Geochemistry International最新文献

First data on the concentrations of a number of trace elements and carbon (organic and carbonate) in the components of the bottom ecosystem of the East Siberian Sea have been obtained. The distribution of a large group of trace elements (Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Mo, Ag, Ba, Tl, Pb, Bi, Th and U) in mass taxa of benthic organisms, including bivalvia Portlandia arctica; crustacean Isopod (Saduria sibirica, Saduria sabini), echinoderms Ophiuroidea Ophiocten sericeum, and Holothuroidea Myriotrochus rinkii, was studied. The role of abiotic and biotic factors in the accumulation of chemical elements in benthic organisms was estimated. The lithological and geochemical characteristics of host bottom sediments, primarily, the organic carbon content and the grain-size composition, reflect the influence of abiotic factors. The biotic factor is responsible for the geochemical properties of trace elements, the level of organic carbon in organisms, and their feeding type. For the first time, a comparative assessment of the levels of organic carbon accumulation in mass taxa and host bottom sediments was made, and an important sedimentological function of detritophages and deposit feeders organisms was shown.

The GEOCHEQ_Isotope software package, previously developed to calculate chemical and isotopic equilibria of carbon and oxygen in hydrothermal and hydrogeochemical systems by minimizing Gibbs energy, was extended to the simultaneous calculation of isotopic effects of carbon, oxygen, and iron (the main objective of the study). As for carbon and oxygen, the β-factor formalism was used to develop algorithms and a database for the calculation of iron isotopic effects. According to the developed algorithm, the Gibbs energy G*(P, T) of formation of a rare isotopologue was calculated through the Gibbs energy of formation of the main isotopologue taking into account the value of the ⁵⁶Fe/⁵⁴Fe β-factor of this substance and the mass ratio of ⁵⁴Fe and ⁵⁶Fe isotopes. The approximation of ideal isotope mixture was used. The temperature dependence of the β-factor is unified in the form of a third-order polynomial by inverse even degrees of absolute temperature. Based on a critical analysis of currently available data on equilibrium isotopic factors obtained by different methods (elastic and inelastic γ-resonance scattering, isotope exchange experiments, and ab-initio calculations), the main result was obtained: for the first time, internally consistent database on iron β-factors of minerals and water complexes was developed. To develop the database, minerals and aqueous complexes for which the estimates of the equilibrium fractionation factors of iron isotopes obtained by different methods exist and consistent within the error of the methods have been identified: metallic iron (α-Fe), hematite, magnetite, siderite, pyrite, and the aqueous complexes ({text{Fe(III)(}}{{{text{H}}}_{{text{2}}}}{text{O)}}_{6}^{{3 + }}) and ({text{Fe(III)(}}{{{text{H}}}_{{text{2}}}}{text{O)}}_{6}^{{2 + }}). The values of the iron β-factors for these minerals and aqueous complexes, accepted as reference ones, formed the “mainstay” of the developed database. Considering that the equilibrium isotopic shifts of iron between minerals and water complexes are estimated much more accurately within the framework of one method rather than the corresponding β-factors, the database was made consistent by linking the ln β values for minerals and water complexes to the reference ln β values. The application of the GEOCHEQ_Isotope software package to the closed carbonaceous hydrothermal system H₂O–CO₂–Fe₂O₃–FeO–CaO (T = 200°C, P = 16–50 bar) has shown the possibility of its use for the calculation of changes in mineral composition and isotopic effects on oxygen, carbon, and iron.

The structure of borosilicate glass and glass-ceramic materials of two compositions with different Cs/Na ratios was studied using Raman spectroscopy. The materials were synthesized in two different modes. The anionic environment of cesium in the glass and the structural rearrangements of the network during the formation of crystalline phases have been studied. X-ray diffraction patterns of glass-ceramic samples made it possible to determine the only crystalline phase CsBSi₂O₆, the structure of which was not clearly determined. The glass-ceramics of the studied composition can be used to immobilize cesium by incorporating it into the crystalline phases of the CsBSi₂O₆ composition, while sodium is retained in the glassy matrix. These studies showed that the composition of the crystalline phase does not depend on the initial ratio of alkali cations, while the proportion of the ordered and amorphous phases is controlled by the kinetics of the melt cooling process.

Bog and lake ecosystems of the boreal region are recognized as important parts of the global biogeochemical carbon cycle. At the same time, many aspects of the gas regime dynamics of bog lakes remain understudied. The paper presents data on the seasonal dynamics of dissolved CH₄ and CO₂ concentrations in the bog lake located in the ridge-lake complex of the Ilassky bog, a typical raised bog in the northern taiga of northwestern Russia, and results of analysis of the seasonal vertical distribution of greenhouse gases in the water column and the dynamics of surface concentrations with increased time resolution. The reasons for and patterns of their variability are considered, including those in relation to the characteristics of the bottom sediments. Concentrations of CH₄ and CO₂ in the water column vary during the year within wide ranges: from 4 to 652 µg/L and from 0.19 to 19 mg/L, respectively. CH₄ concentrations in the surface layer are at approximately the same level from May through August, with values measured in the water (5.9 to 11 µg/L) more than one hundred times higher than the concentrations in equilibrium with the atmosphere (0.04 to 0.05 µg/L), indicating a methane flux to the atmosphere. The CO₂ concentrations decrease throughout the open water period and become lower than the equilibrium concentrations with the atmosphere by the end of August, indicating a change in the flux direction and uptake of CO₂ from the atmosphere. The results showed that, depending on the season, a bog lake can be not only a source but also a sink for atmospheric carbon, 90–99% of which is CO₂ according to literature data.

The geochemical characteristics (REE, trace elements) and Sr and Nd isotopic composition of apatite from corundum-bearing metasomatites of the Khitoostrov occurrence (Belomorian Mobile Belt), associated plagioclasites, and host rocks represented by garnet amphibolites and kyanite–garnet–biotite gneisses of the Chupa sequence have been studied. Apatites from the corundum-bearing metasomatites and kyanite–garnet–biotite gneisses are enriched in medium REE and have a negative Eu anomaly (Eu/Eu* 0.20–0.35). Apatite from the corundum-bearing rocks differs from apatite from the gneisses of the Chupa sequence in the increased content of Sr, LREE, decreased content of HREE, as well as a lower ⁸⁷Sr/⁸⁶Sr(t) ratio and an increased ɛ_Nd(T) value: 0.70 865–0.70 896 and –9.3 ± 0.2 compared to 0.72 533 and –8.1, respectively. Apatite from the garnet amphibolites is enriched in MREE, lacks Eu-anomaly (Eu/Eu* 0.98), and has a low ɛ_Nd(T) = –9.3 and the lowest ⁸⁷Sr/⁸⁶Sr(t) ratio of 0.70 560. The Sm-Nd age estimate of apatite is 1.80 ± 0.15 Ga, which coincides with the Svecofennian metamorphism in the Belomorian Mobile Belt. The geochemical features of the apatite and ⁸⁷Sr/⁸⁶Sr(t) ratios indicate that the metasomatic alteration of the gneisses was caused by the lower crustal fluid and was accompanied by the influx of LREE and the removal of HREE. The slightly lower Eu anomaly and higher Ce vs Th and REE vs La/Sm relations reflect the fact that apatite from the corundum-bearing metasomatic rocks was formed in a more oxidizing environment than apatite from host rocks. Neither the corundum-bearing metasomatites and plagioclasites, nor the host rocks revealed any Sr-isotopic and REE-geochemical traces of interaction with surface (meteoric) waters.

The first data on the composition of organic compounds in thermal waters have been obtained from deep boreholes in the Paratunka geothermal field in Kamchatka. A variety of organic compounds belonging to eleven homological series were identified by capillary gas chromatography–mass spectrometry and solid phase extraction. The thermal waters were found out to be strongly dominated by aromatic and aliphatic hydrocarbons (HC), which were formed in relation to both thermogenic processes (transformation of organic residues under the effect of high temperatures and pressures) and bacterial activity. The Karymshina thermal waters are characterized by a specific molecular mass distribution of HC and contain only even-normal alkanes. It is shown that the composition of organic compounds of medium volatility in the Paratunka geothermal field is similar to the composition of organic matter (OM) in other thermal water occurrences of the Kamchatka Peninsula (Mutnovka and Uzon geothermal fields), which have been previously studied using the same methodology: all the waters are characterized by the prevalence of aliphatic and aromatic HC over other identified compounds.