In this study, we separated global burial rate of organic carbon into terrestrial and marine environments, using compiled data of organic carbon and pyrite sulfur (C/S) ratio from sediments deposited in oxygenated seawater and freshwater environments. As a result, it is indicated that the organic burial in terrestrial environment appeared for the first time from Silurian to Devonian, when first forests were formed after the emergence of vascular plants. Burial rate of organic carbon in terrestrial environment increased a lot in the Late Carboniferous and the Early Permian, when a lot of coal was produced. At Frasnian/Famennian (F/F) and Permian/Triassic (P/T) mass extinction boundaries, burial rate of organic carbon in terrestrial environment has decreased significantly, while that in marine environment has increased during long term, global scale Ocean Anoxic Events (OAEs).

A seamless reconstruction of summer climate variation for all periodicities has been carried out in central Japan by integrating tree-ring oxygen and hydrogen isotopes. By decomposing the time series, I have found that the amplitude of multi-decadal variations is enhanced at every 400 years, inducing societal regime shifts over East Asia. I will discuss its natural and human scientific meanings referring the results of an inter-disciplinary research project in Research Institute for Humanity and Nature.

Tufas are carbonate sediments that develop in freshwater environments in temperate to subtropical limestone regions. Tufas form annual laminations consisting of dense and porous layers, which can be used for dating. Conventional studies have mainly focused on fluvial tufas, but the problem is that a continuous deposition over 40 years is hardly expected due to changes in flow paths. However, longer records can be found in cascade tufas, which are deposited like stalagmites at waterfalls. In this study, we studied cascade tufas developed on the Obaru beach of Tokunoshima Island, Kagoshima Prefecture, Japan to obtain a longer climate record. A 50 cm long specimen of the cascade tufa has a depositional period of about 200 years, which was recognized by observation of thin-sections and CT scan. By comparing the results of oxygen and carbon isotope ratio measurements with meteorological records, we aim to reconstruct long-term quantitative paleoclimate using tufas. Our preliminary results show cyclicity of about 20 years in the oxygen isotopes, which can be correlated to the change in seawater temperature of the western Pacific. This suggested a close relationship between seawater temperature fluctuations and rainfall.

We established a new method to purify the frustules of disc-shaped diatoms using cell sorter, and succeeded in removing the clay-mineral contamination and restricting the number of species for the δ18O analysis.

As a potential isotopic tracer for groundwater hydrological research, isotopic variation of ²³⁴U/²³⁸U ratios was precisely determined by mass spectrometry. Isotopic variation of ²³⁴U/²³⁸U activity ratios was analyzed from a deep groundwater in low permeable aquifer in Horonobe area in Hokkaido. As the result, ²³⁴U/²³⁸U activity ratios showed disequilibrium conditions, and varied with their sampling depth. Moreover, the formation ages of the carbonate samples precipitated in the aquifer were estimated to evaluate long-time lithological stability in this area. The calculated ages for the carbonate precipitations were almost under the secular equilibrium condition, and they formed at least less than about one million years ago.

The Japan Sea sediments are a mixture of detrital materials of various origins, such as eolian dust from Asian continent and Japanese riverine suspensions. Understanding the sources of eolian dust in the sediments can help reconstruct past wind systems and monsoon variability. The sediments from the Integrated Ocean Drilling Program (IODP) Site U1425 were separtated into silt and clay fractions and semi-quantification of the minerals by powder X-ray diffraction (XRD) was conducted. The XRD profiles were statistically unmixed to the endmembers by Parallel Factor Analysis (PARAFAC). As a result, the Taklimakan, Gobi, and Ordos desert regions were identified as sources of eolian dust endmembers, and an endmember originated from riverine suspension from the Japanese Islands was also identified. Relative contribution of each detrital endmember was also determined. A part of the sample set analyzed for XRD was also subjected to Pb isotopes measurement for both silt and clay fractions. In this report, the interrelationship between the mineralogically estimated contribution of each clastic subcomponent and Pb isotopes will be presented, and the more precise interpretation for provenance discrimination will be discussed.

With initial analysis of samples from the C-type asteroid Ryugu in mind, we modified and optimized a commercial continuous-flow elemental analyzer/isotope-ratio mass spectrometer to the ultra-small scale analysis, and applied it to carbonaceous chondrites. We will introduce the results from the ultra-small scale analysis by nano-EA/IRMS over CM2 and C2-ung carbonaceous chondrites, as a part of the Hayabusa2 SOM rehearsal analysis. The multiple isotope data obtained by this method will provide crucial information to understand the initial formation process of organic substances in the extraterrestrial environment.

Calcium and Aluminum rich Inclusion (CAI) from carbonaceous chondrites is the oldest substance that condensed from a gaseous reservoir in the early solar system. The nucleosynthetic isotope anomalies for heavy elements found in CAIs reflect isotopic heterogeneity in the early solar system. Unlike the igneous CAIs (coarse-grained, e.g. Type Bs), the fine-grained CAIs (FG) are considered to have escaped remelting and homogenization by shock heating. As such, FG is expected to preserve primitive isotope features in the solar system. In this study, we measured elemental compositions and Sr isotope ratios in FGs from the Allende meteorite. A variety of Sr isotope anomalies and elemental compositions were found in FGs, which is consistent with previous studies. We consider that the observed elemental and isotopic variabilities in FGs are not due to parent body processes including aqueous alteration. Rather, the variations would be intrinsic properties of FGs, reflecting the diversity in physical and chemical conditions under which they were formed.

The discovery of CO2-rich fluid inclusion in an aqueously altered carbonaceous chondrite will be introduced and a new united model for the formation and evolution of primitive solar materials will be proposed as a working hypothesis based on our recent research results of CP IDPs and carbonaceous chondrites.

Serpentine is a phyllosilicate mineral having several polymorphs. Because the crystal structure is dependent on thermodynamic environment where it was produced, it has been desired for the polymorphs to be distinguished for geoscientific investigation. In the present study, we achieved to unambiguously determine the serpentine’s polymorphs with microscopic Raman spectroscopy. Among various Raman-active vibrational modes, we focused on two vibration mode because layer structure of phyllosilicate layers alters with the crystal structure. With the peak frequencies determined with sub-pixel accuracy, the polymorphs were clearly separated in two-dimensional plot of the peak frequencies. Because microscopic Raman spectroscopy is nondestructive method which requires neither large single crystal nor any pretreatment of samples, our it is applicable to small (＜1 mm), fragile, rare, and/or heterogeneous samples. It is thought to be useful for geoscientific analysis of the mantle, meteorite surface, and identification of hydrous minerals in sample return missions of asteroids.

At 2:32 am on July 2, 2020, a large fireball was observed over the Kanto region, making a loud noise on the second floor of an apartment in Narashino City, Chiba Prefecture, and a 63 g fragment was found in the corridor facing the courtyard. Also, on July 4, a 70g fragment was found in the courtyard. The Natural History Museum and Institute, Chiba was contacted and the fragments were brought to the National Museum of Nature and Science on July 5, and gamma-ray measurements were performed for about a week to detect cosmogenic nuclides. Furthermore, in the investigation on July 18, 14 small pieces were found on the terrace on the 5th floor. It is probable that the meteorite first hit the walls on the 5th floor or above, and the broken pieces fell to the lower floors. On July 22, a roof tile of an apartment in Funabashi City, about 1km northeast of the location of No. 1, was found to be cracked, and fragments of 95g and 73g and eight small pieces of 5g or less were found. In October, a 15g fragment (No. 3) was also discovered. Thin sections were made at the National Institute of Polar Research and, by the analyses of the mineral composition, the meteorite was classified as a H5 chondrite, and registered with the Meteoritical Society as the Narashino meteorite on November 1.

Sugars and sugar derivatives play important biological roles. As a prebiotic sugar formation reaction, the “formose reaction” has been attracted attention. Formose reaction is the reaction that makes various sugars from aldehydes with base catalysts. Meteorite parent bodies are considered to be among the places where the formose-type reaction may have occurred. In order to simulate reactions in the meteorite parent bodies, 3 kinds of the starting mixtures were prepared: (1) formaldehyde : H₂O = 10 : 100, (2) glycolaldehyde : glyceraldehyde : H₂O = 0.009 : 0.09 : 100, (3) formaldehyde : glycolaldehyde : H₂O = 3.6 : 1.8 : 100 (molar ratios). 200 µL of each mixture was heated or irradiated by gamma-ray. An aliquot of each product was derivatized, and analyzed by GC/MS. Aldoses were detected in all the products. In the same starting material, varieties and amounts of aldose produced by gamma-ray irradiation tended to be greater than those of heated samples.

Methane (CH₄) gas in plume of icy satellite is regarded as one of the candidates of signature of extra biota. However, CH₄ gas in icy satellite may have also hydrothermal origin and be affected by gas hydrate. This fact does not let CH₄ detection is sufficient for conclusion for CH₄ origin. Therefore, we consider the evaluation of the elementary process of CH₄ isotopic fractionation (δ¹³C, δD) via room experiment is important for isotopic observation of icy satellite in nearly future, and investigate the isotopic fractionation with gas hydrate formation. Results in isotopic measurement show that δ¹³C and isotopic fractionation coefficient of hydrogen isotope (ε_D) of remained gas phase become lower at higher pressure. Moreover, δ¹³C of remained gas phase also become lower at faster stirring rotation speed of hydrate formation. In this presentation, we will discuss the mechanism of these tendencies.

The isotope ratio variation of ¹⁸²W based on the radiometric decay of ¹⁸²Hf has been used to estimate the core formation time of solar system objects. On the other hand, mass-independent isotope fractionation (MIF) has been reported in ¹⁸³W, and the cause of the MIF has not yet been clarified. Therefore, it is important to understand the isotope fractionation mechanism of tungsten in the study of the ¹⁸²Hf-¹⁸²W system. In this study, the ¹⁸²W isotope ratio variation is investigated from the viewpoint of ”isotope effect”, which has not been paid attention so far, and applied to cosmochemistry. Among the isotope effects, we focused on the ”nuclear volume effect” which is one of the factors of MIF. The exact value of 'δr²', the difference of the mean square radius of the nucleus, which is an index to discuss the MIF, has been reported differently in different papers, and the exact 'δr²' is unknown. In this study, we attempted to constrain the 'δr²' by experimentally estimating the MIF due to the nuclear volume effect.

To understand the growth or dissolution mechanism of minerals in aqueous solution, analyzing the local conditions of the solution around the dissolving or forming minerals is important. Recently, we succeeded in visualizing using a fluorescent probe (i) the distribution of pH and calcium ion concentration simultaneously around a calcium carbonate crystal dissolving in aqueous solution, and (ii) pH distribution for the calcium carbonate formation process in gel media. These results could provide new insights into the knowledge of the dissolution/formation reaction of minerals in aqueous solutions.

To better understand the partition coefficient, Kd, of Fukushima-derived radiocesium in natural water, we determined Kd of ¹³⁷Cs between water and suspended matter in rivers in Fukushima Prefecture. The Kd values, ranged from 22000 to 7000000 L/kg, showed large variability and were greater than that between seawater and sediment. For Yugama crater of Kusatsu-Shirane volcano, low Kd value (20 +/-19 L/kg) was determined between water and sediment collected in Yugama. Examination of chemical factors controlling the partition coefficient of ¹³⁷Cs revealed that the Kd values are closely related to ¹³³Cs (stable isotope) concentrations in natural water, which implies that isotope exchange reaction between ¹³⁷Cs and ¹³³Cs is one of the important chemical processes.