South China Sea Water Research Articles

Analysis of a Rainstorm Process in Nanjing Based on Multi-Source Observational Data and Lagrangian Method

Using multi-source observation data including automatic stations, radar, satellite, new detection equipment, and the Fifth Generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA-5) data, along with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) platform, an analysis was conducted on a rainstorm process that occurred in Nanjing on 15 June 2020, with the aim of providing reference for future urban flood control planning and heavy rainfall forecasting and early warning. The results showed that this rainstorm process was generated under the background of an eastward-moving northeast cold vortex and a southward retreat of the Western Pacific Subtropical High. Intense precipitation occurred near the region of large top brightness temperature (TBB) gradient values or the center of low TBB values on the northern side of the convective cloud cluster. During the heavy precipitation period, the differential propagation phase shift rate (KDP), differential reflectivity factor (ZDR), and zero-lag correlation coefficient (ρHV) detected by the S-band dual-polarization radar all increased significantly. The vertical structure of the wind field detected by the wind profile radar provided a good indication of changes in precipitation intensity, showing a strong correspondence between the timing of maximum precipitation and the intrusion of upper-level cold air. The abrupt increase in the integrated liquid water content observed by the microwave radiometer can serve as an important indicator of the onset of stronger precipitation. During the Meiyu season in Nanjing, convective precipitation was mainly composed of small to medium raindrops with diameters less than 3 mm, with falling velocities of raindrops mainly clustering between 2 and 6 m·s−1. The rainstorm process featured four water vapor transport channels: the mid-latitude westerly channel, the Indian Ocean channel, the South China Sea channel, and the Pacific Ocean channel. During heavy rainfall, the Pacific Ocean water vapor channel was the main channel at the middle and lower levels, while the South China Sea water vapor channel was the main channel at the upper level, both accounting for a trajectory proportion of 34.2%.

Organophosphate ester in surface water of the Pearl River and South China Sea, China: Spatial variations and ecological risks

This study focused on investigating the concentrations, compositional profiles, partitioning behaviors and spatial variations of organophosphate esters (OPEs) in the Pearl River (PR), South China Sea (SCS) region, to evaluate their environmental risks. ∑OPEs concentrations in the surface water of the PR ranged from 117.5 to 854.8 ng/L in the dissolved phase and from 0.5 to 13.3 ng/L in the suspended particulate matter. In the surface seawaters of the northern and western parts of the SCS, ∑OPEs concentrations were 1.3–17.6 ng/L (mean: 6.7 ± 5.2) and 2.3–24.4 ng/L (mean: 7.6 ± 5.5), respectively. The percentage of chlorinated OPEs in surface water samples from the PR to the SCS was 79 ± 15%. Tripentyl phosphate (TPeP) (average: 28.3%) and triphenylphosphate (TPhP) (average: 9.6%) exhibited significant particulate fraction. A significant negative correlation (p < 0.05) between salt concentration and OPE congeners in seawater suggested that river runoff predominantly introduced OPEs into the coastal waters of the SCS. The findings also showed higher levels of OPEs in the PR and estuary than in offshore waters. The OPE loading from the PR into the SCS was estimated to be ∼119 t y−1. The presence of TCEP (RQmax = 2.1), TnBP (RQmax = 0.48) and TPhP (RQmax = 0.3) in PR water samples pose a high risk to aquatic organisms, whereas OPEs (RQ < 0.1) in SCS water samples do not pose a threat to aquatic organisms. This research emphasizes the environmental fate and impact of OPEs on surface waters of the PR and SCS.

Characterizing dissolved inorganic and organic nutrients in the oligotrophic Kuroshio Current off eastern Taiwan during warm seasons

This study conducted sensitive and precise analyses of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) concentrations and trace concentrations of nitrate and nitrite (N+N) and soluble reactive phosphorus (SRP) in seawater. The methods were applied to investigate the distributions and controls of N+N, SRP, DON, and DOP in the oligotrophic Kuroshio Current (KC) area off eastern Taiwan during warm seasons. The water in the studied area was classified into four major types: typical Kuroshio water (KW), KW influenced by the East China Sea water, KC influenced by the South China Sea (SCS) water, and KW influenced by the SCS water and river plumes, which is confined to the coastal zone. Nutrient distributions in KC revealed very low N+N (0.002−0.40 μM) and SRP (0.015−0.125 μM) concentrations but high DON (&amp;lt;8 μM) and DOP (&amp;lt;0.3 μM) concentrations above the nutricline depth, which accounted for &amp;gt;80% of TDN and TDP, respectively; theses concentrations can primarily be attributed to strong, permanent surface stratification. Among the water types, KW had the lowest N+N, SRP, DON, and DOP concentrations but greatest chlorophyll maximum depth and nutricline depth, except for in locations influenced by island-induced upwelling. The concentrations of all nutrients increased by various degrees in the other water types, which was attributed to the exchange and mixing of different water masses and coastal uplift of subsurface waters. KW was not only highly oligotrophic but also N+N-limited reflected from very low [N+N]/[SRP] ratio (0.02−0.15) in the mixed layer (ML). Overall, the N+N limitation and high nitrate anomaly value (N*: 2.47 ± 0.16 μM) above the nutricline depth strongly indicate prevailing N2 fixation at the surface of KW. Very high DON/DOP ratio in KW (16.9−69.1) probably resulted from the release of N-rich organic nutrients from phytoplankton including N2 fixers at the surface and faster recycling of DOP than DON in deep waters. Persistent coastal uplift of subsurface water occurs everywhere over the shore-side region of the KC, resulting in increasing surface concentrations of nutrients and chlorophyll a. Overall, the aforementioned physical and biogeochemical processes determined the upper-ocean distributions of nutrient species in warm seasons.

Effects of internal waves on bottom thermal structures and turbulent mixing in the Xisha Islands

Using velocity and high-resolution temperature mooring data from the fore-reef slope of Yongxing Island in the northwest South China Sea (water depth of 69 m), we examine the effects of internal waves on the temporal variations in temperature, bottom mixed layer (BML) and turbulent mixing. The diurnal tide is found to be the dominant tidal force and the baroclinic tide is highly active, which would account for the 11 d abnormal spring-neap cycle in the barotropic tidal current. During the ebb period (tidal elevation decreases), the bottom diurnal baroclinic current transports cold water upslope, resulting in a decrease in temperature, and vice versa during the flood period. The BML thickness Hbml widely varies around 1.5m, approximately 2% of the water depth. The bottom turbulent mixing is not so active, indicated by the bulk dissipation Eɛ of 10 mWm−2 and turbulent diffusivity κz of 2×10−4m2s−1. Both Hbml and Eɛ approximate a log-normal distribution, demonstrating strong intermittency. The high-frequency (ω) internal bores can increase Hbml by four times and enhance the turbulent mixing by one order, which should be responsible for the slow cascade of Hbml(∼ω−1.5) and Eɛ(∼ω−1.0). In the downslope phase, Hbml is about 30% thicker, and turbulent mixing is enhanced by 3 times stronger than those in the upslope phase. It is revealed that under the forcing of internal waves, turbulent mixing corresponds to a thick BML with Hbml∼〈κz〉0.25, and stratification (N) has a significantly negative correlation with the development of BML, Hbml∼〈N〉−1.8.

Thermal fronts in coastal waters regulate phytoplankton blooms via acting as barriers: A case study from western Guangdong, China

Oceanic fronts play an important role in regulating the distributions of phytoplankton and are subject to climate change. However, the relationship between climate change, oceanic fronts, and coastal phytoplankton blooms requires clarification. Using long-term satellite data, the seasonal, interannual, and decadal variations of the thermal fronts were examined, along with their effects on the distribution of phytoplankton in western Guangdong. Thermal fronts between the cold western Guangdong coastal current waters and the warm South China Sea (SCS) waters were found along the coast of western Guangdong during winter due to northeast winter monsoon. At decadal timescales, an increase (decrease) in frontal activities occurred during the negative (positive) Pacific Decadal Oscillation (PDO) phase. This pattern suggests that the positive (negative) PDO activity decreases (increases) sea level anomaly (SLA) and sea surface temperature in the SCS, thereby weakens (enhances) frontal activities along the coast. Accordingly, extensions and positive anomalies (> 1.5 mg/m3) in chlorophyll-a (Chl a) were observed during the positive PDO phase, whereas Chl a was concentrated in the nearshore areas during the negative PDO phase. These processes are primarily related to the barrier effects of enhanced thermal fronts and positive SLA on offshore materials transport during the negative PDO period. This study highlights the need to incorporate PDO activity into phytoplankton production in coastal oceans.

Characterization of Mixing at the Edge of a Kuroshio Intrusion into the South China Sea: Analysis of Thermal Variance Diffusivity Measurements

Abstract The Kuroshio occasionally carries warm and salty North Pacific Water into fresher waters of the South China Sea, forming a front with a complex temperature–salinity (T–S) structure to the west of the Luzon Strait. In this study, we examine the T–S interleavings formed by alternating layers of North Pacific Water with South China Sea Water in a front formed during the winter monsoon season of 2014. Using observations from a glider array following a free-floating wave-powered vertical profiling float to calculate the fine-scale parameters Turner angle, Tu, and Richardson number, Ri, we identified areas favorable to double-diffusion convection and shear instability observed in a T–S interleaving. We evaluated the contribution of double-diffusion convection and shear instabilities to the thermal variance diffusivity, χ, using microstructure data and compared it with previous parameterization schemes based on fine-scale properties. We discover that turbulent mixing is not accurately parameterized when both Tu and Ri are within critical ranges (Tu &gt; 60; Ri &lt; ¼). In particular, χ associated with salt finger processes was an order of magnitude higher (6.7 × 10−7 K2 s−1) than in regions where only velocity shear was likely to drive mixing (8.7 × 10−8 K2 s−1).

New insights into the South China Sea throughflow and water budget seasonal cycle: evaluation and analysis of a high-resolution configuration of the ocean model SYMPHONIE version 2.4

Abstract. The South China Sea throughflow (SCSTF) connects the South China Sea (SCS) with neighboring seas and oceans, transferring surface water of the global thermohaline circulation between the Pacific and Indian oceans. A configuration of the SYMPHONIE ocean model at high resolution (4 km) and including an explicit representation of tides is implemented over this region, and a simulation is analyzed over 2010–2018. Comparisons with in situ and satellite data and other available simulations at coarser resolution show the good performance of the model and the relevance of the high resolution for reproducing the spatial and temporal variability of the characteristics of surface dynamics and water masses over the SCS. The added value of an online computation of each term of the water, heat, and salt SCS budgets (surface, lateral oceanic and river fluxes, and internal variations) is also quantitatively demonstrated: important discards are obtained with offline computation, with relative biases of ∼40 % for lateral oceanic inflows and outflows. The SCS water volume budget, including the SCSTF, is analyzed at climatological and seasonal scales. The SCS receives on average a 4.5 Sv yearly water volume input, mainly from the Luzon Strait. It laterally releases this water to neighboring seas, mainly to the Sulu Sea through Mindoro Strait (49 %), to the East China Sea via Taiwan Strait (28 %), and to the Java Sea through Karimata Strait (22 %). The seasonal variability of this water volume budget is driven by lateral interocean exchanges. Surface interocean exchanges, especially at Luzon Strait, are all driven by monsoon winds that favor winter southwestward flows and summer northeastward surface flows. Exchanges through Luzon Strait deep layers show a stable sandwiched structure with vertically alternating inflows and outflows. Last, differences in flux estimates induced by the use of a high-resolution model vs. a low-resolution model are quantified.

Recovery of 1887 metagenome-assembled genomes from the South China Sea

The South China Sea (SCS) is a marginal sea characterized by strong land-sea biogeochemical interactions. SCS has a distinctive landscape with a multitude of seamounts in its basin. Seamounts create “seamount effects” that influence the diversity and distribution of planktonic microorganisms in the surrounding oligotrophic waters. Although the vertical distribution and community structure of marine microorganisms have been explored in certain regions of the global ocean, there is a lack of comprehensive microbial genomic surveys for uncultured microorganisms in SCS, particularly in the seamount regions. Here, we employed a metagenomic approach to study the uncultured microbial communities sampled from the Xianbei seamount region to the North Coast waters of SCS. A total of 1887 non-redundant prokaryotic metagenome-assembled genomes (MAGs) were reconstructed, of which, 153 MAGs were classified as high-quality MAGs based on the MIMAG standards. The community structure and genomic information provided by this dataset could be used to analyze microbial distribution and metabolism in the SCS.

The Use of Technology as the Indonesia's Strategy to Counter China's Gray Zone Operations in the North Natuna Sea

Ever since the end of World War II, the Republic of China (ROC), led by the Kuomintang Party and continued by the People’s Republic of China (PRC) led by the Communist Party, with its Eleven Dash Line (EDL), has claimed almost 90% of the South China Sea (SCS) waters, including the Spratly Islands, Paracel Islands, and all sea structures in that area. In 1953, the EDL was renamed to the Nine Dash Line (NDL) because China gave the area of the Tonkin Gulf to North Vietnam, led by Ho Chi Minh, which was still at war against the French and South Vietnam. China’s NDL claim has overlapped with Brunei’s claim, specifically Louisa Reef located on its continental shelf, Malaysia’s claim covering a portion of SCS in northern Kalimantan (Borneo), which includes at least 12 maritime structures in the Spratly Islands, among others, the coral reefs Swallow, Adraiser, and Marivelles. Additionally, the Philippines' claim includes the northernmost part of the Spratly Islands and Scarborough Shoal, known as Kalayaan in the Philippines. Vietnam's claim encompasses the Paracel and Spratly Islands, including 25 rock and sand formations and islands such as Spratly Island, Namyit Island, and Barque Canada Reef. The overlapping claims, which also occurred between Brunei and Vietnam, Malaysia and the Philippines, and Malaysia and Vietnam, have increased tension and incidents in the SCS, particularly between the Philippines, Malaysia, Vietnam against China due to China’s actions forcefully imposing its claim. This has made the situation more complex and fragile, leading the international community to term the overlapping claims as the South China Sea (SCS) Dispute. has no claim in the SCS, and no other country has a claim over Indonesia. However, in 2009, when China registered its new map of NDL claim with the United Nations (UN), it included part of Indonesia’s Exclusive Economic Zone (EEZ) in the North Natuna Sea (NNS). The UN rejected this claim since it was not based on international law, particularly the United Nations Convention on the Law of the Sea (UNCLOS 1982). Indonesia firmly denied that claim as it goes against Indonesia’s law and UNCLOS 1982. Due to increasing Chinese actions in imposing its claim on part of the IEEZ in the NNS, including Gray Zone Operations (GZO) maneuvers, Indonesia has risen to defend its sovereign rights in the NNS. According to UNCLOS 1982, in the IEEZ at the NNS, as a coastal state, Indonesia "has sovereign rights for the purpose of exploring and exploiting, conserving and managing the natural resources, whether living or non-living resources, of the waters superjacent to the sea-bed and off the sea bed and its subsoil, and with regard to other activities for the economic exploitation and exploration of the zone such as the production of energy from water, currents, and winds" (Article 56; 1 a). To overcome any disturbance and threat toward Indonesia’s sovereign rights in its EEZ in the NNS, Indonesia needs to convince China to nullify its IEEZ NNS’ claim. Indonesia needs to launch total diplomacy toward China, including cultural diplomacy, economic diplomacy, and defense diplomacy combined with and supported by defense capability. In this regard, Indonesia should increase its defense capability, particularly in the NNS, to guard the works, personnel, and equipment of the activities of natural resources exploration and exploitation. The enlargement of defense capability, including the quality and quantity of equipment and weaponry such as patrol boats, troopships, warships, hunter jets, fighter jets, radar systems, and Geographic Information Systems (GIS), should be done by optimizing the use of advanced technology. Determining the performance strategy, as well as the use of technology and interoperability systems in developing the defense equipment platform, information and communications technology such as Big Data and Data Links, can be a solution to increase and integrate the defense system, capability, and operational implementation. In this case, particularly by the Indonesia Navy and Air Force, by integrating various defense equipment owned and used. This study provides a comprehensive analysis of Indonesia’s strategy to counter China’s Gray Zone Operations in the North Natuna Sea.

Sea Surface pCO2 Response to Typhoon “Wind Pump” and Kuroshio Intrusion in the Northeastern South China Sea

The Luzon Strait (LS) is a key region for estimating carbon sources and sinks in the South China Sea (SCS) and is highly influenced by the Kuroshio Current (KC) and typhoons. Understanding the variations in the sea surface partial pressure of carbon dioxide (pCO2-sw) under the combined effects of typhoons and KC in this region is crucial for estimating local and regional changes in ocean carbon flux. Based on valuable in situ pCO2-sw and remote sensing data, this study aimed to reveal the temporal variations and the physical mechanisms of pCO2-sw variations under the comprehensive effects of both typhoons and Kuroshio Intrusion (KI) in the LS. One week after the passage of the tropical cyclone (TC) Nanmadol, the concentration in the pCO2-sw and the influencing mechanisms varied in three different regions (W1–W3) on Transect A (120°E). In the region dominated by SCS waters (W1), the average pCO2-sw increased by 5.1 μatm after TC, which was mainly due to the TC “Wind Pump” inducing strong vertical mixing, which brought dissolved inorganic carbon (DIC)-rich deeper water up to the surface. In the region affected by KC (W2 and W3), pCO2-sw decreased after the TC (−8.2 μatm and −1.8 μatm, respectively) with TC-enhanced KI because the invasion of lower pCO2-sw of Kuroshio waters inhibited the TC-induced upwelling. More significant TC-induced upwelling (W3) would alleviate the decrease in pCO2-sw caused by the TC-enhanced KI. This study is a rare case providing a better understanding of the variations in pCO2-sw under TC-enhanced KI, which provides support for regional climate change prediction and carbon flux estimation in the western boundary current regions.

Seasonal distribution of water masses and their impacts on nutrient supply in the southern Beibu Gulf

Dual water isotopes were investigated to reveal the seasonal distribution of water masses and their impacts on nutrient supply in southern Beibu Gulf. In summer and winter, the South China Sea (SCS) water (61–69%) contributed the most to the seawater in the southern Beibu Gulf, followed by the diluted water (24–34%), and the west-Guangdong coastal current (WGCC) (5–7%) had the minimum contribution. However, the major nutrient source shifted from the diluted water in summer (39–73%) to the SCS water (57–90%) in winter. The WGCC's impact on nutrient loads was relatively small (2–10% in summer, 4–34% in winter). Our results highlight the control of nutrient supply was the SCS water (winter) and diluted water (summer), with limited influence from the WGCC, providing new insights into the impact of water mass transportation and its nutrient supply in the Beibu Gulf.

Iron, Nickel, Copper, Zinc, and their stable isotopes along a salinity gradient in the Pearl River Estuary, southeastern China

Although the crucial role that dissolved trace metals (dTMs) play in both carbon cycling and climate have been revealed over the past three decades, much about the oceanic budgets of dTMs remains unknown. Rivers are one of the most important dTM sources to the ocean, and estuaries are a key interface between land and ocean. However, our understanding of how dTMs behave as they pass through the estuarine transition is limited, leading to uncertainties in estimating fluvial metal fluxes to the ocean and balancing oceanic dTM budgets. Alongside concentrations, metal stable isotopes offer an additional dimension to constrain estuarine processes, but data on metal isotopes in estuaries are scarce. Here we present dTM concentrations and their stable isotope ratios along a full salinity gradient in the Pearl River Estuary (PRE), southeastern China. Concentration data show a large apparent loss of dFe (86%) during estuarine mixing, moderate losses of dNi (13%) and dZn (36%), and nearly conservative behavior for dCu. However, examination of metal isotope data (δ56Fe, δ60Ni, δ65Cu, and δ66Zn) reveals more complex biogeochemistry, requiring either a two-stage scenario or a three-endmember mixing process. The two-stage process involves fractionation of dTM isotopes at low salinities, likely driven by particle adsorption and colloidal flocculation, followed by conservative mixing between intermediate-salinity estuarine waters and South China Sea waters. Alternatively, the three-endmember mixing process includes influences from riverine, oceanic endmembers, and external sources such as benthic flux and industrial activities, shaping dTM isotope distributions. Specifically, capturing δ56Fe fully proves challenging, yet it appears strongly influenced by inputs of benthic Fe within the PRE, characterized by dFe > 13 nmol kg−1 and δ56Fe < −0.80‰. δ60Ni and δ66Zn can be described by either two-stage or there-endmember mixing processes. In the former, the Rayleigh fractionation with αd-p of 1.00004 for δ60Ni and 1.0001 for δ66Zn, or the steady state fractionation with αd-p of 1.00005 for δ60Ni and 1.0002 for δ66Zn, could be derived to explain their patterns at low salinity, likely driven by colloidal flocculation. Additionally, a third source with dNi > 33 nmol kg−1 and δ60Ni > +1.26‰ and a third source with dZn > 13 nmol kg−1 and δ66Zn > +0.96‰, both influenced by human activities, could also shape the δ60Ni and δ66Zn patterns in the PRE, respectively. The description of δ65Cu is best achieved by a three-endmember mixing process, with the external source having dCu > 20 nmol kg−1 andδ65Cu < +1.3‰, indicative of processes like organic matter remineralization or discharge from wastewater treatment plant. Our study highlights the need for more extensive and detailed studies on estuarine settings to elucidate their potentially crucial role in global dTMs budgets.

Isolation and Identification of Culturable Bacteria from South China Seawater and Preliminary Screening of Marine Biocontrol Bacteria.

Marine microorganisms have evolved special metabolic pathways to produce numerous bioactive substances with novel structures and unique functions. This study analyzed the diversity of culturable bacteria in marine water samples from the South China Sea and screened the isolated bacteria with pathogenic fungi. A total of 200 culturable strains of 72 different bacteria were obtained from 56 water samples from the South China Sea. They belonged to three phyla and four classes, namely Gammaproteobacteria, Alphaproteobacteria, Bacilli and Actinomycetia. Bacilli was the dominant class, comprising up to 59.72%, followed by Gammaproteobacteria (20.83%). Bacillus, Pseudomonas, Paenibacillus and Rhizobium were the most dominant genera. Among these strains, HY-88 and HY-91 encoding BamC, FenB and PKSI genes were selected and identified as Bacillus subtilis. The respective inhibition rates of the HY-88 caused by plate confrontation against Magnaporthe grisea, Fusarium oxysporum, Botrytis cinerea, anthrax and Botrytis cinerea were 90.91%, 54.29%, 52.17% and 51.72%, in comparison with HY-91 86.36%, 48.57%, 47.83% and 34.48%. In addition, the supernatant of HY-88 showed a lesion inhibition rate of 74.5%, which was significantly higher than HY-91 (60.55%). In addition, HY-88 and HY-91 showed strong antifungal activity to Colletotrichum viniferum on detached Shine Muscat grapes. Tolerance tests showed that the HY-88 and HY-91 grew at 10-40 °C, 7-10% NaCl and pH 3-11. HY-88 and HY-91 could inhibit various fungal plant diseases, which lays a foundation for the development of new biopesticides.

Behaviors of redox-sensitive tungsten and molybdenum in the northern South China Sea: From the Pearl River to the continental slope

To increase the proxy toolbox for the reconstruction of redox conditions, the transition metal tungsten (W) has been increasingly suggested as a promising new candidate during the last few years. However, compared to other trace metals such as molybdenum (Mo), studies on the redox behavior of W in the brackish/marine environment are relatively rare and mainly limited to euxinic settings. To contribute to our understanding of the behavior of W in modern aquatic ecosystems, we here present a water column W and Mo dataset that follows the salinity gradient of the Pearl River Estuary towards the adjacent coastal and offshore waters of the northern South China Sea (water depths range from 36 m to 3735 m) with the latter also including mostly anoxic porewater and rather oxic sediment surface data. Except for deviations of W in the low-salinity reaches of the Pearl River Estuary, both metals are conservatively introduced to the coastal ocean. The contribution of dissolved W via the Pearl River plume was identified in surface waters along the coastline. In line with previous open ocean studies, the conservative behavior of W proceeds towards the remote parts of the study area with surface waters that are possibly also affected by the South China Sea Warm Current. Within the short core porewater profiles, W concentrations increased with sediment depth and reached the highest levels at the more distal sites. These trends are not linked to the formation of more soluble thiotungstate species as indicated by generally non-sulfidic porewaters. Along with porewater gradients of W, the W concentrations in near-bottom waters suggest effective trapping of W at the sediment/water interface by Mn oxides especially at greater water depths and limited contribution to the open water column W inventory. In contrast to W, Mo concentrations show little variation in the reducing porewaters and remain close to or slightly above the ocean level. Enrichments of W and Mo in the surface sediments from the upper and lower continental slope reflect the known affinity of both trace metals to Mn oxides. Positive correlations of W with the heavy mineral-associated metals titanium (Ti) and zirconium (Zr) in sand-rich deposits of the outer continental shelf subjected to stronger near-bottom currents, further indicate a relation of sedimentary W abundances to the depositional environment.

Freshwater Contributions to Decadal Variability of the Indonesian Throughflow

AbstractThe Makassar Strait, the main passageway of the Indonesian Throughflow (ITF), is an important component of Indo‐Pacific climate through its inter‐basin redistribution of heat and freshwater. Observational studies suggest that wind‐driven freshwater advection from the marginal seas into the Makassar Strait modulates the strait's surface transport. However, direct observations are too short (&lt;15 years) to resolve variability on decadal timescales. Here we use a series of global ocean simulations to assess the advected freshwater contributions to ITF transport across a range of timescales. The simulated seasonal and interannual freshwater dynamics are consistent with previous studies. On decadal timescales, we find that wind‐driven advection of South China Sea (SCS) waters into the Makassar Strait modulates upper‐ocean ITF transport. Atmospheric circulation changes associated with Pacific decadal variability appear to drive this mechanism via Pacific lower‐latitude western boundary current interactions that affect the SCS circulation.

HOW CHINA USE CYBER NETWORKS WITH DRONES TO MONITOR THE SPRATLY ISLANDS IN THE SOUTH CHINA SEA

The South China Sea disputes are mainly related to delimitations concerning islands and reefs in the South China Sea and adjoining waters. The claimant states are China, Vietnam, the Philippines, Malaysia, and Brunei. Claimants’ states are keen on holding or gaining the freedom to fish stocks, the investigation and expected abuse of unrefined petroleum and flammable gas in the seabed of different areas of the South China Sea, and the essential control of significant delivery paths. The Spratly Islands issue can be assessed from an assortment of points. Regarding public safety, these islands are significant because of their locations in the South China Sea, where numerous merchant ships carry merchandise, individuals, and energy to Asian-Pacific nations. Drones, as sophisticated tools connected and controlled by cyber technology, are used to observe the conditions of the islands from long distances. The methodology used in this article is the qualitative method. The data was collected from a variety of articles that related to this topic. This article analyses how effectively China uses drones with cyber power to monitor the Spratly Islands. This article focuses more on the operational, tactical, and strategic advantages of drone monitoring of Spratly Island in the South China Sea.

Application of different internal solitary wave theories for SAR remote sensing inversion in the northern South China Sea

This study discusses the theoretical method of the inversion of internal solitary waves (ISWs) characteristic parameters using synthetic aperture radar (SAR) images and ocean reanalysis data. Based on the horizontal distribution characteristics of the pixel intensity of the internal wave fringe in the image, an imaging theoretical model based on the extended Korteweg-de Vries (eKdV) and Benjamin-Ono (BO) theories in SAR was constructed, and the peak-to-peak method and curve-fitting method for calculating the characteristic wavelength of internal solitary waves were determined. The results show that the eKdV theoretical model has the advantage of inverting solitary waves with large amplitudes under the same marine stratified structure, and it provides a more reasonable characteristic parameter estimation than the traditional Korteweg-de Vries (KdV) theory. Although the BO theory is theoretically applicable to deep-water internal waves whose wavelength is far less than the water depth, it can still provide good inversion results in practical applications. Compared to the peak-to-peak method, the curve fitting method fully considers the pixel intensity variation characteristics of the internal wave fringe profile of the image, and the calculated characteristic parameters are more reasonable. Using the maximum buoyancy frequency and internal wave vertical mode to construct the marine stratification model of the deep waters of the northeastern South China Sea may have great uncertainty, and it is better to calculate the interface depth using the relative error of the coefficients of two-layer and continuous internal wave equations. In addition, this study also proposes an internal wave inversion method using continuous SAR images, which provides more reference and support for the selection of internal wave inversion models and reliability test of inversion results in a single SAR image.

Tide drives nutrients variation and exchange flux in the semi-enclosed Shuidong Bay coastal water in winter, South China Sea

Nutrients play a key role in coastal ecosystems. Coastal tide is an important driver of the daily nutrient variability in semi-enclosed bay under the intensive human activities and climate change. However, the extent of tidal effects on the nutrients variation and exchange flux in the semi-enclosed bay in winter is still scarcely. In this study, seawater samples were collected by synchronous continuous observation during winter in 2021, to investigate tide drives nutrients variation and exchange flux between Shuidong Bay (SDB) and South China Sea (SCS). The results showed most nutrients were significantly impacted by the tidal variation in the SDB with the semi-diurnal cycle. Coastal flood water can increase seawater exchange capacity due to strong dilution influenced by the outer SCS water, resulting mitigate adverse effects of nutrient enrichment in the semi-enclosed bay. In addition, the concentrations of total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and silicate (DSi) were 146.75 μmol/L, 1.06 μmol/L, and 6.15 μmol/L. Besides, there was a relative excess of nitrogen, phosphorus and silicate were limiting factors in the SDB, and nutrients significantly impacted the Chlorophyll-a in coastal water. Moreover, both TDP and DSi were transported from the SDB to the SCS with a net exchange flux of 0.23 t and 1.99 t, while TDN was transported from the SCS to the SDB with a net exchange flux of 0.14 t, resulting in nutrients ratio increase in the SDB coastal water. Statistical analysis identified the tide induced hydrological variations and terrestrial inputs dominated nutrient dynamics in the SDB coastal water. This study provided a new understanding of the variation and transport of nutrients driven by tide in the SDB, which is implications for understanding the biogeochemistry of nutrients in daily scale and water quality management in the semi-enclosed bay in future.

Sea Clutter Measurement Test and Amplitude Characteristics Analysis in the South China Sea Nearshore Area

To address the problem of sea clutter amplitude distribution characteristics varying with bandwidth, this paper obtains the raw data of clutter under different polarization methods of HH and VV in X and Ka bands based on the sea clutter measurement experiment carried out in June 2022 in the near-shore waters of South China Sea. For the data in X-band HH polarization mode, the goodness-of-fit test was conducted based on the classical models of Rayleigh, Weibull, log-normal and K distribution for the amplitude distribution characteristics of the sea clutter, and the variation of the estimated parameters of the distribution model with the bandwidth was analyzed. The test data show that: 1, with the increase of bandwidth sea clutter amplitude decreases; 2, with the increase of bandwidth Weibull distribution model parameters are decreasing trend, k distribution parameters are increasing trend; 3, the test conditions, the offshore sea clutter amplitude distribution is the optimal K distribution. The conclusions of this paper can provide a comparison and reference for the subsequent study on the characteristics of sea clutter distribution.

Analysis of the Distribution and Seasonal Variability of the South China Sea Water Masses Based on the K-means Cluster Method

Influenced by local mixing and coastal runoff, water masses in the South China Sea degenerate significantly. The K-means algorithm is used to classify the water masses based on WOD13 temperature and salinity observations from 1966 to 2013 because its principle is consistent with the definition of a shallow water mass. The numbers and initial centers of the water masses are determined using functions of in-cluster distance and density values. The result shows that there are ten water masses in the South China Sea. In combination with the T-S scatter diagram, the properties of the South China Sea water masses were analyzed, including their distribution, the seasonal variability, and the degeneration processes. The temperatures of water masses were higher in summer and lower in winter, with the amplitudes of variation gradually reduced from the surface to the bottom. The seasonal variation in salinity of the surface water masses was high in winter and low in summer, which mainly depends on the amount of river discharge and precipitation. The subsurface water masses were strongly affected by water from the Pacific Ocean; thus, the seasonal variability of these water masses is weak, especially for the intermediate water mass that characterized by prominent low salinity. The water mass formed by the Kuroshio water invading the South China Sea has insignificant seasonal variations in temperature and salinity. The properties and seasonal variabilities of the water masses derived from the K-means algorithm are in agreement with the existing conclusions, suggesting that the improved K-means algorithm is efficient and accurate in the shallow water mass division.