Trace element concentrations in fossil fuels including crude oils are used for geochemical tracers related to their origin and maturity. Inductively coupled plasma mass spectrometry (ICP-MS) has been frequently applied for their determinations. In the case of organic materials, organic matter should be removed beforehand because of carbon-induced spectral and non-spectral interferences. In this study, trace element concentrations in organic materials were analyzed through the Low-Temperature Ashing (LTA) pretreatment technique, which can efficiently remove organic carbon. As a result, quantitative recovery was obtained except depending on factors such as the volatility of element oxides and the solubility of residual ash in various acids. In addition, the measured concentrations were almost consistent with the certified and the reported values. LTA method is useful for the quantification of trace elements in various kinds of organic materials.

The Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST) is proceeding with the geochemical mapping project intendeds to show the standard values for environmental evaluation, and is aiming to obtain more detailed geochemical information by analyzing a large number of samples quickly and efficiently. We have newly introduced ICP-MS fitted with new technologies such as Integrated Sample Introduction System (ISIS 3) and Ultra High Matrix Introduction system (UHMI), and sought a method for efficient simultaneous multi-element analysis. In this presentation, we show the basic performance of the equipment and report the evaluation of spectral interference caused by various factors.

Although the ocean absorbs about a quarter of the CO2 emitted by human activities to mitigate global warming, the warming of the ocean itself and the ocean acidification caused by the absorbed CO2 may have serious impacts on the marine ecosystem. It is important to understand the spatial and temporal variability in carbonate parameters such as CO2 and pH in the ocean in order to predict future climate change and its impact. In this study, we first estimated the spatial and temporal distribution of pCO2 using a neural network method based on pCO2 observations by the National Institute for Environmental Studies, and then evaluated the distribution of carbonate parameters such as pH by combining it with the distribution of alkalinity estimated from water temperature and salinity. In this presentation, we report in the meeting on the interannual variability and trends of air-sea CO2 fluxes, pH, and aragonite saturation in the North Pacific.

According to the changes in ocean circulation and biological processes, oxygen and nutrient has changed its distribution and inventory in the water column of North Pacific. This presentation reviews present knowledges on this issue obtained by retrospective analyses of historical hydrographic data accumulated by the series of Japanese regular monitoring surveys

The mechanism by which nutrients in the deep ocean are uplifted to maintain nutrient-rich surface waters in the subarctic Pacific has not been properly described. The iron (Fe) supply processes that control biological production in the nutrient-rich waters are also still under debate. Here, we report the processes that determine the chemical properties of intermediate water and the uplift of Fe and nutrients to the main thermocline, which eventually maintains surface biological productivity. Extremely nutrient-rich water is pooled in intermediate water (26.8–27.6 σθ) in the western subarctic area, especially in the Bering Sea basin. Increases of two to four orders in the upward turbulent fluxes of nutrients were observed around the marginal sea island chains, indicating that nutrients are uplifted to the surface and are returned to the subarctic intermediate nutrient pool as sinking particles through the biological production and microbial degradation of organic substances. This nutrient circulation coupled with the dissolved Fe in upper-intermediate water (26.6–27.0 σθ) derived from the Okhotsk Sea evidently constructs an area where has one of the largest biological CO2 drawdown in the world ocean. These results highlight the pivotal roles of the marginal seas and the formation of intermediate water at the end of the ocean conveyor belt.

Hirosaki city is surrounded by mountainous areas with different geological settings. One is Towada-Hakkoda mountain area with volcanic eruption product and the other is Shirakami mountain area with old sedimentary rock with oceanic origin. The mountainous river water showed different concentration of silicate, calcium, and magnesium, which mainly come from rock weathering. These rock weathering components showed seasonal increase in summer and minimum concentration in snow melt season. Rivers from Towada-Hakkoda mountain showed high alkalinity and silicate concentrations than rivers from Shirakami mountain. The correlation of alkalinity and silicate was significant. By assuming simple mixing model of rock weathering components of andesite and carbonate, the overall dissolved components in the mountainous rivers are well explained. Silicate in these river are utilized for rice growth during summer growing season in the rice paddy located in the middle river area.

Based on a special report of the Intergovernmental Panel on Climate Change (IPCC) ”Climate Change and Land: IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security and Greenhouse Gas Fluxes in Terrestrial Ecosystems”, the author will introduce how terrestrial environments are currently changing under a changing climate, and how climate actions and their potentials for climate change mitigation and adaptation, sustainable land management, food security, and biodiversity conservation are being considered. In addition, what trade-offs (conflicts) and co-benefits are expected among the different climate actions will be discussed.

The volcanic front temporally moved to eastward ca. 20 km in the middle Miocene during the syn-opening stage of Japan Sea back-arc basin. Tomari Formation (M. Mio.) in the east Shimokita Peninsula, Aomori, NE Japan, was formed the volcanic front at middle Miocene. This volcanic formation demonstrates enriched geochemical characteristics at the rifting progressing stage. On the other hand, volcanic rocks after 20 Ma distributed in the west Shimokita Peninsula, where is the volcanic front in the Quaternary, show more depleted isotopic compositions in the mafic-intermediate rocks than Tomari volcanic rocks, whereas felsic rocks correspond to isotopic composition of lower crustal materials from Ichino-megata maar. In the western area, isotopic composition of volcanic rocks have not changed at least last 20 Myr. In the eastern area, it is implied that Tomari volcanic rocks were affected by lower crustal materials.※This study was supported by Shimokita Geopark research grant in 2020.

The position of paleo-Tsugaru Strait is reexamined using foraminiferal fossils from the lower Pleistocene marine sediments in the Oshima Peninsula, Southwest Hokkaido and Aomori Prefecture, northernmost Honshu. According to the previous research by this author around the Tsugaru Strait, during early Pleistocene, paleo-Tsugaru Current flowed along same route of present Tsugaru Current. Lower Pleistocene foraminiferal fossils from the central part of Tsugaru Peninsula indicate the influence of warm current, supporting the above estimation on the route of paleo-Tsugaru Current. The lower Pleistocene strata in the central part of Oshima Peninsula deposited on upper bathyal zone. However, these strata contain no warm water foraminiferal fossils. This means that this area was not the exit of paleo-Tsushima Current, even if this area connected the Pacific Ocean and Sea of Japan.

In Aomori Prefecture, cold air pool is observed in the southern part of Tsugaru Plain in winter. Previous studies have suggested that distribution of cold air in the plain may affect the snowfall area. In this study, the conditions for the formation of cold air pools in the Tsugaru Plain were investigated by analysis of AMeDAS surface meteorological observation data of the Japan Meteorological Agency, and by using a numerical hydrostatic model. As a result of the model analysis, it was found that cold downward (katabatic) flow was originated in the valleys of Shirakami mountains, and in the saddle between the Shirakami mountains and Hakkoda mountains. This cold flow moved into the Tsugaru Plain. The distribution of cold air pools was classified by the wind speed blowing from the Sea of Japan. When the westerly wind was weak, the whole Tsugaru Plain was covered with cold air. As the wind speed became stronger, the convergence area of the katabatic flow and the westerly wind shifted to inland. When the wind speed became much stronger, the katabatic flow from the Hakkoda side was prevented from moving northward by the westerly wind, then cold air pool was distributed only in the southeast of the plain.

We have examined the chemical characteristics of silica scaling from the Onuma geothermal power plant at Akita Prefecture, Japan. The scale consists of mainly amorphous silica and trace amounts of montmorillonite, kaolinite, and euhedral pyrite. The texture of pyrite suggests that pyrite is possible to crystalize prior to the growth of amorphous silica. Silica scale gradually changes its chemical composition from the production well toward the reinjection well. Most of trace elements including REE in silica scale also significantly decrease toward to the reinjection well, and furthermore HREE decreases more extensively than LREE though alkali and alkali earth elements (Be, Rb, Sr, Cs, and Ba) increase toward to the reinjection well. The change of element concentration in silica scales can be utilized to understand the physical and chemical conditions in the pipes at the geothermal power plant.

Based on the distribution of concentrations and isotope ratios of elements in river water and variations in the chemical forms of elements in river water, the controlling factors of river water quality and transport mechanisms of elements were clarified for river water in Akita Prefecture. The distribution of concentrations and isotope ratios indicates that river water in Akita Prefecture is formed under the influence of air masses that form precipitation, water/rock reactions when the river water exists as groundwater, and thermal water. The variations in the chemical forms of Fe and Al indicate that Fe and Al in river water exist in dissolved and particulate fractions at pH below 6, and that most of the particulate fraction is precipitated, while Fe exists in particulate and microcolloidal fractions and Al in suspended fraction at pH above 7. In river systems with many stagnant water bodies such as dams, the decrease in the amount of T-Al is large. This indicates that in river systems with stagnant water bodies such as dams, elements that are easily precipitated are precipitated in the stagnant water bodies.

The northeastern Japan arc rotated counterclockwise during the early Miocene major opening stage of the Japan Sea, but the timing, amount, and mode of the rotation remain poorly constrained. These issues should be resolved by an interdisciplinary geoscientific approach in areas where the well-dated rock sequences formed in the period of the Japan Sea opening are present. Here we present geological and paleomagnetic data from northern Japan and show that the counterclockwise rotation occurred after the formation of early Miocene volcanic rocks. After mapping geological structures in the field, we collected samples for paleomagnetic analysis at more than 60 sites in two areas (Fukaura and Kodomari) in the Tsugaru region of Aomori Prefecture. In the Fukaura area, andesites and rhyolites of the Odose Formation (ca. 20–18 Ma: Hoshi et al. 2003) have a remanent magnetization direction counterclockwise deflected from the early Miocene expected direction, although several site-mean directions of lava flows are not corrected for bedding tilt due to possible paleotopographic slopes. A similar magnetization direction is recorded in the various types of early Miocene volcanic rocks of the Gongenzaki Formation (ca. 23–20 Ma: Danhara et al. 2005) and Fuyube Formation (ca. 17–16 Ma: Hoshi et al. 2013, 2016) in the Kodomari area. It is noteworthy that a rhyolite lava unit of the Fuyube Formation preserves a westerly magnetization direction, suggesting counterclockwise rotation after 17 Ma. Future research should aim to determine magnetization directions and U–Pb zircon dates of middle Miocene and younger formations in Tsugaru.

Crustal low-frequency earthquakes (LFEQs) are anomalous one with extremely low-frequency oscillation than those expected from earthquake size. Since LFEQs occur at deep depths where no ordinary earthquakes occur, the potential contribution of crustal fluids has been suggested; however, the contribution has not yet been quantitatively explained. Waveform simulation shows that an essential part of long-lived oscillation after the S-wave is a constructive superposition of resonant waves generated in a low-velocity body. However, a detailed examination is needed to explain the variable waveform characteristics of LFEQs. Detection and study of shallow LFEQs are important recent topics because their generation mechanism is closely related to the mechanism of ordinary earthquakes.

A commercial type spent nuclear fuel reprocessing facility is being constructed in Rokkasho, Aomori, Japan. The facility is scheduled to start full-scale operation after completion in 2022. When the facility starts operation, radionuclides such as tritium, radiocarbon and I-129 will be released into the atmosphere and ocean. It is necessary to clarify the behavior of radionuclides derived from the facility in environment. We introduce the results of a preliminary survey on the behavior of radionuclides in the environment surrounding the facility, for the full-scale operation.

Unprecedented amounts of radionuclides were released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and widespread radioactive contamination in the environment has occurred. The 238Pu, 239+240Pu, 241Am, 242Cm and 243+244Cm concentrations in seafloor surface sediments collected at three sampling stations off the FDNPP site during 2012-2020 were determined to elucidate the impacts of the FDNPP accident onto their concentrations in coastal sediments. The 239+240Pu, 241Pu and 241Am concentrations and 240Pu/239Pu atom ratios in a sediment core were also determined to identify the Pu sources.

We have developed new analytical methods for ⁹⁰Sr (28.79 yr) and ¹³⁵Cs (2.3x10⁶ yr) by accelerator mass spectrometry (AMS) for the further development of the research on the environmental fate of artificial radionuclides ⁹⁰Sr and ¹³⁷Cs (30.1 yr). The AMS method enables the analysis of trace amounts of ⁹⁰Sr and ¹³⁵Cs with a simple chemical separation procedure. Having a longer half-life ¹³⁵Cs applies as a proxy for ¹³⁷Cs. For ⁹⁰Sr, SrF₂ targets were prepared from radioactive environmental reference materials with known ⁹⁰Sr concentrations (IAEA) by a chemical separation procedure that takes about two days to complete. ⁹⁰Sr measured by AMS at VERA, University of Vienna. As a result, a limit of detection of ＜0.1 mBq was obtained, which is comparable to the β ray measurement. The detection of ⁹⁰Sr in environmental samples was also successful, indicating that the ⁹⁰Sr AMS can apply to environmental samples. On the other hand, there are still some technical challenges in the ¹³⁵Cs AMS. Therefore, the experimental measurements are in progress.

We improved commercial tritium electrolyte enrichment system. In this system, water sample reservoirs were made of double-glazed glass, and cooling water was circulated in the double glass to cool the sample. As the results, good enrichment efficiency could be obtained.

Our aim of this study is to make seawater anthropogenic radioactive U isotopes widely and conveniently available as ocean circulation tracers. We attempted to optimize the adsorption and desorption process of seawater U isotopes using an ”amidoxime adsorbent” for simple U collection. The results of adsorption experiments showed that the optimum conditions for U adsorption were seawater pH 4 and 0.40 mmol of adsorbed functional group per 1 kg of seawater using a glass beaker, and seawater pH 8 using a closed polyethylene container with a similar ratio of functional group additive for experiments on-board. The results of desorption experiments showed that U recovery (based on seawater) was more than 80 % with 2 mol/dm³ hydrochloric acid. Therefore, the amidoxime adsorbent can be used for simple U collection not only in the laboratory but also on-board ships, which is a great step forward toward the simple use of seawater anthropogenic radioactive U isotopes as tracers for ocean circulation.

The importance of environmental ²³⁷Np has been suggested as a tool for environmental dynamic research, in addition to search for radiation effects, due to physicochemical properties of Np. However, the ultra-trace level of the nuclide is difficult to measure accurately with a mass spectrometer and has not been comprehensively studied because of the lack of a spike for the chemical separation of Np in environmental samples and their measurements. In this study, we attempted to newly produce ^236gNp as an Np spike and establish a chemical separation method for purification of the spike. A purification method of Np with a good recovery rate was established using TEVA, TK400 and UTEVA resins, and was applied to the sample which was irradiated to produce the Np spike. We successfully detect and quantify the by-product ^236mNp in the irradiated samples. From these results, the amount of ^236gNp produced by irradiation could be evaluated. Further, a basic study on the Np collection from seawater using amidoxime-type adsorbent was carried out to apply the Np spiking method to hydrosphere samples.

Cs collection methods from environmental water (seawater) with less interference isotopes for the determination of ¹³⁵Cs by mass spectrometry has been developed in addition to attempt Cs isotope measurement by AMS. Adsorption/desorption experiments of ¹³⁷Cs and ¹³³Ba were using copper-substituted Prussian blue nonwoven fabric (PB). For AMS measurements， Cs negative ion beam extractions from some reagents were attempted using both Rb ion source and conventional Cs ion source. In the 24-hour adsorption experiments with 1 L of seawater, the adsorption rates of ¹³⁷Cs were 39% for PB sizes of 4 cm² and 85% for PB sizes of 25 cm². Adsorption rates of ¹³³Ba were less than 5% for all experiments. In the desorption experiments, only 40% of Cs was desorbed by 30% HNO₃, but more than 95% of Cs was desorbed by 35% HCl. As a result of the AMS experiments, CsS^- and CsF₂^- were observed in Cs beam that were sputtered by Cs and Rb.

The purpose of this study is to quantitatively analyze iodine isotopes in environmental water samples using accelerator mass spectrometry (AMS) and inductively coupled plasma mass spectrometry (ICP-MS). As a result of the iodine recovery experiment by the Pyrohydrolysis method, there were large variations in the recovery rate of both inorganic and organic iodine, so it is difficult to apply this method to environmental water samples and evaluate total iodine. A simple and quantitative method for converting organic iodine in water samples to an inorganic state and recovering inorganic iodine needs to be further investigated and optimized by chemical reaction with reagents and decomposition of organic matter with ultraviolet rays. From the results of long-time measurements of I-127 and some elements by ICP-MS, In-115, which is commonly used as an internal standard, does not function as an internal standard for I-127, particularly in high matrix solutions, suggesting that Re-185 is relatively suitable as an internal standard for I-127.

Since I joined Masuda Laboratory of Department of Chemistry, Faculty of Science, the University of Tokyo, as an undergraduate student in 1985, I have been working in geochemistry field. As I have belonged to ORI (now AORI) of the University of Tokyo and JAMSTEC for a long time, I think, most of the people may regard me as a marine chemist or a chemical oceanographer. Although I admit that the most of my scientific achievements are classified into marine geochemistry, I was also a member of cosmochemistry laboratory of Tokyo Metropolitan University. Based on some kind of peculiar career, I would like to discuss feature aspects of geochemical research.