We present an ongoing research project that was selected for KAKENHI this fiscal year. We aim to comprehensively understand the physical and chemical phenomena of the atmosphere, i.e., meteorological and environmental changes cuased by the aerosol-cloud interaction processes, by conduciting continuous direct observations of aerosols and clouds using Mt. Tsukuba, an isolated amountin with a peak at a typical cloud base altitude (about 1000 m), and by using numerical models that can accurately describe responses to given changes in various meteorological and chemical processes, that are highly nonlinear. The project has not yet produced any results but we will outline the background, progress, and plans, including the past research activities of the participants based on the kick-off meeting scheduled for September 8, 2023.

Anthropogenic activities after Industrial Revolution have had large impacts on earth environment. The same applies to atmospheric environments and aerosols in the atmosphere, and past aerosols records in ice or sediment cores. Therefore, analysis of these records is important for discussion about Anthropocene.In this study, we conducted research on chemical records of past aerosols using ice core from Greenland (SE-II ice core) and sediment core from the Tokyo Palace moat, and clarified how each chemical record reflected anthropogenic activities on various scales (global to local).Specifically, in the SE-II core, existence of large amounts of anthropogenic elements were confirmed by trace metal concentrations, and changes in Fe and Zn species were detected by XAFS. Ca species in SE-II core was also consistent with previous studies. From the Tokyo Palace moat sediment core, Zn isotope ratios were measured and proved that they reflected local human activities.

Anthropogenic, pyrogenic, and lithogenic iron (Fe) aerosols affect marine ecosystems and climate through the food chain starting with phytoplankton (primary producers) by providing vital nutrient (Fe) to the ocean surface layer. However, there is a large uncertainty in the estimate of nutrient supply from those sources. Particularly in the Southern Ocean, underestimates of observed data on the mass concentration of bioaccessible Fe in aerosols have led to hypotheses such as missing sources in global models and underestimation of Fe dissolution rates (Ito et al., Science Advances, 2019). In this review paper, we summarize the progress in research on how bioaccessible Fe in aerosols affects marine biogeochemistry and ecosystems from atmosphere (emission, transformation, radiation, and deposition processes) to post-deposition (leaching into seawater as bioavailable Fe). Future perspectives include interdisciplinary research of field observational, laboratory experimental, and numerical modeling studies.

In this study, we used the triple oxygen isotopic compositions of nitric oxide, nitrogen dioxide, gaseous nitrate, and particulate nitrate determined simultaneously as a tracer to clarify the reaction paths from nitric oxide to gaseous/particulate nitrate. While tropospheric ozone displays anomalous enrichment of oxygen-17 in the terminal positions, we can expect the triple oxygen isotopic compositions close to 0 per mil for the oxygen atoms in tropospheric peroxides derived from either molecular oxygen or water vapor.

In order to quantify the impact of organic iodine gas (VOI) generated from the reaction of seawater and O3 on the global environment and to clarify the mechanism of VOI generation, we developed an experimental system for the reaction of O3 and seawater using ozone detector tubes. In this experiment, we focused on CH2I2 and investigated the quantitative relationship between O3 and CH2I2 and the CH2I2 concentration that increases in seawater after O3 ventilation. From the results of this experiment, it was found that the iodine compound involved in CH2I2 formation in seawater is not IO3- but I-, and that I2 generated by the reaction of I- with O3 acts on organic matter in seawater, and that the Iodoform reaction The results suggest that the I2 generated by the reaction of I- with O3 may be generated from a chemical reaction similar to the iodoform reaction.

Bromine atoms are known as substances that reduce tropospheric ozone. One of the substances that supply bromine atoms to the atmosphere is bromoform, a volatile organic bromine. High concentrations of bromoform have been found on the surface of sea ice in the polar regions, and photochemical reactions and oxidation of Br- by ozone are thought to be factors. The vertical distribution of bromoform concentration in snowpack and sea ice in Lake Saroma, a brackish lake on the coast of the Sea of Okhotsk in Hokkaido, Japan, revealed high concentrations of the organic iodine iodoethane on the sea ice surface, but low concentrations of bromoform. We focused on the temperature difference between the polar regions and Lake Saroma as the cause of this difference, and hypothesized that the reaction between I- and Br- on the sea ice surface is temperature dependent, and developed an experimental method for the reaction between ozone and sea ice to test this hypothesis. To confirm the formation of bromoform by the reaction of Br- and ozone in sea ice in the laboratory, we created artificial sea ice and supplied ozone to the sea ice surface. As a result, high concentrations of bromoform were detected on the sea ice surface.

The photolysis of nitrous acid (HONO) has been recognized as a potentially important source of OH radicals, which is known as a major oxidant in the atmosphere removing reductive trace gases such as methane and NMHCs. Atmospheric HONO originates from both direct emissions (produced via combustion or biologically produced in soil), and secondary formation (chemically produced from NO₂ or NO in the atmosphere), however, their contributions to the atmospheric HONO production have not been well understood. Here, we determined a ¹⁷O-excess of HONO together with that of its precursors (NO₂ and NO), because ¹⁷O-excess of HONO produced via secondary formation is expected to have highly positive values as those of NO₂ or NO, while no ¹⁷O anomaly should be observed for HONO which is emitted directly from various sources on the ground, making it possible to quantify their contribution to the atmospheric HONO production with ¹⁷O-excess measurement.

Total sugars in the aerosols, which have been pointed out to play important roles in the atmospheric environment, for instance to act as cloud condensation nuclei, were quantified with a phenol-sulfuric acid method to discuss their concentration, contribution to the water-soluble organic carbon (WSOC), and sources. Aerosol samples were collected at an urban site in Kofu and a forested site on the northern foot of Mt. Fuji. The total sugars were mainly partitioned into the fine-mode range than the coarse-mode range, and their concentrations were higher at the urban site than the forested site. Primary emissions by dispersal of plant debris and biomass burning are considered to be important sources for coarse and fine aerosols, respectively. The concentration ratios of the total sugars to the WSOC were about 10-20%. This ratio was higher in the coarse-mode range than the fine-mode range and higher at the urban sites than at the forested sites. These results indicate that the total sugars are an important component of the WSOC in the aerosols.

In this study, we investigated the geochemical behavior of Ra focusing on its distribution between sediment and water. We collected surface sediment and water samples for Ra-226 analysis in the Ningyo-toge area. XRD and XAFS analyses indicated that surface sediments were composed of ferrihydrite and goethite. Apparent distribution coefficients of Ra between sediment and water were larger than those determined experimentally for ferrihydrite and goethite. Thus, it is possible that a minor component contributed to an increase in the apparent distribution coefficients. Another possibility is upward flow of pore water containing Ra-226 or diffusion of Ra-226 released from lower sediment layers.

Hg concentration of soils, taken from the south-east low peripheral mountains of Osaka Plain. Average Hg concentration of 209 soils was 135 µg/kg, and 25 soils contained ≥200 µg/kg. High Hg concentrations of some soils would be related to the Hg ore mineralization. High Hg concentration at or near the active faults than the surroundings implies Hg emission along the faults from the deep.

Homeostasis is defined as "the state and function in which the internal organs of an organism maintain the internal environment within a certain range in a unified and purposeful manner in response to changes in the external environment and subjective conditions," and includes the phenomenon in which essential biological elements are maintained at a certain level. The speaker believes that lake, which are stagnant zone of inland water, play a similar role in the environment, and has been collecting data with the aim of evaluating the trace element homeostatic function of lakes. In the presentation, we will discuss (1) comparison of major elements with previous studies (Kobayashi, 1961), (2) classification of river water quality by principal component analysis, (3) analysis of the relationship between trace element level between river water and sediment data published by AIST, and (4) comparison of "local solubility trend" to the world river database, (5) comparison of relative standard deviations of trace element concentrations calculated from certified igneous rock samples (AIST, n=13), river sediment samples (AIST, n=3024), river water samples (n=30), and lake samples (n=200) to discuss homeostatic power of each element in each reservoir is presented.

Smectite is a clay mineral and used for various applications because of useful characteristics such as low water permeability, high degree of swelling and high cation exchange capacity. This study conducted small angle X-ray scattering (SAXS) and methylene blue adsorption methods for samples containing smectite, to estimate the content of smectite in samples. Result of SAXS method shows scattering of amorphous nanoparticles and 001 reflection of smectite. The result was transformed into normalized intensities according to Tsukimura and Suzuki (2020). The normalized scattering was approximated by a simple function and separated from the smectite intensities. Methylene blue adsorption was measured by colorimetric method proposed by JIS Z 2451 (2019). The normalized intensities of smectite were correlated with methylene blue adsorption of some of the samples collected in Japan.

Subsurface biosphere is one of largest biospheres on the Earth. However, most of geochemical processes driven by microbial activities in subsurface setting is still unknown. In this study, we focused on Suwa basin where active microbial methanogenesis is reported from deep subsurface. At the intersection of Itoigawa-Shizuoka Tectonic Line (ISTL) and Median Tectonic Line (MTL), Suwa basin is composed of organic-rich sedimentary layers. There are active faults and hot springs within the complex hydrogeological structure of the basin on the boundary of North American Plate and Eurasian Plate. These geological backgrounds would host the potential of microbial ecosystems with diverse community structures and functional properties in the deep subsurface. In this study, we collected groundwater samples from seven hot springs (max. 1000 meter below ground level) and three monitoring wells (max. 100 mbgl). Using these samples, we reveal microbial community structure with quantifying biomass ratio of bacteria and archaea based on membrane lipid analysis.

As of 2023, radioactive nuclides released due to the Fukushima nuclear accident still persist in the environment. In this study, an example of the dynamics of radioactive nuclides in a terrestrial ecosystem was investigated by measuring the ¹²⁹I and ¹³⁷Cs concentrations in captured Japanese macaques and soil in Fukushima Prefecture. Soil samples were measured at different depths, and the relationship between the half-life of radioactive nuclides in the soil surface and the ecological half-life of radioactive nuclides in Japanese macaques was examined. The results showed that the ¹²⁹I/¹²⁷I ratio in the Japanese macaques decreased as the capture date became more recent, and the rate of decrease was similar to that of ¹²⁹I in the surface soil. Furthermore, when comparing the ¹²⁹I/¹²⁷I ratio in individual macaques with the ¹²⁹I/¹²⁷I ratio in soil samples closest to their capture locations, a positive correlation between the two was observed. Overall, the amount of ¹²⁹I in the Japanese macaques appears to reflect the decay and contamination levels of ¹²⁹I in the surface soil.

Trace elements exist in two forms: dissolved in water and adsorbed on particulate matter. Particulate matter adsorbs dissolved trace elements, converts them to the particulate form, and transports trace elements downward. During the downward-transport process, adsorption of the dissolved forms onto the particles and desorption from the particles also occur. Therefore, in order to truly understand element cycling, it is important to study not only the dissolved but also the particulate forms. In this study, samples obtained from the western North Pacific (155 E section) obtained by water sampling and filtration during the KH-22-7 and KH-23-2 cruises of R/V Hakuho-Maru were analyzed. The north-south longitudinal distributions of trace elements (Al, P, Ti, Mn, Fe, Co, Cu, Zn, Mo, Cd, Pb, and Bi) in suspended particulate matter (SPM) obtained by the analysis are reported from this analysis.

²³⁷Np is recognized as a candidate tracer for the circulation of seawater. However, ²³⁷Np measurements have not been conducted extensively. This is because the concentration of ²³⁷Np in seawater is extremely low, the chemical separation for measurement is complicated, and there is no suitable "spike" for ²³⁷Np measurements. In this study, we propose a comprehensive analysis method for ²³⁷Np in seawater by producing the new spike for ²³⁷Np measurement and by introducing a simple Np concentration method from seawater for application to establish the robust ²³⁷Np seawater circulation tracer.

The objectives of the present study were to determine the ²⁴¹Am, Pu and ²¹⁰Pb concentrations for settling particle and seafloor surface sediment samples collected on the continental margin in the East China Sea and to contribute to better understanding of the scavenging processes of ²⁴¹Am in the studied area. The ²⁴¹Am concentrations in settling particles tended to increase with trap depth. The tendency of the ²⁴¹Am concentration to increase was in good agreement with that of the ²¹⁰Pb concentration to increase. These results strongly suggested that there was a net accumulation of ²⁴¹Am and ²¹⁰Pb on the settling particles with depth, indicating active scavenging of these nuclides from seawater. A scenario for active scavenging could be strong adsorption by fine-grained clay particles, which underwent repeated resuspensions in the nepheloid layer and were flowing down the continental slope of the East China Sea.