Quantitative Conversion of Sulfate Oxygen for High-Precision Triple Oxygen Isotope Analysis.

Triple oxygen isotope composition (Δ'O) of sulfate carries information on the sulfur cycle as well as signatures of atmospheric O, O, and surface water of the geological past. However, existing analytical techniques can only achieve a partial oxygen yield during the conversion from sulfate to the analyte O, which results in isotope fractionation and impedes the Δ'O comparison with other oxygen-bearing compounds (e.g.

Origin of sulfate in post-snowball-Earth oceans: river inputs vs. shelf-derived HS.

A synthesis of global barite sulfate isotope data from approximately 635 million years ago, at the end of a global glaciation, undermines the hypothesis that river sulfate was the primary carrier of the distinctive 17O-depleted atmospheric O2 signature of the time. Instead, an aqueous H2S oxidation model on the shelf emerges as a compelling alternative, though it demands extensive validation across multiple fronts by the scientific community.

High-accuracy measurement of SF signal using an ultrahigh-resolution isotope ratio mass spectrometer.

Rationale: The ΔS standard deviation measured in a conventional isotope ratio mass spectrometer such as MAT 253 is ca 0.1‰ to 0.3‰.

Oxygen Isotope Analysis of Nanomole Phosphate Using PO Fragment in ESI-Orbitrap-MS.

The oxygen isotope composition of phosphate is a useful tool for studying biogeochemical phosphorus cycling. However, the current AgPO method is not only tedious in PO extraction and purification but also requires a large-sized sample at the micromole level, thereby limiting its application. Here, we present an approach to measuring the oxygen isotope composition, δO, of dissolved phosphate at the nanomole level using electrospray ionization Orbitrap mass spectrometry (ESI-Orbitrap-MS).

A new phosphate purification method for igneous weathering profiles.

Rationale: The oxygen isotope composition of phosphate (δ O ) is widely employed for reconstructing paleotemperature and tracing biogeochemical phosphorus cycling. However, existing phosphate purification protocols do not work well for igneous rocks and igneous weathering profiles (IWPs). A reliable purification method is needed for measuring δ O in these materials.

Sulfate triple-oxygen-isotope evidence confirming oceanic oxygenation 570 million years ago.

The largest negative inorganic carbon isotope excursion in Earth's history, namely the Ediacaran Shuram Excursion (SE), closely followed by early animal radiation, has been widely interpreted as a consequence of oceanic oxidation. However, the primary nature of the signature, source of oxidants, and tempo of the event remain contested. Here, we show that carbonate-associated sulfate (CAS) from three different paleocontinents all have conspicuous negative O anomalies (Δ'O values down to -0.

A transient peak in marine sulfate after the 635-Ma snowball Earth.

SignificanceEarth system's response to major perturbations is of paramount interest. On the basis of multiple isotope compositions for pyrite, carbonate-associated sulfate, carbonates, and organics within, we inferred that the much-debated, enigmatic, extremely C-depleted calcite cements in the ∼635-Ma cap carbonates in South China preserve geochemical evidence for marine microbial sulfate reduction coupled to anaerobic oxidation of methane. This interpretation implies the existence of a brief interval of modern-level marine sulfate.

Isotope fractionation during capillary leaking in an isotope ratio mass spectrometer.

Rationale: When isotope composition is measured in dual-inlet mode with an isotope ratio mass spectrometer (IRMS), reference gas may be gradually enriched in heavy isotopes due to preferential loss of light ones from the bellows over time. Quantifying the degree of isotopic enrichment of the reference gas is imperative for high-precision isotopic analysis (i.e.

Vapor isotopic evidence for the worsening of winter air quality by anthropogenic combustion-derived water.

Anthropogenic combustion-derived water (CDW) may accumulate in an airshed due to stagnant air, which may further enhance the formation of secondary aerosols and worsen air quality. Here we collected three-winter-season, hourly resolution, water-vapor stable H and O isotope compositions together with atmospheric physical and chemical data from the city of Xi'an, located in the Guanzhong Basin (GZB) in northwestern China, to elucidate the role of CDW in particulate pollution. Based on our experimentally determined water vapor isotope composition of the CDW for individual and weighted fuels in the basin, we found that CDW constitutes 6.

Large equatorial seasonal cycle during Marinoan snowball Earth.

In the equatorial regions on Earth today, the seasonal cycle of the monthly mean surface air temperature is <10°C. However, deep (>1 m) sand wedges were found near the paleoequator in the Marinoan glaciogenic deposits at ~635 million years ago, indicating a large seasonal cycle (probably >30°C). Through numerical simulations, we show that the equatorial seasonal cycle could reach >30°C at various continental locations if the oceans are completely frozen over, as would have been the case for a snowball Earth, or could reach ~20°C if the oceans are not completely frozen over, as would have been the case for a waterbelt Earth.

Unusual Improvement of Pseudocapacitance of Nanocomposite Electrodes: Three-Dimensional Amorphous Carbon Frameworks Triggered by TiO Nanocrystals.

Both nanocrystals and carbon materials have attracted considerable attention in lithium-ion batteries (LIBs) because of their fast kinetics for lithium storage or long-life cycles. However, the easy aggregation of nanocrystals and high-temperature doping process of carbon materials seriously hindered their application in LIBs. Here, we report the development of unprecedented TiO@C nanocomposite electrodes through a unique "melting low-temperature pyrolysis" strategy.

Transient marine euxinia at the end of the terminal Cryogenian glaciation.

Termination of the terminal Cryogenian Marinoan snowball Earth glaciation (~650-635 Ma) is associated with the worldwide deposition of a cap carbonate. Modeling studies suggest that, during and immediately following deglaciation, the ocean may have experienced a rapid rise in pH and physical stratification followed by oceanic overturn. Testing these predictions requires the establishment of a high-resolution sequence of events within sedimentary records.

Triple oxygen isotope evidence for limited mid-Proterozoic primary productivity.

The global biosphere is commonly assumed to have been less productive before the rise of complex eukaryotic ecosystems than it is today. However, direct evidence for this assertion is lacking. Here we present triple oxygen isotope measurements (∆O) from sedimentary sulfates from the Sibley basin (Ontario, Canada) dated to about 1.

Assessing Pyrite-Derived Sulfate in the Mississippi River with Four Years of Sulfur and Triple-Oxygen Isotope Data.

Riverine dissolved sulfate (SO) sulfur and oxygen isotope variations reflect their controls such as SO reduction and reoxidation, and source mixing. However, unconstrained temporal variability of riverine SO isotope compositions due to short sampling durations may lead to mischaracterization of SO sources, particularly for the pyrite-derived sulfate load. We measured the sulfur and triple-oxygen isotopes (δS, δO, and Δ'O) of Mississippi River SO with biweekly sampling between 2009 and 2013 to test isotopic variability and constrain sources.

Identifying apparent local stable isotope equilibrium in a complex non-equilibrium system.

Rationale: Although being out of equilibrium, biomolecules in organisms have the potential to approach isotope equilibrium locally because enzymatic reactions are intrinsically reversible. A rigorous approach that can describe isotope distribution among biomolecules and their apparent deviation from equilibrium state is lacking, however.

Methods: Applying the concept of distance matrix in graph theory, we propose that apparent local isotope equilibrium among a subset of biomolecules can be assessed using an apparent fractionation difference (|Δα|) matrix, in which the differences between the observed isotope composition (δ') and the calculated equilibrium fractionation factor (1000lnβ) can be more rigorously evaluated than by using a previous approach for multiple biomolecules.

Enantiomer signature and carbon isotope evidence for the migration and transformation of DDTs in arable soils across China.

Due to the adverse impact of DDTs on ecosystems and humans, a full fate assessment deems a comprehensive study on their occurrence in soils over a large region. Through a sampling campaign across China, we measured the concentrations, enantiomeric fractions (EFs), compound-specific carbon isotope composition of DDT and its metabolites, and the microbial community in related arable soils. The geographically total DDT concentrations are higher in eastern than western China.

Non-traditional stable isotope behaviors in immiscible silica-melts in a mafic magma chamber.

Non-traditional stable isotopes have increasingly been applied to studies of igneous processes including planetary differentiation. Equilibrium isotope fractionation of these elements in silicates is expected to be negligible at magmatic temperatures (δ(57)Fe difference often less than 0.2 per mil).

Lost cold Antarctic deserts inferred from unusual sulfate formation and isotope signatures.

The Antarctic ice cap significantly affects global ocean circulation and climate. Continental glaciogenic sedimentary deposits provide direct physical evidence of the glacial history of the Antarctic interior, but these data are sparse. Here we investigate a new indicator of ice sheet evolution: sulfates within the glaciogenic deposits from the Lewis Cliff Ice Tongue of the central Transantarctic Mountains.

Significant human impact on the flux and δ(34)S of sulfate from the largest river in North America.

Riverine dissolved sulfate (SO4(2-)) flux and sulfur stable isotope composition (δ(34)S) yield information on the sources and processes affecting sulfur cycling on different spatial and temporal scales. However, because pristine preindustrial natural baselines of riverine SO4(2-) flux and δ(34)S cannot be directly measured, anthropogenic impact remains largely unconstrained. Here we quantify natural and anthropogenic SO4(2-) flux and δ(34)S for North America's largest river, the Mississippi, by means of an exhaustive source compilation and multiyear monitoring.

Dynamic model constraints on oxygen-17 depletion in atmospheric O2 after a snowball Earth.

A large perturbation in atmospheric CO2 and O2 or bioproductivity will result in a drastic pulse of (17)O change in atmospheric O2, as seen in the Marinoan Oxygen-17 Depletion (MOSD) event in the immediate aftermath of a global deglaciation 635 Mya. The exact nature of the perturbation, however, is debated. Here we constructed a coupled, four-box, and quick-response biosphere-atmosphere model to examine both the steady state and dynamics of the MOSD event.

Sedimentary constraints on the duration of the Marinoan Oxygen-17 Depletion (MOSD) event.

The ~635 Ma Marinoan glaciation is marked by dramatic Earth system perturbations. Deposition of nonmass-dependently (17)O-depleted sulfate (SO4(2-)) in worldwide postglacial sediments is, thus far, unique to this glaciation. It is proposed that an extremely high-pCO2 atmosphere can result in highly (17)O-depleted atmospheric O2, or the Marinoan Oxygen-17 Depletion (MOSD) event.

Thermal-gradient-induced non-mass-dependent isotope fractionation.

Isotope fractionation resulting from gas diffusion along a thermal gradient has always been considered entirely mass-dependent. A previous report, however, showed that non-mass-dependent (17)O anomalies can be generated simply by subjecting O(2) gas in an enclosure to a thermal gradient. To explore the underlying mechanism for the anomalies, we tested the effect of gas pressure, duration of experiment, and geometry of the apparatus on the (17)O anomalies for O(2) as well as on the (33)S or (36)S anomalies for SF(6) gas.