In a pioneering effort, China’s self-developed reanalysis product, CORA v2.0, has incorporated tidal forces, marking a significant advancement in marine environmental data and substantially enhancing research on internal tides (ITs). This study reveals the spatiotemporal characteristics of ITs in the northern South China Sea (SCS) using the CORA v2.0 dataset and compares them with previous studies. At the temporal scale, spectral analysis was employed to extract internal tidal signals from the CORA v2.0 dataset, revealing that the accuracy and strength of these signals closely align with those observed in mooring data. Regarding seasonal characteristics, which are primarily modulated by stratification, ITs in the northern SCS exhibit maximum intensity during summer and autumn, while those in the central and southern SCS peak in autumn and winter. Furthermore, an analysis of internal tide energy flux elucidates the spatial propagation patterns: diurnal internal tides (DITs) propagate predominantly southwestward, whereas semidiurnal internal tides (SITs) bifurcate into two branches propagating northwestward and southwestward, respectively. Along their propagation paths, DITs dissipate more gradually, while SITs attenuate more rapidly. Finally, detailed investigations of the vertical structure were conducted using modal decomposition and tidal ellipse methods. Overall, the findings derived from the CORA v2.0 dataset demonstrate strong consistency with previous research. The CORA v2.0 dataset demonstrates superior performance in simulating DITs compared to SITs. As one of the first reanalysis datasets to incorporate explicit tidal forcing, CORA v2.0 demonstrates a sound overall capacity for representing ITs in the SCS. This study aims to enhance the utility of the CORA v2.0 dataset and maximize its value for future research.
The cycling of rare earth elements (REEs) in the East China Sea is a hot topic due to its potential impact on the global climate and the carbon cycle. However, the cycling and vertical geochemical processes of dissolved REEs across the shelf break of the East China Sea have not yet been fully elucidated. Here we present high-resolution REE profiles of water masses in two transects of the East China Sea, a key region of the global circulation and primary production. The typical increase in REE concentrations with water depth shows similar nutrient profiles, suggesting the biogeochemical behavior of surface scavenging and bottom release. The “mirror-like” shapes of the REE profiles reveal a strong remineralization signal with the REEs removed in surface waters and released in deep waters. The “hook” features with low dissolved heavy rare earth elements (HREEs) at the sediment-water interface, known as boundary scavenging, may be related to the removal of inorganic scavenging. Two distinct types of North Pacific Deep Water (NPDW)-normalized REE patterns in the surface water suggest the limited horizontal advection across the shelf break of the East China Sea. The Kuroshio frontal eddies may induce sinking and intrusion of REEs into subsurface water. Moreover, upwelling and turbulence lead to the homogeneous mixing of REEs in intermediate water. The latitudinal variability in Gd anomalies reflects the impacts of the Kuroshio Current, invasion of the mixed shelf water, and anthropogenic Gd input. This study offers new insights into the geochemical processes of dissolved REEs and highlights their utility as tracers for water mass exchange and terrestrial inputs across the shelf break of the East China Sea.
Under the background of highly variable geothermal gradients in the Baiyun Sag of the Zhujiang (Pearl) River Mouth Basin, the genetic research on the sandstones of the Zhuhai Formation is relatively weak, which has seriously hindered the further exploration and evaluation of the deep reservoirs in this area. By using techniques such as thin section identification, scanning electron microscope observation, physical property testing, diagenetic process reconstruction, and physical property restoration, a systematic study was conducted on the differential diagenetic evolution of the sandstone reservoirs of the Zhuhai Formation in this area, and the differential reservoir pore evolution processes in different zones were discussed quantitatively. The results show that: the reservoirs of the Zhuhai Formation are generally in the middle diagenetic stage B, and have generally experienced strong compaction, three-stage carbonate cementation, feldspar dissolution, and siliceous cementation; the reservoir spaces are mainly composed of various dissolution pores and residual primary pores. Compaction is the main factor leading to the reduction of reservoir porosity; three-stage siliceous cementation and carbonate cementation further reduce reservoir porosity and increase reservoir heterogeneity, while various dissolution processes improve reservoir physical properties. However, there are significant differences in reservoir diagenesis and pore evolution among different zones. With the increase of geothermal gradient, diagenetic evolution accelerates gradually, diagenetic intensity increases continuously, and the pore-reducing effect of thermal compaction is obvious. This leads to a high pore-reduction rate in the high-temperature zone, a significant shallowing of the depth at which clay mineral transformation and iron-bearing carbonate mineral development occur, and the local development of late-stage high-temperature hydrothermal dissolution. The differential burial processes and the highly variable geothermal gradients among different zones lead to differences in compaction rate, dissolution scale, the existence time and duration of open-closed systems, as well as differential cementation. These factors jointly drive the significant differential evolution of reservoir physical properties across the three zones under the control of highly variable geothermal gradients. This study provides a theoretical basis and practical reference for the prediction and evaluation of deep effective reservoirs in the Baiyun Sag and other similar abnormally hot basins.
Tropical cyclones (TCs) in the western North Pacific (WNP) are not merely destructive weather events confined to their immediate pathways; emerging evidences regard them as an important factor in modulating the most powerful interannual climate phenomena on Earth: the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Active WNP TCs contribute to the evolution of an extreme El Niño through a two-season interaction: spring TCs facilitate the warming in the tropical eastern Pacific via westerly wind bursts and downwelling Kelvin waves, while the developing El Niño in turn enhances summer TCs, creating a positive feedback loop that promotes an extreme event. In addition, the unusually active summer TCs also have the ability to contribute to the evolution of a positive IOD (pIOD). The lower-level wind fields associated with TCs can induce an anomalous southwesterly wind from the maritime continent (MC) to the WNP, which, while transporting moisture from the MC to the WNP, can also cause anomalous downwelling over the MC. The suppression of convection over the MC can trigger anomalous lower-level easterly winds on its western side (tropical eastern Indian Ocean), which provides favorable conditions for the occurrence and development of pIOD. The contribution of TCs to pIOD also modulates the correlation of ENSO and IOD to some extent, and even promote some pIODs to occur with La Niña.
Previous studies have indicated that coral reef ecosystems along the eastern coast of Hainan Island function as a net CO2 source. However, the relative contributions of natural biogeochemical processes and anthropogenic activities, including marine aquaculture and coastal environmental management practices, to the dynamics of partial pressure of CO2 (pCO2) remain poorly understood. In this study, we report consistent CO2 outgassing ranging from 0.50 mmol/(m2·d) to 1.28 mmol/(m2·d) in these coral reef ecosystems during a summer cruise in 2025. Specifically, water samples collected from Wenchang and Sanya were classified into three distinct groups: Group I comprises estuarine reef ecosystems in both locations; Group II-Wenchang is dominated by intensive marine aquaculture; and Group II-Sanya represents a coastal ecosystem that has benefited from effective environmental protection measures. In all groups, the calculated pCO2 values based on conservative mixing of three end-members ranged from 467 μatm to 507 μatm, exceeding the atmospheric pCO2 of 415 μatm, indicating that these sub-regions were initially in a state of CO2 outgassing. For samples in Group II-Wenchang, the effects of processes occurring both outside and within the coral reef ecosystems are minor; thus, the high-pCO2 characteristics of the source water, i.e., the mixing of the three endmembers, dominate the observed CO2 outgassing in this region. In contrast, for samples in Group II-Sanya, although organic and inorganic carbon metabolism within the coral reef ecosystems tends to increase seawater pCO2, strong net Dissolved Inorganic Carbon consumption occurring outside the reef systems predominates, resulting in a drawdown of surface seawater pCO2 and shifting the system from a strong CO2 source toward equilibrium with atmospheric CO2 levels. For samples in Group I, the pCO2 increases driven by biological respiration outside the coral reefs and by CaCO3 precipitation within the reefs are comparable in magnitude to the pCO2 drawdown caused by biological production within the reefs. Consequently, the elevated pCO2 signature inherited from the source water remains the dominant factor controlling CO2 outgassing in this case. More importantly, we observed that intensive nearshore aquaculture operations and inadequate municipal wastewater treatment elevate surface seawater pCO2 by 40 μatm in Wenchang. In contrast, comprehensive environmental protection measures reduce pCO2 by 90 μatm. These findings yield a markedly different outcome depending on whether environmental protection measures are implemented, underscoring the critical importance of effective coastal management for coral reef conservation.
