondary mineral in the oxidation zone of ore deposits. Stable isotope characterization can contribute needed information on the formation of malachite by establishing the isotopic composition of the parental waters. The equilibrium oxygen and hydrogen isotope fractionations between malachite and solution were determined by precipitation experiments over the temperature range from 10 to 65 °C and could be distinguished in two sets of fractionation factors depending on the temperature. For 45–65 °C, the fractionation is expressed as 1000lnαmal-soloxygen=2.87(106/T2)+0.96 and 1000lnαmal-solhydrogen=-1.47(106/T2)-22.3 with temperature (T) in Kelvin. With the application of the fractionation factors of oxygen and hydrogen of malachite onto source water from the meteoric water line, we were able to calculate the “malachite line” which represents the isotopic compositions of malachite that would precipitate from such water. We also examined the copper isotope fractionation factors between solution and malachite from 10 to 65 °C: 1000lnαsol-malcopper=0.033(106/T2)-0.19 with fractionation shift of Δ65Cumalachite-solution=-0.17±0.05 ‰. This fractionation shift implies that chemical reactions without change of the redox state yield only minor copper isotope fractionation. The calculated fractionation factors of oxygen and hydrogen were used to determine the oxygen and hydrogen isotopic composition of the parental waters of natural malachite samples from a number of localities worldwide. With δ18OVSMOW values of +22.1 to +29.5 ‰ and δD values of -132 to -61 ‰ for the natural malachite and δ18OVSMOW values of -14.5 to -7 ‰ and δD values of -107 to -36 ‰ for the parental water together with the Cu isotopes, it is to assume that all investigated malachite samples are supergene samples which formed from meteoric water. Even in massive malachite samples from Ural Mts. (Russia), no signs of other fluids were detected from the isotopic composition.

Molybdenum isotope systematics in cumulate rock of the 2.8 Windimurra layered intrusion: A test for igneous differentiation and the composition of the Archean mantle

Molybdenum isotopes (reported as δ98Mo relative to NIST-3134) show resolvable isotope differences in igneous rocks with the continental crust being markedly heavier in isotope composition than mid-ocean ridge lavas, lunar basalts or the Earth’s mantle. The tholeiitic differentiation series at the intra-plate Hekla volcano (Iceland) shows no resolvable Mo isotope differences from basaltic to rhyolitic compositions. In contrast, convergent margin lavas show a transition from isotopically lighter mantle to heavy continental crust, suggesting that subduction processes drive continental crust towards heavier values. Archean komatiitic lavas, presumed probes of the Archean mantle, have Mo isotope values identical to modern depleted mantle, raising the questions if and how the Mo isotope crust-mantle disparity developed so early in Earth’s history. Here we present new Mo isotope data for a set of cumulate rocks from the Upper Zone of late Archean (2.8 Ga) Windimurra Igneous Complex, a mafic/ultramafic layered intrusion. The intrusion is not subduction related and contains no apparent primary hydrous minerals. We tested the effect of crystal fractionation on Mo isotopes in relatively dry melt along a tholeiitic liquid line of descent by using the cumulate effect of normally anhydrous minerals in the layered intrusion. Near mono-mineralic olivine-pyroxene-rich, feldspar-rich and Fe-Ti-rich oxides show small variations (~0.15‰) in Mo isotope signatures. This is consequently to predominantly isotopically light Fe-Ti-oxide-rich and isotopically heavier feldspar-rich rocks, respectively. This is suggesting minor Mo isotope fractionation, even in dry, tholeiitic systems, which however, counterbalance each other and thus potentially remain undetected. On average, the Windimurra mantle source is indistinguishable, or slightly isotopically lighter than the Mo isotope signature of komatiites. This is reinforcing an isotopically light Mo isotope signature of Archean mantle sources of high-degree mantle melts and is extending these signatures to predominantly mafic Archean crust. It remains to be tested if Archean felsic crust resembles modern continental crust in its heavy isotope values and to which extend the mantle was already isotopically depleted in Mo isotopes at Mesoarchean time.

The role of mass loss in chemodynamical evolution of galaxies

AbstractThanks to the long-term collaborations between nuclear and astrophysics, we have good understanding on the origin of elements in the universe, except for the elements around Ti and some neutron-capture elements. From the comparison between observations of nearby stars and Galactic chemical evolution models, a rapid neutron-capture process associated with core-collapse supernovae is required. The production of C, N, F and some minor isotopes depends on the rotation of massive stars, and the observations of distant galaxies with ALMA indicate rapid cosmic enrichment. It might be hard to find very metal-poor or Population III (and dust-free) galaxies at very high redshifts even with JWST.

Impacts of acid mine drainage on karst aquifers: Evidence from hydrogeochemistry, stable sulfur and oxygen isotopes

The pollution of karst aquifers by acid mine drainage (AMD) waters is increasing. Major and minor ions (Ca2+, Mg2+, HCO3−, SO42−, F−, and Fe), stable sulfur and oxygen isotopes of dissolved sulfates (δ34SSO4 and δ18OSO4) and oxygen isotope of water (δ18OH2O), were analyzed in rainwater, surface water, groundwater, and AMD water sampled from the Babu subterranean stream watershed, in Southwest China. The principal aim of this study was to explore the impact of AMD waters on the evolution of karst aquifers. Based on hydrogeochemistry and stable isotopes (δ18OH2O, δ18OSO4 and δ34SSO4): (1) the chemistry of AMD waters was primarily controlled by pyrite oxidation, karst conduit water by AMD waters and mixing with calcite and dolomite dissolution, and spring water by atmospheric precipitation and carbonate dissolution; (2) contamination of the karst conduit water was mainly attributed to the input of AMD waters, resulting in a shift of δ34SSO4 towards more negative values (from 3.4‰ to −13.2‰); (3) the quality of karst conduit water changed from suitable to unsuitable for irrigation and drinking, particularly due to the increase in total Fe, SO42−, and F− concentrations, reflecting the cumulative effect of AMD waters derived from tailings dumps; this influence was enhanced during rainstorm/drought and anthropogenic activities; and (4) the flow of contaminated groundwater through the conduit promoted the dissolution of carbonates, especially during the dry season due to the greater proportion of AMD in the groundwater. This released more CO2 to the atmosphere. We believe that analysis of stable isotopes (δ18OH2O, δ18OSO4, and δ34SSO4), combined with hydrogeochemistry, is effective for exploring the impact of AMD on karst aquifers. Therefore, reasonable treatment methods should be taken to reduce the negative impacts of tailings dumps on karst aquifers.

Geochemical characterization of an urban lake in the centre of Rome (Lake Bullicante, Italy)

Urban lakes have become increasingly important in the planning of urban ecology, green infrastructure and green areas in European cities. This paper describes the chemical, isotope and microbial features of Lake Bullicante, a small artificial lake located within the urban area of the city of Rome. It has an anthropogenic origin due to excavation works that intercepted the underlying aquifer, giving rise to a water body. The lake area is 7.000 m2, with a maximum depth of 7 m and located on the distal deposits of the Alban Hills Volcanic District in an area named Acqua Bullicante (i.e. Bubbling Water), where degassing phenomena were historically recorded. The proximity of this volcanic district motivated the study on Lake Bullicante as a potential open-air laboratory to trace possible degassing phenomena in a highly urbanized area. A preliminary geochemical and microbial sampling survey was carried out in winter 2018. Samples were collected along a vertical profile of the lake from the surface to the maximum depth. Major, minor, trace elements, dissolved gases and stable isotopes (δD-H2O, δ18O- H2O, δ13C-CO2) were analyzed, along with the analysis of 87Sr/86Sr ratio. The microbial community characteristics were analysed by epifluorescence microscopy (CARD-FISH) and flow cytometry. The chemical composition and water isotopes suggest that lake water has a meteoric origin and is related to a Ca-HCO3 shallow aquifer hosted in volcanic rocks. This is confirmed by both the 87Sr/86Sr ratio of lake water, which falls in the range of values of Alban Hills volcanites, and the chemical-isotopic composition of neighboring wells. A relatively high concentration of dissolved CO2, its isotopic signature (δ^13C-CO2 20‰ V-PDB), and the high content in organic matter (DOC 10-30 mg/L) suggest for the lake a eutrophication state with denitrification also occurring. Considering the relatively high concentrations of dissolved CO2, an external input of carbon dioxide cannot be completely excluded and as a consequence, not even the hypothesis of mixing processes between biotic and inorganic CO2. This makes further investigations necessary especially during the summer, when the lake is stratified. A summer survey could be also useful to better understand the microbial processes into the lake, its eutrophication evolution and health status, and to plan eventual proper remediation strategies, providing important tools to the local administration and stakeholders to improve, protect and preserve this ecological niche.

Tracing the Early Emergence of Microbial Sulfur Metabolisms

Hydrogen sulfide (nH2S) and sulfur oxide (SO n ; n = 1, 2, 3) gases in early Earth’s globally anoxic atmosphere were subjected to gas-phase chemical transformations by UV light. A principal photolysis pathway at that time produced elemental sulfur aerosols with mass-independently fractionated (MIF) isotopic values carrying variable minor isotope (33S, 36S) compositions. These rained into the sulfate-deficient Archean (ca. 3.85–2.5 Ga) oceans to react with [Fe2+]aq and form sedimentary sulfides. The MIF-bearing sulfides were incorporated into Archean sediments, including banded iron formations (BIF). Such aerosols may also have fueled microbial sulfur metabolisms, and thus are traceable by the MIF sulfur isotopes. Yet, data show that before ∼3.5 Ga mass-dependent34S/32S values in Early Archean sediments tend to fall within a narrow (±0.1%) range even as they carry mass-independent values. By about 3.5 Ga, 34S/32S values show much greater changes (>1%) in range congruent with microbial metabolic processing. Here, we trace probable pathways of elemental sulfur aerosols into Archean sediments, and couple our study with analysis of the evolutionary relationships of enzymes involved in sulfur metabolism to explain the observed trends. Our model explains why elemental sulfur aerosols were apparently not utilized by the Eoarchean (pre-3.65 Ga) biosphere even though an immediate precursor to the required enzyme may have already been present. Highlights Evolution of microbial sulfur metabolisms is tracked by multiple sulfur isotopes Alkaline hydrothermal vents were an abode for early microbial life Sulfite detoxification prompted anaerobic respiration Reversal of respiratory electron transport chain (ETC) stimulated photothiotrophy Surplus e- acceptors permitted the emergence of elemental sulfur reduction

Environmental isotope and hydrochemical characteristics of groundwater in central portion of Mekelle sedimentary outlier, northern Ethiopia

This study investigated the source and hydrogeochemical processes responsible for variation in groundwater chemical characteristics in multi-layered aquifers in the central portion of Mekelle Mesozoic Sedimentary Outlier. Groundwater samples from Aynalem and Ilala sub-catchments were collected and analyzed for major and trace elements and stable isotopes (δ2H, δ18O and δ13C). The findings showed significant difference in concentrations of dissolved ions in the groundwater in response to residence time and varying degrees of water-rock interaction. The groundwater exhibited a pH between 7.85 and 7.38 (average of 7.59) and electrical conductivity from 2430 to 650 μS/cm (average 1336 μS/cm) and water types that were characterized by the dominance of Ca-HCO3/SO4 and Ca-SO4. Most of samples from Aynalem aquifer displayed relatively low dissolved ions due to rapid infiltration of groundwater through fractured zones. The increased concentrations in groundwater are attributed to significant degree of solubility in aquifer where the groundwater flow is slow. The geochemical analysis was supported by the 2H/H, 18O/16O ratios that revealed the effect of evaporation prior to infiltration in groundwater samples from shale dominated aquifer. The δ13CDIC values ranged from −10.3 to −6.6‰, with a mean value of −8.8‰ suggesting both carbonate dissolution and soil CO2 are major sources in the groundwater system. While rapid recharging water maintains minor isotope exchange, extended water-rock interactions in low permeability aquifers may result in heavier δ13CDIC values as infiltration water had sufficient time to equilibrate. The study integrates hydrochemistry and new isotope tracers to gain a better understanding on source of dissolved ions and hydrogeochemical evolution that influence the groundwater chemical variability in multilayered carbonate aquifers.

Evaluation of Optimized Procedures for High-Precision Lead Isotope Analyses of Seawater by Multiple Collector Inductively Coupled Plasma Mass Spectrometry.

The application of Pb isotopes to marine geochemistry is currently hindered by challenges associated with the analysis of Pb isotopes in seawater. The current study evaluates the performance of multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) measurements of seawater Pb isotope compositions following Pb separation by either solid-phase extraction with Nobias Chelate PA-1 resin or coprecipitation with Mg(OH)2 and using either a Pb double spike or external normalization to Tl for mass bias correction. The four analytical combinations achieve results of similar quality when measuring 1-7 ng of seawater Pb, with reproducibilities (two standard deviations, 2SD) of 100-1200 ppm for 206Pb/207Pb and 208Pb/207Pb and 300-1700 ppm for ratios involving the minor 204Pb isotope. All four procedures enable significantly improved sample throughput compared to an established thermal ionization mass spectrometry (TIMS) double-spike method and produce unbiased seawater Pb isotope compositions with similar or improved precision. Nobias extraction is preferable to coprecipitation due to its greater analytical throughput and suitability for analyses of large seawater samples with high Si(OH)4 contents. The most accurate Pb isotope data are produced following Nobias extraction and double-spike correction as such analyses are least susceptible to matrix effects. However, Nobias extraction with Tl normalization constitutes an attractive alternative as, unlike the double-spike procedure, only a single mass spectrometric measurement is required, which improves analytical throughput and optimizes Pb consumption for analysis. Despite the advantages of solid-phase extraction, coprecipitation represents a useful Pb separation technique for samples with low to moderate Si contents as it is inexpensive, simple to implement, and the data are only marginally less accurate, especially when combined with a Pb double spike for mass bias correction.

Quantitative and specific recovery of natural organic and mineral sulfur for (multi-)isotope analysis

Deciphering the role of sulfur in biogeochemical cycles strongly relies on its stable isotope composition, which ultimately depends on the ability to quantitatively recover different sulfur species from geological samples. For decades most studies have been restricted to the 34S/32S composition of bulk samples, using simple methods based on the analysis of SO2 released by sample combustion combined to mass spectrometry. The wet chemistry procedures required to selectively extract specific sulfur species were generally avoided due to their tediousness and inefficiency for some complex matrices, especially when targeting organic sulfur. With the recent advent of multi-isotope studies (investigating the minor sulfur stable isotopes 33S and 36S) which rely either on the analysis of sulfur as SF6, or on the use of secondary ion or multi-collector inductively coupled plasma mass spectrometry, wet chemistry-based preparation procedures were brought back to the stage with a renewed interest in developing procedures better adapted to the investigation of specific sulfur species.Here we propose a new stepwise chemical procedure for the quantitative recovery and multi-isotope analysis of organic sulfur from both solvent soluble (total lipid extract) and insoluble (kerogen) fractions, based on a wet oxidation by sodium hypochlorite. This procedure also allows the multi-isotope analysis of inorganic sulfur species (elemental sulfur, sulfates and sulfides) in the same sample. Its application to different well-known petroleum source rocks and to an oil demonstrates its relevance for disentangling the interactions between the different sulfur pools and for shedding new light on the sulfur biogeochemical cycle.