Studies of the mineralogy and sulfur isotope composition of sediment-hosted hydrothermal sulfide minerals in cores are important for understanding the seafloor mineralization environment and material source and reconstructing the hydrothermal history. However, the source of ore-forming materials and the history of hydrothermal activity in the southern Okinawa Trough (SOT) remain unclear. Here, the mineralogy and sulfur isotope characteristics of sulfides from gravity core HOBAB4-S2, collected between the Yonaguni Knoll IV hydrothermal field (HF) and the Tangyin HF, was investigated. Enrichments in Zn (up to 321×10⁻⁶), Cu (up to 73.7×10⁻⁶), and Pb (up to 160×10⁻⁶) and the presence of pyrite, galena, pyrrhotite and minor sphalerite and chalcopyrite provide evidence for the input of hydrothermal materials into the sediments. The pyrite morphologies include disseminated cubic, pentagonal dodecahedron, and framboidal forms. Except for minor framboidal pyrite, euhedral pyrite from core HOBAB4-S2 is mainly of hydrothermal origin with Co/Ni ratios >1 and S/Fe atomic ratios <2 in the Cu-Zn-Pb-rich layers. The occurrences of hexagonal pyrrhotite, high-Co (up to 0.17%) pyrite and high-Fe sphalerite indicate that the hydrothermal precipitates formed at medium-high temperatures and low-sulfur fugacity (fS₂) environments. The δ³⁴S values of sulfides (0.21‰–3.45‰) with low- fS₂ mineral assemblages (e.g., pyrrhotite ± high-Fe sphalerite) in the core are significantly lower than those of magmatic rocks and seawater, indicating possible incorporation of previously formed biogenic sulfur in the sediment. Combined with the age model of the core, it is suggested that hydrothermal activity likely began in the Tangyin HF before AD 1445–1483 and that at least three active episodes may have occurred since then.

The grain size distribution of bulk sediment samples was decomposed in a core to reconstruct paleoceanographic evolution over the past 60 ka in the northern Norwegian Sea. The results show that sediments consisted of 3–4 grain populations derived from the North Atlantic Current (NAC) and Barents Ice Sheet (BIS). The grain size data suggest three palaeoceanographic evolution stages: (1) an environment affected by BIS and NAC and changed with the interstadial/stadial transition in phase with the Greenland ice-core record at 60–31 ka BP, during which discharge of icebergs and the content of the coarsest population containing ice-rafted debris (IRD) in the sediments increased significantly during stadial, while the fine silt population containing volcanic glasses increased with the enhancement of NAC during the interstadial; (2) an extreme environment controlled by BIS at 31–13 ka BP. BIS reached to its maximum at about 31 ka BP and the turbid plumes that formed at the leading edge of BIS contributed to a significant increase in the clayey population in sediments. Icebergs drained into the northern Norwegian Sea with periodical calving of the BIS at 31–19 ka BP. Subsequently, the ablation of the BIS discharged massive floods with clayey sediments and icebergs into the Norwegian Sea at 19–13 ka BP, resulting in a constant increase in clay and IRD in sediments; and (3) a marine environment similar to the present one under the strong influence of NAC following the complete melting of the BIS after 13 ka BP, NAC is the dominant transport agent and no IRD occurred in sediments. The fine silt populations containing volcanic glasses transported by NAC significantly increased.

Natural and human-induced changes may exert considerable impacts on the seasonal and nodal dynamics of M₂ and K₁ tidal constituents. Therefore, quantifying the influences of these factors on tidal regime changes is essential for sustainable water resources management in coastal environments. In this study, the enhanced harmonic analysis was applied to extract the seasonal variability of the M₂ and K₁ tidal amplitudes and phases at three gauging stations along Lingdingyang Bay of the Zhujiang River Delta. The seasonal dynamics in terms of tidal wave celerity and amplification/damping rate were used to quantify the impacts of human-induced estuarine morphological alterations on M₂ and K₁ tidal hydrodynamics in inner and outer Lingdingyang Bay. The results show that both tidal amplification/damping rate and wave celerity were considerably increased from the pre-anthropogenic activity period (Pre-AAP) to the post-anthropogenic activity period (Post-AAP) excepting the tidal amplification/damping rate in outer Lingdingyang Bay, and the variations in outer Lingdingyang Bay was larger than those in inner Lingdingyang Bay. The alterations in these two parameters were more significant in flood season than in dry season in both inner and outer Lingdingyang Bay. The seasonal variability of M₂ and K₁ tidal amplitudes were further quantified using a regression model accounting for the 18.61-year lunar nodal modulation, where this study observes a considerable alteration in M₂ constituent owing to human interventions. During the Post-AAP, the M₂ amplitudes at the downstream station were larger than those that would have occurred in the absence of strong human interventions, whereas the opposite was true for the upstream station, leading to a substantial decrease in tidal amplification in outer Lingdingyang Bay. However, it is opposite in inner Lingdingyang Bay. The underlying mechanism can be primarily attributed to channel deepening and narrowing caused by human interventions, that resulted in substantial enlargement of the bay volume and reduced the effective bottom friction, leading to faster wave celerity and stronger amplified waves.

Gas-bearing sediments are widely distributed in five continents all over the world. Most of the gases exist in the soil skeleton in the form of discrete large bubbles. The existence of gas-phase may increase or decrease the strength of the soil skeleton. So far, bubbles’ structural morphology and evolution characteristics in soil skeleton lack research, and the influence of different gas reservoir pressures on bubbles are still unclear. The micro characteristics of bubbles in the same sediment sample were studied using an industrial CT scanning test system to solve these problems. Using the image processing software, the micro variation characteristics of gas-bearing sediments in gas reservoir pressure change are obtained. The results show that the number and volume of bubbles in different equivalent radius ranges will change regularly under different gas reservoir pressure. With the increase of gas reservoir pressure, the number and volume of tiny bubbles decrease. In contrast, the number and volume of large bubbles increase, and the gas content in different positions increases and occupies a dominant position, driving the reduction of pore water and soil skeleton movement.

In consideration of the rapid degradation of coral reef ecosystems, the establishment of models is helpful to comprehend the degradation mechanism of coral reef ecosystems and predict the development process of coral reef communities. According to the characteristics of complex ecosystem of tropical coral reefs in China, the coral reef functional group is the core level variable; combined with the multiple feedback effects of coral reef functional groups and environmental changes, the study presents a coral reef ecosystem dynamics model with hermatypic corals as the core. Based on the simulation of the assumed initial value and the internal feedback of the system, the results show that in the basic simulation (relative health conditions), the coverage area of live corals and coral reefs generally decreased first and then increased, and increased by 4.67% and 6.38% between 2010 and 2050, respectively. Based on the calibration model and the current situation of the studied area, the multi-factor disturbance effects of coral reef communities were simulated and explored by setting up three scenarios involving fishing policy, terrestrial deposition, and inorganic nitrogen emissions. Among them, in the single factor disturbance, the fishing policy exerts the most direct impact on the community decline; and the succession phenomenon is obvious; the terrestrial sedimentation has a faster and more integrated effect on the community decline; the effect of inorganic nitrogen emission on the community decline is relatively slow. In the double/multi-factor disturbance, the superimposed disturbance will aggravate the multi-source feedback effect of the coral reef communities development, accelerate the community decay rate, and make its development trajectory more complicated and diverse. This method provides a scientific and feasible method for simulating the damage of long-term coral reef community and exploring the development law and adaptive management of coral reef ecosystems. In the future, it can be further studied in the ecological restoration process and decision-making direction of coral reefs.

Ferromanganese (Fe-Mn) crusts are potential archives of the Cu and Zn isotope compositions of seawater through time. In this study, the Cu and Zn isotopes of the top surface of 28 Fe-Mn crusts and 2 Fe-Mn nodules were analysed by MC-ICP-MS using combined sample-standard bracketing for mass bias correction. The Zn isotope compositions of the top surface of Fe-Mn crusts are in the range of 0.71‰ to 1.08‰, with a mean δ⁶⁶Zn value of 0.94‰±0.21‰ (2SD, n=28). The δ⁶⁵Cu values of the top surface of Fe-Mn crusts range from 0.33‰ to 0.73‰, with a mean value of 0.58‰±0.20‰ (2SD, n=28). The Cu isotope compositions of Fe-Mn crusts are isotopically lighter than that of dissolved Cu in deep seawater (0.58‰ vs. 0.9‰). In contrast, the δ⁶⁶Zn values of Fe-Mn crusts appear to be isotopically heavy compared to deep seawater (0.94‰±0.21‰ vs. 0.51‰±0.14‰). The isotope fractionation between Fe-Mn crusts and seawater is attributed to equilibrium partitioning between the sorption to crusts and the organic-ligand-bound Cu and Zn in seawater. The Cu and Zn isotopes in the top surface of Fe-Mn crusts are not a direct reflection of the Cu and Zn isotopes, but a function of Cu and Zn isotopes in modern seawater. This study proposes that Fe-Mn crusts have the potential to be archives for paleoceanography through Cu and Zn isotope analysis.

In certain regions, submarine groundwater discharge (SGD) into the ocean plays a significant role in coastal material fluxes and their biogeochemical cycle; therefore, the impact of SGD on the ecosystem cannot be ignored. In this study, SGD was estimated using naturally occurring radium isotopes (²²³Ra and ²²⁴Ra) in a subtropical estuary along the Beibu Gulf, China. The results showed that the Ra activities of submarine groundwater were approximately 10 times higher than those of surface water. By assuming a steady state and using an Ra mass balance model, the SGD flux in May 2018 was estimated to be 5.98×10⁶ m³/d and 3.60×10⁶ m³/d based on ²²⁴Ra and ²²³Ra, respectively. At the same time, the activities of Ra isotopes fluctuated within a tidal cycle; that is, a lower activity was observed at high tide and a higher activity was seen at low tide. Based on these variations, the average tidal pumping fluxes of SGD were 1.15×10⁶ m³/d and 2.44×10⁶ m³/d with ²²⁴Ra and ²²³Ra, respectively. Tidal-driven SGD accounts for 24%–51% of the total SGD. Therefore, tidal pumping is an important driving force of the SGD in the Dafengjiang River (DFJR) Estuary. Furthermore, the SGD of the DFJR Estuary in the coastal zone contributes significantly to the seawater composition of the Beibu Gulf and the material exchange between land and sea.

Permeable coastal sediments act as a reactive node in the littoral zone, transforming nutrients via a wide range of biogeochemical reactions. Reaction rates are controlled by abiotic factors, e.g., salinity, temperature or solute concentration. Here, a series of incubation experiments, using flow-through reactors, were conducted to simulate the biogeochemical cycling of nitrate (${\rm {NO}}_3^- $) and phosphorus (P) in permeable sediments under different ${\rm {NO}}_3^- $ availability conditions (factor I) along a salinity gradient (admixture of river and seawater, factor II). In an oligotrophic scenario, i.e., unamended ${\rm {NO}}_3^- $ concentrations in both river and seawater, sediments acted as a permanent net source of ${\rm {NO}}_3^- $ to the water column. The peak production rate occurred at an intermediate salinity (20). Increasing ${\rm {NO}}_3^- $ availability in river water significantly enhanced net ${\rm {NO}}_3^- $ removal rates within the salinity range of 0 to 30, likely via the denitrification pathway based on the sediment microbiota composition. In this scenario, the most active removal was obtained at salinity of 10. When both river and seawater were spiked with ${\rm {NO}}_3^- $, the highest removal rate switched to the highest salinity (36). It suggests the salinity preference of the ${\rm {NO}}_3^- $ removal pathway by local denitrifiers (e.g., Bacillus and Paracoccus) and that ${\rm {NO}}_3^- $ removal in coastal sediments can be significantly constrained by the dilution related $ {\rm {NO}}_3^-$ availability. Compared with the obtained variation for ${\rm {NO}}_3^- $ reactions, permeable sediments acted as a sink of soluble reactive P in all treatments, regardless of salinity and ${\rm {NO}}_3^- $ input concentrations, indicating a possibility of P-deficiency for coastal water from the intensive cycling in permeable sediments. Furthermore, the net production of dissolved organic carbon (DOC) in all treatments was positively correlated with the measured ${\rm {NO}}_3^- $ reaction rates, indicating that the DOC supply may not be the key factor for ${\rm {NO}}_3^- $ removal rates due to the consumption by intensive aerobic respiration. Considering the intensive production of recalcitrant carbon solutes, the active denitrification was assumed to be supported by sedimentary organic matter.

Two species of Nassarius Duméril, 1805 from the South China Sea are described and illustrated. The specimens are in the Nassariidae collection of the Marine Biological Museum of Chinese Academy of Sciences, Qingdao. Nassarius concavus sp. nov., from the sandy bottom at a depth of 180 m, resembles Nassarius glabrus Zhang and Zhang, 2014 in general shell morphology, but differs from the latter in having a smaller, more slender adult shell without axial ribs on the upper teleoconch whorls. Nassarius nanshaensis sp. nov., from the Nansha Islands at a depth of 56–147 m, is similar to Nassarius maxiutongi Zhang, Zhang and Li, 2019 in the shell sculpture, but differs in having a more slender shell with a higher spire, and fewer cusps on the rachidian tooth (9–11 vs. 13–17).

Identifying distinct tectonic units is key to understanding the geotectonic framework and distribution law of oil and gas resources. The South China Sea and its adjacent areas have undergone complex tectonic evolution processes, and the division of tectonic units is controversial. Guided by block tectonics theory, this study divide the South China Sea and its adjacent areas into several distinguished tectonic units relying on known boundary markers such as sutures (ophiolite belts), subduction-collision zones, orogenic belts, and deep faults. This work suggests that the study area is occupied by nine stable blocks (West Burma Block, Sibumasu Block, Lanping-Simao Block, Indochina Block, Yangtze Block, Cathaysian Block, Qiongnan Block, Nansha Block, and Northwest Sulu Block), two suture zones (Majiang suture zone and Southeast Yangtze suture zone), two accretionary zones (Sarawak-Sulu accretionary zone and East Sulawesi accretionary zone), one subduction-collision zone (Rakhine-Java-Timor subduction-collision zone), one ramp zone (Philippine islands ramp zone), and six small oceanic marginal sea basins (South China Sea Basin, Sulu Sea Basin, Sulawesi Sea Basin, Banda Sea Basin, Makassar Basin, and Andaman Sea Basin). This division reflects the tectonic activities, crustal structural properties, and evolutionary records of each evaluated tectonic unit. It is of great theoretical and practical importance to understand the tectonic framework to support the exploration of oil and gas resources in the South China Sea and its adjacent areas.