共查询到20条相似文献，搜索用时 281 毫秒
1.
In a soil developed on the Cretaceous chalk of the Eastern Paris basin, calcite dissolution begins at the surface. The soil water is rapidly saturated in calcite. Calcite dissolution follows two different pathways according to seasonal pedoclimatic conditions.During winter: the soil is only partly saturated in water and the CO2 partial pressure is low (Ca 10?3 atm.). As a consequence total inorganic dissolved carbon (TIDC) is a hundred times the carbon content of the gaseous phase. Equilibrium is usually observed between the two phases. It is a closed system. The measured carbon 14 activity (87,5%) and 13C content () of the drainage water are very close to theoretical values calculated for an ideal mixing system between gaseous and mineral phases (respectively characterized by the following isotopic values: ; ; ; ).During spring and summer: the soil moisture decreases, the input of biogenic CO2 induces an increase of the soil CO2 partial pressure (Ca from 3.10?3 atm to 7.10?3 atm). The carbon content of the gaseous phase is higher by an order of magnitude compared to winter conditions. Therefore the aqueous phase is undersaturated in CO2 with respect to the latter. This disequilibrium occurs as a result of unbalanced rates of CO2 dissolution and CO2 effusion toward atmosphère. It is an open system. The carbon isotopic ratio of the aqueous phase is regulated by that of the gaseous phase, as demonstrated by the agreement between measured and calculated isotopic compositions (respectively δL mes = from ?9,4%0 to ?11,5%0, δl calc = from ?9,8%0 to ?13,9%0 AL mes = 119%, AL calc = from 119% to 125%).The solutions originating from both systems (open and closed) move downwards without significant mixing together. It has also been observed that no significant variation of the TIDC isotopic composition occurs during precipitation of secondary calcite. 相似文献
2.
, and ratios have been measured on the same samples for carbonatite complexes. The results show that besides the ‘carbonatite box’ of Tayloret al. (1967) there exist higher δ18O and δ13C values than can be explained by late magmatic or deuteric processes. These processes correspond to high concentrations of CO2 and lead to big enrichments in 18O and 13C as well as in some ‘volatile’ elements. Strontium results are consistent with a model of selective contamination of deep-seated material by highly radiogenic strontium. The whole study leads to the opinion that parent magmas of carbonatites differentiated in a crustal environment with or without significant contamination. 相似文献
3.
The fractionation factors () for the reduction of CO2 to CH4 by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation () approximating the observed fractionation. 相似文献
4.
A study was undertaken with the thermophilic green alga Cyanidium caldarium which grows optimally at low pH and high concentrations of CO2. Carbon-isotope fractionation was not found to be a simple linear function of temperature. Maximum enrichment of 12C in cellular material occurred under optimum growth conditions (at approximately pH 2 and at temperatures between 40–50°C in a CO2 atmosphere). A maximum measured fractionation of ?24‰ may account for low values () in Precambrian kerogen presumably derived from algal mats. 相似文献
5.
6.
Numerical modeling of the terrestrial oxygen budget based on the revised δ13Ccarb record by Veizeret al. (1980) has shown that total photosynthetic oxygen has varied between ±7% and ±10% of its average reservoir size (～3.2 × 1022 g) during the last 800 myr as a result of oscillations of the sedimentary reservoir of organic carbon. Calculated curves of oxygen evolution display a distinct minimum in the Early Paleozoic framed by two maxima in the Latest Proterozoic and the Mesozoic. The sympathetic relationship observed between the curves of total oxygen evolution and respective functions for the partial reservoir of sulfate-bound oxygen suggests that the O2 required for an additional conversion of sulfide to sulfate was most probably provided by excess burial of organic carbon, the results of the modeling thus adding credence to current interpretations proposed for the negative correlation between the secular and trends. 相似文献
7.
8.
William H. Schlesinger 《Geochimica et cosmochimica acta》1985,49(1):57-66
Radiocarbon and 230Th-234U dates of calcic horizons from calciorthid soil profiles in the Mojave Desert were used to calculate the rate of deposition of pedogenic CaCO3. A major period of CaCO3 deposition appears to have occurred about 20000 yBP forming calcic horizons below 100-cm depth during a climatic regime with greater effective rainfall than in the present. The overall rate of deposition has been 1.0 to 3.5 g CaCO3/m2/yr during soil formation. This rate is consistent with present-day rates, assuming that the atmospheric deposition of Ca limits the process. Stable isotope ratios in calcic horizons indicate that CaCO3 precipitated from a soil environment with CO2 of ? 15.5%. (vs. PDB) and H2O of + 2.0%. (vs. SMOW). These values suggest that CaCO3 precipitates when seasonal drought simultaneously lowers soil pore pCO2 and enriches soil water 18O by evaporation. The role of soil calcic horizons in the global geochemical cycle of carbon is discussed. 相似文献
9.
Oxygen isotope exchange between BaSO4 and H2O from 110 to 350°C was studied using 1 m H2SO4-1 m NaCl and 1 m NaCl solutions to recrystallize the barite. The slow exchange rate (only 7% exchange after 1 yr at 110°C and 91% exchange after 22 days at 350°C in 1 m NaCl solution) prompted the use of the partial equilibrium technique. However, runs at 300 and 350°C were checked by complete exchange experiments. The temperature calibration curve for the isotope exchange is calculated giving most weight to the high temperature runs where the partial equilibrium technique can be tested. Oxygen isotope fractionation factors (α) in 1 m NaCl solution (110–350°C), assuming a value of 1.0407 for αCO2H2O at 25°C, are: .These data, when corrected for ion hydration effects in solution (Truesdell, 1974), give the fractionation factors in pure water: .In the 1 m H2SO4-1 m NaCl runs, sulfur isotope fractionation between HSO?4 and BaSO4 is less than the detection limit of 0.4%. A barite-sulfide geothermometer is obtained by combining HSO?4H2S and sulfide-H2S calibration data.Barite in the Derbyshire ore field, U.K., appears to have precipitated in isotopic equilibrium with water and sulfur in the ore fluid at temperatures less than 150°C. At the Tui Mine, New Zealand, the barite-water geothermometer indicates temperatures of late stage mineralization in the range 100–200°C. A temperature of 350 ± 20°C is obtained from the barite-pyrite geothermometer at the Yauricocha copper deposit, Peru, and oxygen isotope analyses of the barite are consistent with a magmatic origin for the ore fluids. 相似文献
10.
and ratios were measured for 114 petroleum samples and for several samples of related organic matter. δD of crude oil ranges from ?85 to ?181‰, except for one distillate (?250‰) from the Kenai gas field; δ13C of crude oil ranges from ?23.3 to ?32.5‰, Variation in δD and δ13C values of compound-grouped fractions of a crude oil is small, 3 and 1.1%., respectively, and the difference in δD and δ13C between oil and coeval wax is slight. Gas fractions are 53–70 and 22.6–23.2‰ depleted in D and 13C, respectively, relative to the coexisting oil fractions.The δD and δ13C values of the crude oils appear to be largely determined by the isotopic compositions of their organic precursors. The contribution of terrestrial organic debris to the organic precursors of most marine crude oils may be significant. 相似文献
11.
Calculations based on approximately 350 new measurements (CaT-PCO2) of the solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO3(s) = Ca2+ + CO2?3: where T is in oK. At 25°C the logarithms of the equilibrium constants are ?8.480 ± 0.020, ?8.336 ± 0.020 and ?7.913 ± 0.020 for calcite, aragonite and vaterite, respectively.The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO+3 and CaCO03 ion pairs, revised analytical expressions for CO2-H2O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO2-dependence if the CaHCO+3 association constant is between 0 and 90°C, corresponding to the value logKCahco+3 = 1.11 ± 0.07 at 25°C. The CaCO03 association constant was measured potentiometrically to be between 5 and 80°C, yielding logKCaCO03 = 3.22 ± 0.14 at 25°C.The CO2-H2O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of KH, K1 and K2 are , and logK2 = ?107.8871 ? 0.03252849T + 5151.79/T + 38.92561 logT ? 563713.9/T2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures.Extensive measurements of the pH of Ca-HCO3 solutions at 25°C and 0.956 atm PCO2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH.Earlier arguments suggesting that the CaHCO+3 ion pair should not be included in the CaCO3-CO2-H2O aqueous model were based on less accurate calcite solubility data. The CaHCO+3 ion pair must be included in the aqueous model to account for the observed PCO2-dependence of aragonite solubility between 317 ppm CO2 and 100% CO2.Previous literature on the solubility of CaCO3 polymorphs have been critically evaluated using the aqueous model and the results are compared. 相似文献
12.
Dimitri A Sverjensky 《Geochimica et cosmochimica acta》1984,48(5):1127-1134
A linear correlation exists between the standard Gibbs free energies of formation of calcite-type carbonates (MCO3) and the corresponding conventional standard Gibbs free energies of formation of the aqueous divalent cations (M2+) at 25 °C and 1 bar ΔGMCO30 = m(ΔGf,M2+0) ? 141,200 cal · mole?1 where m is equal to 0.9715. This relationship enables prediction of the standard free energies of formation of numerous hypothetical carbonates with the calcite structure. Associated uncertainties typically range from about ± 250 to 600 cal · mole?1. An important consequence of the above correlation is that the thermodynamic equilibrium constant for the distribution of two trace elements M and N between carbonate mineral and aqueous solution at 25 °C and 1 bar is proportional to the free energy difference between the corresponding two aqueous ions: In Combination of predicted standard free energies, entropies and volumes of carbonate minerals at 25°C and 1 bar with standard free energies of aqueous ions and the equation of state in Helgesonet al. (1981) enables prediction of the thermodynamic equilibrium constant for trace element distribution between carbonates and aqueous solutions at elevated temperatures and pressures. Interpretation of the thermodynamic equilibrium constant in terms of concentration ratios in the aqueous phase is considerably simplified if pairs of divalent trace elements are considered that have very similar ionic radii (e.g., , ). In combination with data for the stabilities of complex ions in aqueous solutions, the above calculations enable useful limits to be placed on the concentrations of trace elements in hydrothermal solutions. 相似文献
13.
Walter Riesen Heinz Gamsjäger Paul W. Schindler 《Geochimica et cosmochimica acta》1977,41(9):1193-1200
The carbonato and hydrogencarbonato complexes of Mg2+ were investigated at 25 and 50° in solutions of the constant ClO4? molality (3 M) consisting preponderantly of NaClO4. The experimental data could be explained assuming the following equilibria: Mg2+ + CO2B + H2O ag MgHCO+3 + H+, , Mg2+ + 2 CO2g + 2 H2Oag Mg(HCO3)02 ± 2 H+, , ?15.37 ± 0.39 (50°), Mg2+ + CO2g + H2Oag MgCO03 + 2 H+, ,?15.23 ± 0.02 (50°), with the assumption γMgCO30 = γMg(HCO3)02, ΔG0(I = 0) for the reaction MgCO03 + CO2g + H2O = Mg(HCO3)02 was estimated to be ?3.91 ± 0.86 and 0.6 ± 2.4 kJ/mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed. 相似文献
14.
The isotopic ratios and show an annual periodicity in the coral Montastrea annularis from Bermuda, Jamaica and Barbados. The abundances of 18O and 13C are positively correlated in the Jamaica and Barbados samples, but inversely related in the Bermuda sample. Annual high density growth bands are formed during the season of warmest water temperature at all 3 sites and are enriched in 16O. M. Annularis has a constant displacement from oxygen isotopic equilibrium and accurately records seasonal temperature variations via the temperature-dependent aragonite-water fractionation factor. Light intensity, through the activity of the coral's endosymbiotic algae, regulates the depth-dependent and seasonal variations in the skeletal carbon isotopic composition. 相似文献
15.
Frank J Millero 《Geochimica et cosmochimica acta》1979,43(10):1651-1661
The apparent constants (K'i) for the ionization of carbonic acid in seawater at various salinities (S,%.) have been fit to equations of the form ln whereKi is the thermodynamic ionization constant in water, Ai, and Bi are adjustable parameters. The temperature dependence (TK) of Ki, Ai and Bi were of the form, a0 + a1/T + a3 ln T. Equations of similar forms have been used to analyze the ionization constants for water and boric acid and the solubility product of calcite in seawater. The effect of pressure on the apparent constants () have been fit to equations of the form ln where the volume (ΔV) and compressibility (ΔK) changes are polynomial functions of temperature. The equations generated for various açids in seawater have been used to examine the carbonate system in seawater. Equations relating the NBS and Tris pH scales have been derived as well as equations of pH as a function of temperature and pressure. The equations from Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Mehrbachet al. (1973, Limnol. Oceanogr.18, 897–907) have been used to examine the components of the carbonate system. At a fixed total alkalinity and total carbon dioxide, differences of ±0.01 m-equiv kg?1 in HCO?3 and CO2?3 were found; however, the [CO2] and Pco2 are nearly the same. The contribution of borate ion, B(OH)?4 determined from the equations of Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Lyman (1957, Ph.D. Thesis, University of California, Los Angeles) differ by ±0.01 m-equiv kg?1 for waters with the same salinity and temperature. 相似文献
16.
Art F White 《Geochimica et cosmochimica acta》1977,41(5):613-625
The coprecipitation of Na and K was experimentally investigated in aragonite. The distribution functions were determined at pH 6.8 and 8.8 over aqueous Na and K concentrations of between 5 × 10?4and 2.0 M and temperatures of between 25 and 75°C.The mole fractions of Na and K in aragonite are related to the aqueous ratios of Na and Ca by a function of the form where C0 and C1 are constants at a given temperature. This equation was derived by a statistical model assuming a heterogeneous energy distribution for the sites of incorporation. The independence of the coprecipitation process from aqueous anion activities suggests that carbonate is the only anionic species in the solid solution. 相似文献
17.
Frank J Millero 《Geochimica et cosmochimica acta》1981,45(11):2085-2089
The stoichiometric, , and apparent, K'HA, constants for the ionization of a number of weak acids (NH4+, HSO4?, HF, H2O, B(OH)3, H2CO3, HCO3?, H3PO4, H2PO4?, HPO42, H3AsO4 H2AsO4? and HAsO42?) in seawater at 25°C diluted with water have been fitted to equations of the form (Millero, 1979). In where In KHA is the thermodynamic constant in water, S is the salinity, A and B are adjustable parameters. The validity of this equation in estuarine waters has been examined by using an ion pairing model (Millero and Schreiber, 1981). The calculated values of and K'HA at S = 35%. are in good agreement with the measured values for all the systems examined. The equation used to extrapolate the measured values to pure water KHA predicted values that agreed with those determined by using the ion pairing model. The exception was the ionization of HPO42? due to the strong interactions of Ca2+ and Mg2+ with PO43?. The differences in the predicted values of in seawater diluted with pure water and average river water were very small for all the acids except HPO42? (the maximum ΔpK = 0.96 in average river water). The larger difference in the for HPO42? in river waters is due to the strong interactions of Ca2+ and PO43?. 相似文献
18.
John Geover 《Geochimica et cosmochimica acta》1974,38(10):1527-1548
For a phase at equilibrium in which two cation species are partitioned ideally between two sub-lattice sites, the excess functions of mixing (free energy, enthalpy and entropy) are directly related to the bulk composition of the phase and ΔGE°(T, P), the standard-state intra- crystalline exchange free energy. If the phase is not at equilibrium internally, an additional ordering parameter is necessary to fix the excess free energy of mixing, GmixEX, unambiguously. Conversely, for any fixed GmixEX there exists an infinity of possible intracrystalline cation dis- tributions, only one of which is the equilibrium distribution for the specified temperature and pressure. As ideal intraphase cation ordering becomes more pronounced, GmixEX decreases. In response, the total free energy of mixing for the phase decreases progressively for non-end member compositions, approaching, at the limits of ordering, values appropriate for stabilizing compounds of intermediate composition.The model-dependent activity coefficient for component A in the phase, γAT, can be calculated for any bulk composition, XAT, either from GmixEX directly or from more basic equations involving the interrelation of chemical potentials at equilibrium. A general form for γAT is ln , where Xjκ denotes the mole fraction of species j in site κ. The first term on the right-hand side of this equation is the contribution to γAT from ideal intracrystalline partitioning, and is common to the several theories lately presented to model intraphase cation partitioning. It can be shown rigorously that this term contributes to a negative deviation from ideality for the bulk phase. The second term is the contribution to the macroscopic activity coefficient from non-ideal intraphase partitioning, and is related to an enthalpy of mixing, HmixN in excess of that resulting from ideal inter-site cation ordering. While the expression represented by Y can take several functional forms, the additional enthalpy can be evaluated explicitly for specific non-ideal partitioning models from the relation .In those cases, GmixEX can also be determined exactly. 相似文献
19.
Frank J Millero 《Geochimica et cosmochimica acta》1982,46(1):11-22
The effect of presure on the solubility of minerals in water and seawater can be estimated from In where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by Values of the partial molal volume () and compressibilty () in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10?3 cm3 bar?1 mol?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In Ksp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of for the solubility of CaCO3, SrSO4 and CaF2 in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered. 相似文献
20.
A direct-sampling, mass-spectrometric technique has been used to measure simultaneously the solubilities of He, Ne, Ar, Kr, and Xe in fresh water and NaCl brine (0 to 5.2 molar) from 0° to 65 °C, and at 1 atm total pressure of moist air. The argon solubility in the most concentrated brines is 4 to 7 times less than in fresh water at 65 °C and 0°C, respectively. The salt effect is parameterized using the Setschenow equation. where M is NaCl moiarity, βio(T) and βi(T) the Bunsen solubility coefficients for gas i in fresh water and brine, and KiM(T) the empirical salting coefficient. Values of KiM(T) are calculated using volumetric concentration units for noble gas and NaCl content and are independent of NaCl molarity. Below about 40°C, temperature coefficients of all KiM are negative. The value of KHeM is a minimum at 40°C. KArM decreases from about 0.40 at 0°C to 0.28 at 65 °C. The absolute magnitudes of the differences in salting coefficients (relative to KArM) decrease from 0° to 65°C. Over the range of conditions studied, all noble gases are salted out, and KHeM ? KNeM < KArM < KKrM < KXeM.From the solubility data, we calculated , , and for the transfer of noble gases from fresh water to 1 molar NaCl solutions. At low temperatures , is positive, but decreases and becomes negative at temperatures ranging from about 25°C for He to 45°C for Xe. At low temperatures, the dissolved electrolyte apparently interferes with the formation of a cage of solvent molecules about the noble gas atom. At higher temperatures, the local environment of the gas atom in the brine appears to be slightly more ordered than in pure water, possibly reflecting the longer effective range of the ionic fields at higher temperature.The measured solubilities can be used to model noble gas partitioning in two-phase geothermal systems at low temperatures. The data can also be used to estimate the temperature and concentration dependence of the salt effect for other alkali halides. Extrapolation of the measured data is not possible due to the incompletely-characterized minima in the temperature dependence of the salting coefficients. The regularities in the data observed at low temperatures suggest relatively few high-temperature data will be required to model the behavior of noble gases in high-temperature geothermal brines. 相似文献