Detrital apatite is a promising accessory mineral for reliable fingerprinting of the protolith composition of detrital sediment. Here, we present the geochemical compositions of detrital apatites from four sections of a high-resolution (~140 cm/kyr) sedimentary archive from the southern Okinawa Trough (SOT) for constraining sediment source rock types and establishing changes in provenance. A series of diagrams based on the geochemical data show that apatites in Section 1 derived mainly from mafic/intermediate rocks, while apatites in the three younger sections largely originated from mafic/intermediate rocks and acid rocks. Further, the four sections included a few contributions of apatites from alkaline rocks and metamorphic rocks. Through a comprehensive analysis of controlling factors and regional stratigraphy in the study area, we concluded that sediments in the SOT are the weathering/erosion products of sedimentary and meta-sedimentary rocks in the western and northeastern Taiwan Island, with ultimate sources containing a wide variety of rock types. The sediment from rivers in eastern Taiwan did not significantly contribute to deposition in the SOT. Apatites in Sections 2–4 showed strong geochemical similarity but differed from those in Section 1, indicating that the types of weathered/eroded sedimentary rocks in the weathering profile of river drainage basins of Taiwan Island changed in Section 2 (2010–1940 cal. yr BP) and have remained stable since then.

Determination of high sulfur content in sulfide minerals is crucial for various applications, including geochemistry, mining, and environmental monitoring. While inductively coupled plasma optical emission spectrometry (ICP-OES) is the preferred method for sulfur analysis, conventional sample preparation techniques often fall short when dealing with high sulfur concentrations. This study investigated optimized digestion conditions for accurate sulfur determination in sulfide minerals using ICP-OES. We employed anti-corrosion acid digestion bombs, an aqua regia–hydrofluoric acid system, and a digestion temperature of 180 °C, achieving exceptional results. Certified reference material recoveries ranged from 99.9 to 100.5%, with relative standard deviations between 0.42 and 0.84%. These results demonstrate the high accuracy and precision of the method. The optimized digestion protocol presented in this study provides a robust and reliable approach for accurate sulfur analysis in sulfide minerals, particularly for high concentrations.

Strontium (Sr), hydrogen (H) and oxygen (O) in vent fluids are important for understanding the water–rock interaction and hydrothermal flux in hydrothermal systems. We have analyzed the Sr, H and O isotopic compositions of seawater, vent fluid and hydrothermal plume samples in the Kueishantao hydrothermal field, as well as their calcium (Ca), total sulfur (S), Sr, arsenic (As), stibium (Sb), chlorine (Cl) and manganese (Mn) concentrations for understanding the origin and processes of fluids. The results suggest that most As, Sb and Mn are leached from andesitic rocks into the fluids, and most Ca and Cl remained in the deep reaction zone during the fluid–andesitic rock interaction. The ranges of ⁸⁷Sr/⁸⁶Sr, δD_V-SMOW and δ¹⁸O_V-SMOW values in the yellow spring, white spring and plumes are small. The ⁸⁷Sr/⁸⁶Sr, δD_V-SMOW and δ¹⁸O_V-SMOW values of fluids and plumes are like those of ambient seawater, indicating that the Sr, H and O of vent fluids and hydrothermal plumes are derived primarily from seawater. This suggests that the interaction of andesite and subseafloor fluid is of short duration and results in the majority of As, Sb and Mn being released into fluids, while most Ca and Cl remained in the deep reaction zone. In addition, there was no significant variation of Sr, H and O isotopic compositions in the upwelling fluid, keeping the similar isotopic compositions of seawater. There are obvious correlations among the pH values, As and Sb concentrations, and H isotopic compositions of the vent fluids and hydrothermal plumes, implying that the As and Sb concentrations and H isotopic compositions can trace the dispersion of plumes in the ambient seawater. According to the Sr concentrations and ⁸⁷Sr/⁸⁶Sr values, the water/rock ratios are 3076~8124, which is consistent with the idea that the interaction between fluid and andesite at the subseafloor is of short duration. The hydrothermal flux of Sr discharged from the yellow spring into the seawater is between 2.06 × 10⁴ and 2.26 × 10⁴ mol/yr, and the white spring discharges 1.18 × 10⁴~1.26 × 10⁴ mol/yr Sr if just andesites appear in the reaction zone.

In deep underground environments, temperature is one of the key factors affecting the geochemistry behaviors of rare earth elements (REE) in organic-rich fluid. However, the influence of temperature on the interaction between humic acids (HA) and REE is not well known. In the present study, the influence of temperature on the HA–REE-binding behavior was evaluated based on heating experiments of REE-doped HA solution. Lignite-extracted HA and REE-binding experiments were conducted over a temperature range of 20 to 200 °C to quantify HA–REE complexation and the influence of temperature on HA binding sites. Results showed that increasing temperature and decreasing [REE]/[HA] ratio cause an increase of K_d value (the partition coefficient of REE between HA and aqueous solution). During heating $K_{\mathrm{d}}^{\mathrm{REE}}$ $K_{\mathrm{d}}^{\mathrm{REE}}$ patterns gradually change from middle REE-enriched-type (M-type) at 20 °C to light and middle REE-enriched-type (L-M-type) at 50 and 100 °C, and to light REE-enriched-type (L-type) at 150 °C and 200 °C. The increase of REE bonded with HA and modifications of $K_{\mathrm{d}}^{\mathrm{REE}}$ patterns during the thermal treatment may be attributed to the increase of REE-binding sites, especially carboxylic sites, as a consequent of HA decomposition. This study provides a glimpse into the HA–REE-binding behaviors in the deep underground environment, which may shed light on the geochemical characteristics of REE in some organic-bearing rocks, and their changes during the coalification process.

Based on the analysis of geochemical and mineralogical compositions, deep sea clay sediment characteristics and their material sources were examined in the eastern flank of the Gagua Ridge. The mineralogy mainly consists of detrital clay minerals, quartz, and authigenic phillipsite. There is scarce biogenic debris (siliceous or calcareous). The consolidated sediments are more enriched in Si, Al, K, Na, Li, Sc, Cr, Rb, and Cs than the associated crusts and nodules. The unmixed sediment samples were mainlycontributed by Asian eolian dust. The onset of the outer Fe-Mn crust growth nearly coincides with the Central Asia aridification event at ~3.5 Ma, which resulted in an abrupt increase in eolian flux of Asian dust. Intensified surface primary productivity is assumed to bring more metals to deep waters, and eventually facilitate the outer Fe-Mn crust formation. Authigenic phillipsite may come from the alteration of local basic volcanic glasses and cause excess Al, high Al/Ti, and low Si/Al ratios. However, phillipsites hardly affect the abundance of rare earth elements (REEs) and their patterns. In addition, the investigation of two kinds of burrows inside the consolidated sediments reveals that the inner nodules of the amalgamated crusts may remain on the oxic sediment surface, due to frequent benthic activities.

Utilizing seawater samples collected during the summer of 2025 in the Dingzi Bay region, South Yellow Sea, this study conducted a comprehensive analysis of the contents and concentrations of dissolved gases (N₂, O₂, Ar, CO₂), hydrocarbon gases (such as methane, ethane, and propane), and noble gases (including helium, neon, krypton, and xenon). The findings reveal that the dissolved gases in the study area are predominantly composed of N₂ and O₂, with average proportions of 77.8% and 21.6%, respectively. Notably, significant CO₂ anomalies were detected at certain stations, with concentrations reaching as high as 58.46%, which may indicate intense organic matter degradation or the introduction of external fluids. Furthermore, hydrocarbon gases, including methane and propane, were identified in several samples, with methane concentrations peaking at 37.9 mg/L, suggesting potential submarine oil and gas seepage or microbial activity. Spatial analysis revealed that anomalous points were primarily concentrated at stations CJ01, CJ08, CJ10, and CQ01, with no significant correlation to water depth, suggesting that their distribution may be influenced by local geological structures or bottom currents. This study elucidates the complexity and heterogeneity of dissolved gas composition in the waters of Dingzi Bay, thereby providing a novel scientific foundation for regional carbon cycle research, seabed resource exploration, and marine environmental monitoring.