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Rationale: The analysis of the three sulfur stable isotope ratios (33S/32S, 34S/32S, 36S/32S) is routinely performed by gas‐source isotope ratio mass spectrometry (IRMS) on the SF6 gaseous molecule, collecting SF5+ ions at m/z ~ 127, 128, 129 and 131. High precision and accuracy are commonly achieved owing to a lack of correction because fluorine has only one isotope and the inert nature of the SF6 molecule. The analysis of the 36S/32S ratio is, however, complicated by the low abundance of 36S (~0.015%) and the possible occurrence of trace amounts of fluorocarbon compounds leading to 12C3F5+ ions at m/z ~ 131, i.e. where 36SF5+ ions are collected. Methods: We used gas‐source high‐resolution IRMS to better characterize the nature of possible interferences, and we tested novel types of filaments in order to investigate their influence on possible interferences. Results: We confirm that the 12C3F5+ ion represents the main isobaric interference at m/z ~ 131. We also demonstrate that tungsten fluoride adducts are formed from the reaction of fluorine ions derived during fragmentation of the SF6 molecule with the hot tungsten filament. These reactions lead to the formation of e.g. WF5+, WF4+, WF3+ ions, including doubly charged ions. WF4++, in particular, leads to isobaric interference on m/z ~ 128, 129 and 131 from 180WF4++, 182WF4++ and 186 WF4++ ions, respectively. Because 180W (0.12%) is at low abundance, its influence on δ33S measurements would remain negligible, but 182W (26.5%) and 186W (28.4%) lead to scale contraction for both δ34S and δ36S. Conclusions: Rather than correcting for these interferences, or working at high mass resolution, we suggest avoiding W isobaric interferences by using other types of filaments, with initial reports on both pure Re filaments and Y2O3‐coated W filaments. [ABSTRACT FROM AUTHOR]

Nephrite jade is a rare and highly prized rock consisting mainly of finely intergrown amphibole of tremolite-actinolite composition which has been culturally used from the Paleolithic to modern times. Understanding and tracing its provenance is key for solving geological, archaeological, and gemmological problems. Previous approaches to identify nephrite sources utilized a wide range of visual, spectroscopic, and geochemical methods (based on analysis of major elements, trace elements, or isotopes), but these approaches are often limited by their discriminatory power, destructiveness, and/or analytical throughput. Here, we introduce O-isotopic analysis of nephrite using secondary ion mass spectrometry (SIMS) which affords superior spatial resolution and speed compared to other isotopic methods. By analysing a large number (n = 56) of geological samples from nephrite-bearing regions in the vicinity of Lake Baikal in southern Siberia, Russia, we assess intra- and inter-specimen heterogeneity and test the sensitivity of O-isotopes to discriminate the provenance regions for nephrite. Intra-sample variability at the centimetre scale is ≤0.8‰, and typically less at the sub-millimetre scale when sampled by multiple ion beam spots ∼20 μm in diameter and with a depth resolution of few μm. Accurate SIMS analysis of nephrite requires correction for matrix-dependent instrumental mass fractionation, for which we developed an empirical calibration based on Mg + Ca cation allocation on the crystallographic B-site of amphibole. Ranges in SIMS δ18O for individual nephrite-bearing regions are +3.98 to +8.04‰ (East Sayan; n = 36), +5.21 to +11.76‰ (Dzhida; n = 13), and −17.16 to −22.95‰ (Vitim; n = 7). These results indicate that SIMS O-isotope analysis permits rapid discrimination not only for nephrite of different geologic origins (serpentinitic ultramafic or S-nephrite from East Sayan and Dzhida vs. dolomitic carbonate or D-nephrite from Vitim), but also for distinct geographic provenance of the same nephrite type (S-type nephrite from East Sayan vs. Dzhida regions). [ABSTRACT FROM AUTHOR]

Abstract: In both laboratory experiments and natural environments where microbial dissimilatory sulfate reduction (MDSR) occurs in a closed system, the ((34S/32S)sample/(34S/32S)standard −1) for dissolved SO4 2− has been found to follow a typical Rayleigh-Distillation path. In contrast, the corresponding ((18O/16O)sample/(18O/16O)standard)−1) is seen to plateau with an apparent enrichment of between 23‰ and 29‰ relative to that of ambient water under surface conditions. This apparent steady-state in the observed difference between and can be attributed to any of these three steps: (1) the formation of adenosine-5′-phosphosulfate (APS) from ATP and SO4 2−, (2) oxygen exchange between sulfite (or other downstream sulfoxy-anions) and water later in the MDSR reaction chain and its back reaction to APS and sulfate, and (3) the re-oxidation of produced H2S or precursor sulfoxy-anions to sulfate in environments containing Fe(III) or O2. This study examines the first step as a potential pathway for water oxygen incorporation into sulfate. We examined the structures and process of APS formation using B3LYP/6-31G(d,p) hybrid density functional theory, implemented in the Gaussian-03 program suite, to predict the potential for oxygen exchange. We conducted a set of in vitro, enzyme-catalyzed, APS formation experiments (with no further reduction to sulfite) to determine the degree of oxygen isotope exchange between the APS–sulfate and water. Triple-oxygen-isotope labeled water was used in the reactor solutions to monitor oxygen isotope exchange between water and APS sulfate. The formation and hydrolysis of APS were identified as potential steps for oxygen exchange with water to occur. Quantum chemical modeling indicates that the combination of sulfate with ATP has effects on bond strength and symmetry of the sulfate. However, these small effects impart little influence on the integrity of the SO4 2− tetrahedron due to the high activation energy required for hydrolysis of SO4 2− (48.94kcal/mol). Modeling also indicates that APS dissociation via hydrolysis is achieved through cleavage of the P–O bond instead of S–O bond, further supporting the lack of APS–H2O–oxygen exchange. The formation of APS in our in vitro experiments was verified by HPLC fluorescence spectroscopy, and triple-oxygen isotope data of the APS–sulfate indicate no oxygen isotope exchange occurred between APS–sulfate and water at 30°C for an experimental duration ranging from 2 to 120h. The study excludes APS formation as one of the causes for sulfate–oxygen isotope exchange with water during MDSR. [Copyright &y& Elsevier]

Given the global dearth of Hadean (>4 Ga) rocks, 4.4–4.0 Ga detrital zircons from Jack Hills, Narryer Gneiss Complex (Yilgarn Craton, Western Australia) constitute our best archive of early terrestrial materials. Previous Lu–Hf investigations of these zircons suggested that felsic (low Lu/Hf) crust formation began by ∼4.4 to 4.5 Ga and continued for several hundred million years with evidence of the least radiogenic Hf component persisting until at least ∼4 Ga. However, evidence for the involvement of Hadean materials in later crustal evolution is sparse, and even in the detrital Jack Hills zircon population, the most unradiogenic, ancient isotopic signals have not been definitively identified in the younger (<3.9 Ga) rock and zircon record. Here we show Lu–Hf data from <4 Ga Jack Hills detrital zircons that document a significant and previously unknown transition in Yilgarn Craton crustal evolution between 3.9 and 3.7 Ga. The zircon source region evolved largely by internal reworking through the period 4.0–3.8 Ga, and the most ancient and unradiogenic components of the crust are mostly missing from the record after ∼4 Ga. New juvenile additions to the crust at ca. 3.9–3.8 Ga are accompanied by the disappearance of unradiogenic crust ca. 3.9–3.7 Ga. Additionally, this period is also characterized by a restricted range of δ 18 O after 3.8 Ga and a shift in several zircon trace element characteristics ca. 3.9–3.6 Ga. The simultaneous loss of ancient crust accompanied by juvenile crust addition can be explained by a mechanism similar to subduction, which effects both processes on modern Earth. The oxygen isotope and trace element information, although less sensitive to tectonic setting, also supports a transition in zircon formation environment in this period. [ABSTRACT FROM AUTHOR]

Abstract: We modeled the Δ17O of atmospheric O2 using 27 ordinary differential equations comprising a box model composed of the stratosphere, troposphere, geosphere, hydrosphere and biosphere. Results show that 57% of the deficit in 17O in O2 relative to a reference water fractionation line is the result of kinetic isotope fractionation attending the Dole effect, 33% balances the positive Δ17O of O(1D) in the stratosphere, and 10% is from evapotranspiration. The predicted Δ′17O O2 relative to waters is −0.410‰ as measured at the δ18O of air. The value for Δ′17O O2 varies at fixed δ18O with the concentration of atmospheric CO2, gross primary production, and net primary production as well as with reaction rates in the stratosphere. Our model prediction is consistent with our measurements of the oxygen isotopic composition of air O2 compared with rocks if rocks define a fractionation line with an intercept in δ′17O=103ln(δ17O/103 +1) vs. δ′18O=103ln(δ18O/103 +1) space less than SMOW but more positive than some recent measurements imply. The predicted Δ17O is less negative than that obtained from recent measurements of O2 directly against SMOW. Underestimation of Δ′17O O2 can only be ameliorated if the integrated (bulk) Δ′17O for stratospheric CO2 is significantly greater than measurements currently allow. Our results underscore the need for high-precision comparisons of the 17O/16O and 18O/16O ratios of atmospheric O2, VSMOW, and rocks. [Copyright &y& Elsevier]

Molecular nitrogen (N 2 ) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15 N 15 N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N 2 yield much smaller proportions of 15 N 15 N in N 2 . Electrical discharge experiments, however, establish 15 N 15 N excesses of up to +23‰. We argue that 15 N 15 N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15 N 15 N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.

Establishing the age of the Moon is critical to understanding solar system evolution and the formation of rocky planets, including Earth. However, despite its importance, the age of the Moon has never been accurately determined. We present uranium-lead dating of Apollo 14 zircon fragments that yield highly precise, concordant ages, demonstrating that they are robust against postcrystallization isotopic disturbances. Hafnium isotopic analyses of the same fragments show extremely low initial 176 Hf/ 177 Hf ratios corrected for cosmic ray exposure that are near the solar system initial value. Our data indicate differentiation of the lunar crust by 4.51 billion years, indicating the formation of the Moon within the first ~60 million years after the birth of the solar system.