The absolute date of the Millennium Eruption (ME) of Changbaishan Volcano is widely recognized as AD 946. The Baegdusan-Tomakomai (B-Tm) tephra dispersed during the ME is a robust-age key bed. In order to identify the tephra, refractive index and major-element compositions of volcanic glass shards are conventionally used. Meanwhile, trace-element analysis using the inductively coupled plasma mass spectrometry (ICP-MS) technique for the volcanic glass shards and bulk samples of the B-Tm tephra is still limited. Here we give a detailed description of major- and trace-element compositions for the glass shards and bulk sediments of the B-Tm and Towada caldera eruptions (To-a) tephra deposits from the Lake Ogawara sediment core, Tohoku region, northern Japan to identify the tephras. The depth profiles of the major and trace elements show the significant peaks for the K₂O and some trace elements (Zn, Rb, Zr, Nb, Sn, Y, La, Ce, Nd, Th, and U) at the B-Tm tephra layer in the Lake Ogawara sediment core, but no peaks of these elements at the To-a tephra layer. High concentrations of the trace elements in the B-Tm tephra layer were observed in individual glass shards as well as in the bulk sediment. These concentrations are highlighted by the elemental abundance pattern normalized by the crustal abundance. The elemental pattern in individual glass shards from other Japanese tephras showed significant differences from those of the B-Tm tephra, especially in REE compositions. The trace-element compositions of the glass shards and bulk sediments show a strong tool for distinguishing the B-Tm tephra from other Japanese tephras.

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The volume variable cluster model method, which is an improvement proposed by Rustad and coworkers, has been successfully used to calculate equilibrium isotope fractionations between solids and solutions. The biggest difference between these two cluster model methods is that the fixed layer of atoms in the method of Rustad et al. has been removed and the whole cluster is freely optimized under the “VVCM” (the volume variable cluster model method) treatment. In this paper, several sulfides have been chosen whose sulfur isotope fractionations have been theoretically studied by previous researchers but with disagreements on calculating sulfur isotope fractionations. HS^-_(aq) and H₂S_(aq) solutions are used to model sulfur-bearing aqueous solutions under different conditions. The calculated results of the first-principles DFT method are quite different from those based on Mössbauer data. The VVCM-based method is completely different from both of the above methods and can therefore provide an independent evaluation of their results. The results in this article show that the β-factors of sulfides decrease in the order of pyrite > sphalerite > galena and that the sulfur isotope fractionation magnitudes are in good agreement with previous results.

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Handheld X-ray fluorescence (HHXRF) has many applications in earth and the environmental sciences including Ta-Nb-Sn-W ore exploration, mining and trading. HHXRF provides more accurate results in samples with low concentration of desired elements; concentrated samples such as ore specimens are commonly challenging due to matrix effects and peak overlap. Assay data of such samples can be improved if the elements show good correlation between HHXRF data and values obtained by laboratory analysis of known samples or standards. This research shows that in the Ta-Nb-Sn-W ores, the factory calibration provides acceptable and accurate results up to a certain concentrations: 3% Ta, 10% Nb, 29% Sn, and 4% W. Using one or more user calibrations for samples with higher than these thresholds, improves the HHXRF data significantly.

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The vertical distributions of seven dissolved trace metals (Mn, Fe, Co, Ni, Cu, Zn and Cd) in seawater were investigated in Mikawa Bay of central Japan. We collected seawater samples two times in summer, 2012, when a hypoxic layer developed at the bottom, and analyzed them by an inductively coupled plasma mass spectrometer (ICP-MS) following filtration through a 0.45-μm membrane filter and pre-concentration using a chelating resin column. Different distribution patterns are observed in the vertical profiles of the analyzed metals in spite of the shallow water depth up to 14 m. Firstly, Mn, Fe and Co showed high concentrations at the lower hypoxic layer. It is very likely that Mn and Fe oxides in sediments dissolved into seawater under reducing environment. At the same time, Co adsorbed onto Mn/Fe oxides may also have been released into water column. The maximum Mn concentration reached 565 nmol/kg at the hypoxic layer. This value exceeded predicted no-effect concentration of Mn²⁺ for marine biota (496 nmol/kg) defined by Ministry of the Environment, Japan. Secondly, Cu, Cd and Zn concentrations decreased with increasing water depth like scavenged-type distribution although they are normally observed as recycled-type in open ocean and Suruga Bay, another bay in central Japan. These metals had negative correlations with salinity, suggesting that their distributions were regulated by dilution with open seawater. Moreover, sediments might uptake these metals under reducing condition. Surprisingly, Cd depleted in all the layers; its concentration was quite low (0.030 nmol/kg on average) compared with other bays and North Pacific Ocean. Lastly, Ni showed more complex pattern similar both to Mn and Cu depending on sampling stations and times. In this research, we could make it clear that DO in seawater and inflowing river water are important factors to control the distribution of the seven bioactive trace elements. Given that whole of the area is photic in shallow Mikawa Bay, where phytoplankton grows from the surface to the bottom, hypoxia here will directly influence primary production and marine biota in terms of rich in or lack of the bioactive trace elements as well as a shortage of oxygen.

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Nickel (Ni), copper (Cu), and zinc (Zn) are commonly used in human activities and pollute aquatic environments including rivers and oceans. Recently, Ni, Cu, and Zn isotope ratios have been measured to identify their sources and cycles in environments. We precisely determined the Ni, Cu, and Zn isotope ratios in rain, snow, and rime collected from Uji City and Mt. Kajigamori in Japan, and investigated the potential of isotopic ratios as tracers of anthropogenic materials. The isotope and elemental ratios suggested that road dust is the main source of Cu in most rain, snow, and rime samples and that some of the Cu may originate from fossil fuel combustion. Zinc in the rain, snow, and rime samples may be partially attributed to Zn in road dust. Zinc isotope ratios in the Uji rain samples are lower than those in the road dust, which would be emitted via high temperature processes. Nickel isotope ratios are correlated with V/Ni ratios in the rain, snow, and rime samples, suggesting that their main source is heavy oil combustion. Furthermore, we analyzed water samples from the Uji and Tawara Rivers and the Kakita River spring in Japan. Nickel and Cu isotope ratios in the river water samples were significantly heavier than those in rain, snow, and rime samples, while Zn isotope ratios were similar. This is attributed to isotopic fractionation of Cu and Ni between particulate-dissolved phases in river water or soil.

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During the Middle-to-Late Miocene, diatomaceous sediments were deposited in the North Pacific margin and marginal basins. The Onnagawa Formation is one of such deposits, which shows cyclic sedimentary rhythms reflecting oscillations of the marine environment in the Japan Sea. However, the age of the Onnagawa Formation is still poorly constrained due to the poor preservation of siliceous microfossils. To better constrain its age, we performed U-Pb dating of zircon grains from a tuff layer from the middle part of the Onnagawa Formation, and obtained an age of 11.18 ± 0.37 Ma. By combining our data with previously reported radiolarian biostratigraphy from the same section, we improved the age model of the diagenetically altered and lithified sediments of the Onnagawa Formation.

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For organic C content and stable isotope analysis of a sediment sample, an essential pretreatment procedure is acidification to remove carbonates in the sample. Although strong acids are required for removal of recalcitrant carbonates (e.g., siderite, magnesite, and dolomite), the long duration of acidification for frequently results in destruction of the Ag foil capsule in which the sample is placed. Another troublesome issue with the acid treatment is that capillary action of acids through wrinkles in the capsule wall leads to the sample spilling out. In this study, we successfully develop a new capsule preparation method by combining two improvements of 1) smoothing the capsule and creating the “bowl” shape that mitigates the acid spill and 2) plasma ablation to coat an Ag capsule with Au nanoparticles that prevents the destruction of the capsule. Through electron microscopy and energy dispersive X-ray analysis, we confirm that the plasma ablation removes ingrained C compounds on the capsule surface, contributing to a reduction in the C blank, and that the coating of Au nanoparticles protects the Ag surface from acid attack. None of 24 Au capsules and only one of 24 Ag capsules failed after the pretreatment procedure, which took 6 days with 6 M hydrochloric acid at 60°C and achieved more than 99% carbonate removal. We emphasize that the method developed here (smoothing and Au coating) is most helpful when dealing with recalcitrant carbonates that require more extensive acidification taking days versus overnight for calcite.

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