We have succeeded in developing a new analytical method to estimate the concentration of hydrous chemical species (molecular water; H₂O_m and hydroxyl groups; OH) and total water (H₂O_total) in rhyolitic glass using secondary ion mass spectrometry (SIMS). This method makes it possible to estimate the H₂O_m contents, OH contents, and H₂O_total contents at the micrometer scale (<10 μm) in silicate glasses such as melt inclusions by SIMS. With a ¹⁶O^– primary ion beam, a linear correlation between ¹H⁺/³⁰Si⁺ ratios and H₂O_total contents is observed. On the other hand, there is a linear correlation between ¹H^–/³⁰Si^– ratios and OH contents when using a ¹³³Cs⁺ primary ion beam. These results suggest that the ¹H⁺/³⁰Si⁺ ratios reflect the H₂O_total contents, while the ¹H^–/³⁰Si^– ratios mainly reflect the OH contents. Therefore, the selective estimation of the H₂O_total or OH contents can be achieved through the selection of the primary ion beam (¹⁶O^– and ¹³³Cs⁺). This new method will aid in the estimation of the pressure and temperature of the magma reservoir in the Earth’s interior depending on the solubilities of H₂O_m, OH, and H₂O_total in silicate melts, and in the understanding of water transport in the silicate glasses and melts.

The stable oxygen isotope (δ¹⁸O) values of biogenic calcium carbonates (CaCO₃) present in hard tissues of marine organisms vary with the δ¹⁸O of the surrounding seawater (δ¹⁸O_sw) and water temperature. Consequently, the ambient water temperature when marine organisms existed can be estimated using δ¹⁸O of CaCO₃ with δ¹⁸O_sw. Thus, the aims of this study were to reveal the spatiotemporal variations in δ¹⁸O_sw and their correlations with salinity in the East Asian marginal seas. We collected seawater samples (n = 2222) at 1394 stations around Japan, primarily from the surface layer of the East China Sea (ECS) and Sea of Japan (SOJ), from 2015 to 2021. We analyzed δ¹⁸O_sw and the stable hydrogen isotope of seawater (δD_sw) along with the measured water temperature and salinity. The δ¹⁸O_sw and δD_sw values ranged from –3.48‰ to +0.45‰, and –21.5‰ to +2.3‰, respectively. In our full data, both δ¹⁸O_sw and δD_sw had positive linear relationships with salinity as follows: δ¹⁸O_sw = 0.235 × salinity – 7.94 (r² = 0.85) and δD_sw = 1.56 × salinity – 52.9 (r² = 0.85). Furthermore, the relationship between δ¹⁸O_sw and δD_sw for full data as follows: δD_sw = 6.44 × δ¹⁸O_sw – 0.18 (r² = 0.96). These relationships varied across seasons, areas (the ECS or SOJ), and water depths. In particular, δ¹⁸O_sw and δD_sw of less-saline water were different in the ECS and SOJ. These fine-scale, wide-range, and high-precision δ¹⁸O_sw and δD_sw datasets can contribute to paleoceanography, environmental analysis, oceanography, and fisheries science.

Geochemical data are presented for flood basalts from the Adigrat area in the northwestern Ethiopian Plateau to determine their genesis and mantle source compositions. Stratigraphically, Adigrat flood basalts can be subdivided into upper and lower basalts that are both sub-alkaline in composition. The lower basalts show a wider range of MgO content (6.41–11 wt. %) relative to the upper basalts (4.77–4.9 wt. %). The geochemical variations between the upper and lower basalts cannot be explained by crystal fractionation from a common magma source but might reflect either the involvement of variable mantle sources or different depths and degrees of partial melting. The trace element patterns of the upper basalts resemble those of ocean island basalt (OIB), whereas those of the lower basalts are more akin to enriched asthenospheric mantle (E-MORB). Trace elements and their ratios show the involvement of at least three mantle components (OIB, E-MORB, and N-MORB) in the genesis of the Adigrat flood basalts. We envisage a scenario wherein the Oligocene continental flood basalts of the northwestern Ethiopia plateau were triggered by the arrival of the Afar mantle plume. Low-degree melts of the plume metasomatized the depleted asthenosphere (N-MORB component) and subsequently the thermal effect of the hot mantle plume triggered melting of the metasomatized asthenosphere (E-MORB component) in the garnet-spinel transition zone. The mixing of these E-MORB and N-MORB mantle components generated the lower basalts. decompression melting of the mantle plume generated an OIB component in garnet stability field, which mixed with the E-MORB component to produce the upper basalts.

We present a detailed study of hyperalkaline springs (pH > 10) sampled during fieldworks in 2022 and 2023 within the ultramafic Mt. Soldatskaya massif on the Kamchatsky Mys Peninsula in Kamchatka. The chemical composition of the springs and the dependence of the concentrations of some components on pH are consistent with the formation of these waters due to the present-day serpentinization of ultrabasic rocks. In the most alkaline springs (pH 12.59), dissolved hydrogen was detected at a concentration of about 0.8 mmol/L. Furthermore, the springs with high pH have a sodium chloride composition, with a maximal chloride content up to 300 mg/L in the springs with the highest pH. The isotopic composition of carbonate travertines deposited from these springs (δ¹³C and δ¹⁸O) demonstrates a trend that differs from the known trend for ‘meteogenic’ travertines, likely due to the extremely low temperatures of the springs (2–7°C). The age of the travertines, determined by the radiocarbon method, varies from modern in springs with the highest pH to approximately 6300 years for a fragment of travertine found in alluvial deposits. The Sr isotope ratio for travertines (0.7051 to 0.7070) indicates a mixed source of Sr, between magmatic rocks and marine sediments. An attempt to use data on the age and isotopic composition of travertines for paleoclimatic purposes failed: travertine aged 6300 years showed a much colder climate than the reconstruction of palobotanical data.