Variations In Isotope Fractionation Research Articles

In situ trace elements and sulfur isotope analyses of layered sphalerite as a record of ore-forming processes in the world-class Jinding sediment-hosted Zn-Pb Ore Deposit, China

The Jinding deposit is well-known to contain high concentrations of metals Zn, Pb, Cd, Tl, Ag, etc. in the world. The associated critical metals and their substitution mechanisms were wildly concerned. This study investigated and compared sphalerites using a combination of textural, trace element, and sulfur isotopic analyses to give insights into element substitution mechanisms and possible sources of ore-forming fluids and to constrain processes involved in ore genesis of the world-class Jinding sediment-hosted Zn-Pb deposit. LA-ICP-MS analyses reveal chemical zoning in the sphalerites together with the coupling of two main groups of trace elements substitution mechanisms: one is Fe + Ge + Mn + Pb + As + Tl and vacancies to substitute Zn, and the other is Cd + Cu + Ag + Sb to substitute Zn. The incorporation of trace elements is facilitated by the replacement of Zn by Cd and Fe. These two group elements have distinct color oscillatory zonation and are intertwined in the trace element LA-ICP-MS element maps. The sulfur isotopic values show high isotope fractionation in the sphalerite from −28.4 to −0.5 ‰, suggesting a bacteriogenic sulfur origin at Jinding. Sphalerite sample has observed that sulfur isotope is correlated with Fe concentration and anti-correlated with Cd concentration. These variations in isotope fractionation and trace element disequilibrium partitioning were interpreted as the effects of temperature and pH with less influence from sulfur activity. These variability zones of sphalerite alternately enriched in Cd- and Fe-related elements suggested that ore fluids may flow from metal-fertile sedimentary/basement sequences during their ascent, and colloform sphalerite was likely formed by a high degree of supercooling, over-saturation, and rapid mixing between bacteriogenic sulfur and metal-rich in spaces of collapse dome. Based on our observations, we suggested that these variability zones of layered sphalerite alternately enriched in Cd and Fe would likely provide useful insight for a potential economic Zn-Pb and associated critical metals mineral exploration deposit.

Isotopic fractionation and trophic position of zooplankton species in the Upper Paraná River floodplain

This study aimed to evaluate the isotopic fractionation and trophic position of three zooplankton species (Notodiaptomus amazonicus, Moina minuta and Bosmina hagmanni) in the Upper Paraná River floodplain. We predict that phytoplankton is the main food resource used by these species. Three zooplankton samples and three phytoplankton samples were taken from each sampling site, with three to four samples collected for each species. The number of individuals for samples varied according to the body size: from 100 to 130 individuals for Notodiaptomus amazonicus; 150 to 200 for Moina minuta; and from 250 to 300 for Bosmina hagmanni. The isotopic values for δ13C and δ15N were determined using mass spectrophotometer. The isotopic fractionation of 13C was performed according to the relationship Δ = δ13C zooplankton - δ13C phytoplankton. To determine the possible trophic position of these species, we used the expression TL = (δ15N zooplankton - δ15N phytoplankton)/Δ+ 1. The species showed high variation in isotopic fractionation and in trophic position in the different environments. We verified that the species use other food resources in addition to phytoplankton. The elucidation and understanding of the trophic position of the organisms based on stable isotopic analysis offers complementary information to traditional techniques. This analysis helps explain the flow of matter and energy in the food chain of floodplain aquatic environments as well as trace the trophic relationships involved in the ecological roles and strategies of distinct species.

Stable C and N Isotopes: A Tool to Interpret Interacting Environmental Stresses on Soil and Plant

Natural abundances of stable isotopes of nitrogen and carbon (<TEX>${\delta}^{15}N$</TEX> and <TEX>${\delta}^{13}C$</TEX>) are being widely used to study N and C cycle processes in plant and soil systems. Variations in <TEX>${\delta}^{15}N$</TEX> of the soil and the plant reflect the potentially variable isotope signature of the external N sources and the isotope fractionation during the N cycle process. <TEX>$N_2$</TEX> fixation and N fertilizer supply the nitrogen, whose <TEX>${\delta}^{15}N$</TEX> is close to 0%o, whereas the compost as. an organic input generally provides the nitrogen enriched in <TEX>$^{15}N$</TEX> compared to the atmospheric <TEX>$N_2$</TEX>. The isotope fractionation during the N cycle process decreases the <TEX>${\delta}^{15}N$</TEX> of the substrate and increases the <TEX>${\delta}^{15}N$</TEX> of the product. N transformations such as N mineralization, nitrification, denitrification, assimilation, and the <TEX>$NH_3$</TEX> volatilization have a specific isotope fractionation factor (<TEX>${\alpha}$</TEX>) for each N process. Variation in the <TEX>${\delta}^{13}C$</TEX> of plants reflects the photosynthetic type of plant, which affects the isotope fractionation during photosynthesis. The <TEX>${\delta}^{13}C$</TEX> of C3 plant is significantly lower than, whereas the <TEX>${\delta}^{13}C$</TEX> of C4 plant is similar to that of the atmospheric <TEX>$CO_2$</TEX>. Variation in the isotope fractionation of carbon and nitrogen can be observed under different environmental conditions. The effect of environmental factors on the stomatal conductance and the carboxylation rate affects the carbon isotope fractionation during photosynthesis. Changes in the environmental factors such as temperature and salt concentration affect the nitrogen isotope fractionation during the N cycle processes; however, the mechanism of variation in the nitrogen isotope fractionation has not been studied as much as that in the carbon isotope fractionation. Isotope fractionation factors of carbon and nitrogen could be the integrated factors for interpreting the effects of the environmental factors on plants and soils.

Hydrogen Concentration and Stable Isotopic Composition of Methane in Bubble Gas Observed in a Natural Wetland

Bubble gas samples were collected at three different vegetation sites and two different depths (surface and 40 cm) in a natural wetland, Mizorogaike in Kyoto city, to investigate hydrogen concentration and δD and δ13C values of CH4. Hydrogen concentration in bubble gas varied from 1 to 205 ppm, and that collected during summer was higher than that during winter. Bubble samples collected at 40 cm at sphagnum site usually showed the lowest H2 concentration among the samples collected at the three sites and two depths on the same day. The lowest H2 concentration observed at 40 cm at sphagnum site was similar to that expected for environmental water in which H2 producer and consumer need to assemble for free energy requirement. Low δ13C and high δD (relatively small hydrogen fractionation; \(\Delta\delta\hbox{D}_{{\rm water}-{\rm CH}_4}\cong 220\)‰) were observed in CH4 collected at a deeper (40 cm) layer of sphagnum site during winter, when H2 concentration was low (typically 2–4 ppm). On the other hand, CH4 in the bubble samples collected during summer showed high δ13C and low δD (relatively large hydrogen fractionation; \(\Delta\delta\hbox{D}_{{\rm water}-{\rm CH}_4}\cong300\)‰), when H2 concentration was high. Carbon and hydrogen isotope fractionation during CH4 production were variable, possibly depending on the H2 concentration and the production rate. Difference in enzymatic reaction and magnitude of hydrogen isotope exchange among water, CH4, and H2 may cause the variation in isotope fractionation during CH4 production.

Early Cenozoic benthic foraminiferal isotopes: Species reliability and interspecies correction factors

Oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions, with those of benthic foraminifera providing information on the deep oceans. Reconstructions are complicated by interspecies isotopic offsets that result from microhabitat preferences (carbonate precipitation in isotopically distinct environments) and vital effects (species‐specific metabolic variation in isotopic fractionation). We provide correction factors for early Cenozoic benthic foraminifera commonly used for isotopic measurements (Cibicidoides spp., Nuttallides truempyi, Oridorsalis spp., Stensioina beccariiformis, Hanzawaia ammophila, and Bulimina spp.), showing that most yield reliable isotopic proxies of environmental change. The statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies. Interspecies isotopic offsets appear to have changed through the Cenozoic, either (1) as a result of evolutionary changes or (2) as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies. Regardless of the reason, the assumption that isotopic offsets have remained constant through the Cenozoic has introduced an ∼1–2°C uncertainty into deep sea paleotemperature calculations. In addition, we compare multiple species isotopic data from a western North Atlantic section that includes the Paleocene‐Eocene thermal maximum to determine the most reliable isotopic indicator for this event. We propose that Oridorsalis spp. was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time; it may be the best recorder at other locations and for other extreme events also.

Variation in δ15N and δ13C trophic fractionation: Implications for aquatic food web studies

Use of stable isotope techniques to quantify food web relationships requires a priori estimates of the enrichment or depletion in δ15N and δ13C values between prey and predator (known as trophic fractionation; hereafter Δδ15N and Δδ13C). We conducted a broad‐scale analysis of Δδ15N and Δδ13C from aquatic systems, including three new field estimates. Carnivores had significantly higher Δδ15N values than herbivores. Furthermore, carnivores, invertebrates, and lab‐derived estimates were significantly more variable than their counterparts ( f‐test, p &lt; 0.00001). Δδ13C was higher for carnivores than for herbivores (p = 0.001), while variances did not differ significantly. Excluding herbivores, the average Δδ15N and Δδ13C were 3.4‰ and 0.8‰, respectively. But even with unbiased fractionation estimates, there is variation in isotopic fractionation that contributes to error in quantitative isotope model outputs. We simulated the error variance in δ15N‐based estimates of trophic position and two‐source δ13C diet mixing models, explicitly considering the observed variation in Δδ15N and Δδ13C, along with the other potential error sources. The resultant error in trophic position and mixing model outputs was generally minor, provided that primary consumers were used as baseline indicators for estimating trophic position and that end member d13C values in dietary mixing models were sufficiently distinct.

Biodegradation of hydrocarbons and biogeochemical sulfur cycling in the salt dome environment: Inferences from sulfur isotope and organic geochemical investigations of the Bahloul Formation at the Bou Grine Zn/Pb ore deposit, Tunisia

Combined organic geochemical and stable isotope (S) analyses of samples from the Cretaceous Bahloul Formation (Tunisia) provide insight to oil accumulation processes, biogeochemical alteration of hydrocarbons, microbial sulfate reduction, and mineral deposition at the flanks of the Triassic Jebel Lorbeus diapir, forming the Bou Grine Zn/Pb deposit. The sulfur isotopic composition of the metal sulfides correlates with the degree of biodegradation of hydrocarbons, with the base-metal content and with the proportion of aromatics in the organic extracts. The δ 34S-values are interpreted to reflect bacterial sulfate reduction in a more or less closed system rather than a thermogenic contribution. The extent of H 2S production by the activity of the sulfate-reducing bacteria probably was limited by the availability of sulfate, which in turn was governed by the permeability of the respective sedimentary sequence and by the distance to the anhydrite cap rock. Evidence is provided that biodegradation of hydrocarbons and microbial sulfate reduction contribute to the formation of the high-grade mineralization inside the Bahloul Formation at the contact with the salt dome cap rock. The metals probably were derived through leaching of deeper sedimentary sequences by hot hypersaline basinal brines, evolved by dissolution of salt at the flanks of the diapirs. These hot metalliferous brines are proposed to migrate up around the diapir, finally mixing with near-surface, sulfate-rich brines in the roof zone. When the fluids came in contact with the organic-rich sediments of the Bahloul Formation, the dissolved sulfate was reduced by the sulfate-reducing bacteria. Hydrocarbons generated or accumulated in the Bahloul Formation were utilized by sulfate reducers. The occurrence of high amounts of native sulfur in high-grade ore samples suggest that the production rate of H 2S by bacterial sulfate reduction exceeded its consumption by metal-sulfide precipitation. The supply of dissolved metals probably was the limiting reaction. The trend of δ 34S of native sulfur (S 0) towards lower values to the top of the highly mineralized Bahloul profile provides evidence for a biogenic origin of S 0 by sulfide oxidizers. The variation in isotopic fractionation between native sulfur and sulfide sulfur in the ore minerals reflects the kinetic isotope fractionation factor connected with metabolic processes and the respective reaction rate during biogenic oxidation of sulfur.