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1.
The stable carbon and oxygen isotope compositions of fossil ostracods are powerful tools to estimate past environmental and climatic conditions. The basis for such interpretations is that the calcite of the valves reflects the isotopic composition of water and its temperature of formation. However, calcite of ostracods is known not to form in isotopic equilibrium with water and different species may have different offsets from inorganic precipitates of calcite formed under the same conditions. To estimate the fractionation during ostracod valve calcification, the oxygen and carbon isotope compositions of 15 species living in Lake Geneva were related to their autoecology and the environmental parameters measured during their growth. The results indicate that: (1) Oxygen isotope fractionation is similar for all species of Candoninae with an enrichment in 18O of more than 3‰ relative to equilibrium values for inorganic calcite. Oxygen isotope fractionation for Cytheroidea is less discriminative relative to the heavy oxygen, with enrichments in 18O for these species of 1.7 to 2.3‰. Oxygen isotope fractionations for Cyprididae are in-between those of Candoninae and Cytheroidea. The difference in oxygen isotope fractionation between ostracods and inorganic calcite has been interpreted as resulting from a vital effect. (2) Comparison with previous work suggests that oxygen isotope fractionation may depend on the total and relative ion content of water. (3) Carbon isotope compositions of ostracod valves are generally in equilibrium with DIC. The specimens’ δ13C values are mainly controlled by seasonal variations in δ13CDIC of bottom water or variation thereof in sediment pore water. (4) Incomplete valve calcification has an effect on carbon and oxygen isotope compositions of ostracod valves. Preferential incorporation of at the beginning of valve calcification may explain this effect. (5) Results presented here as well as results from synthetic carbonate growth indicate that different growth rates or low pH within the calcification site cannot be the cause of oxygen isotope ‘vital effects’ in ostracods. Two mechanisms that might enrich the 18O of ostracod valves are deprotonation of that may also contribute to valve calcification, and effects comparable to salt effects with high concentrations of Ca and/or Mg within the calcification site that may also cause a higher temperature dependency of oxygen isotope fractionation.  相似文献   

2.
The stable isotopes of sulfate are often used as a tool to assess bacterial sulfate reduction on the macro scale. However, the mechanisms of stable isotope fractionation of sulfur and oxygen at the enzymatic level are not yet fully understood. In batch experiments with water enriched in 18O we investigated the effect of different nitrite concentrations on sulfur isotope fractionation by Desulfovibrio desulfuricans.With increasing nitrite concentrations, we found sulfur isotope enrichment factors ranging from −11.2 ± 1.8‰ to −22.5 ± 3.2‰. Furthermore, the δ18O values in the remaining sulfate increased from approximately 50-120‰ when 18O-enriched water was supplied. Since 18O-exchange with ambient water does not take place in sulfate, but rather in intermediates of the sulfate reduction pathway (e.g. ), we suggest that nitrite affects the steady-state concentration and the extent of reoxidation of the metabolic intermediate sulfite to sulfate during sulfate reduction. Given that nitrite is known to inhibit the production of the enzyme dissimilatory sulfite reductase, our results suggest that the activity of the dissimilatory sulfite reductase regulates the kinetic isotope fractionation of sulfur and oxygen during bacterial sulfate reduction. Our novel results also imply that isotope fractionation during bacterial sulfate reduction strongly depends on the cell internal enzymatic regulation rather than on the physico-chemical features of the individual enzymes.  相似文献   

3.
Phosphoric acid digestion has been used for oxygen- and carbon-isotope analysis of carbonate minerals since 1950, and was recently established as a method for carbonate ‘clumped isotope’ analysis. The CO2 recovered from this reaction has an oxygen isotope composition substantially different from reactant carbonate, by an amount that varies with temperature of reaction and carbonate chemistry. Here, we present a theoretical model of the kinetic isotope effects associated with phosphoric acid digestion of carbonates, based on structural arguments that the key step in the reaction is disproportionation of H2CO3 reaction intermediary. We test that model against previous experimental constraints on the magnitudes and temperature dependences of these oxygen isotope fractionations, and against new experimental determinations of the fractionation of 13C-18O-containing isotopologues (‘clumped’ isotopic species). Our model predicts that the isotope fractionations associated with phosphoric acid digestion of carbonates at 25 °C are 10.72‰, 0.220‰, 0.137‰, 0.593‰ for, respectively, 18O/16O ratios (1000 lnα∗) and three indices that measure proportions of multiply-substituted isotopologues . We also predict that oxygen isotope fractionations follow the mass dependence exponent, λ of 0.5281 (where ). These predictions compare favorably to independent experimental constraints for phosphoric acid digestion of calcite, including our new data for fractionations of 13C-18O bonds (the measured change in Δ47 = 0.23‰) during phosphoric acid digestion of calcite at 25 °C.We have also attempted to evaluate the effect of carbonate cation compositions on phosphoric acid digestion fractionations using cluster models in which disproportionating H2CO3 interacts with adjacent cations. These models underestimate the magnitude of isotope fractionations and so must be regarded as unsucsessful, but do reproduce the general trend of variations and temperature dependences of oxygen isotope acid digestion fractionations among different carbonate minerals. We suggest these results present a useful starting point for future, more sophisticated models of the reacting carbonate/acid interface. Examinations of these theoretical predictions and available experimental data suggest cation radius is the most important factor governing the variations of isotope fractionation among different carbonate minerals. We predict a negative correlation between acid digestion fractionation of oxygen isotopes and of 13C-18O doubly-substituted isotopologues, and use this relationship to estimate the acid digestion fractionation of for different carbonate minerals. Combined with previous theoretical evaluations of 13C-18O clumping effects in carbonate minerals, this enables us to predict the temperature calibration relationship for different carbonate clumped isotope thermometers (witherite, calcite, aragonite, dolomite and magnesite), and to compare these predictions with available experimental determinations. The success of our models in capturing several of the features of isotope fractionation during acid digestion supports our hypothesis that phosphoric acid digestion of carbonate minerals involves disproportionation of transition state structures containing H2CO3.  相似文献   

4.
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5.
To better understand reaction pathways of pyrite oxidation and biogeochemical controls on δ18O and δ34S values of the generated sulfate in acid mine drainage (AMD) and other natural environments, we conducted a series of pyrite oxidation experiments in the laboratory. Our biological and abiotic experiments were conducted under aerobic conditions by using O2 as an oxidizing agent and under anaerobic conditions by using dissolved Fe(III)aq as an oxidant with varying δ18OH2O values in the presence and absence of Acidithiobacillus ferrooxidans. In addition, aerobic biological experiments were designed as short- and long-term experiments where the final pH was controlled at ∼2.7 and 2.2, respectively. Due to the slower kinetics of abiotic sulfide oxidation, the aerobic abiotic experiments were only conducted as long term with a final pH of ∼2.7. The δ34SSO4 values from both the biological and abiotic anaerobic experiments indicated a small but significant sulfur isotope fractionation (∼−0.7‰) in contrast to no significant fractionation observed from any of the aerobic experiments. Relative percentages of the incorporation of water-derived oxygen and dissolved oxygen (O2) to sulfate were estimated, in addition to the oxygen isotope fractionation between sulfate and water, and dissolved oxygen. As expected, during the biological and abiotic anaerobic experiments all of the sulfate oxygen was derived from water. The percentage incorporation of water-derived oxygen into sulfate during the oxidation experiments by O2 varied with longer incubation and lower pH, but not due to the presence or absence of bacteria. These percentages were estimated as 85%, 92% and 87% from the short-term biological, long-term biological and abiotic control experiments, respectively. An oxygen isotope fractionation effect between sulfate and water (ε18OSO4-H2O) of ∼3.5‰ was determined for the anaerobic (biological and abiotic) experiments. This measured value was then used to estimate the oxygen isotope fractionation effects between sulfate and dissolved oxygen in the aerobic experiments which were −10.0‰, −10.8‰, and −9.8‰ for the short-term biological, long-term biological and abiotic control experiments, respectively. Based on the similarity between δ18OSO4 values in the biological and abiotic experiments, it is suggested that δ18OSO4 values cannot be used to distinguish biological and abiotic mechanisms of pyrite oxidation. The results presented here suggest that Fe(III)aq is the primary oxidant for pyrite at pH < 3, even in the presence of dissolved oxygen, and that the main oxygen source of sulfate is water-oxygen under both aerobic and anaerobic conditions.  相似文献   

6.
The variations of δ17O and δ18O in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle. In order to close significant information gaps in the present distribution of δ17O and δ18O of meteoric water, we have run precise measurements, with respect to VSMOW, on samples distributed globally from low to high latitudes. Based on the new and existing data, we present the Global Meteoric Water Line (GMWL) for δ17O and δ18O as:
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7.
Understanding the relationship between stable isotope signals recorded in speleothems (δ13C and δ18O) and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability. Here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open-closed conditions with respect to CO2.The water entering the cave flows as a thin film towards the drip site. CO2 degasses from this film within approx. 10 s by molecular diffusion. Subsequently, chemical and isotopic equilibrium is established on a time scale of several 10-100 s. The δ13C value of the drip water is mainly determined by the isotopic composition of soil CO2. The evolution of the δ18O value of the carbonate species is determined by the long exchange time Tex, between oxygen in carbonate and water of several 10,000 s. Even if the oxygen of the CO2 in soil water is in isotopic equilibrium with that of the water, dissolution of limestone delivers oxygen with a different isotopic composition changing the δ18O value of the carbonate species. Consequently, the δ18O value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time.After the water has entered the cave, the carbon and oxygen isotope composition of the drip water may be altered by CO2-exchange with the cave air. Exchange times, , of about 3000 s are derived. Thus, only drip water, which drips in less than 3000 s onto the stalagmite surface, is suitable to imprint climatic signals into speleothem calcite deposited from it.Precipitation of calcite proceeds with time constants, τp, of several 100 s. Different rate constants and equilibrium concentrations for the heavy and light isotopes, respectively, result in isotope fractionation during calcite precipitation. Since Tex ? τp, exchange with the oxygen in the water can be neglected, and the isotopic evolution of carbon and oxygen proceed analogously. For drip intervals Td < 0.1τp the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time. The calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water.For long drip intervals, when calcite is deposited from a stagnant water film, long drip intervals may have a significant effect on the isotopic composition of the DIC. In this case, the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval. Such processes must be considered when speleothems are used as proxies of past climate variability.  相似文献   

8.
It is widely recognised that a significant limitation to the ultimate precision of carbon stable isotope ratio measurements, as obtained from dual-inlet mass spectrometric measurements of CO2 isotopologue ion abundances at m/z 44, 45, and 46, is the correction for interference from 17O-bearing molecular ions. Two long-established, alternative procedures for determining the magnitude of this correction are in widespread use (although only one has IAEA approval); their differences lead to small but potentially significant discrepancies in the magnitude of the resulting correction. Furthermore, neither approach was designed to accommodate oxygen three-isotope distributions which do not conform to terrestrial mass-dependent behaviour. Stratospheric CO2, for example, contains a strongly ‘mass-independent’ oxygen isotope composition. A new strategy for determining the 17O-bearing ion correction is presented, for application where the oxygen three-isotope characteristics of the analyte CO2 are accurately known (or assigned) in terms of the slope λ of the three-isotope fractionation line and the ordinate axis intercept 103 ln(1 + k) on a 103 ln(1 + δ17O) versus 103 ln(1 + δ18O) plot. At the heart of the approach is the relationship between 17R, which is the 17O/16O ratio of the sample CO2, and other assigned or empirically determined parameters needed for the δ13C evaluation:
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9.
The origin of Zn isotope fractionation in sulfides   总被引：2，自引：0，他引：2  
Isotope fractionation of Zn between aqueous sulfide, chloride, and carbonate species (Zn2+, Zn(HS)2, , , ZnS(HS)−, ZnCl+, ZnCl2, , and ZnCO3) was investigated using ab initio methods. Only little fractionation is found between the sulfide species, whereas carbonates are up to 1‰ heavier than the parent solution. At pH > 3 and under atmospheric-like CO2 pressures, isotope fractionation of Zn sulfides precipitated from sulfidic solutions is affected by aqueous sulfide species and the δ66Zn of sulfides reflect these in the parent solutions. Under high PCO2 conditions, carbonate species become abundant. In high PCO2 conditions of hydrothermal solutions, Zn precipitated as sulfides is isotopically nearly unfractionated with respect to a low-pH parent fluid. In contrast, negative δ66Zn down to at least −0.6‰ can be expected in sulfides precipitated from solutions with pH > 9. Zinc isotopes in sulfides and rocks therefore represent a potential indicator of mid to high pH in ancient hydrothermal fluids.  相似文献   

10.
Soil-water interactions in coastal tundra soils are a potential source of nutrients for surrounding fjordal and coastal ecosystems. Changes in water chemistry and stable isotope composition from three streams in west Spitsbergen were examined to assess the sources and losses of nitrogen, sulfur and carbon in thin organic tundra soils overlying sediments. Studies were undertaken from snowmelt (mid June) through to the end of the summer (September) in both 2001 and 2002. Drainage water chemistry was dominated by the solution of Ca-Mg carbonates with δ13C values in the waters being uncharacteristically high (approx. −2‰ at the end of the season), reflecting a largely open system in which the CO2 is derived equally from the atmosphere and plant/soil sources. Early melt waters had δ34S values dominated by sea salt reflecting the close proximity to the ocean. However, as the season progressed the marine influence lessened. Extrapolation of the data suggests that the origin of non-sea salt δ34S was the oxidation of reduced sulfur from coal particles in the subsoil. Concentrations of inorganic N in stream waters were generally very low. However, values were found to increase as the season progressed, possibly through increased microbial activity in the soil and the early senescence of tundra plants reducing demand. Dual isotope analysis of δ15N and δ18O suggested that the vast majority of snow-pack was assimilated by the soil microbial biomass before being released, recycled and lost to drainage waters. Organic N concentrations in drainage waters were generally equal to or greater than losses of inorganic N from tundra soils. The study demonstrated the effectiveness of stable isotope data for understanding biogeochemical cycling and soil-water interactions in tundra ecosystems. The implications of the results are discussed in relation to climate warming.  相似文献   

11.
The oxygen isotope fractionation between the structural carbonate of inorganically precipitated hydroxyapatite (HAP) and water was determined in the range 10-37 °C. Values of 1000 ln α() are linearly correlated with inverse temperature (K) according to the following equation: 1000 ln α() = 25.19 (±0.53)·T−1 − 56.47 (±1.81) (R2 = 0.998). This fractionation equation has a slightly steeper slope than those already established between calcite and water ( [O’Neil et al., 1969] and [Kim and O’Neil, 1997]) even though measured fractionations are of comparable amplitude in the temperature range of these experimental studies. It is consequently observed that the oxygen isotope fractionation between apatite carbonate and phosphate increases from about 7.5‰ up to 9.1‰ with decreasing temperature from 37 °C to 10 °C. A compilation of δ18O values of both phosphate and carbonate from modern mammal teeth and bones confirms that both variables are linearly correlated, despite a significant scattering up to 3.5‰, with a slope close to 1 and an intercept corresponding to a 1000 ln α() value of 8.1‰. This apparent fractionation factor is slightly higher or close to the fractionation factor expected to be in the range 7-8‰ at the body temperature of mammals.  相似文献   

12.
Ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic-inorganic interactions during diagenesis as well as of the devolatilization history and fluid/rock interaction during metamorphism. In this study, a collection of geochemically well-characterized biotite separates from a series of graphite-bearing Paleozoic greenschist- to upper amphibolite-facies metapelites, western Maine, USA, were analyzed for ammonium nitrogen () contents and isotopic composition (δ15NNH4) using the HF-digestion distillation technique followed by the EA-IRMS technique. Biotite separates, sampled from 9 individual metamorphic zones, contain 3000 to 100 ppm with a wide range in δ15N from +1.6‰ to +9.1‰. Average contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade (∼500 °C) down to 218 ppm for the highest metamorphic grade (∼685 °C). Decreasing abundances in are inversely correlated in a linear fashion with increasing K+ in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect. Despite expected increasing δ15NNH4 values in biotite with nitrogen loss, a significant decrease from the Garnet Zones to the Staurolite Zones was found, followed by an increase to the Sillimanite Zones. This pattern for δ15NNH4 values in biotite inversely correlates with Mg/(Mg + Fe) ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between or , reflecting devolatilization history and redox conditions during metamorphism.  相似文献   

13.
Dissolved inorganic nitrogen, largely in reduced form (), has been documented in thermal waters throughout Yellowstone National Park, with concentrations ranging from a few micromolar along the Firehole River to millimolar concentrations at Washburn Hot Springs. Indirect evidence from rock nitrogen analyses and previous work on organic compounds associated with Washburn Hot Springs and the Mirror Plateau indicate multiple sources for thermal water NH4(T), including Mesozoic marine sedimentary rocks, Eocene lacustrine deposits, and glacial deposits. A positive correlation between NH4(T) concentration and δ18O of thermal water indicates that boiling is an important mechanism for increasing concentrations of NH4(T) and other solutes in some areas. The isotopic composition of dissolved NH4(T) is highly variable (δ15N = −6‰ to +30‰) and is positively correlated with pH values. In comparison to likely δ15N values of nitrogen source materials (+1‰ to +7‰), high δ15N values in hot springs with pH >5 are attributed to isotope fractionation associated with loss by volatilization. NH4(T) in springs with low pH typically is relatively unfractionated, except for some acid springs with negative δ15N values that are attributed to condensation. NH4(T) concentration and isotopic variations were evident spatially (between springs) and temporally (in individual springs). These variations are likely to be reflected in biomass and sediments associated with the hot springs and outflows. Elevated NH4(T) concentrations can persist for 10s to 1000s of meters in surface waters draining hot spring areas before being completely assimilated or oxidized.  相似文献   

14.
Excess N from agriculture induces eutrophication in major river systems and hypoxia in coastal waters throughout the world. Much of this N is from headwaters far up the watersheds. In turn, much of the N in these headwaters is from ground-water discharge. Consequently, the concentrations and forms of N in groundwater are important factors affecting major aquatic ecosystems; despite this, few data exist for several species of N in groundwater and controls on speciation are ill-defined. Herein, we report N speciation for a spring and well that were selected to reflect agricultural impacts, and a spring and well that show little to no agricultural-N impact. Samples were characterized for NO3−, NO2−, N2O, NH4+, urea, particulate organic N(), and dissolved organic N(). These analytes were monitored in the agricultural spring for up to two years along with other analytes that we reported upon previously. For all samples, when oxidized N was present, the dominant species was NO3− (88-98% of total fixed N pool) followed by (<4-12%) and only trace fractions of the other N analytes. In the non-agriculturally impacted well sample, which had no quantifiable NO3− or dissolved O2, comprised the dominant fraction (68%) followed by NH4+ (32%), with only a trace balance comprised of other N analytes. Water drawn from the well, spring and a wetland situated in the agricultural watershed also were analyzed for dissolved N2 and found to have a fugacity in excess of that of the atmosphere. H2O2 was analyzed in the agricultural spring to evaluate the O2/H2O2 redox potential and compare it to other calculated potentials. The potential of the O2/H2O2 couple was close in value to the NO3−/NO2− couple suggesting the important role of H2O2 as an O2-reduction intermediate product and that O2 and NO3− are reduced concomitantly. The O2/H2O2 and NO3−/NO2− couples also were close in value to a cluster of other inorganic N and Fe couples indicating near partial equilibrium among these species. Urea mineralization to NO2− was found to approach equilibrium with the reduction of O2 to H2O2. By modeling as amide functional groups, as justified by recent analytical work, similar thermodynamic calculations support that mineralization to NO2− proceeds nearly to equilibrium with the reduction of O2 to H2O2 as well. This near equilibration of redox couples for urea- and -oxidation with O2-reduction places these two couples within the oxidized redox cluster that is shared among several other couples we have reported previously. In the monitored agricultural spring, [NO3−] was lower in the summer than at other times, whereas [N2O] was higher in the summer than at other times, perhaps reflecting a seasonal variation in the degree of denitrification reaction progress. No other N analytes were observed to vary seasonally in our study. In the well having no agricultural-N impact, Corg/Norg = 5.5, close to the typical value for natural aqueous systems of about 6.6. In the agricultural watershed Corg/Norg varied widely, from ∼1.2 to ?9.  相似文献   

15.
Nitrate-contaminated groundwater from an aquifer in the Osona region (NE Spain) was chemically and isotopically (δ15NNO3,δ18ONO3,δ34SSO4,δ18OSO4, δD, δ18OH2O and δ13CDIC) characterized. Diffuse- contamination reached values of 366 mg/L. Nearly 75% of the 37 sampled sites had higher concentrations than the 50 mg/L in limit for drinking water. To identify the source of pollution δ15NNO3 and δ18ONO3 were used with results, for most samples, in the range of pig manure . Nitrification processes were evaluated by means of the δ18O of and water. Isotopic data suggested that natural attenuation of was taking place. This process was confirmed using the δ18ONO3 coupled with the ratio, avoiding the influence of continuous inputs. A further insight on denitrification processes was obtained by analyzing the ions involved in denitrification reactions. Although the role of organic matter oxidation could neither be confirmed nor discarded, this approach showed a link between denitrification and pyrite oxidation. Therefore, in areas with no adequate infrastructure (e.g. multipiezometers), such as the one studied, this approach could be useful for implementing better water management.  相似文献   

16.
Sphalerite oxidation is a common process under acid-mine drainage (AMD) conditions and results in the release of , Zn and potentially toxic trace metals, which can pollute rivers and oceans. However, there are only a few studies on the mechanisms of aerobic sphalerite oxidation. Oxygen and S isotope investigations of the produced may contribute to the understanding of sphalerite oxidation mechanisms so helping to interpret field data from AMD sites. Therefore, batch oxidation experiments with an Fe-rich sphalerite were performed under aerobic abiotic conditions at different initial pH values (2 and 6) for different lengths of time (2–100 days). The O and S isotope composition of the produced indicated changing oxidation pathways during the experiments. During the first 20 days of the experiments at both initial pH values, molecular O2 was the exclusive O source of . Furthermore, the lack of S isotope enrichment processes between and sphalerite indicated that O2 was the electron acceptor from sphalerite S. As the oxidation proceeded, a sufficient amount of released Fe(II) was oxidized to Fe(III) by O2. Therefore, electrons could be transferred from sphalerite S sites to adsorbed hydrous Fe(III) and O from the hydration sphere of Fe was incorporated into the produced as indicated by decreasing δ18OSO4 values which became more similar to the δ18OH2O values. The enrichment of 32S in relative to the sphalerite may also result from sphalerite oxidation by Fe(III).The incorporation of O2 into during the oxidation of sphalerite was associated with an O isotope enrichment factor εSO4–O2 of ca. −22‰. The O isotope enrichment factor εSO4–H2O was determined to be ?4.1‰. A comparison with O and S studies of other sulfides suggests that there is no general oxidation mechanism for acid-soluble sulfides.  相似文献   

17.
The δ37Cl values of volcanic fumarole gases and bubbling springs were measured from the Central American and the Kurile arcs. Low temperature gas samples from the Central American arc have δ37Cl values generally between −2 and 2‰, whereas high-temperature fumaroles (>100 °C) range from 4 to 12‰, with several outliers. This is in contrast to the high-temperature fumaroles from the Kurile island Kudryavy which have slightly positive δ37Cl values, averaging 0.8‰ (±0.6, 1σ), and from our previous work on Izu and Mariana arc samples in which the δ37Cl values of fumarole and ash samples are similar to each other and negative. Assuming that the source for the high-T Central American fumaroles has typical subduction δ37Cl values (−2.5 to 1‰), then there must be a large Cl isotope fractionation in the near-surface fumarolic system. The most likely fractionation mechanism for the high δ37Cl values is between Cl−aq − HCl(g), but published theoretical fractionation for this pair is only ∼1.5‰, insufficient to explain the large range of values observed in the fumaroles. Three experiments were undertaken in order to identify a process that could cause the wide range of δ37Cl values observed in the high-temperature fumaroles. Results are the following: (1) A sub-boiling equilibration experiment between aqueous chloride and HCl gas had , in agreement with the theoretical calculations. (2) Evaporation of HCl(g) from hydrochloric acid at room temperature had fractionation in the opposite sense, with a . (3) A ‘synthetic fumarole’ gave large positive fractionations up to 9‰, with 37Cl strongly partitioned into the vapor phase. The ‘fumarole’ experiments were made by bubbling dry air through boiling hydrochloric acid in an Erlenmeyer flask, and collecting the evolved HCl(g) in a second ‘downstream’ flask filled with distilled water. This extreme enrichment is likely due to a distillation process in which 37Cl-enriched HCl(g) is stripped from the hydrochloric acid followed by a significant fraction of the light HCl(g) redissolving into the constantly condensing water vapor on the walls of the first flask. This distillation experiment creates a Cl isotope fractionation that is the same order of magnitude as observed in the high-temperature fumaroles in Central America. These results suggest that there must be a H2O liquid-vapor region in the sub-surface fumarole conduit where light Cl is stripped from the HCl gas as it passes through the fumarole. Similar 37Cl enrichments are expected in fossil epithermal boiling systems.  相似文献   

18.
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19.
Although the stable oxygen isotope fractionation between dissolved sulfate ion and H2O (hereafter ) is of physico-chemical and biogeochemical significance, no experimental value has been established until present. The primary reason being that uncatalyzed oxygen exchange between and H2O is extremely slow, taking ∼105 years at room temperature. For lack of a better approach, values of 16‰ and 31‰ at 25 °C have been assumed in the past, based on theoretical ‘gas-phase’ calculations and extrapolation of laboratory results obtained at temperatures >75 °C that actually pertain to the bisulfate system. Here I use novel quantum-chemistry calculations, which take into account detailed solute-water interactions to establish a new value for of 23‰ at 25 °C. The results of the corresponding calculations for the bisulfate ion are in agreement with observations. The new theoretical values show that sediment -data, which reflect oxygen isotope equilibration between sulfate and ambient water during microbial sulfate reduction, are consistent with the abiotic equilibrium between and water.  相似文献   

20.
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