The frequency of past occurrences of the Kuroshio large meander is analyzed by examining the Mg/Ca ratio of planktonic foraminiferal shells in marine sediment cores using Individual Foraminifera Analysis (IFA). The core samples were collected off the coast of the Tokai region, where there is a temperature difference between non-large meander periods and large meander periods. IFA involves picking approximately 100 individual planktonic foraminifera from a single stratigraphic layer and analyzing the Mg/Ca ratio temperature of each individual. From the temperatures of 100 individuals, the temperature frequency distribution recorded over an approximate 100-year sedimentation period is reconstructed. The frequency of large meander occurrences is analyzed from the distribution characteristics of the high-temperature side of the bimodal temperature distribution.

To estimate the Holocene sea-level changes, we analyzed bromine and other chemical compositions in a Lake Kibagata sediment core (core length: 444cm) from Hokuriku region, northern central Japan.

Recently, our research has focused on six sites of K-Pg boundaries in Colorado and North Dakota in the United States. The primary focus of this study is the North Dakota formation named Pyramid Butte (PB). The K-Pg boundary at this site is a peat layer about 5 cm thick containing spherulite, below which is a peat layer about 1 m thick in total thickness and above which is a silt layer about 1 m thick in total thickness. The silt layer showed significantly higher concentrations of SiO2, Sc, Ce, Nd and Th than the peat layer. No Ir spike (>>1 ppb) was observed in the K-Pg layer, but significantly higher quantitative values of Ni were obtained in the uppermost 5-10 cm portion of the peat layer. For Cr, higher values were obtained in the K-Pg layer and up to the lower 10 cm of the silt layers.

Formaldehyde (HCHO) was a significant precursor for forming atmospheric organic molecules in the early Earth. And HCHO could have been produced by photochemical reactions[1]. Besides, the atmosphere in the Archean era was weakly reducing with less sunlight intensity than the present atmosphere. To understand the evolution of our Earth, in this study, we investigated the atmospheric formation of HCHO in the Archean using a 1D photochemical model. The model named PATMO[2] consists of 56 chemical species and 412 chemical reactions which simulated the atmosphere from surface to 100 km in 100 years. This model considered the attenuation of sunlight and the photodissociation reaction rate over time which helps estimate the photochemical HCHO concentration in the Archean. The results show that photochemical HCHO in Archean atmosphere ranging from 0.0002 to 0.017 ppm. The maximum HCHO concentration occurred at an altitude of 61 km corresponding to the maximum level of H2O in the Archean atmosphere.

Palaeoenvironmental studies deal with archives, and providing a reliable age model to the archives being studied is the first step in understanding the global environmental system. There are two methodologies to establish an age model for a target archive. One is to compare proxy fluctuations to the series of fluctuations with reliable age model. The other is radiometric dating. We can send our samples to an analytical institute to obtain the data, but understanding the basics of each methodology is important to properly interpret the reported data . Here I introduce the methods used in palaeoenvironmental studies and some of the resent developments.

In this study, we quantitatively evaluated vital effects on oxygen stable isotope ratio in two species of bivalve shells and one species of fish otolith. oxygen stable isotope ratio was different in each species even after excluding the contribution of temperature dependent fractionation, suggesting a species-specific vital effects on oxygen isotope fractionation. Significant correlation between oxygen stable isotope ratio and metabolic rate M(%) was observed in bivalves, suggesting that the oxygen isotope fractionation is affected by metabolism.

The aim of this study was to examine the necessary pre-processing methods for understand the habitat history of precious coral by using carbon and oxygen stable isotope ratios. The study was conducted on white corals (Corallium konojoi) collected off Hahajima Island, Ogasawara. A growth model was created using thin section images and EPMA mapping images, and powder subsamples were scraped along the annual ring structure. Organic material removal was verified with reference to previous studies and pre-treatment with a 10% hydrogen peroxide solution was carried out, followed by carbon-oxygen stable isotope ratio analysis.Anormal analysis values have obtained for the untreated samples and those pretreated as small pieces due to contamination by impurities such as organic matter. On the other hand, no such effects were observed in the pre-treated powder samples. There was no significant difference in the analyzed values between the untreated and pre-treated samples, and it can be said that the effect of pre-treatment on the analyzed values was minimal.

Tree-ring width, density, and isotopic data can be used for paleoclimate reconstruction. Recently, due to the advantage of being less affected by tree physiological factors, the use of tree-ring cellulose isotope ratios in paleoclimate reconstruction has become a new research focus. Specifically, intra-annual isotope ratios have shown high-resolution potential for paleoclimate reconstruction, with feasibility demonstrated in multiple studies in central Japan. However, such high-resolution paleoclimate reconstruction studies in the relatively high-latitude region of northern Japan are still relatively scarce. Therefore, in this study, we collected tree-ring samples from northern Japan to explore whether the same reconstruction methods are applicable to this colder climate region.

Pristine samples from the asteroid (162173) Ryugu by the Hayabusa2 spacecraft provided a valuable opportunity to reveal the organic astrochemistry in the Solar System [1]. Hayabusa2 soluble organic matter (hereafter, SOM) team [2,3] evaluated aggregate fine grain samples from the first and second touchdown sites (hereafter, TD1 and TD2) for the surface (A0106) and possibly subsurface (C0107) environments of Ryugu. The SOM team determined the elemental profiles on carbon (C), nitrogen (N), hydrogen (H), pyrolyzable oxygen (O), sulfur (S) elements and their isotopic compositions [2,3], amino acids and their molecular chirality [4], pyrimidine nucleobase and N-heterocycles [5], primordial salts and sulfur-bearing labile molecules between the organic and inorganic interface [6], polycyclic aromatic hydrocarbons (PAHs) [7], sub-mm scale spatial imaging for organic homogeneity and heterogeneity in the mineral assemblage [8], and comprehensive organic molecular profiles on cold hydrothermalism on the asteroid [9]. The systematics for elemental and organic chemical surveys for CNHOS and hydrophilic molecular groups were summarized to formulate the TD1 and TD2 profiles; e.g., total CNHOS in the initial bulk of A0106 and C0107 are ~21.3 wt% and ~23.7 wt%, respectively [2,3]. Within these overviews of surface and potential subsurface sample analysis, we evaluated the average chemical composition and diversity of hydrophilic molecules to determine whether there is potential organic heterogeneity or homogeneity in Ryugu regolith. We newly identified the series of hydrophilic organic molecules as a crucial record of indigenous water-organic interactions [3,6] among these molecular surveys. Here, we discuss the primordial aqueous alteration signatures in the asteroid Ryugu based on unique hydrophilic molecular isomerism.References: [1] Tachibana et al. (2022) Science; Yada et al. (2022) Nature Astron. [2] Naraoka et al. (2023) Science. [3] Takano et al. (2024) Nature Commun. [4] Parker et al. (2023) Geochim. Cosmochim. Acta. [5] Oba et al. (2023) Nature Commun. [6] Yoshimura et al. (2023) Nature Commun. [7] Aponte et al. (2023) Earth Planet Space.; Zeichner et al. (2023) Science. [8] Hashiguchi et al. (2023) Earth Planet Space. [9] Schmitt-Kopplin et al. (2023) Nature Commun. [10] Oba et al. (2023) Nature Commun.; Lauretta et al. (2024) Meteorit. & Planet. Sci.

CM carbonaceous chondrites are the possible supply of building blocks of life to the early Earth, recording prebiotic chemical reaction. Sugars, including ribose, a component of RNA, have been identified from chondrites. However, the impact of aqueous alteration on these sugars are unclear. In this study, sugars in the LON 94101 (CM2.2-2.3) were investigated and four pentoses, including ribose, and three hexoses were detected. The total pentose content was lower than that of the Murchison meteorite (CM2.5), which experienced less aqueous alteration. Additionally, the formose-type reaction, a plausible sugar-forming reaction in parent bodies, was conducted. The sugar composition of the long-term reaction products resembled that of the meteorite. These findings suggest that sugars formed through reactions in the early stages of aqueous alteration and that the composition of these sugars changed over time. This indicates that meteorites and cometary dust with lower degrees of aqueous alteration were likely the primary carriers of sugars to early Earth.

A slight excess of L-amino acids has been reported in meteorites, and its origin is attributed to circularly polarized ultraviolet light in space, but the origin of homochirality remains unclear. This study investigated the possibility of L-amino acid enrichment under high-pressure conditions inside an icy planet to clarify how enantiomeric condensation occurred. Aqueous solutions containing L-alanine and D-alanine in different ratios were pressurized to 3 GPa, and the precipitation of alanine crystals and high-pressure phases of ice, VI and VII, were observed in situ by measuring X-ray diffraction patterns. DL-alanine precipitated from the solutions with L:D ratios of 7:3, 6:4, and 5:5. Despite the excess of L-amino acids, no L-alanine crystals were observed. This study suggests that enantiomeric enrichment may occur associated with DL-alanine precipitation.

Carbon, N, O and Si isotopic compositions of five large presolar SiC grains have been analyzed. All five grains are mainstream grains. ²⁹Si/²⁸Si and ³⁰Si/28Si ratios of the grains are 7 to 14%, and 8 to 12% higher than the solar ratios, respectively. Their Si isotopic ratios show that those grains are more enriched in ²⁹Si and ³⁰Si than smaller SiC grains. Although more analysis is needed, large SiC grains might have originated from high-metallicity AGB stars.

To extract cosmochemical information such as nucleosynthesis processes from particles in meteorites, it is essential to sample the particles from the matrices and perform elemental and isotopic analyses on individual particles. Given this background, the presenters have been conducting elemental and isotopic analyses of individual meteorite particles by combining laser ablation in liquid (LAL) with ICP mass spectrometry (ICP-MS). Through previous research, it has been revealed that using water as the solvent in LAL poses issues with the extraction of elements from sample. Therefore, this study investigates the use of low-polarity organic solvents in LAL to reduce the dissolution caused by the release of water-soluble components and reactions with the solvent. In this presentation, we will apply LAL with ultrapure water and various organic solvents with different polarities (ethanol, isopropyl alcohol, and toluene) to two meteorite samples and discuss the changes in element dissolution caused by the solvents and the differences in element dissolution depending on the type of meteorite.

In this study, we aim to apply LA-ICP-TOF-MS mapping to CM chondrites to determine (i) the elemental abundances in the constituent minerals, (ii) the most enriched phase(s) of an element, and (iii) the elemental distribution among the constituent minerals, which may reveal the elemental re-mobilization during aqueous alteration in the parent bodies and then the environmental condition of the aqueous alteration.

Since small bodies like asteroids preserved important clues to elucidate the planetary processes within the protoplanetary disk, sample return missions represent a valuable opportunity to study pristine materials. Samples returned from asteroid Ryugu have been reported to exhibit small-scale chemical heterogeneity which likely stems from secondary processes in the parent body, such as aqueous alteration. Therefore, this study aims to investigate the small-scale variation in the elemental abundance of Ryugu to gain better insights into the history of its parent body. For this purpose, the abundance of 54 elements were measured in eight Ryugu grains from the first touchdown. The bulk chemical compositions of the eight grains show a wide variation for most elements. In particular, P, Ca, Mn, Sr, Y, and rare earth elements exhibit broader ranges compared to the average CI composition. The enrichment or depletion in these elements can be attributed to the presence of secondary minerals, such as carbonates and phosphates, formed during aqueous alteration in the parent body.

The Ryugu samples collected by Hayabusa2 show kinship with CI chondrites in terms of mineralogy, chemistry, and isotopic composition. However, for small samples (＜ 25 mg), the epsilon-⁵⁴Cr values vary beyond the range of literature values for CI, whereas the epsilon-⁵⁰Ti values were relatively uniform. We performed Cr and Ti isotope analysis on eight Ryugu particles (1.6-4.3 mg) provided by JAXA's Announcement of Opportunity (AO2). The epsilon-⁵⁴Cr values of the Ryugu samples ranged from +0.89 (+/-) 0.11 to +2.24 (+/-) 0.13, and the variation was larger than in previous studies. However, in contrast to previous studies, the epsilon-⁵⁰Ti values of the Ryugu samples also varied widely, from +0.75 (+/-) 0.20 to 2.18 (+/-) 0.16. These results suggest that the Ryugu sample contains microscale heterogeneity in Cr and Ti isotopic compositions due to the heterogeneous distribution of ⁵⁴Cr- and ⁵⁰Ti-rich presolar grains. This heterogeneous distribution is possibly due to the selective destruction of chemically labile phases with low epsilon-⁵⁴Cr and epsilon-⁵⁰Ti values by aqueous alteration of the parent body and the removal of low epsilon-⁵⁴Cr and epsilon-⁵⁰Ti components by fluids.

We analyzed the chemical species of each element in the Hayabusa2 return sample by X-ray absorption near edge structure (XANES) analysis. In addition, the major minerals of Ryugu were analyzed by EPMA elemental analysis, and the composition of phyllosilicate was analyzed. Based on these results, chemical equilibrium calculations of the cation selectivity coefficients and solubilities between the phyllosilicate layers were performed to estimate the aqueous environment of Ryugu's parent body, especially the redox potential (Eh) and pH. As a result, Ryugu's water is estimated to be highly reductive (Eh = -0.5~-0.6V) and basic (pH = 10~11). The valence of trace elements such as vanadium and chromium were also measured and found to be consistent with these results. The estimated Eh values are reductive to the extent that water is reduced and produces hydrogen gas at each pH, suggesting that Ryugu's water may have been lost not only through ice sublimation and mineral hydration, but also through water-reduction reactions.

The current ocean is an "oxide world" in which adsorption of oxides dominates the dissolved concentration of trace elements. On the other hand, the paleo ocean is estimated to be a "sulfide world" in which the reaction with sulfides dominates the water solubility of the element. In this study, I examine the factors that govern the solubility of elements in water in the early materials of the solar system. By clarifying which elements are affected by sulfides in the sulfide world, I aim to contribute to the evolution of life, the behavior of elements, and the elucidation process of metal concentration. I focused on trace elements such as manganese, nickel, zinc, and iron, and identified the host phase of these elements by X-ray absorption fine structure (XAFS) using the resin-embedded samples of Ryugu as C-type asteroid and the Orgueil meteorite. I attempted to identify the factors that govern the water solubility of each element. Based on the results, adsorption experiments on sulfides (mainly pyrrhotite) under various conditions are conducted, the partition coefficient is determined. The host phase is determined by XAFS, and the systematics of the water solubility of elements in a system where sulfides dominate solid-liquid partitioning are examined.

In this study, as a new attempt for better understanding the neutron energy balance occurred in planetary materials, the use of Yb isotopic variations in fourteen lunar meteorites is discussed. Currently, isotopic work of six of fourteen samples is still in progress. Then, ¹⁶⁸Yb isotopic decrement possibly derived from neutron capture reactions was found in three of the eight samples that have been analyzed. In this presentation, we will discuss the consistency of the isotopic variations of Yb with those caused by neutron capture reactions of other elements like Sm and Er.

Chondrules and isolated grains of olivine, pyroxene, spinel, and corundum were found in the Yamato(Y)-980115 CI chondrite. A peak of size distribution of chondrules and anhydrous minerals occurs at 1-3 um, which is smaller than those of chondrules and anhydrous minerals in other chondrites. Most of the olivine grains have FeO-rich compositions, which is distinct from olivine in other carbonaceous chondrites. Most of the chondrules are type II with porphyritic textures, and the olivine phenocrysts show Fe-Mg zoning. While parent bodies of CI chondrites and asteroid Ryugu are considered to have accreted in the outer regions of the protoplanetary disk, chondrules, CAIs, and anhydrous minerals are considered to have formed in the inner regions. Transport mechanisms from the inner to outer regions and olivine Mg# distributions of Y-980115, Ryugu samples, and comet Wild2 particles are discussed.

Recently, an "isotopic dichotomy" has been identified between carbonaceous (CC) and non-carbonaceous (NC) meteorites. This dichotomy may reflect the location of formation of the meteorite parent bodies, indicating that CC and NC materials originated in the outer and inner regions of the Solar System, respectively. While many differentiated meteorites fall into the NC category, some unclassified achondrites exhibit CC-like isotopic compositions. As for Northwest Africa (NWA) 6693/6704, they are considered to be CC-like achondrites showing isotopic affinity to CR chondrites.The radionuclide ¹⁴⁶Sm has a half-life of 103 million years and undergoes decay to ¹⁴²Nd. The initial ¹⁴⁶Sm/¹⁴⁴Sm ratios are crucial for understanding the evolution of planetary materials in the early Solar System. These primary ratios have been determined from the calcium-aluminum-rich inclusions (CAIs) of the Allende meteorite and the oldest andesitic meteorite, Erg Chech 002. However, these ratios have not been measured in materials from the CC region. In this study, we conducted high-precision neodymium isotope ratio analyses of NWA 6693/6704 using TIMS. The obtained ¹⁴⁶Sm/¹⁴⁴Sm primary ratios align with those found in the NC region and in CAIs.