4m piston corings were conducted by the Shinyo-Maru in the Tokyo Submarine Canyon in November 2019. Sediment samples were collected onboard for dissolved ions and dissolved gas in interstitial water. In order to understand the origin of methane and to evaluate the methane flux, we measured dissolved ion and gas concentrations as well as ¹²⁹I/¹²⁷I. In this presentation, we present the vertical distribution of methane, sulfate, and iodine dissolved in interstitial water.

The recent changes in the marine and terrestrial environment in the Arctic are urgently needed to be clarified and their impacts assessed. In this study, we examine whether the changes in the marine and terrestrial environment during the 20th and 21st centuries were rapid and significant in amplitude, which has not been seen in the recent past, based on the results of paleoenvironmental analysis. MR22-06C cruise was conducted in August and September 2022, and 32 sediment cores (total length 56 m) were collected at four sites in the Beaufort Sea. In November 2022, the cores were measured, described, and split at the Kochi Core Center, and samples were distributed to research institutes. Continuous environmental reconstructions are possible at the MT1 and MT2 sites near the mouth of the Mackenzie River with a 6-year resolution for the past 3000 years, at the BC2 site off Barrow with a 3-year resolution for the past 1500 years, and at the BC2-2 with a 1-year resolution for the past 500 years. The high-time-resolution environmental reconstructions using the marine cores are expected to recover various environmental information and provide new knowledge.

The Arctic Ocean is the most severely affected by global warming and ocean acidification on the Earth. How are biological production and material cycles responding to these changes? To clarify this, we have investigated using a sediment trap mooring system and various sensors such as pH/pCO2 in the western Arctic Ocean since 2010, collected biogenic particles and acquired data in a time series, and described the changes in biogeochemical processes. We have also clarified that nitrogen fixation, considered a local biogeochemical process, is found to occur in polar oceans where nitrate and ammonia are abundant. In addition, we have had the opportunity to challenge biogeochemical research in the Southern Ocean, East Antarctica. Using an Event-Based Vision Sensor (EVS) developed by Sony, we plan to capture particles of previously unmeasured sizes and estimate the total amount of particles originating from marine organisms with the results of giant particles by sediment trap observations. Numerical simulations are also making progress. In this presentation, I will introduce the results of achievements in the Arctic Ocean and a new challenging research related to the biogeochemical processes through observations in the Southern Ocean.

The 61st Japanese Antarctic Research Expedition conducted the sediment coring using the icebreaker Shirase for the first time. Sediment samples were collected off Totten Glacier and Lützow-Holm Bay on the East Antarctic coast. Working-half-core transported to Japan and kept in a refrigerator at the AIST for about two years. In this study, to understand records of fresh and brackish water input into the environment of marine interstitial water associated with the retreat of ice shelves.Interstitial water was extracted from the sediment samples stored for two years using a squeezer and centrifuge. The concentrations of the major ions were determined by ion chromatography. This study presents the effects of evaporation and sample alteration due to two years of storage and the effects of fresh and brackish water input into the seafloor environment due to the retreat of ice shelves along the East Antarctic coast.

The intermittent volcanic activities of Nishinoshima from 2013 were characterized by the effusive eruption of the andesite magma (episodes 1-3, until 2019) and subsequent explosive eruption of basalte to basaltic-andesite magma (episode 4, 2019-2020). Furthermore, possible episode 5 activity has been observed from August 2021. This study investigated the geochemical characteristics of the episodes 4 & 5 magma based on the on-land and seafloor samples collected in and around Nishinoshima, taking special care of the redox state of the glass using micro-XANES. The episode 4 eruption was characterized by the reduced felsic magma and the injection of oxidized mafic magma, while the episode 5 magma shows the oxidized felsic glass. The observed characteristics suggest that the episode 5 eruption has different features from neither episodes 1-3 nor 4 activities.

The formation process of continental crust on the early Earth remains unresolved due to a lack of physical evidence. In contrast, Hadean zircons are one of the few clues to the early Earth and are important for understanding the early Earth environment. In this study, we examine the formation process of the continental crust on early Earth using trace elements in Hadean zircons, with a focus on Sc/Yb ratios. Detrital zircons from Jack Hills were used as samples and analyzed for ²⁰⁶Pb-²⁰⁷Pb ages and trace elements using LA-MC-ICP-MS and LA-ICP-MS/MS. The rare-earth patterns showed characteristics similar to igneous zircons. Sc/Yb ratios were below 0.1 before ca. 4.2 billion years, and zircons with ratios above 0.1 appeared after ca. 4.2 billion years. The Zr/Hf ratio exhibited a decreasing trend throughout the Hadean. Based on these results, it can be inferred that there was a transition from high-temperature ocean-island igneous activity in the early Hadean to low-temperature continent-arc igneous activity in the late Hadean.

Dissolved inorganic carbon analysis of water samples requires treatment to stop the activity of microorganisms living in the sample. We tested low environmental impact filtration treatment and addition of benzalkonium chloride using seawater and groundwater. Filtration treatment alone did not eliminate the effects of biological activity. The addition of benzalkonium chloride alone was effective in groundwater, but caused negligible changes in seawater. However, the combined treatment of filtration and addition of benzalkonium chloride was shown to eliminate the effects of biological activity even in seawater.

The oxygen isotopic dendrochronology was put to practical use in Japan in the 2010s. The 775 AD cosmic ray event was discovered in the Yakusugi cedar trees. I will review these achievements and discuss the prospects for high-precision dating research.

Scientific estimation of production regions for edible marine vivalves is important in the context of authentication of the region on the distribution and the improvement of food safety. Aiming at utilizing lead isotopes in bivalve shells as an index for the production region we have carried out fundamental experiments of decontamination, dissolution and isotope analysis of the shells. The test shell samples used in this study were collected from European mussels. In this study, we mainly describe results on analytical experiments, such as removal of organic mater on the shell surface using mixed solutions of various oxidizing agents and strong acid or base, and the stepwise dissolution of shell substances using acids.

The analysis of rare earth elements in food products has been neglected even though rare earth elements are valued as fingerprints of samples in the earth sciences. In this study, we analyzed heavy metal elements and rare earth elements in seaweed food products commercially available in Japan (80 samples of cultivated seaweed from various regions of Japan and 20 samples of imported seaweed from Korea). The distinction between Japanese and Korean products was made for cadmium and thorium, which can be distinguished next to threshold values of 0.5 ppm and 3.3 ppm, respectively, but not between regions of origin within Japan. Among the analytical values of rare earth elements, anomalous values of europium were found to reflect the geology of the junior locality and are helpful for the classification of the locality of origin for Ariake Sea and Seto Inland Sea, Japan's two major seaweed production areas and also made-in-Korea. This study suggests that the analysis of rare earth elements in foods is beneficial for provenance traceability.

The formation process of carbonate concretions might involve the supply of organic matter from organisms, but the detailed early stages of this process remain unclear. Therefore, our research has focused on determining how long it takes for carbonate concretions to form after the death of organisms. We conducted radiocarbon dating on biogenic remains from carbonate concretion samples collected from the fluvial deposits around Nagoya Port (Minami et al., 2022). The results showed that both had approximately the same age (8000-7800 cal BP), suggesting that these samples rapidly concretized and formed after the death of organisms. In this study, we applied the same methodology used for Nagoya Port concretions to the concretion samples collected from Shimizu Port. By summarizing the results obtained from both concretions, we aim to explore the formation process of carbonate concretions.

Acid mine drainage containing heavy metals is usually generated in metal mines; it is generally neutralized using limes to precipitate those metals as hydroxides and carbonates. The neutralizing condition is determined by a rule of thumb. However, an elucidation of each chemical reaction in AMD could help to set more suitable treatment process: geochemical code such as PHREEQC is used to evaluate quantitatively these reactions. Furthermore, solid analysis such as XAFS of precipitates can also give an important geochemical data (e.g., formation condition and crystalline structure) of rare minerals. In this presentation, we show geochemical model of AMD treatment which was constructed by neutralizing test of various AMD samples and their future perspectives.

The formation age of ore deposit is one of the most essential information in the genesis analysis of the deposits and provides clues to clarify the relationship between the deposit and the host rocks and to search for new ore deposits. Indirect dating of ore deposits using the ⁴⁰K-⁴⁰Ar and ⁸⁷Rb-⁸⁷Sr methods has been conducted for intrusive rocks and alteration minerals previously, but the inadequate sample selection of alteration minerals affects the reliability of the ages of ore deposits. In recent years, direct dating of ore minerals of the deposits has also been attempted. One example is the direct dating of pyrite, a sulfide mineral that is universally associated with various types of metal deposits, by applying the ⁸⁷Rb-⁸⁷Sr method, which is widely used to determine the age of igneous rocks and to estimate magma sources. Although the Rb and Sr contents in pyrite are extremely low, their Rb/Sr ratios show a wide range of values, and thus it is expected that highly accurate ⁸⁷Rb-⁸⁷Sr isochron ages can be obtained. In this study, with the aim of expanding the range of application of the ⁸⁷Rb-⁸⁷Sr method to pyrite, we attempted to apply the ⁸⁷Rb-⁸⁷Sr method to millimeter-sized pyrite single grains and discussed the results of quantitative analysis of major and trace elements and Sr isotopic analysis of pyrites.

Tephrochronology is important to understand geotectonic events for the last few Myr. Tephra is usually characterized by petrographic characteristics and chemical compositions (mainly major elements) of volcanic glass shards. Trace element composition is useful in identifying tephras with similar characteristics. In this study, we aimed to enhance the database of trace elements compositions in widespread tephras, which is not reported enough. We used EPMA and LA-ICP-MS for major and trace element concentration of volcanic glass shards in Znp-Ohta tephra and Tng tephra, of which major elements similar to Znp-Ohta tephra. It was clear that Znp-Ohta tephra had zirconium concentration [Zr] = 44-58 ppm and Zr/Pb = 2.5-3.4, while Tng tephra had [Zr] = 70-81 ppm and Zr/Pb = 3.8-4.6. Znp-Ohta and Tng tephras were discriminated not only by characteristic type, Ba/La, and La/Y of glass shards (Tamura and Yamazaki, 2004) but also by Zr-Pb correlation. In the future, we compare the trace element concentrations of Znp-Ohta tephra at multiple sites for evaluation of secondary effects during or after the deposition.