Sulfur isotope ratios of Icelandic lava incrustations and volcanic gases

Sulfur isotope ratios were measured in eight lava incrustations and three volcanic gas samples and their corresponding lava flows. The lava incrustations of sulfate composition are from five recent eruptions and occur as thenardite or as aphtitalite-thenardite mixtures, with abundant trace elements. The incrustations show small sulfur isotope fractionation of 1–2‰ compared with corresponding lavas and the volcanic gas samples. The sulfate incrustations are formed through oxidation of SO₂ from the emitted volcanic gas and subsequent reaction with metal halides. The volcanic gas samples show a distribution of decreasing δ³⁴S through time from +3.4 to −1.8‰; sulfate was preferentially degassed compared to sulfide. The data indicate that sulfate incrustations serve as a late-stage volcanic gas sample with respect to sulfur isotopes.     

Stratification and mixing of a post-glacial Neoproterozoic ocean: Evidence from carbon and sulfur isotopes in a cap dolostone from northwest China

To improve our knowledge about the geochemical and environmental aftermath of Neoproterozoic global glaciations, we analyzed stable isotopes (δ¹³C, δ¹⁸O, δ³⁴S) and elemental concentrations (Ca, Mg, S, Sr, Fe, and Mn) of the ～ 10-m-thick Zhamoketi cap dolostone atop the Tereeken diamictite in the Quruqtagh area, eastern Chinese Tianshan. Available chemostratigraphic data suggest that the Tereeken diamictite is probably equivalent to the Marinoan glaciation. Our new data indicate that organic and carbonate carbon isotopes of the Zhamoketi cap dolostone show little stratigraphic variations, averaging ? 28.2‰ and ? 4.6‰, respectively. In contrast, sulfur isotopes show significant stratigraphic variations. Carbonate associated sulfate (CAS) abundance decreases rapidly in the basal cap dolostone and δ³⁴S_CAS composition varies between + 9‰ and + 15‰ in the lower 2.5 m. In the overlying interval, CAS abundance remains low while δ³⁴S_CAS rises ～ 5‰ and varies more widely between + 10‰ and + 21‰. The range of δ³⁴S_py of the cap dolostone overlaps with that of δ³⁴S_CAS, but direct comparison shows that δ³⁴S_py is typically greater than δ³⁴S_CAS measured from the same samples. Hypotheses to explain the observations must account for both the remarkable sulfur isotope enrichment of pyrites and the inverse fractionation. We propose that CAS and pyrite were derived from two isotopically distinct reservoirs in a chemically stratified basin or a basin with a sulfate minimum zone. In this model, CAS was derived from shallow, oxic surface waters with moderate sulfate concentration and depleted in ³⁴S due to the post-glacial influx of sulfur from continental weathering. In contrast, pyrite was derived from anoxic bottom waters (or a sulfate minimum zone) with low sulfate concentration and ³⁴S enrichment due to long-term syn-glacial sulfate reduction. The rapid shift in CAS abundance and sulfur isotope composition within the cap dolostone is interpreted to reflect the mixing of the two reservoirs after initial deglaciation. Comparison with other post-Marinoan cap carbonates shows significant spatial heterogeneity in δ³⁴S_CAS, which together with strong temporal variation in δ³⁴S_CAS, points to generally low sulfate concentrations in post-Marinoan oceans.     

Cenozoic evolution of the sulfur cycle: Insight from oxygen isotopes in marine sulfate

We report new data on oxygen isotopes in marine sulfate (δ¹⁸O_SO4), measured in marine barite (BaSO₄), over the Cenozoic. The δ¹⁸O_SO4 varies by 6‰ over the Cenozoic, with major peaks 3, 15, 30 and 55 Ma. The δ¹⁸O_SO4 does not co-vary with the δ³⁴S_SO4, emphasizing that different processes control the oxygen and sulfur isotopic composition of sulfate. This indicates that temporal changes in the δ¹⁸O_SO4 over the Cenozoic must reflect changes in the isotopic fractionation associated with the sulfide reoxidation pathway. This suggests that variations in the aerial extent of different types of organic-rich sediments may have a significant impact on the biogeochemical sulfur cycle and emphasizes that the sulfur cycle is less sensitive to net organic carbon burial than to changes in the conditions of that organic carbon burial. The δ¹⁸O_SO4 also does not co-vary with the δ¹⁸O measured in benthic foraminifera, emphasizing that oxygen isotopes in water and sulfate remain out of equilibrium over the lifetime of sulfate in the ocean. A simple box model was used to explore dynamics of the marine sulfur cycle with respect to both oxygen and sulfur isotopes over the Cenozoic. We interpret variability in the δ¹⁸O_SO4 to reflect changes in the aerial distribution of conditions within organic-rich sediments, from periods with more localized, organic-rich sediments, to periods with more diffuse organic carbon burial. While these changes may not impact the net organic carbon burial, they will greatly affect the way that sulfur is processed within organic-rich sediments, impacting the sulfide reoxidation pathway and thus the δ¹⁸O_SO4. Our qualitative interpretation of the record suggests that sulfate concentrations were probably lower earlier in the Cenozoic.     

Sulphur isotope equilibrium during sulphur hydrolysis at high temperatures

Studies of the sulphur hydrolysis reaction, 4S + 4H₂O /ag 3H₂S + HSO₄^? + H⁺, were conducted between 200 and 320°C in sealed silica glass tubes. The isotope exchange reaction: H₂¹⁸O + HS¹⁶O₄^? /ag H₂¹⁶O + HS¹⁸O₄^? is so rapid at the low pH (1.5–3) as to be unquenchable. However, the sulphur isotope exchange reaction: H₂³⁴S+ H³²SO₄^? /ag H₂³²S + H³⁴SO₄^? gave t12 values of 0.1, 0.3 and 1.7 days at 320, 260 and 200°C respectively and equilibrium H₂S - HSO₄^? sulphur isotope fractionation values of 20.9, 22.4, 24.8, 26.7 and 29.3‰ at 320, 290, 260, 230 and 200°C respectively. This latter data is represented by: 1000lnα_(HSO4^??H2S) = 5.07 (10⁶T^?2) + 6.33, and has valuable applications in geothermal and ore deposit studies.     

Diagenetic fluid evolution and water-rock interaction model of carbonate cements in sandstone: An example from the reservoir sandstone of the Fourth Member of the Xujiahe Formation of the Xiaoquan-Fenggu area,Sichuan Province,China

Carbonate cement is the most abundant cement type in the Fourth Member of the Xujiahe Formation in the Xiaoquan-Fenggu area of the West Sichuan Depression. Here we use a systematic analysis of carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and enclosure homogenization temperatures to study the precipitation mechanism, pore fluid evolution, and distribution of different types of carbonate cement in reservoir sand in the study area. Crystalline calcite has relatively heavy carbon and oxygen isotope ratios(δ13C = 2.14‰, δ18O = -5.77‰), and was precipitated early. It was precipitated directly from supersaturated alkaline fluid under normal temperature and pressure conditions. At the time of precipitation, the fluid oxygen isotope ratio was very light, mainly showing the characteristics of a mixed meteoric water-seawater fluid(δ18O = -3‰), which shows that the fluid during precipitation was influenced by both meteoric water and seawater. The calcite cement that fills in the secondary pores has relatively lighter carbon and oxygen isotope ratios(δ13C = -2.36‰, δ18O = -15.68‰). This cement was precipitated late, mainly during the Middle and Late Jurassic. An important material source for this carbonate cement was the feldspar corrosion process that involved organic matter. The Ca2+, Fe3+ and Mg2+ ions released by the clay mineral transformation process were also important source materials. Because of water-rock interactions during the burial process, the oxygen isotope ratio of the fluid significantly increased during precipitation, by about 3‰. The dolomite cements in calcarenaceous sandstone that was precipitated during the Middle Jurassic have heavier carbon and oxygen isotope ratios, which are similar to those of carbonate debris in the sandstone(δ13C = 1.93‰, δ18O = -6.11‰), demonstrating that the two are from the same source that had a heavier oxygen isotope ratio(δ18O of about 2.2‰). The differences in fluid oxygen isotope ratios during cement precipitation reflect the influences of different water-rock interaction systems or different water-rock interaction strengths. This is the main reason why the sandstone containing many rigid particles(lithic quartz sandstone) has a relatively negative carbon isotope ratio and why the precipitation fluid in calcarenaceous sandstone has a relatively heavier oxygen isotope ratio.     

Multiple sulfur isotope chemostratigraphy across the Permian–Triassic boundary at Chaotian,China: Implications for a shoaling model of toxic deep-waters

Previous studies on multiple sulfur isotopes (³²S, ³³S, and ³⁴S) in sedimentary pyrite at the end-Permian suggested a shoaling of anoxic/sulfidic deep-water contributing to the extinction. This scenario is based on an assumption that the sedimentary sulfur cycle was largely controlled by benthos activity, though a stratigraphic correlation between the sulfur records and ichnofabrics of the sediments at the end-Permian has not yet been examined. We report the multiple sulfur isotopic composition of pyrite in the Permian–Triassic boundary interval at Chaotian, South China. Our data can be generally explained by a mixing of sulfur in sulfide from two different sources: one produced via sulfate reduction in an open system with respect to sulfate and the other produced in a closed system. In particular, the former with the substantially low δ³⁴S (<−40 ‰) and high ∆³³S (up to +0.100 ‰) values was likely produced via water-mass sulfate reduction or via sulfate reduction in oxic sediments with common burrows. The frequent occurrence of small pyrite framboids (mostly <5 μm in diameter) in the Lopingian (Late Permian) Dalong Formation of deep-water facies supports the enhanced water-mass sulfate reduction in an anoxic deep-water mass. The negative ∆³³S values are observed only in the oxic limestones, and no substantial ∆³³S change is observed across the extinction horizon despite of the disappearance of bioturbation. Our results are apparently inconsistent with the previous shoaling model. We expand the model and infer that, when the deep-water was sulfidic and its shoaling rate was high, a substantial amount of hydrogen sulfide (H₂S) was supplied onto the shelf via the shoaling; that resulted in the positive ∆³³S value of the bulk sediments. The observed ∆³³S variation on a global scale suggests a substantial variation in H₂S concentration and/or in upwelling rate of shoaling deep-waters during the Permian–Triassic transition.     

Isotopic evidence of TSR origin for natural gas bearing high H<Subscript>2</Subscript>S contents within the Feixianguan Formation of the northeastern Sichuan Basin,southwestern China

The northeastern area of Sichuan Basin, southwestern China, is the area with the maximal reserve of natural gas containing higher hydrogen sulphide (H₂S) that has been found among the petroliferous basins of China, with the proven and controlled gas reserve of more than 200 billion cubic meters. These gas pools, with higher H₂S contents averaging 9%, some 17%, are mainly distributed on structural belts of Dukouhe, Tieshanpo, Luojiazhai, Puguang, etc., while the oolitic-shoal dolomite of the Triassic Feixianguan Fm. (T₁f) is the reservoir. Although many scholars regard the plentiful accumulation of H₂S within the deep carbonate reservoir as the result of Thermochemical Sulfate Reduction (TSR), however, the process of TSR as well as its residual geological and geochemical evidence is still not quite clear. Based on the carbon isotopic analysis of carbonate strata and secondary calcite, etc., together with the analysis of sulfur isotopes within H₂S, sulphur, gypsum, iron pyrites, etc., as well as other aspects including the natural gas composition, carbon isotopes of hydrocarbons reservoir petrology, etc., it has been proved that the above natural gas is a product of TSR. The H₂S, sulphur and calcite result from the participation of TSR reactions by hydrocarbon gas. During the process for hydrocarbons being consumed due to TSR, the carbons within the hydrocarbon gas participate in the reactions and finally are transferred into the secondary calcite, and become the carbon source of secondary calcite, consequently causing the carbon isotopes of the secondary calcite to be lower (−18.2‰). As for both the intermediate product of TSR, i.e. sulfur, and its final products, i.e. H₂S and iron pyrites, their sulfur elements are all sourced from the sulfate within the Feixianguan Fm. During the fractional processes of sulfur isotopes, the bond energy leads to the ³²S being released firstly, and the earlier it is released, the lower δ ³⁴S values for the generated sulphide (H₂S) or sulfur will be. However, for the anhydrite that participates in reactions, the higher the reaction degree, the more ³²S is released, while the less ³²S remains and the more δ ³⁴S is increased. The testing results have proved the process of the dynamic fractionation of sulfur isotopes.     

Isotopic Characterization of Sulfate in a Shallow Aquifer Impacted by Agricultural Fertilizer

The stable isotope ratios of groundwater sulfate (³⁴S/³²S, ¹⁸O/¹⁶O) are often used as tracers to help determine the origin of groundwater or groundwater contaminants. In agricultural watersheds, little is known about how the increased use of sulfur as a soil amendment to optimize crop production is affecting the isotopic composition of groundwater sulfate, especially in shallow aquifers. We investigated the isotopic composition of synthetic agricultural fertilizers and groundwater sulfate in an area of intensive agricultural activity, in Ontario, Canada. Groundwater samples from an unconfined surficial sand aquifer (Lake Algonquin Sand Aquifer) were analyzed from multi-level monitoring wells, riverbank seeps, and private domestic wells. Fertilizers used in the area were analyzed for sulfur/sulfate content and stable isotopic composition (δ¹⁸O and/or δ³⁴S). Fertilizers were isotopically distinct from geological sources of groundwater sulfate in the watershed and groundwater sulfate exhibited a wide range of δ³⁴S (−6.9 to +20.0‰) and δ¹⁸O (−5.0 to +13.7‰) values. Quantitative apportionment of sulfate sources based on stable isotope data alone was not possible, largely because two of the potential fertilizer sulfate sources had an isotopic composition on the mixing line between two natural geological sources of sulfate in the aquifer. This study demonstrates that, when sulfate isotope analysis is being used as a tracer or co-tracer of the origin of groundwater or of contaminants in groundwater, sulfate derived from synthetic fertilizer needs to be considered as a potential source, especially when other parameters such as nitrate independently indicate fertilizer impacts to groundwater quality.     

Isotopic and hydrochemistry spatial variation of sulfate for groundwater characterization in karstic aquifers

The Sierra Gorda aquifer is one of the most extensive of southern Spain. The main groundwater discharge is produced at its northern boundary through several high‐flow springs. In this study, stable isotopes of dissolved sulfate (δ³⁴S and δ¹⁸O) and groundwater chemistry were used to determine the origin of the sulfate and to characterize the groundwater flow. We sampled the main springs, as well as other minor outlets related to perched water tables, in order to determine the different sources of SO₄^2? (e.g., dissolution of evaporites and atmospheric deposition). The substantial difference in the amount of dissolved SO₄^2? between the springs located in its northwestern part (≈25 mg/L) and those elsewhere in the northern part (≈60 mg/L) suggests zones with separate groundwater flow systems. A third group of springs, far from the northeastern boundary of the permeable outcrops, shows higher SO₄^2? content than the rest (≈125 mg/L). The isotopic range of sulfate (?0.3‰ to 14.82‰ V‐CTD) points to several sources, including dissolution of Triassic or Miocene evaporites, atmospheric deposition, and decomposition of organic material in the soil. Among these, the dissolution of Triassic gypsum—which overlies the saturated zone as a consequence of the folds and faults that deform the aquifer—is the main source of SO₄^2? (range from 12.79‰ to 14.82‰ V‐CTD). This range is typical for Triassic gypsum. The higher karstification in the western sector, together with important differences in the saturated thickness between the western and eastern sectors, would also be due to the tectonic structure and could explain the difference in SO₄^2? contents in the water. This singular arrangement may cause a higher residence time of groundwater in the eastern sector; thus, a higher contact time with Triassic evaporitic rocks is inferred. Accordingly, the stable isotopes of SO₄^2? are found to be a valuable tool for identifying areas with different flow systems in the saturated zone of karstic aquifers, as well as for evaluating aspects such as the degree of karstification .     

Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece

The chemical and isotopic compositions (δD_H2O, δ¹⁸O_H2O, δ¹⁸O_CO2, δ¹³C_CO2, δ³⁴S, and He/N₂ and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ¹⁸O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H₂–Ar, H₂–N₂, and H₂–H₂O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H₂O–H₂–CO₂–CO–CH₄ system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.     

Coupled silicon–oxygen isotope fractionation traces Archaean silicification

Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa.The δ³⁰Si and δ¹⁸O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (?0.64‰ < δ³⁰Si < ?0.01‰ and + 8.6‰ < δ¹⁸O < + 11.9‰) to silicified basalts (δ³⁰Si and δ¹⁸O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ < δ³⁰Si < + 1.05‰ and + 10.9 < δ¹⁸O < + 17.1), except two cherts, which have negative δ³⁰Si values, but high δ¹⁸O (up to + 19.5‰).The pronounced positive correlations between δ³⁰Si, δ¹⁸O and SiO₂ imply that the isotope variation is driven by the silicification process which coevally introduced both ¹⁸O and ³⁰Si into the basalts. The oxygen isotope variation in the basalts from about 8.6‰ to 15.6‰ is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.     

Modern stable isotopic (δ18O, δ2H, δ13C) variation in terrestrial,fluvial, estuarine and marine waters from north‐central Sarawak,Malaysian Borneo

Stable isotope data on humid tropical hydrology are scarce and, at present, no such data exist for Borneo. Delta¹⁸O, δ²H and δ¹³C were analysed on 22 water samples from different parts of the Sungai (river) Niah basin (rain, cave drip, rainforest pool, tributary stream, river, estuary, sea) in north‐central Sarawak, Malaysian Borneo. This was done to improve understanding of the modern stable isotope systematics of the Sungai Niah basin, essential for the palaeoenvironmental interpretation of the Late Quaternary stable isotope proxies preserved in the Great Cave of Niah. The Niah hydrology data are put into a regional context using the meteoric water line for Southeast Asia, as derived from International Atomic Energy Agency/World Meteorological Organization isotopes in precipitation network data. Although the Niah hydrological data‐set is relatively small, spatial isotopic variability was found for the different subenvironments of the Sungai Niah basin. A progressive enrichment occurs towards the South China Sea (δ¹⁸O ?4·6‰; δ²H ?29·3‰; δ¹³C ?4·8‰) from the tributary stream (δ¹⁸O ?8·4‰; δ²H ?54·7‰; δ¹³C ?14·5‰) to up‐river (δ¹⁸O c. ?8‰; δ²H c. ?51‰; δ¹³C c. ?12‰) and down‐river values (δ¹⁸O c. ?7·5‰; δ²H c. ?45‰; δ¹³C c. ?11‰). This is thought to reflect differential evaporation and mixing of different components of the water cycle and a combination of depleted biogenic δ¹³C (plant respiration and decay) with enriched δ¹³C values (due to photosynthesis, atmospheric exchange, mixing with limestone and marine waters) downstream. Cave drip waters are relatively enriched in δ¹³C as compared to the surface waters. This may indicate rapid degassing of the cave drips as they enter the cave atmosphere. Copyright © 2005 John Wiley & Sons, Ltd.     

Calibration method affects the measured δ2H and δ18O in soil water by direct H2Oliquid–H2Ovapour equilibration with laser spectroscopy

The direct H₂O_liquid–H₂O_vapour equilibration method utilizing laser spectroscopy (DVE-LS) is a way to measure soil pore water stable isotopes. Various equilibration times and calibration methods have been used in DVE-LS. Yet little is known about their effects on the accuracy of the obtained isotope values. The objective of this study was to evaluate how equilibration time and calibration methods affect the accuracy of DVE-LS. We did both spiking and field soil experiments. For the spiking experiment, we applied DVE-LS to four soils of different textures, each of which was subjected to five water contents and six equilibration times. For the field soil experiment, we applied three calibration methods for DVE-LS to two field soil profiles, and the results were compared with cryogenic vacuum distillation (CVD)-LS. Results showed that DVE-LS demonstrated higher δ²H and δ¹⁸O as equilibration time increased, but 12 to 24 hr could be used as optimal equilibration time. For field soil samples, DVE-LS with liquid waters as standards led to significantly higher δ²H and δ¹⁸O than CVD-LS, with root mean square error (RMSE) of 8.06‰ for δ²H and 0.98‰ for δ¹⁸O. Calibration with soil texture reduced RMSE to 3.53‰ and 0.72‰ for δ²H and δ¹⁸O, respectively. Further, calibration with both soil texture and water content decreased RMSE to 3.10‰ for δ²H and 0.73‰ for δ¹⁸O. Our findings conclude that the calibration method applied may affect the measured soil water isotope values from DVE-LS.     

Estimating thermal inflow to El Chichón crater lake using the energy-budget,chemical and isotope balance approaches

El Chichón crater lake appeared immediately after the 1982 catastrophic eruption in a newly formed, 1-km wide, explosive crater. During the first 2 years after the eruption the lake transformed from hot and ultra-acidic caused by dissolution of magmatic gases, to a warm and less acidic lake due to a rapid “magmatic-to-hydrothermal transition” — input of hydrothermal fluids and oxidation of H₂S to sulfate. Chemical composition of the lake water and other thermal fluids discharging in the crater, stable isotope composition (δD and δ¹⁸O) of lake water, gas condensates and thermal waters collected in 1995–2006 were used for the mass-balance calculations (Cl, SO₄ and isotopic composition) of the thermal flux from the crater floor. The calculated fluxes of thermal fluid by different mass-balance approaches become of the same order of magnitude as those derived from the energy-budget model if values of 1.9 and 2 mmol/mol are taken for the catchment coefficient and the average H₂S concentration in the hydrothermal vapors, respectively. The total heat power from the crater is estimated to be between 35 and 60 MW and the CO₂ flux is not higher than 150 t/day or ~ 200 gm^− 2 day^− 1.     

Continuous real‐time analysis of the isotopic composition of precipitation during tropical rain events: Insights into tropical convection

To investigate stable isotopic variability of precipitation in Singapore, we continuously analysed the δ‐value of individual rain events from November 2014 to August 2017 using an online system composed of a diffusion sampler coupled to Cavity Ring‐Down Spectrometer. Over this period, the average value (δ¹⁸O_Avg), the lowest value (δ¹⁸O_Low), and the initial value (δ¹⁸O_Init) varied significantly, ranging from ?0.45 to ?15.54‰, ?0.9 to ?17.65‰, and 0 to ?13.13‰, respectively. All 3 values share similar variability, and events with low δ¹⁸O_Low and δ¹⁸O_Avg values have low δ¹⁸O_Init value. Individual events have limited intraevent variability in δ‐value (Δδ) with the majority having a Δδ below 4‰. Correlation of δ¹⁸O_Low and δ¹⁸O_Avg with δ¹⁸O_Init is much higher than that with Δδ, suggesting that convective activities prior to events have more control over δ‐value than on‐site convective activities. The d‐excess of events also varies considerably in response to the seasonal variation in moisture sources. A 2‐month running mean analysis of δ¹⁸O reveals clear seasonal and interannual variability. Seasonal variability is associated with the meridional movement of the Intertropical Convergence Zone and evolution of the Asian monsoon. El Niño–Southern Oscillation is a likely driver of interannual variability. During 2015–2016, the strongest El Niño year in recorded history, the majority of events have a δ¹⁸O value higher than the weighted average δ¹⁸O of daily precipitation. δ¹⁸O shows a positive correlation with outgoing longwave radiation in the western Pacific and the Asian monsoon region, and also with Oceanic Niño Index. During El Niño, the convection centre shifts eastward to the central/eastern Pacific, weakening convective activities in Southeast Asia. Our study shows that precipitation δ‐value contains information about El Niño–Southern Oscillation and the Intertropical Convergence Zone, which has a significant implication for the interpretation of water isotope data and understanding of hydrological processes in tropical regions.     

Oxygen isotope variations in marginal basin and ocean-ridge basalts

Oxygen isotope analyses have been made on 27 tholeiitic basalts from the Lau and Mariana marginal ocean basins and from mid-ocean ridges. The ¹⁸O values are related to the extent of hydration by submarine weathering as indicated by H₂O^? and total water content. Extrapolation to zero H₂O^? content gives a δ¹⁸O value of 5.5‰ on the SMOW scale for unaltered marginal basin basalts, in exact agreement with the oxygen isotope “signature” of ocean-ridge tholeiites. Three alkali basalts from seamount provinces also fit the tholeiite relationship. A Lau Basin gabbro has the tholeiitic ¹⁸O content, but an Indian Ocean gabbro is unusually light (δ¹⁸O = 4.0 for whole rock, plagioclase, and amphibole), and resembles the low -¹⁸O Iceland basalts. The basalt data confirm petrologic and chemical evidence for origin of marginal basins by extensional processes with production of basalts from depleted mantle material isotopically identical to the source of ocean-ridge tholeiites.     

Stable and radiogenic isotopes as tracers for the origin,mixing and subsurface history of fluids in submarine shallow-water hydrothermal systems

The shallow-water hydrothermal system in Tutum Bay on the west side of Ambitle Island, Papua New Guinea provides us with an exceptional opportunity to study isotope systematics in a near shore setting. Compared to seawater, the hydrothermal fluids in Tutum Bay have lower values for δD, δ¹⁸O, δ¹³C, and ⁸⁷Sr and higher values for ³H, δ³⁴S(SO₄) and δ¹⁸O(SO₄). The δ¹⁸O and δD records for vents 1 and 4 indicate that fluid compositions remained stable over an extended period. Interpretation of isotope data clearly demonstrates the predominantly meteoric origin of Tutum Bay hydrothermal fluids, despite their location in a marine environment. δ¹⁸O and δD values are identical to mean average annual precipitation in eastern Papua New Guinea. The hypothesis that these fluids are a simple product of mixing between seawater and onshore hydrothermal fluids from the Waramung (W-1) and Kapkai (W-2) thermal areas has been rejected, because the observed δ³⁷Cl, ³H, δ³⁴S(SO₄) and δ¹⁸O(SO₄) values cannot be explained by a simple mixing model. The application of δ¹⁸O(SO₄) and δ¹³C thermometers in combination with ³H values corroborates the three-step model of Pichler et al. [Pichler, T., Veizer, J., Hall, G.E.M., 1999. The chemical composition of shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New Guinea and their effect on ambient seawater. Marine Chemistry 64 (3) 229–252], where (1) phase separation in the deep reservoir beneath Ambitle Island produces a high temperature vapor that rises upward and subsequently reacts with cooler ground water to form a low pH, CO₂-rich water of approximately 150–160 °C, (2) caused by the steep topography, this CO₂-rich fluid moves laterally towards the margin of the hydrothermal system where it mixes with the marginal upflow of the deep reservoir fluid. This produces a dilute chloride water of approximately 165 °C, and (3) possibly the entrainment of minor amounts of ground or seawater during its final ascent.     

Detection of Mixing Dynamics During Pumping of a Flooded Coal Mine

In complex hydrogeological environments the effective management of groundwater quality problems by pump‐and‐treat operations can be most confidently achieved if the mixing dynamics induced within the aquifer by pumping are well understood. The utility of isotopic environmental tracers (C‐, H‐, O‐, S‐stable isotopic analyses and age indicators—¹⁴C, ³H) for this purpose is illustrated by the analysis of a pumping test in an abstraction borehole drilled into flooded, abandoned coal mineworkings at Deerplay (Lancashire, UK). Interpretation of the isotope data was undertaken conjunctively with that of major ion hydrochemistry, and interpreted in the context of the particular hydraulic setting of flooded mineworkings to identify the sources and mixing of water qualities in the groundwater system. Initial pumping showed breakdown of initial water quality stratification in the borehole, and gave evidence for distinctive isotopic signatures (δ³⁴S(SO4) ? ?1.6‰, δ¹⁸O(SO₄) ? +15‰) associated with primary oxidation of pyrite in the zone of water table fluctuation—the first time this phenomenon has been successfully characterized by these isotopes in a flooded mine system. The overall aim of the test pumping—to replace an uncontrolled outflow from a mine entrance in an inconvenient location with a pumped discharge on a site where treatment could be provided—was swiftly achieved. Environmental tracing data illustrated the benefits of pumping as little as possible to attain this aim, as higher rates of pumping induced in‐mixing of poorer quality waters from more distant old workings, and/or renewed pyrite oxidation in the shallow subsurface.     

Geochemical constraints on the depositional environment of the 1.84 Ga Embury Lake Formation,Flin Flon Belt,Canada

The Flin Flon Belt of Canada contains Paleoproterozoic volcanic–sedimentary sequences that are related to the Trans‐Hudson Orogeny. The sequences include island arc volcanic and volcaniclastic rocks (Amisk Group) that are unconformably overlain by subaerial sedimentary rocks (Missi Group), and younger deep facies sediments. In the Flin Flon area, several north–south trending faults divide the sequences into blocks and obscure the depositional environment of the deep facies sediments. Locally, within the Flin Flon area, the Embury Lake Formation is in fault contact with island arc volcanic–sedimentary sequences of the Amisk and Missi Groups. To identify the depositional environment of the Embury Lake Formation, we used lithologic and geochemical approaches. Here, we report carbon isotopic values in organic matter (δ¹³C_org) and sulfur isotopes (δ³⁴S), as well as total organic carbon and total sulfur measurements for the black shale in the formation. Samples were taken from a drill core that contains alternating bands of sandstone and black shale. Pyrite in the black shale is divided into four textural types: euhedral, vein‐type, elliptical, and microcrystalline. Microcrystalline pyrite is typically generated by microbially mediated sulfate reduction. An extremely low S/C ratio (avg. = 0.04) is consistent with lacustrine deposition. The ranges of δ¹³C_org (?36 ‰ to ?27 ‰) and δ³⁴S (+3.0 ‰ to +7.7 ‰) values can be explained by bacterial photosynthesis that involved Calvin cycle and acetyl CoA pathways, and sulfate reduction in a low‐sulfate environment. Considering the depositional age reported in a previous study of < 1.84 Ga, the Embury Lake Formation was likely emplaced in a lacustrine setting during the Trans‐Hudson Orogeny.     

Sulfur and carbon isotopic systematics of Guadalupian‐Lopingian (Permian) mid‐Panthalassa: δ34S and δ13C profiles in accreted paleo‐atoll carbonates in Japan

Immediately before the extinction of the end‐Guadalupian (Middle Permian; ca 260 Ma), a significant change to the global carbon cycle occurred in the superocean Panthalassa, as indicated by a prominent positive δ¹³C excursion called the Kamura event. However, the causes of this event and its connection to the major extinction of marine invertebrates remain unclear. To understand the mutual relationships between these changes, we analyzed the sulfur isotope ratio of the carbonate‐associated sulfate (CAS) and HCl‐insoluble residue, as well as the carbon isotope ratio of bulk organic matter, for the Middle‐Upper Permian carbonates of an accreted mid‐oceanic paleo‐atoll complex from Japan, where the Kamura event was first documented. We detected the following unique aspects of the stable carbon and sulfur isotope records. First, the extremely high δ¹³C values of carbonate (δ¹³C_carb) over +5 ‰ during the Capitanian (late Guadalupian) were associated with large isotopic differences between carbonate and organic matter (Δ¹³C = δ¹³C_carb ? δ¹³C_org). We infer that the Capitanian Kamura event reflected an unusually large amount of dissolved organic matter in the expanded oxygen minimum zone at mid‐depth. Second, the δ³⁴S values of CAS (δ³⁴S_CAS) were inversely correlated with the δ¹³C_carb values during the Capitanian to early Wuchiapingian (early Late Permian) interval. The Capitanian trend may have appeared under increased oceanic sulfate conditions, which were accelerated by intense volcanic outgassing. Bacterial sulfate reduction with increased sulfate concentrations in seawater may have stimulated the production of pyrite that may have incorporated iron in pre‐existing iron hydroxide/oxide. This stimulated phosphorus release, which enhanced organic matter production and resulted in high δ¹³C_carb. Low δ³⁴S_CAS values under high sulfate concentrations were maintained and the continuous supply of sulfate cannot by explained only by the volcanic eruption of the Emeishan Trap, which has been proposed as a cause of the extinction. The Wuchiapingian δ³⁴S_CAS–δ¹³C_carb correlation, likely related to low sulfate concentration, may have been caused by the removal of oceanic sulfate through the massive evaporite deposition.