To investigate whether diatoms dissolve silicate minerals by secreting polysaccharides or TEP, we carried out cultivation experiments with feldspar particles being doped.

Zirconium (Zr), hafnium (Hf), niobium (Nb),and tantalum (Ta) are known as high-field strength elements (HFSE) since they form highly charged ions. Because the mole ratios of Zr/Hf and Nb/Ta in seawater change significantly depending on water masses, they are considered to be useful as their tracers. We will report the concentration profiles of the four elements in dissolved (d) and total dissolvable (td) fractions at eleven stations from 40^oE, 62^oS to 86^oE, 17^oN in the Indian Ocean. We will also compare them with our results in the subarctic North Pacific Ocean and previous studies in the Atlantic Ocean.

Tellurium is assigned as one of technology-critical elements (TCEs) useful for industrial products such as a DVD. Marine ferromanganese oxides on the seafloor contain high concentration of Te. In seawater, Te present as different oxidation states (Te(IV) and Te(VI)) with very low concentration below 2 pmol/kg. Redox transformation between Te(IV) and Te(VI) and variability of Te(IV)/Te(VI) ratios in marine environment are crucial for better understanding of marine biogeochemical cycles of Te. However, reliable data of Te in seawater is sparse due to difficulty in the analysis. We developed a new analytical method to obtain reliable data of Te species in seawater and clarified vertical profiles of Te species in station BD7 found in the western North Pacific. Te species showed a scavenged type distribution, high concentration in surface and decreasing with depth. These results suggested that scavenging processes controlled Te species distribution in typical oxic ocean. In this study, we perform determination of Te species in the eastern Indian Ocean having a specific anoxic environment such as oxygen minimum zone and report Te species distribution and its oceanographic features.

This study reports distributions of dissolved trace metals in the Bay of Bengal in 2013. Trace metal concentrations in low-salinity waters were relatively high, implying the freshwater intrusion and coastal-derived input. High concentrations of Fe at northern margin showed continental sediment, water mass movement, and ventilation might control the transport of Fe from the continental shelf.

The goal of this study is to determine the d¹⁵N values for low concentrations of dissolved organic nitrogen (DON) in surface and subsurface water and to gain new insight into nitrogen cycle in the North Pacific Subtropical Gyre. We analyzed concentrations and d¹⁵N for both DON and nitrate at two sites, KEO (32.3N, 144.5E) and KEOS (25N, 145E), in the North Pacific Subtropical Gyre.The water sampling was performed in December 2021 and April 2022. The results showed that nitrate concentrations were below 0.4 uM from the surface to 150 m depths and the d¹⁵N of them could not be determined, except in April at KEO. DON concentrations were 4.7 +- 0.3 uM (n = 7) and 4.6 +- 0.3 uM (n = 7) in December and April at KEO, respectively, and were 4.5 +- 1.9 uM (n = 10) and 4.5 +- 0.9 uM (n = 8) at KEOS, respectively. The d¹⁵N_DON (permil Air) was +2.2 +- 0.7 and +3.4 +- 0.3 at KEO, and +5.3 +- 1.0 and +1.9 +- 1.8 at KEOS, respectively. These results suggest that the DON sources in the surface layers of KEO and KEOS is the contribution of organic matter derived from nitrogen fixation, which exhibits lower d¹⁵N than that of nitrate in the Mesopelagic zone.

Gaseous elementary mercury (Hg⁰) is present throughout seawater, yet its production mechanisms are poorly understood. Vertical profiles of Hg⁰ production potential along 155º E in the North Pacific using stable Hg isotope tracers were investigated in this study. The produced Hg⁰ amounts from the inorganic Hg tracer were nearly uniform throughout the water column, on the other hand, the produced Hg⁰ amounts from the monomethyl Hg tracer in the deep ocean were much larger than the shallow mixed layer. The inverse relationships between Hg⁰ production amounts and seawater temperature, and dissolved oxygen concentrations were indicated.

Osaka Bay has two openings. Osaka Bay is a highly enclosed sea area where various large and small rivers such as the Yodo River, Yamato River, and Inagawa River flow into the bay. As for the topography of the sea area, the eastern sea area is shallow and flat with a depth of less than 20m, while the western sea area is deeper toward the strait, reaching a maximum depth of 100m. In the past, during the high economic growth period, Osaka Bay became eutrophic due to nutrients such as nitrate and phosphorus supplied from factories and household wastewater, and red tides were frequently observed. After that, nutrients gradually decreased due to legal regulations, and in recent years, it has become oligotrophic. Regarding the chemical composition of Osaka Bay, there is many information on nutrients such as nitrate and phosphorus from the viewpoint of eutrophication, but there is few information on bioactive trace elements which essential for phytoplankton growth. The purpose of this study is to clarify the vertical distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb and Se, which are classified as bioactive trace elements, and elucidate the factors that govern its distribution.

ESR dating of barite is useful to estimate the age of sea-floor hydrothermal activities. The method is based on the fact that radiation from Ra in barite creates SO3- radical which is detected by ESR. Short-lived 228Ra is not detectable in older sample but the radiation from this nucleus cannot be neglected, therefore, the initial value of 228Ra/226Ra in barite is important. In the present study, 228Ra/226Ra was measured by a pure Ge gamma ray spectrometer with Mn fiber dipped in hydrothermal water. Spring waters in Chugoku-area show values of 5-15 while it was 35 for sea-floor hydrothermal fluid in Okinawa Trough.

Halophilic Archaea produce a C₂₅C₂₀ diether as a core lipid with one C₂₅ isoprenoid, and this compound could be used as an indicator of high salinity environments. On the other hand, two regioisomer of C₂₅C₂₀ diether are existed structurally, but different isomers are reported to exist in biological and rock-salt samples. I developed a method to show the presence of two isomers by characteristic fragments of the mass spectra with chemically synthesized standard. The results of recent study showed that a certain micro-organism have two isomers in the biological sample and a small amount of isomers in the rock-salt sample. For the quantitative analysis of the two isomers which is independent with the comparison of intensity of the fragment ions, a quantitative analysis through the regiospecific degradation of the ether was investigated.Currently, trace amounts of rock-salt isomers appear to be the result of minor fragmentation in mass spectrometry, confirming previously reported results of most microorganisms. However, this method is also applicable to the differentiation of positional isomers of asymmetric diether lipids in bacteria.

Sr isotopes (87Sr/86Sr) are useful tracers to reconstruct migration histories of extinct animals. When applied to fossil samples, it is essential to evaluate the effects of diagenesis. In some cases, acetic acid treatment, which is conventionally used, did not sufficiently remove the influence of diagenetic effects. In this study, as a preliminary survey to reconstruct the ecological history of fossil vertebrates using the 87Sr/86Sr ratio, we investigated the diagenetic process in phosphate fossil by combining acetic acid pretreatment with local composition analysis of elements (Si, Fe, Mn, and REE) as indicators of diagenetic effects. The results showed that the concentrations of Si, Fe, Mn, and REE in enamel-like tissue were about 1/5~1/10 of those in dentin. In the enamel-like tissues, REE/Ca was about 1000 times higher than that in the teeth of the dentin of modern animal, whereas Sr/Ca was about 2 times higher. Furthermore, acetic acid treatment reduced Sr/Ca in enamel-like tissues by about 30%. These results suggest that after acetic acid treatment, enamel-like tissues retain enough Sr isotopic information from the fossil animal's life.

Photosymbiosis (endosymbiosis with algae) is widely observed in marine organisms and is considered to be an adaptive strategy to live in oligotrophic oceans. Many species of planktonic foraminifera, which are microfossil organisms, are also known to be photosymbiotic. From the viewpoint of improving the accuracy of paleoenvironmental proxies based on planktonic foraminiferal tests, there is much interest in how the photosynthesis of symbiotic algae affects the geochemical composition of their tests. However, the dynamics of carbon directly related to photosynthesis are still not well known due to the limited number of experimental studies. In this study, we conducted culture experiments on planktonic foraminifera and photosynthesis measurements on them in order to clarify the carbon dynamics of photosymbiotic systems. By measuring and comparing photosynthesis using two different techniques (14C tracer method and fast repetition rate fluorometry method) in two different foraminifera-algal symbiotic systems, it became clear that the origin of the carbon used for photosynthesis was different between the two species. The results suggest that the degree of influence on the chemical composition of the shell may differ between the two species.

In this study, we conducted a food web analysis of aquatic organisms using radiocarbon in Lake Suwa, where deep-derived methane seeps into the lake. Lake Suwa is a fault lake located at the intersection of the Itoigawa-Shizuoka Tectonic Line and the Median Tectonic Line, and its sedimentary layers contain methane reserves. Previous studies have reported that this methane is depleted in radiocarbon, and that some of the methane is incorporated into the lake water as dissolved inorganic carbon (DIC). To assess the influence of deep methane on the entire lake, we performed radiocarbon analysis of DIC in the surface lake water, including major outflow and inflow rivers, and found that the radiocarbon values in the lake water were lower than those in the inflow rivers. While aquatic organisms, wakasagi and largemouth bass indicated radiocarbon values intermediate between those of lake water and river water. In this presentation, we will discuss multidimensional isotope systematics with stable carbon and radiocarbon dynamics in the entire hydrosphere, together with the results of ecosystem structure analysis using compound-specific isotope analysis for Amino acids.

The change in reaction Gibbs free energy (D_rG [kJ mol^-1]) is an indicator of the energy value of a reaction. However, there are microorganisms capable of "splitting" reactions with low D_rG. Based on theoretical research using reaction models described by differential equations, this study revealed the existence of conditions where the reaction rate and power generation of the split reaction surpass those of the "complete" reaction. Particularly, in reactions with relatively large standard reaction Gibbs free energy change (D_rGº), it is suggested that the selectivity of microbial oxidation-reduction reactions may not be solely determined by the value of D_rG. ("D" in this abstract should be replaced by Delta.)

The ultraviolet absorption spectrum of the stable isotope carbon monoxide, which is applicable to cosmochemistry and isotope budgets in the Martian atmosphere, was calculated from first-principles calculations and optical absorption cross sections considering the Doppler width.

The Archean era is important for understanding the evolution of our planet and Earth-like exoplanets. Sulfur Mass-Independent Fractionation (S-MIF) has been widely applied as a geochemical tracer that can provide chemical and physical clues for the state of a given atmosphere. To understand thoroughly the enrichment processes of stable sulfur isotopes and the S-MIF photochemical mechanisms in chamber photochemical experiments under reducing conditions, a 1D photochemical model for the S-MIF generation mechanism inside a chamber was developed by using the Krome package[1]. All related chemical reactions to the chamber photochemical experiment of 32S, 33S, 34S, 36S isotope species were added to the model. Three main proposed mechanisms of S-MIF such as the wavelength effect, self-shielding effect, and intersystem crossing effect were also included. Experimental data[2], [3] were used for model validation. Although there are several issues with the Archean S-MIF sources and large differences between the experiment data and the rock record. This model can quantify the contribution of each reaction to the total S-MIF measured during experiments.

While it is often believed that the origins of life required participation of early biomolecules, non-biomolecules could have also played a part. In particular, recent research has highlighted the various ways by which polyesters, could have played a major role during the origins of life. Polyesters could have been synthesized readily on early Earth through simple dehydration reactions at mild temperatures involving abundant non-biological alpha hydroxy acid (AHA) monomers. This dehydration synthesis process results in a polyester gel, which upon further rehydration, can assemble into membraneless droplets proposed to be protocell models. These protocells can provide functions to a primitive chemical system such as analyte segregation, which could have further led to chemical evolution from prebiotic chemistry to nascent biochemistry. Here, we highlight the assembly, structure, and function of membraneless polyester microdroplets as a window to the the first proto(cells) on Earth.

We developed a method to detect trace elements directly from Precambrian fossiliferous organic matter using a high spatial resolution secondary ion mass spectrometer (NanoSIMS). Although the analysis of bio-essential trace elements is considered to be useful for identifying metabolic pathways of microorganisms, it has not been applied to fossiliferous organic matter due to technical limitations. In this study, we improved the conventional acid treatment method for sedimentary rocks and succeeded in separating microfossils from host rock while maintaining the original shape. The low sensitivity and the difficulty of peak separation from interference ions were improved by using an RF source in O- primary ion beam. As a result, we succeeded in detecting trace amounts of phosphorus (P), molybdenum (Mo), potassium (K), iron (Fe), and magnesium (Mg) directly from fossiliferous organic matter. These elements are cations used in various enzymatic reactions and in biological functions. The detected elements may be their residues. This method of in situ trace element analysis at the level of individual microfossils could be a new method that can contribute to constraining metabolic pathways in individual microorganisms at that time.

We investigated variations in the bulk Fe and Mg isotopic ratios on ferruginous sedimentary rocks that were deposited in a shallow ocean in ~3.2 Ga Moodies Group in the Barberton Greenstone Belt, South Africa. The bulk Fe isotope ratios of the samples tend to decrease with decreasing the Fe/Al ratios of the bulk chemical compositions as well as clay/sand ratio of the detrital components, suggesting that they preserve isotope fractionation during primary precipitation of dissolved ferrous iron from seawater. On the other hand, the bulk Mg isotope ratios are explained by the mixing of the two endmembers: carbonate and silicate minerals. The uniform isotope ratio of the endmember carbonate Mg implies that the carbonate minerals were formed during very early diagenesis.

Ribose is a sugar of the essential building blocks of RNA and is an essential molecule for life. It is known that ribose can be formed by the formose reaction, a formaldehyde condensation reaction, but its low stability and selectivity have been considered a problem for ribose accumulation. It was also reported that while borate stabilizes ribose, it may inhibit ribose formation. Therefore, this study investigates the effects of borate on ribose formation by formose-type reactions in order to quantify how these opposing effects affect ribose accumulation in the early earth. Results showed that the maximum concentration of ribose decreased with higher borate concentrations, but the decreasing rate of ribose with borate is lower than that without borate. In addition, borate has the effect of increasing the relative abundance of ribose among the linear aldopentoses. These results suggest that borate is effective in the accumulation of ribose when considering the long geologic time on the early Earth.

We studied boron partitioning and isotopic fractionation between amorphous silica and water to understand a pH proxy in paleo-ocean. The pH of solvents ranged from 8.5 to 9.9, and the boron concentration was adjusted to 5 mg/L. The boron partitioning coefficient showed a bell-shaped pattern having a maximum value at pH 9.3. The isotopic fractionation factor ranged between -37 per mil and -28 per mil, decreasing at pH 9.1. Our result suggests that the precipitation experiment of amorphous silica can reproduce the pH dependent boron isotopic fractionation during the formation of biogenic silica.

During the middle to late Miocene global cooling, diatomaceous sediments were widely deposited in the North Pacific region including the Japan Sea. It is proposed that the organic carbon burial associated with the diatomaceous sediments might have a great influence on the global cooling through the carbon cycle. In this study, we reconstructed the Ge/Si ratios of diatom frustules extracted from the Miocene diatomaceous sediments on Sado Island in Niigata Prefecture and in Suzu City in Ishikawa Prefecture in Japan to obtain information about the silica cycle during the Miocene. The obtained Ge/Si ratios in the Japan Sea during the Miocene show higher values than those in the open ocean, which might result from the depletion of the dissolved silica in the sea surface water or the contribution of the hydrothermal input characterized by the extremely high Ge/Si ratios. Our new data will lead to progress in understanding the mechanism of the formation of the diatomaceous sediments in the Japan Sea during the Miocene.

The review process by the Anthropocene Working Group to select one GSSP site from among nine candidates, including the marine sediments of Beppu Bay, Japan, began around October of last year, and the lake sediment in Crawford Lake, Canada, was finally selected. A Standard Auxiliary Boundary Stratotype site will be announced soon. However, although a boundary age for the onset of the Anthropocene is given by a global marker that can be correlated within a few years, the stratigraphic onset age of the Great Acceleration, which is considered a rationale for the Anthropocene onset, is still unclear. Based on 56 proxy records in marine sediments from Beppu Bay (Kuwae et al., 2023, The Anthropocene Review) and 267 proxy records based solely on globally distributed, varve counting-based age-dated varve sediments, corals, annual rings, and ice cores, this paper will discuss when the precise age of the Great Acceleration is and how the onset of the Anthropocene should be defined stratigraphically.

Ontong Java Plateau is the largest oceanic plateau on the Earth and its association with the mid-Cretaceous Oceanic Anoxic Event (OAE) 1a has been debated so far. Deep Sea Drilling Project (DSDP) Site 167 is an oceanic core that was drilled at the Magellan Rise. The core contains thick volcanic ash intercal which is considered to be derived from the Ontong Java volcanism. In this study, we reconstructed bio-, osmium isotope, and carbon isotope stratigraphy of this core and constrained the sedimentary ages of volcanic ash interval. As a result, we found that the deposition of volcanic ash is almost contemporaneous with the oceanic anoxic event 1a. Our results suggest the causal linkages between these two events.