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Basement buried hill reservoirs represent significant emerging prospects among the newly discovered growth poles in the deepwater areas of the northern South China Sea. Addressing the unclear key factors contributing to their formation, this study dissects successful global exploration cases of basement buried hill reservoirs and analyzes the common characteristics of basement reservoir accumulation under different basin types, structural backgrounds, basement lithologies, and oil and gas geological conditions. A three-element coupling relationship, termed "sourcereservoir- cap", is proposed as the dominant mechanism controlling basement buried hill reservoir formation. The genesis of these reservoirs requires adequate oil and gas supply, appropriately sized accumulation bodies, and effective sealing layers. The optimal configuration of the "source-reservoir-cap" relationship directly influences the efficient charging and preservation of oil and gas within basement buried hill reservoirs. Four configurations are identified, including circumstances such as the source-underlying low-positioned basement buried hill with a "sourcereservoir cover docking migration type", the source-border middle-positioned basement buried hill with a "source-reservoir lateral window docking migration type", and the source-outside high-positioned basement buried hill with both "source-reservoir short-distance transport and migration type" and "source-reservoir long-distance transport and migration type". The first to three models present favorable accumulation conditions. Based on the "source-reservoir-cap" three-element coupled model, this study identifies the Yunkai basement buried hill in the Pearl River Mouth Basin, the central depression in the Qiongdongnan Basin, and the northern and southern basement buried hills belts as crucial exploration targets in the deepwater areas of the northern South China Sea. [ABSTRACT FROM AUTHOR]

To facilitate the recovery of natural gas hydrate (NGH) deposits in the South China Sea, we have designed and developed the world's largest publicly reported experimental simulator for NGH recovery. This system can also be used to perform CO2 capture and sequestration experiments and to simulate NGH recovery using CH4/CO2 replacement. This system was used to prepare a shallow gas and hydrate reservoir, to simulate NGH recovery via depressurization with a horizontal well. A set of experimental procedures and data analysis methods were prepared for this system. By analyzing the measurements taken by each probe, we determined the temperature, pressure, and acoustic parameter trends that accompany NGH recovery. The results demonstrate that the temperature fields, pressure fields, acoustic characteristics, and electrical impedances of an NGH recovery experiment can be precisely monitored in real time using the aforementioned experimental system. Furthermore, fluid production rates can be calculated at a high level of precision. It was concluded that (1) the optimal production pressure differential ranges from 0.8 to 1.0 MPa, and the wellbore will clog if the pressure differential reaches 1.2 MPa; and (2) during NGH decomposition, strong heterogeneities will arise in the surrounding temperature and pressure fields, which will affect the shallow gas stratum. [ABSTRACT FROM AUTHOR]

This article analyses the demands and interests of the Natuna Regency of Indonesia and interprets the disputes in the South China Sea from the perspective of local factors. Based on an analysis of numerous documents and reports, as well as field research trips to Natuna and online interviews with local government leaders, members of nongovernmental organisations and businesspeople, the study concludes that the securitisation of Natuna Regency, with its rich resources and special strategic position, has attracted great attention. The local government has no authority over the waters around Natuna, and while it can share a small portion of the profits made from local resources, it cannot promote local economic development or protect the rights of fisheries. The local government can only promote the policies of the central government in economic development and cooperate with the military to ensure the safety of the surrounding waters and local fishing vessels. The local government continues to actively petition the central government to designate Natuna-Anambas a special province to gain more management rights. The development demands of resource-rich areas drive local leaders to seek cooperation with the military and the international community, increasing the uncertainty of the situation in the South China Sea. [ABSTRACT FROM AUTHOR]

Gas hydrates have been found in the western continental margin of South China Sea, which are revealed by widespread bottom simulating reflectors (BSRs) imaged from a three-dimensional (3D) seismic volume near the Guangle carbonate platform in the western South China Sea. Fluid-escape structures (faults and gas chimneys) are originated below BSR were distinguished. A comprehensive model in three-level structure was proposed to depict the gas hydrate accumulation in the study area. In Level 1, regional major faults and gas chimneys provide the first pathways of upward migration of gas near basement. In Level 2, pervasive polygonal faults in carbonate layer promote the migration of gas. In Level 3, gases sourced from near-basement accumulate within shallow sediment layers and form gas hydrate above the unit with faults once appropriate temperature and pressure occur. The gas hydrates in the study area are mainly in microbial origin, and their accumulation occurs only when fluid-escape structures align in all the three levels. The proposed model of the gas hydrate accumulation in western SCS margin provides new insights for further studies in this poorly studied area. [ABSTRACT FROM AUTHOR]

Sea surface salinity (SSS) is an essential variable of ocean dynamics and climate research. The Soil Moisture and Ocean Salinity (SMOS), Aquarius, and Soil Moisture Active Passive (SMAP) satellite missions all provide SSS measurements. The European Space Agency (ESA) Climate Change Initiative Sea Surface Salinity (CCI-SSS) project merged these three satellite SSS data to produce CCI L4 SSS products. We validated the accuracy of the four satellite products (CCI, SMOS, Aquarius, and SMAP) using in-situ gridded data and Argo floats in the South China Sea (SCS). Compared with in-situ gridded data, it shows that the CCI achieved the best performance (RMSD: 0.365) on monthly time scales. The RMSD of SMOS, Aquarius, and SMAP (SMOS: 0.389; Aquarius: 0.409; SMAP: 0.391) are close, and the SMOS takes a slight advantage in contrast with Aquarius and SMAP. Large discrepancies can be found near the coastline and in the shelf seas. Meanwhile, CCI with lower RMSD (0.295) perform better than single satellite data (SMOS: 0.517; SMAP: 0.297) on weekly time scales compared with Argo floats. Overall, the merged CCI have the smallest RMSD among the four satellite products in the SCS on both weekly time scales and monthly time scales, which illustrates the improved accuracy of merged CCI compared with the individual satellite data. [ABSTRACT FROM AUTHOR]

Bivalve shell fossils, cemented by authigenic carbonates, are widely spread in the Haima cold seep, Qiongdongnan Basin of the South China Sea (SCS). In this study, we examined an element profile of Gigantidas platifrons in the Haima cold seeps at a water depth of 1 381 m. Based on the scanning electron microscope (SEM) analyses, the prismatic layer and nacreous layer were identified, which are characterized by prismatic structure and stratified structure, respectively. In addition, the profile can be subdivided into two parts: altered and unaltered zones. Laser inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping shows that the element concentrations of the altered zones were influenced by the authigenic carbonate rocks, whereas the element concentrations of unaltered zones remain stable. In-situ X-ray diffraction (XRD) analyses show that the mineral constituent of the nacreous layer is mainly composed of aragonite. Along with the growth profile, Mg/Ca ratios of unaltered zones have minor variations, ranging 0.72–0.97 mmol/mol (mean=0.87 mmol/mol), with estimated temperatures of 3.8–4.1 °C, indicating that the temperature of the surrounding seawater remains constant and agree with the measured data of 3.9 °C which was conducted by a conductivity-temperature-depth system (CTD). The minor variations of Ba/Ca ratios (0.01–0.06 mmol/mol; mean=0.04 mmol/mol) indicate a relatively stabilized salinity of the surrounding seawater. S/Ca ratios show large variations of 0.04–4.15 mmol/mol (mean=1.37 mmol/mol). S/Ca ratios have regular variations which generally correspond to the variations of the Mg/Ca ratios, highlighting that the S/Ca ratios of bivalve shells show the potential to reflect the growth rate of the Gigantides. However, further studies should be carried out on the understanding of the links between the S/Ca ratios and seepage intensity of cold-seep fluids. [ABSTRACT FROM AUTHOR]

The Shenhu Submarine Canyon Group on the northern slope of the South China Sea consists of 17 slope-confined canyons, providing a good example for investigating their hosting sediments. Three drilling sites, including W07, W18, and W19, have proven the occurrence of gas hydrate reservoirs in the inter-canyon area between canyons C11 and C12. Whereas, variations of the geomorphology and seismic facies analyzed by high-resolution 3D seismic data indicate that the gas hydrate-bearing sediments may form in different sedimentary processes. In the upper segment, a set of small-scale channels with obvious topographic lows can be identified, revealing fine-grained turbidites supplied from the shelf region during a very short-term sea-level lowstand. In the middle part, gas hydrate units at Site W07 showing mounded or undulation external configuration are interpreted as sliding sedimentary features, and those features caused by gravity destabilization were the main formative mechanism of gas hydrate-bearing sediments that were sourced from the upper segments. In contrast, for the canyon transition zone of lower segments between C11–C12 inter-canyon and C12 intra-canyon areas, where W18 and W19 sites are located, the gas hydrate-bearing sediments are deposited in the channelized feature in the middle to lower segment and slide erosive surface. Gas hydrate-bearing sediments of the lower segment were migrated through channelized features interconnecting with the middle to lower slope by gravity-driven flows. The majority of deposits tended to be furtherly moved by lateral migration via erosive surface created by sediment failed to intra-canyon area. The conclusion of this study may help better understand the interaction between the formation mechanism of gas hydrate-bearing sediments and the geomorphologic effects of inter-canyon areas. [ABSTRACT FROM AUTHOR]

Wind and wave data are essential in climatological and engineering design applications. In this study, data from 15 buoys located throughout the South China Sea (SCS) were used to evaluate the ERA5 wind and wave data. Applicability assessment are beneficial for gaining insight into the reliability of the ERA5 data in the SCS. The bias range between the ERA5 and observed wind-speed data was −0.78–0.99 m/s. The result indicates that, while the ERA5 wind-speed data underestimation was dominate, the overestimation of such data existed as well. Additionally, the ERA5 data underestimated annual maximum wind-speed by up to 38%, with a correlation coefficient >0.87. The bias between the ERA5 and observed significant wave height (SWH) data varied from −0.24 to 0.28 m. And the ERA5 data showed positive SWH bias, which implied a general underestimation at all locations, except those in the Beibu Gulf and central-western SCS, where overestimation was observed. Under extreme conditions, annual maximum SWH in the ERA5 data was underestimated by up to 30%. The correlation coefficients between the ERA5 and observed SWH data at all locations were greater than 0.92, except in the central-western SCS (0.84). The bias between the ERA5 and observed mean wave period (MWP) data varied from −0.74 to 0.57 s. The ERA5 data showed negative MWP biases implying a general overestimation at all locations, except for B1 (the Beibu Gulf) and B7 (the northeastern SCS), where underestimation was observed. The correlation coefficient between the ERA5 and observed MWP data in the Beibu Gulf was the smallest (0.56), and those of other locations fluctuated within a narrow range from 0.82 to 0.90. The intercomparison indicates that during the analyzed time-span, the ERA5 data generally underestimated wind-speed and SWH, but overestimated MWP. Under non-extreme conditions, the ERA5 wind-speed and SWH data can be used with confidence in most regions of the SCS, except in the central-western SCS. [ABSTRACT FROM AUTHOR]

Magnetic data has been widely applied in the tectonic division. High-resolution magnetic data were used to analyze the geotectonic zoning of the South China Sea. Based on the newly compilated magnetic data, the processing results and the distribution of known faults, we consider that the U-shaped line approximately along the South China Sea national boundary of China shown in the magnetic map is a significant geological and geophysical boundary. We first described the linear characteristics of the magnetic data and then applied pseudo-gravity, Euler deconvolution, tilt derivatives, and the texture segmentation method to process the data. Results show that the dividing line between the South China Sea and the surrounding blocks is approximately along this U-shaped line. The dividing line between the South China domain and the South China Sea domain is along with the Dongsha Islands to Xisha Trough, which is different from the previous geophysical zoning results. Our results are almost consistent with those of the gravity data indicating roughly the tectonic zonation along the U-shaped line. [ABSTRACT FROM AUTHOR]

Clear underwater images can help researchers detect cold seeps, gas hydrates, and biological resources. However, the quality of these images suffers from nonuniform lighting, a limited range of visibility, and unwanted signals. CycleGAN has been broadly studied in regard to underwater image enhancement, but it is difficult to apply the model for the further detection of Haima cold seeps in the South China Sea because the model can be difficult to train if the dataset used is not appropriate. In this article, we devise a new method of building a dataset using MSRCR and choose the best images based on the widely used UIQM scheme to build the dataset. The experimental results show that a good CycleGAN could be trained with the dataset using the proposed method. The model has good potential for applications in detecting the Haima cold seeps and can be applied to other cold seeps, such as the cold seeps in the North Sea. We conclude that the method used for building the dataset can be applied to train CycleGAN when enhancing images from cold seeps. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is an important repository for natural gas hydrates (NGHs), where some NGH deposits and their overlying sediments (OSs) are in an underconsolidated state. During the exploitation of NGHs, the stability of the OSs of the NGH deposits is one of the key factors in ensuring mining safety. Especially under different consolidation degrees, the mechanical response and stability of the OSs will vary, which directly affects the safety and efficiency of the NGH mining. This research explores the influence of different consolidation degrees on the mechanical properties of the OSs of NGH deposits in the SCS. The strength and pore pressure characteristics were analyzed through undrained triaxial shear tests. The findings indicate that an increase in consolidation degree enhances the strain softening behavior, and an increase in initial effective stress enhance the strain hardening and shear contraction behaviors of the samples. The failure strength, modulus, and maximum excess pore pressure increase with the consolidation degree and initial effective stress, and there is an approximately linear correlation between failure strength and consolidation degree. Therefore, the exploitation of NGHs in the SCS must comprehensively consider the burial depth and consolidation degree of the OSs. The findings of this study will assist in optimizing mining plans and enhancing safety during the exploitation process. • Increases in consolidation degree enhance the strain softening behavior. • Failure strength increase linearly with consolidation degree. • Secant modulus increase with the consolidation degree. • Maximum excess pore pressure increase with the consolidation degree. [ABSTRACT FROM AUTHOR]

The El Niño-Southern Oscillation (ENSO) is the principal climatic system in the modern Pacific Ocean, and it potentially influences the global climate. The South China Sea (SCS), in the western tropical Pacific, is significantly affected by ENSO activity. We have conducted a high-resolution oxygen isotope study of the shells of one modern and four fossil Tridacna from the Xisha Islands in the SCS. The results for the modern sample reveal that the shells of Tridacna are a good proxy of ENSO variability. We used the results of the oxygen isotope composition of four fossil Tridacna to produce high-resolution records of ENSO activity during four time slices in the Holocene. The results indicate that ENSO variability in the early Holocene was comparable to that of today, and that a minimum in the frequency and intensity of ENSO activity occurred in the mid Holocene. These findings are consistent with paleoclimatic results from corals, mollusks and sedimentary records. However, the observed extremely low frequency and moderate ENSO intensity at 4.7 ka indicate an anomalous pattern of ENSO changes within this interval of climatic transition. In addition, seasonal temperature variations during the Holocene were different from those of today and extreme seasonality may also occur during warmer periods. [ABSTRACT FROM AUTHOR]

Spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethyl sulfoxide (DMSO) in the northern South China Sea were determined in the summer of 2015. The mean concentrations of DMS, particulate DMSP (DMSPp), dissolved DMSP (DMSPd), dissolved DMSO (DMSOd), and particulate DMSO (DMSOp) in the surface seawater were 2.8 ± 1.0, 6.8 ± 1.5, 14.0 ± 3.1, 12.2 ± 3.2, and 9.2 ± 2.6 nmol L−1, respectively. The contributions of three principal removal pathways of DMS were investigated. The average biological production and consumption rates of DMS in the surface seawater were 6.15 ± 1.12 and 4.63 ± 1.32 nmol L−1 day−1. Deck incubation experiments showed that the photooxidation rates of DMS for different radiation bands followed the order: KUVB > KUVA > Kvisible light. The DMS photooxidation rates were higher in the coastal waters than in the open ocean, which might be associated with the higher concentrations of dissolved organic matter of terrigenous input. The sea‐to‐air fluxes of DMS ranged from 1.6 to 50.3 μmol m−2 day−1 with an average value of 15.6 ± 11.6 μmol m−2 day−1. Based on the respective turnover times of DMS, the contributions of biological consumption, photooxidation, and sea‐to‐air exchange to the sink of DMS were 32.6 ± 11.0%, 23.2 ± 8.9%, and 44.1 ± 19.2%, respectively, suggesting that the three removal pathways were all critical to the migration and transformation of DMS in the surface seawater during summer. Plain Language Summary: Dimethylsulfide (DMS) is an important gas that is mainly produced by phytoplankton in seawater. This compound conveys sulfur from the ocean to the atmosphere, playing a significant role in global sulfur cycling. DMS is also an antigreenhouse gas that influences the Earth's radiative budget and has effects on the global climate (Charlson et al., 1987, https://doi.org/10.1038/326655a0; Quinn et al., 2017, https://doi.org/10.1038/ngeo3003). DMS emission from the ocean to the atmosphere depends directly on its concentration in the surface seawater. In our study, the distribution of DMS and related sulfur compounds were studied for the first time in the northern South China Sea, the largest marginal sea in the western Pacific. Higher concentrations were observed in coastal areas than in the open ocean due to biological activity. Deck incubation experiments were also carried out to assess the relative contributions of three removal pathways of DMS, including biological consumption, photooxidation, and sea‐to‐air diffusion. All three removal processes of DMS were contributors to the turnover of DMS in this study. Key Points: Distributions of biogenic sulfur compounds were measured in the northern SCS for the first timeThe contributions of different radiation bands to DMS photooxidation were determinedThe major DMS turnover rates and turnover times were estimated simultaneously [ABSTRACT FROM AUTHOR]

This study explores synoptic‐scale circulation conditions that favor vertical motion on heavy rainfall days (HRDs) over North China (NC) and analyzes the quantitative contribution to vertical motion by different forcings using the quasi‐geostrophic (QG) omega equation. On HRDs, moisture is brought from the South China Sea and East China seas by surface cyclonic vortex activity. When South Asian High is located anomalously northward, NC is on the south side of the upper‐level jet (ULJ) stream entrance region. Diagnosis of the QG omega equation shows that vertical motion on HRDs is caused by dynamic forcing, diabatic forcing, and topographic forcing. The greatest contribution to vertical motion is from diabatic forcing, while topographic contributes to vertical motion at low levels. The dynamic forcing, which is manifested by the Q‐vector, indicates that both the ULJ and baroclinic trough generate the vertical motion. Furthermore, the effect of the baroclinic trough is larger than that of the ULJ. On medium rainfall days, the contributions from dynamic forcing, diabatic forcing, and topographic forcing are clearly weaker than on HRDs, with reductions of 62.3%, 71.3%, and 73.8%, respectively. Plain Language Summary: Previous studies have suggested that vertical moisture transport is more important than horizontal moisture advection in heavy rainfall events over North China. However, quantitative contributions to vertical motion during heavy rainfall days (HRDs) from the effects of atmospheric circulation, water vapor, geostrophy, and topographic forcing remain unclear. Using in situ measurements and reanalysis, and based on theoretical analysis, we first analyze the favorable synoptic scale circulation with rich moisture for vertical motion, accompanying the heavy rainfall. Results from the quasi‐geostrophic omega equation then show that latent heat release by condensed water vapor is the greatest impact factor for vertical motion, whereas topographic forcing affects mainly vertical velocity at lower levels, and atmospheric dynamic disturbance affect vertical velocity at mid‐upper levels. Moreover, east‐west dynamic variations are more important than north‐south variations. The structure of the effective dynamical driver more closely resembles the atmospheric baroclinic trough structure than the confluence of the upper‐level jet stream. All of the forcing contributions are clearly weaker on medium rainfall days than on HRDs. Key Points: Synoptic‐scale circulation conditions that favor vertical motion on heavy rainfall days over North China are identifiedContributions of diabatic, dynamic, and topographic forcings to vertical motion are quantified using the quasi‐geostrophic omega equationBoth upper level jet and baroclinic trough generate vertical motion with the latter being more important for heavy rainfall over the NC [ABSTRACT FROM AUTHOR]

Metapenaeus affinis is a crustacean with important commercial value in the fishery of the South China Sea. Overfishing has resulted in the decline of the wild population and germplasm degradation. However, there is little background knowledge about its gonadal development, and there is a lack of research on the development of this species. To better understand the molecular regulatory mechanisms during gonadal development, here, we performed RNA-Seq on immature and mature ovaries and compared their transcriptomic signatures. 126,930,488 and 122,677,356 clean sequencing reads were obtained from the Illumina sequencing platform, respectively. 394 differentially expressed genes (DEGs) were identified, of which 136 were up-regulated, and 258 were downregulated. Further analysis revealed rich transcriptional sequences, which have homology with genes related to reproduction and development. Expression patterns of COX, GPX, E3s, PCNA, STPK, and other genes were changed during ovarian development. Validation by qRT-PCR demonstrated the reliability of RNASeq. This study has made a significant contribution to the currently available sequence data of M. affinis and provided reference data for the development of genetic and breeding work. [ABSTRACT FROM AUTHOR]

Internal waves play important roles in modulating the temperature variations and heat transfers in stratified oceans. However, due to the deep ocean measuring approach limitations, it is still challengeable to characterize the temperature fluctuations induced by internal waves in the deep oceans below 2,000 m. In this study, a fleet of rapid‐sampling deep profiling floats with an approximately daily sampling rate was deployed in the northeastern South China Sea (SCS), Philippine Basin (PB), Mariana Arc (MA), and Kuroshio Extension (KE). Results show that the internal waves, internal tides or near‐inertial waves, have considerable imprints on local temperature fluctuations. Geographically, the internal wave induced temperature fluctuations are generally larger in the PB and MA, indicative of a strong deep signature of internal tides generated by local energetic tide‐topography interactions or radiation from remote sources. The temperature fluctuations at 4,000 m can reach up to 7 m°C in most regions, which may cover up real signals of temperature change, posing challenges to assess the deep ocean warming rate through currently insufficient deep profiling floats. Besides, the amplitude of isopycnal displacement in the PB and MA is evidently larger than in KE at 4,000 m, which implies enhanced diapycnal diffusivity and mixing in the deep layers of open oceans with rough topography. Plain Language Summary: Internal waves are ubiquitous in the global ocean, and their propagations are accompanied by the rise and falls of isopycnals which induce fluctuations in local temperature. However, in situ observations of high‐frequency temperature fluctuations in the deep ocean are still insufficient. Here we used a fleet of rapid‐sampling deep profiling floats to assess the temperature fluctuations induced by internal waves. We found that the magnitude of internal wave induced deep ocean temperature fluctuations is evidently stronger than the long‐term trend, especially in the Philippine Basin (PB) and Mariana Arc (MA) with rough topography. Therefore, a more cautious approach should be used to assess the deep ocean warming rate in areas with strong internal waves. Key Points: Internal waves are found to have considerable imprints on temperature fluctuations using rapid‐sampling deep profiling floatsThe temperature fluctuations can reach 7 m °C at 4,000 m, posing challenges to assess the real deep ocean warming rateThe internal waves induced temperature fluctuations in the deep ocean are generally larger in the Philippine Basin and Mariana Arc [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is a high biodiversity region in the world ocean, supports abundant marine resources to the peripheral nations, and affects weather/climate in southeast Asia. A better understanding of its circulation is important to better prediction and management of the SCS. Here we reveal sizable intraseasonal oscillations at period ~ 50 days between May and November 2017 in the acoustic Doppler current profiler observed velocity in the central SCS. Satellite observed wind and sea level data together with a process-oriented numerical experiment suggest that the oscillations were caused by locally-generated and remotely-penetrated westward-propagating Rossby waves. The summer southwesterly monsoon strengthening/weakening and the resultant Ekman pumping velocity and shoreward Ekman transport increase/decrease and consequent coastal sea level rise/fall off the west coast of Palawan create westward-propagating Rossby waves causing velocity oscillations in the central SCS. Besides the local generation, Rossby waves with sea level anomaly > 0.2 m propagating from the Pacific through the Sulu Sea into the SCS could contribute to the intraseasonal velocity oscillations in the central SCS. [ABSTRACT FROM AUTHOR]

Interactions between the open ocean and marginal seas have been suggested to be critical to the redistribution and dissipation of global energy. Here, we propose a mechanism for the upper open ocean influencing the deep flow in marginal seas that hinges on the formation and propagation of topographic Rossby waves (TRWs). Observations and high‐resolution simulations suggest substantial intraseasonal variability with periods of 5–60 days associated with the deep flow over continental slopes of the northern South China Sea (NSCS). These fluctuations generally account for over 40% of the total deep kinetic energy variability and the number can reach 70% over the slopes to the west of the Luzon Strait, southwest of the Dongsha Islands, and northeast of the Xisha Islands. By examining the spatiotemporal features of the fluctuations, we demonstrate that the intraseasonal variability of the deep flow in the NSCS is closely associated with TRWs. Using a recently developed multiscale energetics analysis in combination with a ray tracing model, we show that the energy sources of TRWs can be traced back to the east of the Dongsha Islands, where the Kuroshio intrusion and related eddies energize the TRWs primarily through pressure work. These waves propagate westward across the NSCS and drive the intraseasonal variability of the deep flow over continental slopes. Our findings highlight an energy pathway from the open ocean western boundary current to the abyssal marginal sea that could modulate regional circulation as well as exchanges between major ocean basins. Plain Language Summary: The Kuroshio intrusion can substantially modulate the circulation of the South China Sea (SCS), affecting the Indo‐Pacific exchange, climate, and ecosystem. Traditionally, its dynamic impact is thought to be confined to the upper layer. However, in this study, we propose a mechanism that links the Kuroshio to deep processes in the northern SCS (NSCS). We suggest that the deep flow intraseasonal variability over the continental slopes of the NSCS could be dynamically tied to the Kuroshio intrusion and related eddies via topographic Rossby waves. The results highlight an energy pathway from the upper open ocean to the abyssal marginal sea, which could be critical to the redistribution and dissipation of global energy. Key Points: Observations and simulations suggest substantial intraseasonal variability in the deep flow over slopes of the northern South China SeaDeep‐flow variability is dynamically linked to the Kuroshio intrusion and related eddies via topographic Rossby wavesThis study highlights an energy pathway from the open ocean into the abyssal marginal sea that could be critical to the global energy budget [ABSTRACT FROM AUTHOR]

The bottom parameters of the deep ocean are difficult to obtain through in situ measurement. These parameters demonstrate a significant physical meaning for predicting sound field accurately. Thus, geoacoustic inversion is required. An acoustic experiment was performed on a reliable acoustic path (RAP) in the Philippine Sea in 2013. A single bottom-moored hydrophone was deployed as the receiver, and the explosive charges were chosen as the sources. The experimental bottom loss (BL) versus angle was obtained with the water depth above 5000 m for bottom parameter inversion. The inversion sediment parameters show a clay-silt feature. The marginal probability distributions (MPDs) represent that the inversion results have a high credibility. This method provides a feasible solution for the inversion of the bottom parameters in the deep ocean. [ABSTRACT FROM AUTHOR]

Marine benthic dinoflagellates in the genus Coolia were reported in both tropical and temperate regions. We conducted a morphological and phylogenetic characterization of Coolia species from Hainan Island, South China Sea. The morphologies of three Coolia species were similar to those of the original descriptions of Coolia canariensis, C. tropicalis, and C. malayensis. In phylogenetic analyses based on the LSU rDNA and ITS regions (ITS1-5.8S-ITS2), the Hainan strains of C. canariensis, C. tropicalis, and C. malayensis clustered within the clades of these species with other isolates from different areas. No differences (p-distance) in LSU rDNA sequences were found between the Hainan C. malayensis strains and the strains from New Zealand, Florida of USA, Malaysia, Japan, Dominican Republic and Guangxi and Hong Kong of China. For C. canariensis and C. tropicalis, no differences (p-distance) in the LSU rDNA sequences were found between the Hainan strains (D1C2 and DS5F4, respectively) and the Australian strains (NQAIF252 and NQAIF90, respectively). Our study reveals the morphological and genetic diversity of Coolia species from Hainan Island, South China Sea, which provides a detailed understanding of Coolia species of this area. [ABSTRACT FROM AUTHOR]

The temperature-salinity (T-S) diagram is widely used in water mass analysis, but the boundaries between water masses are vaguely distinguished by conventional T-S-based methods. Herein, we propose a new method based on the potential density-potential spicity (sigma-pi) diagram. The new method has been applied to the conductivity-temperature-depth data collected in the northern South China Sea during a spring cruise in 2011. The water masses in the study region are classified into 13 types according to both the standard deviation of potential spicity in each potential density layer and the water volumetric distribution in the sigma-pi space. The results suggest that this new method is reasonable and robust for classifying water masses in the sigma-pi space as compared to previous methods based on the traditional T-S space. In addition, the westward intrusion of the West Pacific Ocean water to the northern South China Sea can be clearly detected by the tongue-like potential spicity structure and relatively high potential spicity patches on potential density layers, further verifying the robustness and efficiency of our method in the water mass analysis. [ABSTRACT FROM AUTHOR]

Compared to the natural production of 14C, thermonuclear tests have produced a globally abnormal 14C signal. To examine and reconstruct ocean circulation in the South China Sea (SCS), we generated a prebomb to postbomb 14C time series from a Porites lobata coral from the west side of Palawan Island, Philippines. Results show a diluted early bomb 14C intrusion in late 1955. We use this record to extend our understanding of the surface ocean circulation in and around the SCS by tracing 14C labeled water from nuclear test sites. Our postbomb Δ14C peaked at 154‰ in 1975, which lags ~10 years from the atmospheric peak, consistent with other marine records. This coral record also displayed clear seasonal Δ14C cycles indicating different surface waters passed the Palawan Island coral site due to seasonal variations of the East Asian Monsoon. [ABSTRACT FROM AUTHOR]

The South China Sea disputes involve both island and maritime claims among several sovereign states within the region, namely China, Malaysia, the Philippines, Brunei, Vietnam and Taiwan. Framing an analysis of international news and diplomatic relations allows researchers to examine how news organisations provide their audiences with context regarding news stories through content promotion and exclusion. This study examined how the Malaysian and Chinese newspapers reported about the South China Sea disputes and Malaysia–China bilateral relations. The findings indicated that the newspapers reported the topics with different intensity and prominence, while different news sources were employed. It was also found that conflict was a salient frame used by the various newspapers. In addition, this study found that the Malaysian and Chinese newspapers exhibited different valence in reporting the South China Sea disputes. Among the Malaysian newspapers under examination in this study, Sin Chew Daily (a Chinese-language daily) employed the most similar frame to that of the Chinese newspapers, where the coverage was pervasive with supportive valence towards China. [ABSTRACT FROM AUTHOR]

Blue holes are unique geomorphological features with steep biogeochemical gradients and distinctive microbial communities. Carbon cycling in blue holes, however, remains poorly understood. Here we describe potential mechanisms of dissolved carbon cycling in the world's deepest blue hole, the Yongle Blue Hole (YBH), which was recently discovered in the South China Sea. In the YBH, we found some of the lowest concentrations (e.g., 22 μM) and oldest ages (e.g., 6,810 years before present) of dissolved organic carbon, as well as the highest concentrations (e.g., 3,090 μM) and the oldest ages (e.g., 8,270 years before present) of dissolved inorganic carbon observed in oceanic waters. Sharp gradients of dissolved oxygen, H2S, and CH4 and changes in bacterially mediated sulfur cycling with depth indicated that sulfur‐ and/or methane‐based metabolisms are closely linked to carbon cycling in the YBH. Our results showed that the YBH is a unique and easily accessible natural laboratory for examining carbon cycling in anoxic systems, which has potential for understanding carbon dynamics in both paleo and modern oceans—particularly in the context of global change. Plain Language Summary: Here, we report for the first time concentrations and isotopic composition of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) along with geomorphological and geochemical parameters in the Yongle Blue Hole (YBH), South China Sea, the world's deepest blue hole. We found some of the lowest concentrations of DOC and the highest concentrations of DIC observed in coastal waters, that were both very old (their 14C ages are 6,810 and 8,270 years, respectively). Such low DOC concentrations have not been observed in relatively shallow oceanic environments. DIC in surface waters of the YBH is mainly controlled by air‐sea exchange, which only impacts the upper 80 m. The decomposition of organic carbon and the sulfidic acid dissolution of carbonates in the YBH enhance the production of DIC in deep waters of the YBH. The profiles of physical, chemical, and microbial parameters in the YBH provide a natural laboratory for examining carbon cycling and other redox‐sensitive elements. Understanding the key mechanisms of biogeochemical pathways in anoxic systems is critical in our understanding of carbon cycling in both paleo and modern oceans. Key Points: Concentrations and isotopic composition of dissolved carbon in the world's deepest blue hole were examined for the first timeLowest concentrations of DOC and highest concentrations of DIC in oceanic waters were observed, and both were radiocarbon depletedCarbon cycling in the Yongle blue hole is unique from those of the open ocean [ABSTRACT FROM AUTHOR]

A striation-based method with a vertical line array is proposed for source depth estimation. Broadband striation structures of direct and surface-reflected arrivals after propagating to receivers near the ocean bottom are applied. A tracking algorithm for the striation structures is proposed based on the extended Kalman filter. A cost function for source depth estimation is presented by matching the traces of the measured striations with a library of model-based traces under different source depths. The method is demonstrated on array data collected during an acoustic research experiment in the South China Sea in 2016. [ABSTRACT FROM AUTHOR]

Hydroxylated glycerol dialkyl glycerol tetraethers (OH-GDGTs) have been recently proposed as novel proxies for sea surface temperature (SST) estimation. However, it is still unclear whether these proxies are applicable to the tropical South China Sea (SCS). We assessed the possible impact of extraction methods on the OH-GDGT distribution in marine sediments. A batch of marine sediments from the SCS was subjected to lipid extraction using a modified Bligh/Dyer method (BDM) and an ultrasonic extraction (UE) method, respectively. A systematic difference in the concentration and distribution of OH-GDGTs was observed between the two methods. Sample-by-sample comparison also demonstrated that the BDM had a higher extraction efficiency for OH-GDGTs than UE. The concentration of OH-GDGTs for the BDM dataset was generally higher than that for the UE dataset. The fractional abundance of OH-GDGTs with one cyclopentyl ring was higher for the BDM, resulting in a different OH-GDGT distribution between the BDM and UE datasets. The BDM dataset was thus further used to explore the potential of OH-GDGTs as a proxy for SST in the SCS. OH-2/OHs, the ratio of OH-GDGTs with two cyclopentyl moieties to total OH-GDGTs, exhibited a negative correlation with annual SST when SST was > 25 °C, as opposed to the positive correlation between them when SST was < 25 °C. This suggests that OH-2/OHs holds promise for the reconstruction of SST in the SCS where the SST is close to the warm threshold and proxies, like U K' 37 and TEX 86 H , do not work well. [ABSTRACT FROM AUTHOR]

Internal Solitary Wave (ISW) normally converts its polarity from depression wave to elevation wave during shoaling process. This phenomenon has been verified by model studies and field observations. However, through the comparison between theoretical studies and observations, we find that Extended Kortweg-de Vries (EKdV) theory, often used by numerical simulations, cannot well predict the polarity conversion area of shoaling ISWs. Here we trace seismic reflectors within the water column, captured by exploration seismic data, and systematically analyze the polarity conversion area of the shoaling ISWs in the northeastern South China Sea (SCS). The results show that the ISWs in the northeastern SCS generally begin to convert their polarities from depression to elevation waves at the seafloor depth of about 200 m, and turn into elevation waves at the seafloor depth of about 100 m. The ISWs between depression and elevation waves are newly defined as transition waves, which are distributed between the seafloor depth of 130 m and 220 m; while elevation waves are distributed between 80 m and 120 m. We compared the observation with the theoretical critical conversion depth estimation by the two-layer model based on EKDV equation. The result suggests that the depth of the upper layer in the two-layer model can be selected as the depth of the maximum buoyancy frequency not the base of the mixing layer. Such selection can get better estimation of critical conversion depth of shoaling ISWs. Our analysis also suggests that the polarity conversion process is amplitude-dependent. The ratio of amplitude to depth for elevation waves is more than two times larger than that of the transition waves. This implies that the seafloor plays a more important role in shallow water than in deep water in controlling the amplitudes of ISWs during shoaling process. [ABSTRACT FROM AUTHOR]

The Qiongdongnan Basin is one of the largest Cenozoic rifted basins on the northern passive margin of the South China Sea. It is well known that since the Late Miocene, approximately 10 Ma after the end of the syn-rift phase, this basin has exhibited rapid thermal subsidence. However, detailed analysis reveals a two-stage anomalous subsidence feature of the syn-rift subsidence deficit and the well-known rapid post-rift subsidence after 10.5 Ma. Heat-flow data show that heat flow in the central depression zone is 70-105 mW m−2, considerably higher than the heat flow (<70 mW m−2) on the northern shelf. In particular, there is a NE-trending high heat-flow zone of >85 mW m−2 in the eastern basin. We used a numerical model of coupled geothermal processes, lithosphere thinning and depositional processes to analyse the origin of the anomalous subsidence pattern. Numerical analysis of different cases shows that the stretching factor βs based on syn-rift sequences is less than the observed crustal stretching factor βc, and if the lithosphere is thinned with βc during the syn-rift phase (before 21 Ma), the present basement depth can be predicted fairly accurately. Further analysis does not support crustal thinning after 21 Ma, which indicates that the syn-rift subsidence is in deficit compared with the predicted subsidence with the crustal stretching factor βc. The observed high heat flow in the central depression zone is caused by the heating of magmatic injection equivalently at approximately 3-5 Ma, which affected the eastern basin more than the western basin, and the Neogene magmatism might be fed by the deep thermal anomaly. Our results suggest that the causes of the syn-rift subsidence deficit and rapid post-rift subsidence might be related. The syn-rift subsidence deficit might be caused by the dynamic support of the influx of warmer asthenosphere material and a small-scale thermal upwelling beneath the study area, which might have been persisting for about 10 Ma during the early post-rift phase, and the post-rift rapid subsidence might be the result of losing the dynamic support with the decaying or moving away of the deep thermal source, and the rapid cooling of the asthenosphere. We concluded that the excess post-rift subsidence occurs to compensate for the syn-rift subsidence deficit, and the deep thermal anomaly might have affected the eastern Qiongdongnan Basin since the Late Oligocene. [ABSTRACT FROM AUTHOR]

Background: A large-scale systematical investigation of the influence of Pleistocene climate oscillation on mangrove population dynamics could enrich our knowledge about the evolutionary history during times of historical climate change, which in turn may provide important information for their conservation. Results: In this study, phylogeography of a mangrove tree Sonneratia alba was studied by sequencing three chloroplast fragments and seven nuclear genes. A low level of genetic diversity at the population level was detected across its range, especially at the range margins, which was mainly attributed to the steep sea-level drop and associated climate fluctuations during the Pleistocene glacial periods. Extremely small effective population size (Ne) was inferred in populations from both eastern and western Malay Peninsula (44 and 396, respectively), mirroring the fragility of mangrove plants and their paucity of robustness against future climate perturbations and human activity. Two major genetic lineages of high divergence were identified in the two mangrove biodiversity centres: the Indo-Malesia and Australasia regions. The estimated splitting time between these two lineages was 3.153 million year ago (MYA), suggesting a role for pre-Pleistocene events in shaping the major diversity patterns of mangrove species. Within the Indo-Malesia region, a subdivision was implicated between the South China Sea (SCS) and the remaining area with a divergence time of 1.874 MYA, corresponding to glacial vicariance when the emerged Sunda Shelf halted genetic exchange between the western and eastern coasts of the Malay Peninsula during Pleistocene sea-level drops. Notably, genetic admixture was observed in populations at the boundary regions, especially in the two populations near the Malacca Strait, indicating secondary contact between divergent lineages during interglacial periods. These interregional genetic exchanges provided ample opportunity for the re-use of standing genetic variation, which could facilitate mangrove establishment and adaptation in new habitats, especially in the context of global climate changes. Conclusion: Phylogeogrpahic analysis in this study reveal that Pleistocene sea-level fluctuations had profound influence on population differentiation of the mangrove tree S. alba. Our study highlights the fragility of mangrove plants and offers a guide for the conservation of coastal mangrove communities experiencing ongoing changes in sea-level. [ABSTRACT FROM AUTHOR]

Gas hydrates represent a huge reservoir of methane in marine sediments, prone to dissociation in response to environmental changes. There is consensus that past events of gas hydrate dissociation in the marine environment mainly occurred during periods of low sea level. Here, we report geochemical data for 2‐m‐thick layers of seep carbonate collected from a hydrate‐bearing drill core from ~800‐m water depth in the northern South China Sea. The aragonite‐rich carbonates reveal positive δ18O values, confirming a genetic link with gas hydrate dissociation. Uranium‐thorium dating of seep carbonates indicates that gas hydrates at the study site dissociated between 133,300 and 112,700 years BP, hence coinciding with the Last Interglacial (MIS 5e) sea‐level highstand. We put forward the concept that a climate‐driven increase in temperature was responsible for a period of pronounced gas hydrate dissociation. Plain Language Summary: The gas hydrate reservoir is a dynamically changing system extremely susceptible to variations of seafloor temperature and pressure. Therefore, gas hydrate dissociation and subsequent methane seepage frequently occur during times of global climate change, especially during sea‐level lowstands with reduced seabed pressure. However, this conclusion was mainly based on dating of seep carbonates sampled from the seabed. As a consequence, one cannot exclude that previous results have been compromised by a sampling bias since seafloor samples are easier to collect. Authigenic seep carbonates from drill cores represent a continuous record of gas hydrate dynamics. Our uranium‐thorium dating of seep carbonate from drill cores provides a unique example of the effects of temperature and pressure on the stability of the hydrate system in the Dongsha area, northern South China Sea (SCS), during the last interglacial stage (MIS 5e, about 130,000 years BP). Representing the most similar and most contemporary analog to the current interglacial, the study of a methane release event in the SCS during MIS 5e will shed light on the expected trend of methane release events in the future, while providing insight into the response of low‐latitude oceans to climate change. Key Points: U/Th dating of seep carbonates from a gas hydrate‐bearing sediment drill core provides constraints on the timing of methane seepageCarbonates precipitated from 18O‐enriched pore fluids derived from methane hydrate dissociationMethane hydrate dissociation occurred during sea‐level highstand (MIS 5e) possibly induced by increasing bottom‐water temperatures [ABSTRACT FROM AUTHOR]

To better understand eddy‐induced heat and salt transport, a targeted joint hydrographic investigation focusing on an anticyclonic eddy was carried out in July 2017 in the northern South China Sea. In situ and satellite observations together with Hybrid Coordinate Ocean Model (HYCOM) output show the transport of subsurface saline Kuroshio water into the northern South China Sea by an anticyclonic eddy. Subsurface high‐salinity cores are consistent with the anticyclonic eddy centers. The transport of saline Kuroshio water occurs in two stages accompanied by eddy shedding. First, saline Kuroshio water is trapped within the anticyclonic eddy at its generation location. Then, although the salinity within the eddy gradually weakens as the eddy carries the saline water westward, the quantity of saline water (>34.70 psu) shows a sharp increase, dominated by eddy‐induced salinity advection. A diagnosis of the salinity budget further confirms that the contribution of eddy flow advection is greater than that of mean flow advection. The saline Kuroshio water is trapped and conveyed in this anticyclonic eddy, providing vital evidence and important implications for eddy‐induced salt transport and water exchange. Key Points: Hydrographic investigation and glider data show the transport of subsurface saline Kuroshio water into the northern South China SeaThe eddy‐induced transport of saline Kuroshio water occurs in two stages with different dominant transport mechanismsA diagnosis of salinity budget confirms that the eddy flow advection plays a major role in salinity transport in the second stage [ABSTRACT FROM AUTHOR]

Four current-meter moorings and 12 pressure sensor–equipped inverted echo sounders (PIES) were deployed during summer 2011 in the South China Sea. The goal of the experiment was to obtain synoptic observations of the large-amplitude nonlinear internal waves from the near field to the far field as they propagated west-northwest across the sea. The program was unique because it was the first to observe the latitudinal variability of the wave crests in addition to the transformations along a single east–west transect. The waves were strongest down the center of the PIES array along roughly 20°45′N and were weaker off axis in both directions. Both a-waves and b-waves arrived earlier in the south than the north, but with different lag times indicating different propagation directions and therefore different sources. The waves were classified by their arrival patterns and source locations and not by their amplitude or packet structure. The Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) model, calibrated against the array, showed that the a-waves developed out of the internal tide spawned in the southern portion of the Luzon Strait and the b-waves originated in the north. The northern tides were refracted and suffered large dissipative losses over the shallow portion of the western ridge, whereas the southern tides propagated west-northwest unimpeded, which resulted in a-waves that were larger and appeared sooner than the b-waves. The results were consistent with previous observations that can now be understood in light of the full three-dimensional structure of the internal waves and tides in the northeastern South China Sea. [ABSTRACT FROM AUTHOR]

Using a high‐resolution (0.1° × 0.1°) regional ocean model, this study investigates the impact of strait transport variability on the South China Sea (SCS) circulation and Indonesian throughflow, with a focus on the Mindoro‐Sibutu pathway via the Sulu Sea, upon closing various straits within the Maritime Continent. Closing the Sibutu Strait reduces the Luzon Strait throughflow into the SCS by 75%, and the Mindoro–Sibutu deep exchange is reversed, thus flowing into the SCS. No significant change occurs over the shallow Sunda Shelf of the southern SCS, which is primarily driven by local monsoon winds. The impact of closing the Karimata Strait is limited to the Sunda Shelf and the Java Sea. The Sibutu Strait throughflow is fundamental in governing the SCS's low salinity, buoyancy, and upper layer injection into the Makassar Strait, which is the primary component of the Indonesian throughflow, thus inhibiting the transport within the upper 200 m of the throughflow. Closing both the Sibutu and Karimata Straits increases the southward Makassar Strait throughflow transport by ~3 Sv, which is derived entirely from the Mindanao Current. Key Points: A high‐resolution regional ocean model is used to investigate impact of strait transport variability on SCS circulation and ITFSibutu Strait is essential for the SCS circulation and the subsurface Makassar throughflowImpact of the Karimata Strait is limited on the Sunda Shelf and the ITF surface flow [ABSTRACT FROM AUTHOR]

Increasing intense landfalling typhoons (LFTYs) are of great coastal threatens to southern China. However, changes in genesis location and landfalling frequency of western North Pacific (WNP) LFTY dedicated to southern China remain unclear. Here we identified such LFTYs during peak summer and found that most LFTYs formed south of 20°N and the LFTY genesis locations over southern WNP have also experienced a sharp interdecadal shift since 1998, which are mainly attributed to the large‐scale environment changes induced by the Mega‐La Niña‐like climate shift. However, LFTY frequency (= "landfalling frequency of southern China typhoon") shows a slight increasing trend but without significant interdecadal variation. Variations of LFTY frequency are mainly affected by the easterly steering flows near 20°N over the South China Sea and the Philippine Sea, which are closely linked to the WNP subtropical high activity. Our results provide a new perspective on the LFTY activities dedicated to southern China. Plain Language Summary: We explore the changes in frequency and genesis location of landfalling typhoon (LFTY) dedicated to southern China during peak summer over 1979–2015, which is important for people's life and property from the coastal risk perspective. Results show that the LFTY genesis location is primarily modulated by the Pacific interdecadal variation via modifying the large‐scale atmospheric and oceanic responses over the western North Pacific. While the LFTY frequency (= "landfalling frequency of southern China typhoon") is significantly affected by the easterly steering flows near 20°N over the South China Sea and the Philippine Sea, which are closely linked to the western North Pacific subtropical high activity. Key Points: Landfalling frequency and genesis location of southern China typhoon are affected by different mechanisms during peak summerInterdecadal changes in landfalling typhoon (LFTY) genesis location are primarily attributed to the late‐1990s Mega‐La Niña‐like regime shiftVariations of LFTY frequency are mainly driven by the easterly steering flows near 20°N associated with the western North Pacific subtropical high activity [ABSTRACT FROM AUTHOR]

The Kuroshio Intrusion (KI) into the South China Sea (SCS) is a key process that greatly modulates the variability of dominant phenomena in the northern SCS. Using the Regional Ocean Modeling System, the optimal precursor (OPR) triggering the KI is obtained by the Conditional Nonlinear Optimal Perturbation (CNOP) approach. The OPRs exhibit the anticyclonic eddies (AEs) spatial pattern in the southern region (19°N–20.3°N, 119°E–122°E) of the Luzon Strait. The evolution processes of the OPRs indicate that the northwestward movement and rapid growth of AEs force the Kuroshio to bend westward continuously, which leads to the transition of the Kuroshio path from leaping state to intruding state. Eddy‐energetic analyses suggested that the barotropic instabilities are responsible for the evolution of the OPRs and thus triggering the KI, while the local wind stress plays a minor role in the triggering process. Additional examinations based on satellite altimeter data and ocean reanalysis data further confirm that the AE‐like perturbation similar to the obtained OPR indeed plays a key role in the KI triggering process. Plain Language Summary: The Kuroshio Intrusion (KI) is a key process greatly modulating the variabilities of dominant phenomena in the northern South China Sea (SCS). Therefore, a reliable forecast of the KI is crucial to the predictions of other processes in the SCS. To facilitate the KI forecast, the study of its optimal precursors (OPR) viewed as the omens of the KI occurrence is carried out in this paper. Based on the numerical model and an optimal method, it is found that anticyclonic eddy (AE)‐like perturbations featuring clockwise rotating velocities in the southern part of Luzon Strait act as the OPRs of the KI. Further examination based on the HYbrid Coordinate Ocean Model reanalysis and remote sensing Absolute Dynamic Topography data validate the crucial role of the AE‐like structure perturbations in the KI occurrence. In other words, predictors may successfully forecast the KI event before it occurs by capturing the oceanic perturbations similar to the OPR. Key Points: The anticyclonic eddy‐like perturbations from the southern part of Luzon Strait act as the precursors of Kuroshio IntrusionThe rapid growth and northwestward movement of the OPR trigger the Kuroshio IntrusionThe Kuroshio Intrusion trigger is mainly attributed to the barotropic instabilities [ABSTRACT FROM AUTHOR]

Xi, H.; Zhang, Z.; Lu, Y., and Li, Y., 2019. Long-term and interannual variation of the steric sea level in the South China Sea and the connection with ENSO. Journal of Coastal Research, 35(3), 489–498. Coconut Creek (Florida), ISSN 0749-0208. Multisource observation and model data sets, including satellite altimetry, satellite gravimetry (the Gravity Recovery and Climate Experiment mission [GRACE]), ocean model (Estimation of the Circulation and Climate of the Ocean [ECCO]), and oceanographic reanalysis data (Ishii), are used to explore the long-term and interannual sea-level variation (SLV) in the South China Sea (SCS) and the connection with El Niño–Southern Oscillation (ENSO). From 1993 to 2012, the sea level rose at a rate of 4.7 ± 0.3 mm/y, and the steric component contributed approximately 40–55% of the increase shown in the Ishii data (1.9 ± 0.3 mm/y) and the ECCO model (2.6 ± 0.3 mm/yr). Using the GRACE observations from 2003 to 2012 for independent validation, the ECCO-derived steric trend was consistent with the mass-corrected altimetry result, whereas the Ishii data failed to capture the sea-level rise in the central basins. On the interannual scale, both the empirical orthogonal function (EOF) and the wavelet coherence (WTC) analysis indicate that the total SLV and the steric SLV have positive correlations with ENSO. The correlation is stronger between the Southern Oscillation index (SOI) and the ECCO-derived steric SLV than it is between the SOI and the Ishii-based steric SLV. In the time-frequency domain, the WTC shows a clear in-phase coherence in the 2-year cycle between the SOI and the ECCO-derived steric SLV over the entire time span; no significant coherence appears between the SOI and the Ishii-based steric SLV after 2003. The abnormal northerly winds and the increasing intrusion of low-temperature Kuroshio water into the SCS through the Luzon Strait during El Niño years may explain the connection between ENSO and the interannual steric SLV. [ABSTRACT FROM AUTHOR]

A new steroid, (3S,5R,9R,10S,13R,17R,20R,24S,22E)-ergosta-6,8,22-triene-3,25-diol (1), and its sulfonated analogue (2) together with a known one, 5α,8α-epidioxy-cholest-6-en-3β-ol (3) were isolated from the marine sponge Dactylospongia elegans collected from the South China Sea. The new structures including absolute configurations were established by the HRESIMS and 1D and 2D NMR analysis coupled with the X-ray crystal analysis. Both of 1 and 2 exhibited cytotoxicity against cancer cell line MCF-7 with IC50 values of 9.7 and 8.5 μM, respectively. [ABSTRACT FROM AUTHOR]

It is well known that coral thermal bleaching is mainly caused by abnormally high temperatures, but the spatial/intergeneric variation in coral‐algal symbiosis and its linkage to coral bleaching susceptibility is not well understood. In this study, 654 coral samples were collected from six coral reef regions (CRRs) in the South China Sea (SCS), between the Nansha Islands (~10°N) and Daya Bay (22°50′N). They were analyzed to explore how geographical/environmental variation affects coral bleaching susceptibility. The results showed significant spatial and intergeneric variation in zooxanthellae density, Chl a content, and tissue biomass. Massive corals generally showed higher values than branching corals for all three parameters across CRRs. Spatial analysis showed that these parameters were lowest in the Nansha Islands and highest in Daya Bay, indicating increases with latitude. Several factors may have accounted for this trend, with the most important being sea surface temperature and nutrients. Additionally, we observed a relationship between physiological parameters and bleaching susceptibility, which was that branching corals had greater bleaching susceptibility than massive corals. Coral community composition and live coral cover data showing increasing dominance of massive corals in the SCS support the above inference. Relatively high‐latitude areas have been proposed as potential refuges for corals under continued global warming and the physiological parameters in the present study seem to support this. However, in spite of the aforementioned results, the smallest live coral cover was found in the northern CRRs. This suggests that this refuge function is currently compromised, mainly due to increasing destructive anthropogenic actions. Key Points: The spatial variation in all of the coral physiological parameters used suggests significant increase with the increase in latitudeThe intergeneric variation in the parameters used affects coral bleaching susceptibility and adaptability to environmental stressThe potential of the northern South China Sea to serve as a coral refuge is currently being compromised by local anthropogenic activities [ABSTRACT FROM AUTHOR]

This study documents the seasonal variation of precipitation over the whole Indochina Peninsula (ICP) and associated changes in atmospheric winds and surface heat fluxes and investigates the impact of the ICP precipitation‐related heating and circulation on spring sea surface warming in the South China Sea (SCS). Climatologically, most of the ICP experiences the rainy season from May to October and the period from November to April is the dry season. The summer wet‐winter dry pattern dominates the seasonal rainfall variation in most regions and the maximum rainfall along the west coast occurs during June through August in association with monsoon westerly winds. A pronounced semi‐annual rainfall variation is observed along central Vietnam with a primary peak in October and a secondary peak in May, which is related to northeasterly and southwesterly winds, respectively. Surface heat fluxes change drastically over the ICP in March–April and play an important role in increasing the thermal contrast with the neighbouring waters and heating the atmospheric column, which causes upward motion and precipitation over the ICP. The induced compensatory downward motion over the northern SCS leads to an increase in downward shortwave radiation and a decrease in surface wind speed and turbulent heat fluxes, which contributes to the SCS warming before the summer monsoon onset. Downward shortwave radiation heats the atmospheric column through sensible heat flux, increasing the thermal contrast with the neighbouring waters, causing upward motion and precipitation over the ICP. The upward motion over the ICP in March–April triggers a regional zonal vertical circulation, inducing compensatory downward motion over the SCS. In turn, the downward motion over the SCS leads to an increase in downward shortwave radiation and a decrease in surface wind speed and turbulent heat fluxes, contributing to the SCS warming. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Magnetic fabric and grain size properties are used to reconstruct the bottom current. • The increased deep water bottom current corresponds to Heinrich Stadials. • The evolution of bottom current is closely related to the global climate. Abstract Deep water bottom current (DWBC) plays a central role in global climate. Relative to the Atlantic, due to poor preservation of marine carbonate in the Pacific sediments, the evolution of Pacific deepwater circulation is still unclear. The South China Sea (SCS), connection to the Pacific through Luzon Strait, at a depth of about 2400 m, offers a unique opportunity to monitor the changes of western Pacific deep water circulation. We present a magnetic and grain size analysis of two sediment cores (PC111 and PC83) located in Xisha Trough, northern SCS in order to reconstruct past changes of DWBC during the last 150 kyrs. Variations in the mean size of sortable silt are interpreted to indicate past changes of DWBC, which suggest abrupt, millennial-scale increasing DWBC strength during Heinrich Stadials (HS1, HS2, HS3, HS4, HS5, HS6, HS7, HS8, HS9, HS10, HS11) for past 150 kyr. The flow orientation of DWBC revealed by the anisotropy of magnetic susceptibility (AMS) are mostly NW–SE direction in Core PC111 and Core PC83, which are both parallel to the local topography. Combined with the published studies, we suggest the increase bottom current in northern SCS during the Heinrich Stadials (HS1 to HS11), times of weak North Atlantic Deep Water formation, demonstrating the tight coupling between the Atlantic and Pacific Oceans. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Inconsistent changing trends of SST and SSS at different parts of the northern SCS. • Declined trend of SSS near Luzon Strait is affected by the western tropical Pacific. • Increased SST and SSS in central northern SCS is linked to weakened Asian monsoon. Abstract The South China Sea (SCS) is an important moisture and heat source in the Asian monsoon system, and its environmental changes influence economic and social stability in Southeast Asia and East Asian. Previous records on sea surface temperature (SST) and salinity (SSS) were mostly from one sediment core, and/or only showed fragmentary information. It is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern SCS. In this study, paired δ18O and Mg/Ca records of planktonic foraminifer Globigerinoides ruber from Core S0204B nearby the Luzon Strait (21°13.818′N, 118°3.077′, water depth 1822 m), and Core GHE 27L (19.85°N, 115.34°E, water depth of 1533 m) in the central northern SCS, were analyzed, so as to better understand the physical process of the SST and SSS changes in the northern SCS and its relationship with the tropical Pacific. The results demonstrate that the SST is relatively stable and seawater δ18O (δ18O sw) values, a salinity proxy, shows a decrease trend since 7.0 ka BP in Core S0204B. By contrast, SST and δ18O sw in Core GHE 27L exhibit an overall increasing trend at the same time, indicating apparent regional discrepancy on the changing trend of the SST and SSS in the northern SCS. We suggest that the thermal and hydrographic conditions in Core S0204B were primarily influenced by the outer western Pacific water. However, the thermal and hydrographic conditions in Core GHE 27L may be predominantly controlled by the weakened Asian monsoon during the mid-late Holocene, which was induced by the southern migration of Intertropical Convergence Zone (ITCZ) and stronger EI Niño Southern Oscillation. [ABSTRACT FROM AUTHOR]

The calcareous sand from an island of the South China Sea is solidified by curing agent, and the unconfined compressive strength is measured by the unconfined compressive strength test. The microscopic images of calcareous sand are gained by Scanning Electron Microscope (SEM). The image is dealt with by Image-Pro Plus (IPP), and the fractal dimension is computed which includes particle size fractal dimension Dps, particle surface fractal dimension Dpr and aperture fractal dimension Dbs. The connection between unconfined compressive strength and fractal dimension is to be done. The research indicates that the curing agent can improve the compressive strength of the calcareous sand, that is to say, adding the curing agent can effectively improve the properties of soil. The unconfined compressive strength has a linear relation with the fractal dimensions. Compared with the other two fractal dimensions, the function of the particle surface fractal dimension Dpr on the compressive strength is greater. [ABSTRACT FROM AUTHOR]

Geographic information describing coral reefs plays an important role in constructing electronic chart systems and protecting the ecological environment of the ocean. To derive geographic information of coral reefs more effectively, this paper proposes a methodology to detect coral reefs by combining airborne LiDAR bathymetry (ALB) bottom waveform and bathymetric feature data. A feature vector was established by deriving bottom waveform variables (the peak amplitude, pulsewidth, area, skewness, kurtosis, and backscatter cross section) and bathymetric variables (the depth standard deviation, slope, bathymetric position index, Gaussian curvature, mean curvature, and roughness). Using a support vector machine classifier, coral reefs were detected by distinguishing two classes (coral reefs and others) on the seafloor. To evaluate the classification performance of coral reefs, the developed method was applied to Yuanzhi Island, South China Sea surveys, and verified by field data (aerial digital camera images and underwater video images). The results showed that the classification overall accuracy of coral reefs can be greatly improved from 80.59%/90.31% when ALB bottom waveform or bathymetric variables features were used separately to 93.57% when using a combination of ALB bottom waveform and bathymetric features. In addition, the kappa coefficient can also be greatly improved from approximately 0.61/0.80 to 0.87. And the new proposed method performs better compared to the current classification method using ALB data to detect coral reefs with an overall accuracy of 90.92% and Kappa of 0.81. This highlights the potential of ALB data, combining waveform data and bathymetric data, for precisely detecting coral reefs in shallow water areas. [ABSTRACT FROM AUTHOR]

This study investigates the impact of the south Indian Ocean Dipole (SIOD) on the frequency of tropical cyclones (TCs) over the South China Sea (SCS) in summer (May–August) and winter (September–December) for 1975–2012. The frequency of TCs over the SCS shows significant inter‐annual variations in the two seasons and relatively obvious inter‐decadal variability in summer. A prominent relationship occurs between the TC generation over the SCS and the SIOD, and the latter can be regarded as a good predictor of the former on inter‐annual scale. In winter, vertical circulation is obvious due to a strong SIOD induces intensified ascending motions and high sea surface temperature over the northern SCS with sufficient moisture that supplies a favourable environment for TC formation. The impact of SIOD is weaker in summer but a convergent zone with upwards motion also can be found over northeastern SCS. In addition, the SIOD and El Niño–Southern Oscillation are two primary impacting factors in winter and TC numbers increase when La Niña and positive SIOD events occur simultaneously. However, the SIOD is a dominant and independent impacting factor in summer and El Niño events just play a secondary role. (a) Monthly TC frequency over SCS averaged from 1975 to 2012. (b) The standardized time series of SCS TC numbers during 1975–2012 (bars from IBTrACS and blue curves from JMA data set). (c) Same as (b), but for summer (MJJA). (d) Same as (b), but for winter (SOND). "R" means correlation coefficient. [ABSTRACT FROM AUTHOR]

Gas permeability is a key physical parameter to determine the exploitation efficiency of natural gas hydrate (NGH). However, the relevant research mainly focuses on the permeability of homogeneous hydrate reservoirs, there have been no studies of non-homogeneous hydrate reservoirs. Therefore, a novel permeability measurement apparatus was designed in this study, which used two core holders in parallel to achieve the spatio-temporal continuous measurements of gas permeability for non-homogeneous reservoirs. Marine soils obtained from the South China Sea were used to remold the non-homogeneous hydrate reservoirs, including two homogeneous hydrate reservoirs with water saturation of 40% (reservoir A) and 80% (reservoir B), respectively. The constant gas flow of 0.5 ml/s and constant back pressure of 3 MPa was carried out to measure the gas permeability. The experimental results showed that the gas permeability measured in this work had similar regularities with other literature data. When the effective pressure increased from 1 MPa to 6 MPa, the permeability of reservoir A, reservoir B, and non-homogeneous hydrate reservoir decreased from 15.2 mD to 10.9 mD, 10.5 mD to 4.6 mD, and 12.5 mD to 8.5 mD, respectively. In addition, the variation in the non-homogeneous coefficient showed three stages: 1–2 MPa stage, 2–3 MPa stage, and 3–6 MPa stage. What's more, the permeability damage rate of non-homogeneous reservoirs increased by nearly 35% with the increase of effective pressure. These findings obtained by this apparatus will enhance the understanding of gas permeability in the non-homogeneous hydrate reservoirs, and guide further field exploitation of hydrate reservoirs. • Non-homogeneous reservoirs were remolded using two parallel core holders. • Gas permeability of non-homogeneous reservoirs was continuously measured. • Gas permeability of reservoirs under different effective pressure was measured. • Higher water saturation caused the higher permeability damage rate of reservoir. • Non-homogeneous coefficient showed a three-stage-trend with increase of effective pressure. [ABSTRACT FROM AUTHOR]

Dibenzothiophenes (DBTs) and benzo[ b ]naphthothiophenes (BNTs) are important sulfur heterocyclic aromatic compounds in oils and sedimentary rock extracts. Based on both migration fractionation effects and differences in thermal stability of different isomers, DBTs and BNTs can be used to trace oil migration orientations and filling pathways. They are present in significant abundances in oils, including light oils and condensates, in which biomarkers are commonly absent or present only in extremely low concentrations. Molecular biomarker compositions indicate that all oils and condensates in the Eocene clastic reservoir of the Fushan Depression (Beibuwan Basin, South China Sea) belong to a single oil population. In this study, three geochemical indicators relating to DBTs and BNTs, namely; (1), 4-/1-methyldibenzothiophene (4-/1-MDBT); (2), total content of DBTs; and (3), benzo[ b ]naphtha[2,1- d ]thiophene/(benzo[ b ]naphtha[2,1- d ]thiophene+benzo[ b ]naphtho[1,2- d ]thiophene) ([1,2]BNT/([1,2]BNT+[1,2]BNT)) were applied to trace oil migration orientations and filling pathways. The results show that these parameter values gradually decrease from northeast to southwest, towards the Huachang Uplift, and from north to south towards the Bailian Faulted-Belts. Therefore, the source kitchen for identified oil accumulations in the Huachang Uplift is likely to be located in the Bailian Sag, which lies to the northeast of the Huachang Uplift. Zones in the Bailian Sag, situated upstream of the preferred oil filling pathways are likely to be the most favorable prospecting regions. It is concluded that relative parameters of DBTs and BNTs are practical molecular indicators for tracing oil migration orientations and filling pathways. [ABSTRACT FROM AUTHOR]

The effects of low- to high-angle (>30°) normal faults on sedimentary architectural units in the Eocene Wenchang Formation, Enping Sag, Pearl River Mouth Basin (PRMB), South China Sea were investigated utilising a high-quality 3D seismic data set and restored paleogeomorphology. It has been shown that sequence stratigraphic units and sedimentary architecture are significantly controlled by the low- to high-angle normal faults. The Wenchang Formation, a second-order sequence, can be subdivided into two para-second-sequences (the Lower and Upper Wenchang sequences, E2WLand E2WU) and seven third-order sequences (from base to top: SQ1∼SQ7). The low-angle fault confined sequence architecture of the Wenchang Formation is mainly characterised by lateral stacking with the ratio of the vertical subsidence (V) to horizontal slip (H) being reduced from 1/2 for E2WLto 1/6 for E2WU. In contrast, the high-angle fault confined sequence is characterised by vertical stacking with the ratio of V/H close to 1 for sequences SQ1 to SQ7. In the 3D seismic area, the features of sediment-dispersal pattern were interpreted based on an integrated analysis of paleogeomorphology, seismic reflection characteristics, stratal thickness distribution and multiple attribute clustering. The results show that the large-scale fan delta, belt-shape lacustrine deposit and bird-foot braided delta systems mainly developed in the low-angle fault confined sequences, whereas small-scale fan delta, rhombus-shaped lacustrine deposit and lobe-shaped braided delta systems inherited tectono-sedimentary architectures in the high-angle fault confined sequences. [ABSTRACT FROM AUTHOR]

There are numerous studies showing that there is a constant increase in the ocean ambient noise level and the ever-growing demand for developing algorithms for detecting weak signals in ambient noise. In this study, we utilize dynamical and statistical complexity to detect the presence of weak ship noise embedded in ambient noise. The ambient noise and ship noise were recorded in the South China Sea. The multiscale entropy (MSE) method and the complexity-entropy causality plane (C-H plane) were used to quantify the dynamical and statistical complexity of the measured time series, respectively. We generated signals with varying signal-to-noise ratio (SNR) by varying the amplification of a ship signal. The simulation results indicate that the complexity is sensitive to change in the information in the ambient noise and the change in SNR, a finding that enables the detection of weak ship signals in strong background ambient noise. The simulation results also illustrate that complexity is better than the traditional spectrogram method, particularly effective for detecting low SNR signals in ambient noise. In addition, complexity-based MSE and C-H plane methods are simple, robust and do not assume any underlying dynamics in time series. Hence, complexity should be used in practical situations. [ABSTRACT FROM AUTHOR]