Microbial uranium reduction from hexavalent to tetravalent is of interest in terms of bioremediation and paleontology. During microbial reduction, heavier isotopes are more concentrated in tetravalent products, whereas abiotic reductions show various isotopic trends. In this study, to clarify the isotope fractionation mechanism of biological reduction, theoretical calculations of the equilibrium isotope fractionation coefficient for each elementary reaction was carried out using relativistic ab initio method. We also introduce a steady-state model and interpret the experimental values obtained by the Rayleigh fitting in biotic and abiotic reductions.Microbial uranium reduction from hexavalent to tetravalent is of interest in terms of bioremediation and paleontology. During microbial reduction, heavier isotopes are more enriched in tetravalent products, whereas abiotic reductions show various isotopic trends. In this study, to clarify the isotope fractionation mechanism of microbial reduction, theoretical calculations of the equilibrium isotope fractionation coefficient for each reaction step were carried out using relativistic ab initio method. We also introduced a steady-state model and interpreted the experimental values obtained by the Rayleigh fitting in biotic and abiotic reductions.

This study aims to investigate the role of CS₂ as a source of OCS and its effect in the sulfur cycle. A new CS₂ network is generated and added to the current sulfur cycle. The result is computed by using the 1D photochemical model. The new CS₂ network gives three pathways to form OCS, which may improve the conversion ratio of CS₂ to OCS compared to the previous studies. The newly added intermediate SCSOH provides a new channel to generate SO₂ which is the main sulfurous gas in atmosphere.

High level of Cr(Ⅵ)pollution is observed in water in street inlet Komatsugawa, Edogawa-Ku, Tokyo. Although Cr(Ⅵ) is easily reduced to Cr(Ⅲ) under reducing conditions, the concentration is very high(＞150 mg/L)under the high pH(＞11) and low Eh (＜0 mV) condition in the inlet. In order to explain why such high concentration of Cr(Ⅵ) has been detected under the reductive condition, influence of pH, Eh on redox reaction of Cr(Ⅵ) was investigated by batch experiment using Cr(Ⅵ) solution prepared from chemicals and the contaminated water sample collected from the polluted inlet. Iron sulfate(Ⅱ) was used as reductant. When the Cr(VI) chemical was used, Cr(Ⅵ) was reduced less with higher pH condition. When contaminated water sample was used, the redox reaction was also suppressed in the higher pH condition. The results of batch experiment also showed that, with the lower Eh condition, the more Cr(Ⅵ) was reduced when sample water collected form the polluted inlet was used. And it is also showed that pH is a stronger factor which influence on concentration of Cr(Ⅵ) than Eh. The reason why high concentration of Cr(Ⅵ) was detected under low Eh condition at Komatsugawa seemed to be the suppression of reducing reaction by the high pH.

The isotope effect includes a mass-dependent effect caused by intramolecular vibrational energy and a mass-independent effect caused by the nuclear volume effect. The mass-independent effect is called the ”Odd-Even mutation” because odd-mass isotopes behave differently than even-mass isotopes. A phenomenon similar to this effect was also discovered in heavy elements in meteorites, and it is considered important to elucidate the mechanism of the nuclear volume effect in the field of cosmochemistry (Fujii et al., 2006). Solvent extraction experiments show similarities in isotope even / odd differences and mass ratio-dependent isotope fractionation (MIF) results (Moynier et al., 2008) to understand the mechanism of MIF variation. Solvent extraction experiments are considered useful. In this experiment, we focused on Sn, which shows a large MIF in solvent extraction, and aimed to clarify the relationship between MIF and the nuclear volume effect by performing isotope analysis of Sn during solvent extraction.

The Finero phlogopite peridotite in Northern Italy is an alpine-type peridotite and it had been metazomatized by slab dehydration in the mantle wedge from Palezoic to Mesozoic time. We focused on the effect of water in mantle region on the deformation characteristics. In order to reveal the water-rock interaction and the deformation history, we performed microstructural observation mainly using electron microscopies and noble gases analysis of the fluid/melt inclusions in mineral grains that provide information of the origin of them.In field research, we found the stress concentration zone in the phlogopite peridotite unit. With an optical microscope, it was found that the rock of the stress concentration zone may have been deformed with forming microcracks under hydrous condition and subsequently being trapped the fluid/melt inclusions. No such characteristic was observed in the samples away from the stress concentration zone.The results of the olivine slip systems suggest that fluid may have penetrated the rock of the stress concentration zone during brittle-ductile deformation. On the other hand, noble gases analysis of the fluid/melt inclusions in all samples (He, Ar and Ne isotopic and elemental ratios) show three component mixture of atmosphere, crust and mantle. To identify whether the fluid/melt with such noble gases components are related to the deformation structure, we need to additional measurements of each separate minerals.

Earthquakes around Yakedake volcano have increased since late April 2020, and abnormal discharge of high-temperature hot spring water was observed at the abandoned well in the Okuhida hot spring area. As the Okuhida hot spring area is located near the Yakedake volcano, the major chemical and stable isotopic compositions of hydrogen and oxygen of the discharged water were analyzed to investigate the relationship between this abnormal discharge and the volcanic activity of the Yakedake volcano. As a result, no relationship was found between this abnormal discharge and the volcanic activity of the Yakedake volcano.

Nitrogen, the main component of the Earth's atmosphere, is a geochemically important volatile element, but its behavior in the Earth's interior remains still unclear. Although previous studies suggested that mantle minerals can store nitrogen in the Earth's deep interior from high-pressure and high-temperature experiments (Li et al., 2013; Yoshioka et al., 2018), there are few experimental reports about nitrogen solubilities in the lower-mantle minerals.In this study, we investigated the nitrogen incorporation to bridgmanite (MgSiO3) and periclase (MgO), the major minerals in the lower mantle. High-pressure and high-temperature experiments were conducted using multi-anvil apparatus installed at Geodynamics Research Center. For analysis of nitrogen in recovered samples, we used high-resolution SIMS installed at Centre de Recherches Pétrographiques et Géochimiques and NanoSIMS installed at Atmosphere and Ocean Research Institute. 14N+-implanted standards for NanoSIMS were prepared at National Institute for Materials Science.We found that the maximum nitrogen solubility in bridgmanite was 5.7 ppm and almost no nitrogen dissolves into periclase. In the solidification of magma ocean, the first crystallized bridgmanite can store nitrogen in the lower mantle, while the second crystallized periclase might trap nitrogen in the lower mantle.

Chemical and isotopic compositions of spring water distributed along the southeastern coast of Yonaguni Island, which is the westernmost part of Japan, have been determined. The chemical and isotopic compositions of these springs suggest that they contain a few percent of seawater. The chemical and isotopic compositions of the springs indicate that they are affected by summer rainfall. On the other hand, the sulfur hexafluoride concentration shows the atmospheric equilibrium concentration with groundwater in 2016, which indicates a residence time of about three years. However, all of the springs were supersaturated with respect to calcium carbonate, suggesting that the effects of seawater were immediate and may have been due to the immediate influence of seawater, and thus may have been discharged before re-equilibrium was reached.

The helium isotope ratio (³He/⁴He ratio) of volcanic gas has a potential as a monitoring tool of volcanic activity because that value varies depending on the contribution of magmatic and crustal helium. Continuous analysis is necessary to monitor volcanic activity; however, it is difficult because a large magnetic-sector mass spectrometer is currently used to analyze helium isotopes for requests of high mass resolution and sensitivity. We have been developing a new technique of noble gas analysis using multi-turn time-of-flight mass spectrometer (MULTUM). When we adopted the “static operation” (i.e. the spectrometer is isolated from the vacuum pumps so that sample gas molecules are closed off within the spectrometer envelope) and pulse counting method to MULTUM, significant number of ³He in the helium standard gas has been successively detected. Although as high sensitivity as that of the magnetic-sector mass spectrometer has not yet been achieved, precision of ³He/⁴He ratio will be improved enough to distinguish the origin of helium in volcanic gas sample by accumulating number of ³He signals.