The El Niño-Southern Oscillation (ENSO) includes both low-frequency ocean-atmosphere coupling and high-frequency processes, yet the nonlinearity in ENSO dynamics prevents any quantitative estimation of the contributions of the two to ENSO development. The online low-frequency filtering technique was proposed in a recent work to exclude the high-frequency part of wind stress during ocean-atmosphere coupling in model, thus can be used to scale the impact of low-frequency ocean-atmosphere interaction on the ENSO dynamics. By comparing model simulations with and without the online low-pass filtering module, we found that removing the high-frequency wind forcing prolongs ENSO period and decreases El Niño diversity. The results confirm that the high-frequency momentum processes play a crucial role in the genesis of El Niño diversity.

Based on the data of the comprehensive scientific cruise survey in eastern Indian Ocean from 2010 to 2019, Argo (array for real-time geostrophic oceanography) and SODA (simple ocean data assimilation), the interannual variability of subsurface high salinity water (SHSW) in eastern equatorial Indian Ocean was studied and its formation mechanisms was explored. The observation results limited to spring show that the high salinity water from Arabian Sea is distributed in 70~130m in eastern Indian Ocean equatorial section and exhibits significant interannual variations. And the result based on monthly SODA reveals that the trend of anomalous salinity of SHSW varies significantly in different periods, with a relatively stable trend from 2010 to 2015 and an obvious increasing trend from 2016 to 2019. Wind field and subsurface zonal current are dominant factors that control the interannual variability of the high salinity water by regression analysis of SHSW. Further analysis indicates that the anomalous easterly wind in equatorial Indian Ocean leads to the westward accumulation of water masses, then generates an eastward pressure gradient force, which in turn stimulates the anomalous subsurface eastward flow, and causes the increases of anomalous salinity of SHSW eventually. The dynamical connection is particularly remarkable in Indian Ocean Dipole, which further indicates that the interannual variability of SHSW is modulated by Indian Ocean Dipole.

Based on the horizontal velocity data observed by ship-board ADCP in the Gulf Stream for 14 years (2005-2018), we use the methods of Helmholtz decomposition and wavenumber spectrum analysis to decompose the balanced geostrophic motions and unbalanced wave motions of ocean, and analyze the transition scale between them. We also discuss the main factors that affect the transition scale of the Gulf Stream. The results show that the balanced geostrophic motions in the strong current region of the Gulf stream is more active, its transition scale is less than 10 km with small seasonal difference. The unbalanced motions in the weak current region are significantly stronger than that in the strong current region, and its transition scale is about 15 km, which is significantly larger in summer (~28 km) than in winter (~13 km). The transition scale of the Gulf Stream is affected by the near-inertial wave energy input by frequent hurricanes in summer and autumn. Further, the results of transition scale dependence on depth show that the transition scale is negatively correlated with the kinetic energy level of the balanced geostrophic motions at submesoscale. When the kinetic energy of balanced geostrophic is active, the transition scale decreases accordingly. The smaller transition scale corresponds to the smaller kinetic energy level of unbalanced wave motions and the larger of balanced geostrophic motions. The effective separation of balanced geostrophic motions and unbalanced wave motions in this study is helpful to understand the dynamic processes and the energy transformation at different scales.

Storm surge disasters occur frequently along the Pearl River Estuary and are significantly affected by typhoon. This study analyzed the extreme surge at the Chiwan Station in the Pearl River Estuary during the past 30 years (1990-2019). The results show that the average annual storm surge in this region has not changed significantly recent years, but the extreme storm surge (99.9 quantile) has increased greatly (1.62 cm·a^-1), which means that the extreme storm surge disasters have continued to increase. In the past 30 years, the annual maximum storm surge in 20 years occurred during typhoons (accounting for 66.7%). In 2018, the maximum storm surge caused by super typhoon “mangkhut” reached 254 cm, which was the largest storm surge disaster in the past 30 years. The maximum response distance of storm surge to typhoon is about 500~800 km. Within the influence range of typhoon, the storm surge has an approximate linear relationship with typhoon intensity, and an exponential relationship with the distance from typhoon center. Different indexes of typhoon intensity (minimum pressure, maximum wind speed and maximum wind speed radius of typhoon center) were used to fit the storm surge with the distance from the observation station to the typhoon center, and it was found that the combination of wind speed and distance had the best description effect on storm surge (S_w=3.23e^-0.0036D×Γ_w-3.90)+4.48, R²=0.78, RMSE=9.69 cm). These results can improve the understanding of local storm surge disaster, provide validation data for typhoon storm surge simulation and reference for storm surge disaster risk assessment and response decision.

Marine primary production is an important part of the ocean carbon cycle, affecting biogeochemical cycles and global climate change. Phytoplankton, as the main contributor to marine primary production, can be classified as micro- (>20μm), nano- (2~20μm), and pico- (<2μm) phytoplankton depending on particle size. Different phytoplankton size classes contribute differently to primary production (PP_size) and thus play different roles in the oceanic circulation of matter or energy and ocean carbon cycle. Based on the bio-optical dataset collected at 12 stations in the western South China Sea in 2019, this study presented the spatial variability of size-fractionated primary production and chlorophyll a concentration of phytoplankton and their percentage contribution. The size-fractionated primary productivity of phytoplankton was well estimated from the product of size-fractionated phytoplankton absorption coefficient at 670nm [a_ph-size(670)] and photosynthetically active radiation (PAR) [a_ph-size(670)×PAR]. The coefficients of determination R² between log[a_ph-size(670)×PAR] and log(PP_size) were 0.64, 0.76, and 0.67 for the micro-, nano-, and pico-phytoplankton dataset, respectively. The cross-validation of the algorithm based on the size-fractionated phytoplankton absorption coefficient and PAR has shown a good generalization performance. This algorithm could better predict the size-fractionated primary productivity compared to the size-fractionated phytoplankton absorption coefficient as the only input. This result indicates that PAR is one of the important factors to estimate the size-fractionated primary productivity. Meanwhile, the performance of the chlorophyll a concentration-based algorithm for estimating primary productivity at each size was closer to that of the algorithm constructed in this paper for both micro- and pico- phytoplankton dataset, but significantly lower for the nano-phytoplankton, probably due to the weak correlation between the absorption coefficients and chlorophyll a concentration of nano-phytoplankton.

The quantity and the bacterial communities in the digestive tract, gill, and foot of Haliotis discus hannai after infection with Vibrio harveyi were studied using Illumina sequencing technology. Results showed that nine phyla of bacteria were detected in the digestive tract, gills, and foot muscles of H.discus hannai, with Proteobacteria being the dominant phylum, accounting for 30.1%~64.4%, 37.45%~70.6%, and 71.1%~85.9% of the tissues. Bacteroidetes (5.53%~46.09%), Fusobacteria (4.43%~36.80%) and Tenericutes (0.60%~28.77%) were the sub-dominant phyla, while five other phyla including Actinobacteria and some unknown taxa were also detected. At the genus level, the dominant genera in the digestive tract of H.discus hannai were Mycoplasma (15.85%~34.55%) and in the gill was Pseudomonas (54.81%). The dominant genera in the foot muscles were Pseudomonas (44.83%~69.76%) and Curvibacter (21.24%). There were also genera such as Pelomonas. After the introduction of the pathogenic V. harveyi, the quantity of vibrios in the digestive tract increased from 7.2×10⁵cfu·mL^-1 to 10.9×10⁵cfu·mL^-1 as the stress time increased; the quantity of vibrio in the blood increased from 2×10³cfu·mL^-1 to 4.7×10³cfu·mL^-1; the quantity of vibrios in the foot muscle decreased after 48 h of V. harveyi stress and increased in the foot muscle at all other time. The Ace and Chao indices of the abalone digestive tract, gills, and foot muscles were lower than those of the control group at all time, except for the Ace and Chao indices of the abalone digestive tract after 24 h of V. harveyi stress and the Ace index of the digestive tract after 96 h of stress. The Shannon index was higher than the control in the digestive tract and foot at 24 h and in gill at 96h after V. harveyi infection and lower than the control at the remaining time. The introduction of V. harveyi increased the abundance of the Bacteroidetes as well as Fusobacteria in the digestive tract; the abundance of Proteobacteria in the gill decreased while that of Fusobacteria increased; the abundance of Proteobacteria in the foot muscles increased and that of Bacteroidetes decreased. At the genus level, the abundance of Pseudomonas, Bacteroides, and Propionibacterium increased and the abundance of Mycoplasma decreased in the digestive tract, except for a few time; the abundance of Bacteroides, Kordia, and Propionibacterium increased in gill; and the abundance of Pseudomonas increased in foot muscles. This study investigated the effect of the common pathogen V. harveyi on the quantity and the bacterial communities of the host flora from a microecological perspective and provided a new idea for further research on the response mechanism of the host to the pathogen V. harveyi and the prevention and control of vibriosis.

Keywords Vibrio harveyi; Haliotis discus hannai; bacterial diversity

A total of 88 threatened fish species were selected for the study, and their spatial distribution was predicted using publicly available data and the MaxEnt model. The conservation gap analysis was performed based on the predicted distribution, and recommendations for the conservation of the East China Sea and adjacent sea areas were proposed. The results showed that the hotspot areas of threatened fish covered 1.58×10¹¹m², mainly located in the southern coastal area of the Yangtze estuary and the Taiwan Strait. Among them, the top 10%of the hotspot areas was about 5.68×10¹⁰m², mainly located in the coastal waters of Fujian and Guangdong provinces, and sea areas adjacent to Taiwan Island and Penghu Islands. Further investigation of the distribution patterns revealed that there were six different zones in the current distribution of threatened fish in the East China Sea. The existing marine protected areas are mainly concentrated in zones I and Ⅳ, while no protected area has been established in zones Ⅱ and Ⅲ, indicating that habitats of most threatened fish have not been effectively protected. These results provide a scientific basis for improving and optimizing the fish biodiversity conservation strategies in the East China Sea and adjacent sea areas.

Calcified macroalgae, an important calcifying group widely distributed in reef ecosystems, plays vital roles in the primary productivity and reef frameworks construction. Furthermore, several species of calcified algae can induce the coral larval settlement, which is closely related to the sustained development of coral reef ecosystem. However, it is not clear how calcified algae will response to ocean acidification and warming. In this study, healthy and bleached Porolithon cf. onkodes were exposed to different pCO₂ (400 µatm, 1200 µatm, 1800 µatm) and temperatures (27 ℃, 30 ℃, 32 ℃) for one month, respectively. The results showed that the growth rate and net calcification rate of living P. onkodes were not significantly affected when the temperature increased from 27 ℃ to 30 ℃, however, these physiological parameters declined significantly at 32 ℃. The net calcification rate decreased from 206.99 nmol·cm^-2·h⁻¹ (400 µatm pCO₂ + 27 ℃) to -42.22 nmol·cm^-2·h⁻¹ (1200 µatm pCO₂ + 32 ℃). Similarly, the enhancement of pCO₂ also significantly inhibited the growth and calcification in living P. onkodes. Additionally, warming and acidification had interactive effects on the chlorophyll a content and net calcification rate. Compared with living P. onkodes, dead or bleached algal skeletons were more susceptible to warming and acidification. When the temperature was 30 ℃ or the pCO₂ was 1200 µatm, the net dissolution rate of dead algal skeletons increased significantly. Furthermore, the adverse effects of warming were exacerbated when high temperatures coincided with acidification. The results revealed that acidification and warming not only affected the growth and calcification rates of living algae, but also accelerated the dissolution rate of calcium carbonate skeleton, which can affect the coral reef ecosystem. The study may contribute to predict the impacts of climate change on reef ecosystem to protect reef ecosystems.

Deep-water coral (DWC) skeletons record the fine changes in the environment where corals grow. However, the factors influencing the growth of DWCs in the South China Sea, evolutionary stages, and their responses to marine environmental changes are not well understood at present. In this paper, the chemical elements and U-Th ages of DWC skeletons in the Southwest sea area of Dongsha were determined and studied to reveal the development and evolution characteristics of DWCs since 8000 a BP and the factors controlling their growth. Major and trace elements and factor analysis of DWCs show that the growth and evolution of DWCs in the Southwest sea area of Dongsha are influenced by bottom current activity, primary productivity, and terrigenous materials. The evolution of DWCs can be divided into four stages according to U-Th age, Ⅰ: 8000~4500 a BP; Ⅱ: 4500~2500 a BP; Ⅲ: 2500~1200 a BP; Ⅳ: 1200 a BP till now. The drastic fluctuation of bottom current velocity, organic particulate matter, seawater temperature and heat content, and the supply of biogenic materials resulted in the development discontinuity of DWCs at 4500~2500 a BP. The strong bottom current activity, strong winter monsoon, and the supply of organic particulate matter affected the evolution stage and characteristics of DWCs in the southwest sea area of Dongsha. The results provide a new perspective for further exploring the influencing factors, development, and evolution characteristics of DWCs at ocean margins and their responses to ocean processes.

A comprehensive understanding of the geological characteristics of shallow strata of seabed is the basis for identifying and evaluating shallow marine geological hazards, which is of great significance to the development of marine resources and marine engineering construction. Multiple oil and gas fields are being explored and developed in northern Dongsha, South China Sea. However, there is a lack of systematic analysis of the fine geological characteristics of the shallow strata in this place. Based on the diverse data of AUV (autonomous underwater vehicle), multi-beam, AUV shallow stratum profile, 2D seismic data and sediment test, the factors of shallow strata geological hazards were identified and their risks were evaluated in the area of 100~400m water depth in northern Dongsha, South China Sea. The survey found that the seabed surface sediments in the study area were generally relatively stable, and several micro-geomorphologies of the seabed, such as sand waves, steep steps and gullies developed. Shallow gas below the seabed was not observed, and numerous paleovalleys are developed. Significant spatial differences are featured in the shape and distribution characteristics of seabed sand waves. The sand waves with wave height greater than 1m are mainly distributed in the depths of 134~143m, 168~187m and 205m, they can move positions under modern dynamic conditions. The observation results show that the development of seabed sand waves is related to the process of internal waves. The steep steps are more than 20°, which is considered to be related to the faults running through the shallow strata.

The Pacific plate is subducting beneath the North Island of New Zealand along the Hikurangi Trench to depths of ~300 km, and is colliding with the South Island to the south, causing clockwise rotation of the North Island. Study on deformation of the mantle wedge in the subduction zone is essential to understand the mantle material movement and its dynamic mechanism. In this study, we investigate the anisotropy in the mantle wedge beneath the Taranaki region in the western backarc area of the North Island using the S-wave splitting measurement of local events with depths ranging from 70 km to 150 km. The results show spatial variations in the fast wave direction and delay time. The NE-SW trending dominant fast direction from the events with depths above 120 km is approximately trench-parallel, reflecting the crystallographic preferred orientation of olivine caused by the trench-parallel mantle flow in the mantle wedge. The events below 120 km depth are mainly from north of the Taranaki region. The predominant fast direction of these events is NNE-SSW, which delay times increase with depth. The Pacific slab steepens abruptly to a near-vertical plane at about 100~150 km depth, which could induce stronger shear deformation of upper mantle material in the deep mantle wedge. Therefore, the NNE-SSW trending anisotropy with larger delay times in the deep mantle wedge north of the Taranaki region may be caused by the combination of trench-parallel mantle flow and strong deformation of deep mantle wedge due to steepening of the dipping Pacific slab. The stronger extension in the deep mantle wedge of the northern backarc is the main reason for the spatial variation of anisotropy.

Thickness and elastic wave velocity are important parameters for evaluating the size and structural stability of coral reef. This study collected the receiver functions from two portable seismic stations on the Chenhang Island and Yongxing Island in the Xisha area, South China Sea. Travel times of the P-to-S converted waves and their multiple phases generated at the base of the carbonate platform are accurately picked up. At the same time, the thickness, average P-wave velocity, and velocity ratio of the carbonate platform sediments were calculated based on the drilling data and artificial seismic exploration results. The results show that the average P-wave velocity of the platform sediments on the Yongxing Island and Chenhang Island is about 3.5 km·s^-1, the V_p/V_s ratio is 2.42, and the average thicknesses are about 1.35 km and 1.55 km, respectively. The calculated thicknesses are consistent with that of the well on the Yongxing Island which reaches the reef bottom at about 1.257 km. The sediment thickness of the Chenhang Island is slightly larger than that of the Yongxing Island (about 200m), which reflects the fluctuation of the basement beneath the island or is related to the reef growth faces.

Keywords carbonate platform; velocity structure; V_p/V_s ratio; receiver function; Xisha Islands

Quorum sensing inhibitors (QSIs) can regulate the pathogenicity by mediating the bacterial quorum sensing system, and it is not easy to cause resistance mutations. To deal with the bacterial drug resistance, QSIs might be useful in treating or cooperated treating bacterial infections. In this study, the anti-quorum sensing substances from a marine derived actinobacterium Nocardiopsis dassonvillei JS106 was investigated. Six compounds, 1, 6-dihydroxyphenazine (1), 6-hydroxy-1-methoxyphenazine (2), 4', 7-dimethoxyisoflavone (3), N-(2-hydroxyphenyl) acetamide (4), 1-methoxyphenazine (5) and 2-aminophenoxazin-3-one (6), were isolated from the spent culture medium of JS106 using VLC and HPLC. All of the pure compounds showed significant anti-quorum sensing activity that inhibited the violacein production of Chromobacterium violaceum ATCC 12472 without visible growth inhibition at the test concentrations. N. dassonvillei JS106 can produce many phenazines and has higher potential in anti-quorum sensing application.

Keywords marine actinomycetes; bioactivity; anti-quorum sensing activity; Nocardiopsis; phenazines

To investigate the physicochemical properties in vivo antithrombotic activity and their effects on the bleeding time of different molecular weights of clam heparinoid, native clam heparinoid G2 (60.25 kDa), and its two different degradation products, DG1 (24.48 kDa) and DG2 (6.75 kDa), were taken as the research objects in this study. The content of glucuronic acid and the sulfate group was respectively determined by the modified sulfuric acid-carbazole method and BaCl₂-gel turbidimetric method, the particle size and zeta potential were determined by nanoparticle sizer, and the thermal stability was analyzed by the simultaneous thermal analyzer. Then the antithrombotic activity and the effect on bleeding time were investigated by the mice black tail model and mice broken tail model, respectively. The results showed that as the molecular weight of clam heparinoid decreased, the sulfate content increased, the glucuronic acid content decreased, the initial degradation temperature increased and then decreased, the particle size decreased, and the Zeta potential increased. The moderate degradation product of G2, DG1, has a higher ability to inhibit tail thrombosis with a lower risk of hemorrhage compared to the natural clam heparinoid G2.

This experiment aims to study the secondary metabolites of fungus Penicillium sp. SCSIO 40438 from the South China Sea. The solid fermentation products of the strain were isolated and purified by a variety of separation methods, including silica gel column, Sephadex LH-20 gel column, and preparative high performance liquid chromatography. The structures of the isolated compounds were identified by nuclear magnetic resonance, high resolution electrospray ionization mass spectroscopy and comparison with the previously reported data. Nine compounds were obtained and identified as 1-(2-Methylbut-3-en-2-yl)-1H-indole-3-carbaldehyde (1), 1-methyl-2(1H)-quinazolinone (2), fructigenine A (3), fructigenine B (4), 2-[(s)-hydroxy(phenyl)methyl]-3-methylquinazolin-4(3H)-one (5), 3-Methylviridicatin (6), 3-O-methylviridicatol (7), viridicatol (8), (+)-cyclopenol (9), and compounds 1 and 2 are two new natural products. Compound 8showed moderate antibacterial activities against Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus with minimal inhibition concentration (MIC) values of 8.0 μg·mL^-1.

Keywords fungi; Penicillium sp.; secondary metabolites; antibacterial activity

Temperature, salinity and nutrients were obtained from four seasonal in-field cruises during 2019 on the Northern South China Sea (NSCS). Due to the Pearl River plume and shelf seawater intrusion, nutrients distribution in the nearshore waters of the western Peal River Estuary (PRE) showed remarkable seasonal and regional variations, which was phosphorus limitation in three seasons, especially significant in spring, while showing potential nitrogen limitation in autumn. Influenced by the strength of southwest monsoon and seafloor topography variation, upwelling intensity of the cross-shelf section outside of the PRE (Section A) was greater than that of the cross-shelf section east of Hainan Island (section B) in spring and summer, and climbing height and range of the nutrient contours were greater in summer than that in spring. Nutrients was diluted by the intrusion of Kuroshio water on the slope area of NSCS, the nutrient concentration between 75 to 150 m in winter decreased more than 25% compared with that in summer, while the nutrient concentration near the Dongsha Island of the section A was less than the adjacent stations by above 20% in spring and autumn, since the reduced Kuroshio water intrusion during El Niño. The nutrients in the centre of the cold eddy increased 6.42μmol·L^-1 DIN, 0.71μmol·L^-1 PO₄^3--P and 10.03μmol·L^-1 SiO₃^2--Si, respectively, compared with the adjacent stations outside of the eddy. The concave structure of nutrient distribution in section A was resulted from the co-effects of upwelling and mesoscale eddy in summer. It is summarized that the spatiotemporal variations of nutrient distribution in the NSCS were complicated, mainly effected by the independent or coupled factors including Pearl River plume, coastal upwelling, Kuroshio intrusion and mesoscale eddies.

Keywords northern South China Sea; water mass; mesoscale phenomenon; nutrients; spatiotemporal distributions

With the rapid development of economy and population in coastal areas, the water quality of the main bays around the world has been affected by human activities which results in the deterioration of the ecological environment. Based on the survey and statistical data from 1995 to 2014 in the Daya Bay, Guangdong Province, China, coefficient of variation method, bivariate correlation analysis, principal component analysis and linear regression analysis were used to identify the key controlling indicators from the anthropogenic pressure indicators and coastal carrying indicators, which have significant impact on the water quality of the Daya Bay. The proportion of the carrying capacity of each important controlling factor was used to quantify the water quality effect. The results showed that the key controlling indicators contained three anthropogenic pressure indicators, including land reclamation, domestic sewage discharge and industrial wastewater discharge. The key controlling indicators had remarkable variation and greater loading values, and they were significantly correlated to the C_DIN which was the main pollutant in the Daya Bay. The quantitative assessment results showed that the carrying capacity of key controlling indicators (land reclamation, domestic sewage discharge and industrial wastewater discharge) were 6.19%, 5.07% and 17.51%, respectively, of which the proportion of industrial wastewater discharge is the highest and has the greatest impact on the Daya Bay. Therefore, human activities were the main cause for the deterioration of water quality in the Daya Bay. These results illustrated that the control of land-based pollution and the regulation of the coastline should be implemented to promote the sustainable development of social economy around the Daya Bay.

Artificial reefs are submerged structures artificially placed on the seabed to mimic some characteristics of natural reefs. They are able to exert the functions of enhancing the proliferation of fishery resources, promoting the restoration of marine habitats and supporting coastal recreation. Its origins date back to thousands of years, but systematic research and applications on artificial reefs only began in the last century. In recent years, with the increasing number of artificial reef studies, a large number of new materials, new structures, new methods and new applications have been proposed and practiced. By reviewing the research progress of artificial reefs in China and abroad, the current situation in this field is reviewed from three aspects: the design, research and application of artificial reefs. The research and application direction of artificial reefs in the future are prospected, aiming to guide the future relevant works on artificial reefs in China.

By analyzing reanalysis data and conducting ocean modes experiments, this study investigates the seasonal variation and dynamics of the norward Somali current (NSC) in the tropical Indian Ocean. The results show that the NSC starts from May, gradually strengthens and extends norward to 15°N during August-September, and forms a strong anti-cyclonic circulation — the Great Whirl. The NSC weakens significantly in late October, and disappears in November. The NSC results from local alongshore wind forcing and westward propagational Rossby waves. During May-July, alongshore wind forcing induces the East African Coast Current (EACC) to cross the equator to form the NSC. From August to October, even without alongshore wind forcing, the Rossby waves together with EACC can still form the NSC. Further analysis suggests that, although alongshore wind forcing incudes near-shore current, the Great Whirl is caused primarily by the Rossby waves. This research reveals dynamics of the NSC, and provides substantial evidences for ocean waves modulating ocean currents.

The Huangmaohai Estuary (HE) is a horn-shaped estuary in the southwest of the Pearl River Delta. In the last few decades, the morphology of the HE has undergone tremendous changes under the combined action of natural processes and human activities. Based on the historical charts and satellite remote sensing images from 1972 to 2016, this paper quantitatively analyzes the changes of the coastline and underwater topography, and constructs a three-dimensional hydrodynamic model to discuss the dynamic response to the topographic changes. The results showed that land reclamation caused the mouth and coastline of the outlet to extend sharply to the sea, and the water area was greatly reduced. As a result, the tidal volume of the estuary decreased from 1.113 billion cubic meters in 1972 to 895 million cubic meters in 2016, a decrease of nearly 19.61%. At the same time, the narrowing of the estuary also causes changes in the hydrological dynamics, such as the rise of the water level, the enhancement of the runoff power, the reduction of the tidal range, the shortening of the high tide duration, and the extension of the ebb tide duration. In the future, with the silting and filling of the estuary, the tidal power of the estuary will be further weakened.

Based on the observations and the global climate model simulation outputs of historical run and future warming scenarios from phase 5 and phase 6 of the coupled model intercomparison project (CMIP), we assessed the performance of 23 CMIP6 and 32 CMIP5 models in reproducing El Niño diversity, and then projected the responses of the eastern Pacific (EP) and central Pacific (CP) type of El Niño to global warming. The results show that most CMIP5/6 models can reasonably simulate the characteristics of El Niño diversity, and the simulation performance of CMIP6 models is significantly improved compared with CMIP5 models. Not only do the CMIP6 models weaken the discreteness of the simulated EP El Niño-related spatial patterns, but also significantly improve the simulation ability of the CP El Niño-associated spatial patterns. The CMIP5/6 models can basically simulate the seasonal phase-locking characteristics of the EP and CP El Niño events, however, compared to the observation, the decay time of the simulated CP El Niño is obviously delayed by 3 months. The intensity of EP El Niño simulated by CMIP5/6 is close to the observation, but the counterpart of CP El Niño is stronger than the observation. Under global warming, the frequency of CP El Niño will tend to decrease relative to EP El Niño. The amplitudes of EP and CP El Niño will be enhanced along with the intensification of global warming, and the enhanced amplitude of EP El Niño is greatly stronger than that of CP El Niño.

The tropical ocean-atmosphere system in spring may simultaneously respond to the El Niño-Southern Oscillation (ENSO) in the Pacific ocean. At the same time, it can affect the ENSO development through coupled regional ocean-atmosphere interactions. Based on the joint empirical orthogonal function and open-source datasets, we identify two major global climate modes. The first EOF mode presents the ENSO pattern along with the spring meridional mode in the Atlantic and asymmetric mode in the Indian Ocean, in which the sea surface temperature warms up and precipitation increases in the tropical central and eastern Pacific ocean, accompanied by the equator-asymmetric pattern of precipitation in the tropical Atlantic and Indian Oceans as well as anomalous sea surface temperature gradient in the trans-equatorial. Further analyses suggest that the ENSO influences the intertropical convergence zone by adjusting atmospheric circulation during its mature phase and then induces regional ocean-atmosphere feedback resulting in the spring meridional modes. The differences in spring asymmetric modes of precipitation in the tropical Atlantic and the Indian Ocean are determined by the different positions of the intertropical convergence zone in winter and spring. The second mode shows a meridional sea surface temperature and precipitation anomalies in the tropical Pacific, i.e., the Pacific meridional mode. The warm pole of the spring Pacific meridional mode extends over the equator, causing westerly wind anomalies that favor the El Niño development. This study reveals the relationship between the Pacific ENSO and the global spring meridional mode, contributing to a better understanding of the seasonal 'footprint' of tropical climate modes.

Due to the complexity and variability of marine environments, marine bacteria may have evolved unique environmental adaptation mechanisms. Genomic islands usually carry genes related to the environmental adaptation of host bacteria and play an important role in driving bacterial adaptation and genome diversification. Pseudoalteromonas is an important genus that is widely distributed in various marine habitats, and has attracted attention due to the important industrial application and ecological restoration potential. In this study, we focused on Pseudoalteromonas sp. SM9913 isolated from marine sediments. By comparative genomics analysis of SM9913 with the closely related strain Pseudoalteromonas haloplanktis TAC125 isolated from surface seawater, an 18-kb genomic island GIPspSM9913 integrated in the yicC gene was identified. This genomic island encodes an integrase and an excisionase, as well as multiple restriction modification systems. Sequence analysis showed that GIPspSM9913 homologs are widely distributed in marine bacteria such as Pseudoalteromonas, Shewanella, Vibrio and Aeromonas. Quantitative PCR assays showed that GIPspSM9913 can excise when the excisionase is produced, resulting in the removal of GIPspSM9913. Sequencing analysis indicated that excision of GIPspSM9913 did not affect the expression of flanking genes. We also compared the swimming motility, electroporation efficiency and conjugation efficiency of the GIPspSM9913 deleted strain and the wild-type strain SM9913, and found that the presence of GIPspSM9913 can increase the swimming motility of the host bacteria and offer the host defense against the invasion of foreign DNA.

Siphonosoma australe is a local fishery resource in Hainan, which belongs to Siphonosoma. The taxonomic status of the genus in the phylum Sipuncula has been highly controversial. In this study, the mitogenome of S. australe in the Wenchang coast of Hainan was determined by high-throughput sequencing, and compared with the mitochondrial genomes collected from GenBank, characteristics of mitogenome sequence was analyzed, furthermore, the evolutionary position of the genus Siphonosoma in the phylum of Sipuncula was explored. The results show that the mitogenome of S. australe has 16483 base pairs and encodes a set of 38 genes (13 protein-coding, 23 transfer RNAs, and 2 ribosomal RNAs). The mitochondrial genome shows AT bias, and the content of nucleotides A+T is 65.87%. By the analysis of the relative synonymous codon usage (RSCU), the mitochondrial protein-coding genes of S. australe have obvious preference to the codons ending with A and U. The number of amino acids of mitochondrial protein coding genes (COX1, COX3 and ND5) of S. australe is quite different from that of other species. Compared with the mitochondrial genomes of sipunculans from GenBank, it was found that among the major coding genes of sipunculans, the proportions of variable sites in COX1, COX2 and CYTB genes are low, while the proportions of variable sites in ND2, ND4L and ND6 genes are high, and the highest proportion of variable sites in ATP8 gene is 83.33%. Based on the DNA sequences of sipunculan mitogenomes, the phylogenetic tree constructed using the methods of NJ (neighbor-joining), ML (maximum likelihood) and BI (Bayesian inference) showed that the genus Siphonosoma, as an independent clade, is between the genera of Phascolosoma and Sipunculus, even close to the genus of Phascolosoma instead far from the genus of Sipunculus. This result is inconsistent with the previously traditional classification based on morphological analyses. Taxonomically, Siphonosoma mixes the morphological characteristics of Phascolosoma and Sipunculus. The phylogenetic tree constructed with mitochondrial genome sequences could truly reflect the unique phylogenetic status of Siphonosoma. The mitogenome data of S. australe provides a theoretical basis for explaining the evolutionary relationship of the Siphonosoma in the phylum Sipuncula, and are beneficial to the protection and development of genetic resource of S. australe.

Porites lutea, the representative species of reef building corals around the Hainan Island, is a spawning, massive coral with strong environmental adaptability. Exploring the genetic structure and connectivity of this species helps to reveal the genetic diversity pattern and larval migration path of coral metapopulation around the Hainan Island, thus clarifying the recovery potential of coral reefs. In this study, 11 P. lutea microsatellite markers were screened to analyze the genetic structure of 10 populations of the Hainan fringing reefs and 1 population (XsR) in the Xisha Islands. The results showed that, overall the genetic diversity of all populations was medium to low, with the average allelic richness Rs ranging from 2.8 ± 1.3 (Basuo population, Bs) to 3.7 ± 1.7 (Linchang Reef population, LcR), and the average observed and expected heterozygosity ranged from 0.31 (Tongguling population, Tgl) to 0.54 (Dachan Reef population, DcR) and 0.50 (Leigong Island population, LgI) to 0.64 (Haiwei population, Hw), respectively. Except for the Longwan Reef population (LwR) and the Dazhou Island population (DzI), which located in the east of the Hainan Island, and the Basuo population (Bs) and the Dachan Reef population DcR (in the west of Hainan Island), all other populations (7/11) showed evidence of heterozygote deficiency. According to genetic differentiation, the Hainan Island populations were divided into two groups: the north-south-east genetically connected zone and the west coast, and the differentiation between the two branches (AMOVA, 0.092) was significant. The former group included Bs, Luhuitou population (Lht), DzI, LgI and Mulantou population (Mlt), due to the significant gene flow created by exchange of ocean currents, there was no obvious genetic differentiation among these five coastal populations, whereas the gene flow of the offshore populations (LcR, DcR and Hw) of the west coast was blocked due to the discontinuity of coastal reefs and slow coastal currents. LwR in the east coast also converges to the west branch, which may be due to the isolation by environment and the convergent adaptation to offshore environment. Although the distance between Hw and Bs is less than 50 km, but they are obviously differentiated, possibly due to the isolation by salinity fluctuation and suspended sediments caused by the runoff of the Changhua River. Tgl showed strong inbreeding, low heterozygosity and non-random mating characteristics because it was located in the wave shadow area of the Tongguling headland, and the runoff of the Bamen River restricted its gene exchange with other coastal reef populations. Represented by P. lutea metapopulations, the fringing reefs of the Hainan Island has the natural resilience responding to environmental stress due to the strong gene flow and the genetic differentiation caused by ocean current, runoff and complex fringing reef structure, as well as the environmental differences between nearshore and offshore. The genetic differentiation between the Xisha Islands population and the coastal reef populations of the Hainan Island was large, showing significant geographical isolation. The Qilianyu Island may have lost the ability to replenish the Hainan Island with coral larvae because the coral reefs have declined there.

In this experiment, 'Acanthopagrus latus', an important economic fish in the southeast coast of China, was used as the experimental material. The SNPs were discovered by DNA re-sequencing in fifty A. latus, and partial SNPs were genotyped using MassARRAY^® DNA mass spectrometry. The results are presented as followed: 1) the re-sequencing of 50 wild A. latus generated a total of about 233.48 GB raw data. After filtering adapters and low-quality data, 233.43 Gb clear data were obtained. The average data size of each sample was 4.67 GB, and the average GC content was 42.85%, Q20 is above 96.56%, Q30 is above 91.1%, and the comparison rate between the clear data and the reference genome is 98.06% ~ 99.47%; 2) a total of 13843766 SNPs were discovered from 50 individuals by GATK, and 6501 high-quality SNPs were obtained after filtering; 3) thirty SNPs from the high-quality SNP were selected randomly and genotyped using MassARRAY technology. The detection rate (loci that can be genotyped) was reached at 98%. The consistency between the genome re-sequencing and the MassARRAY results was 64.83%, which indicated that the two techniques were different in detecting SNPs. In summary, a method for mining, filtering and validating SNP markers of A. latus bream has been established in this study, and the developed SNP loci can be used in evaluation of proliferation and stocking effect and genome selection breeding of A. latus in the future.

To understand the vertical distributions of zooplankton in regions of the “Haima” cold seep and the possible effects of seep activities, zooplankton samples were collected from 0 to 1250 m at five stations in September 2020. These zooplankton samples were analyzed using ZooScan image analysis system. The abundance, biovolume and size spectra of zooplankton in different water layers were obtained in this study. The results showed that zooplankton abundance and biovolume were mainly occurred in the 0 ~ 100 m water layer. Below 100 m, zooplankton abundance and biovolume decreased rapidly with increased depth. The average abundance and biovolume of zooplankton were only 8.33 ind·m^-3 and 12.10 mm³·m^-3 at the layer of 1000 ~ 1250 m. In general, copepods were the dominant zooplankton in each water layer, and the proportion of gelatinous zooplankton increased in deep layer. The slope of normalized biovolume size spectra (NBSS) in the regions of the “Haima” cold seep ranged from -0.94 to -0.57, and the intercept ranged from -2.10 to 5.94. From surface to bottom, the slope of NBSS increased while the intercept decreased gradually. This indicated that the productivity of planktonic ecosystem declined gradually from surface to bottom, but the energy transfer efficiency of pelagic food web increased gradually. The layer of 1000 ~ 1250 m at ROV1 station showed abnormal size spectrum characteristics, and the slope “a” is significantly lower than that of other stations in the same water layer. It suggested that the zooplankton community might be affected by cold seep activities.

Zooplankton collodarians with symbiontes play important roles in the organic carbon cycle and silicon cycle in the oligotrophic waters. However, studies on the collodiarian geographic distribution were few. In this study, the biodiversity, biogeography and seasonal variation of collodarians in the surface water of the northern Indian Ocean (NIO), the Malacca Strait (MLS) and the South China Sea (SCS) are revealed for the first time by using the ship-board plankton net to collect samples and using the Rose Bengal stains to distinguish between “living” and “dead” specimens. Totally, the 17 species of collodarians occurred in spring, with 27 species in winter. The collodarian diversity in NIO and MLS is generally less than that in SCS in spring, while in the winter, the former is higher than the latter, indicating that the regional biodiversity from NIO to the SCS is considerably affected by the East Asian monsoon. Moreover, the changes of collodarian community structure have biogeographic differences under the influence of East Asian monsoon. For example, the family Collosphaeridae is obviously dominant both in spring and winter, while the family Sphaerozoidae is dominant only in winter; the composition of dominant species is also different between the spring and the winter, suggesting the collodairian community in surface water is significantly affected by the seasonal changes. Under the influence of East Asian monsoon, the mixing of surface water enhanced, resulting in obvious changes in the compostion of collodarian species, which indicates that seasonal changes are the main factor that controls the community structure of collodarians in the study sea area. The abundance of collodarians is closely related to the regional environment. For instance, the collodarian abundance is very low in spring and winter from MLS to the Sunda Shelf, followed by SCS, and is high in NIO, reflecting their adaptability to specific marine environment. It is assumed that the influence of habitat on a large scale is higher than the control of monsoon change. Therefore, the biodiversity and abundance of collodarians can reflect the different ecological environmental signals, which further provides important observation data and a basic reference for the reconstruction of palaeooceanography and palaeoenvironment by using the collodarian substitution indexes in the future.

The Zhongsha Atoll is in the center of the South China Sea, and is a key location that connects the Dongsha, Xisha and Nansha Islands. This paper is based on the survey data of the Zhongsha Atoll topography, geological sampling, and multi-channel seismic profiles. We selected five influencing factors of water depth, sediment type, structural distance, landslide-prone area, and slope, and used the K-means clustering algorithm and analytic hierarchy process method to quantitatively analyze the stability of the Zhongsha Atoll. The study area was divided into five grades of stability: good, fair, medium, poor, and worse. We discussed the influence of different factors affecting the stability of Zhongsha Atoll. The deposition type, slope, and water depth are the main factors that affect the stability of the platform. The slope’s stability around the platform is mainly controlled by the factors such as slope, structure, and landslide-prone areas. However, the slope factor in the deep-water area outside the slope around the platform has the largest contribution. Overall, the stability of the north and west of the atoll is better than the east and south, in addition, the stability of the platform and the deep-water area outside the slope around the platform is the best. The evaluation results can provide basic geological services for development and planning, submarine pipeline engineering, disaster prevention and mitigation in the study area.

The Qinzhou Bay in Guangxi province is an important estuarine bay in south China. With recent intensive engineering construction and coastal reclamations, the topography evolution of the Qinzhou Bay is changed, which may influence the port shipping and shoreline stability. Based on two sets of coastline and underwater topographic data, we developed a coupled hydrodynamic-sedimentary dynamic numerical modelling system to simulate the impact of human activities on the dynamics of underwater topography evolution of the Qinzhou Bay in the past 35 years. Our results show that the reclamations optimize the spatial distribution of the flow field by slightly increasing the tidal flow velocity in the Longmen waterway and the outer bay; meanwhile, the reclamations changed the tidal asymmetry distribution, which may affect the development trend of the channel-beach pattern and the local erosion and deposition, mainly in the area of the northern Maowei Sea, the Longmen waterway, the middle of the outer bay, and around the Sandun Highway; moreover, the coastal reclamations had overall weakened the underwater geomorphology change of the Qinzhou Bay, and slightly increased the changes in the central Longmen waterway, but the spatial distribution of the change is more concentrated. The magnitude of change in the outer bay area decreased slightly, the trend of change was concentrated in the eastern and western waterway, while the change in the central waterway tended to be stable. Overall, maintaining a stable topography of the Qinzhou Bay is of great importance for the sustainable development of port shipping and coastal zone economy in the future.

Penicillium sp. S2014503 was isolated from a rotten whale bone sample. Constituent analysis and bioactivity evaluation of S2014503 were carried out to find more bioactive compounds from this fungus. Chemical structures of the purified compounds produced by S2014503 were determined by comprehensive analysis of NMR (nuclear magnetic resonance), MS (Mass spectrum) data of each compound. Stereochemistry of chiral compounds were elucidated by comparison of specific rotation value with the reported ones or determined by X-ray diffraction analysis. Ten compounds emodin (1), citreorosein (2), tetrahydro altersolanol B (3), conioxanthone A (4), chrysogine (5), pyramidamycin B (6), germicidin O (7), 2-(6-hydroxy-5,7-dimethylbenzefuranone-4-yl) acetaldehyde (8), astrophenone (9), and chenopodolans A (10) were found in the fermentation product of S2014503 which was cultured on a solid state rice medium. Bioactivities of all the isolated compounds were evaluated for the antibacterial activities and cytotoxicity against brine-shrimp larvae. Compounds 1 and 2 showed weak activity against Gram positive bacteria Micrococcus luteus. Compounds 1, 2 and 4 were significantly cytotoxic against brine-shrimp larvae (Artemia salina) after 6 hours of incubation at room temperature. Interestingly, compound 1 was a well-known laxative ingredient of Traditional Chinese Medicine Rheum officinale and Polygonam cuspidatum. This work is the first report on the emodin analogs from a whale bone derived fungus Penicillium sp.

In this paper, oyster hydrolysis products were prepared from Crassostrea hongkongensis as raw materials, and the basic nutrition and amino acid composition of oyster hydrolysis products were analyzed, and the improvement effect of oyster hydrolysis products on the lactation function of rats with postpartum lactation caused by Bromocriptine mesylate was explored. The results showed that protein content of oyster hydrolysis products was higher, which is followed by sugar, fat content was lower, and peptide content was 33.4%. The essential amino acids in oyster hydrolysis products accounted for 39.8% of the total amino acids and contained a high proportion of branched amino acids. The results of animal experiment showed that compared with model group, the lactation volume of rats in oyster hydrolysis products of high-dose group was significantly increased (p < 0.05), which was better than that in the positive control group. The index of mammary tissue and organ in each oyster hydrolysis products dose group was significantly increased (p < 0.01), which was close to the positive control group, but did not return to normal level. HE staining showed that there were more acinus in mammary gland tissues in all oyster hydrolysis products dose groups, which were round and full with more secretions, and the acinus had obvious enlargement and hyperplasia. Compared with the model group, the acinus had obvious recovery. Compared with model group, the contents of prolactin (PRL) and prolactin receptor (PRLR) in serum and mammary tissue of oyster hydrolysis products groups were largely increased (p < 0.05), indicating that oyster hydrolysis products could promote the secretion of prolactin in lactation-deficient rats, while the content of serum dopamine (DA) was greatly decreased (p < 0.01). These results showed that oyster hydrolysis products can reduce the high level of dopamine induced by bromocystine. In addition, oyster hydrolysis products strongly increased the contents of lactose (LC) and triglyceride (TG) in breast tissue (p < 0.05), and improved the nutritional composition of milk. The average hemoglobin (MCHC) and red blood cell (RBC) contents in all oyster hydrolysis products dose groups were also greatly increased (p < 0.05), which had a certain improvement effect on postpartum deficiency of qi and blood. Conclusion: Oyster hydrolysis products can improve the symptoms of lactation deficiency and increase milk yield after delivery, which has the potential to promote lactation.

A Reasonable interspecific composition structure of mangrove is the premise of effectively bringing into play the ecological value of mangrove wetland, and clear information of interspecific distribution of mangrove is an effective basis for mangrove ecosystem management and planning. For the mangrove wetland in the Hainan Bamen bay, based on GF-3 fully polarimetric Synthetic Aperture Radar (SAR) and GF-6 multi-spectral remote sensing data, 35 mangrove remote sensing features were extracted, and the importance ranking, feature screening and inter-species classification of mangrove were carried out using eXtreme Gradient Bo3osting (XGBoost) algorithm. The accuracy of XGBoost was compared with the traditional Support Vector Machine (SVM) and Random Forest (RF) machine learning algorithms, and the classification accuracy of three feature combination methods (preferred feature, multispectral feature and full polarization SAR feature) is compared based on the XGBoost algorithm.The purpose is to explore the applicability of XGBoost to mangrove interspecific classification and the ability of optical and fully polarized SAR data for mangrove interspecific classification. The results showed that: 1) The dominant features of mangrove species identification were multi-spectral spectral bands, polarization decomposition parameters, spectral vegetation index, and only the first eight (G, B, Y_s, NIR, EVI, RVI, NDVI, F_s) were used to achieve high classification accuracy. 2) XGBoost has the highest overall classification accuracy of 86.16%, and Kappa has 0.836. The classification accuracy of this algorithm is 3% ~ 8% higher than SVM and RF. The accuracy of mangrove interspecific classification using multispectral and fully polarimetric SAR was 10% ~ 12% higher than that used multispectral or fully polarimetric SAR alone. 3) The total area of mangroves in the Bamen bay was 797.58 hm², and there were 9 dominant true mangrove species, Avicennia marina, Bruguiera sexangular, Rhizophora stylosa, Sonneratia alba, Rhizophoraceae, Bruguiera gymnorrhiza, Lumnitzera racemosa Willd, Rhizophora apiculate, and Excoecaria agallocha Linn. The area of Sonneratia alba and Lumnitzera racemosa Willd were larger, accounting for 45.46% and 21.21% of the total mangrove area, respectively. In this paper, the interspecific classification of mangroves in the Bamen bay, Hainan province was studied based on high-resolution optics and fully-polarimetric SAR, which can provide data support and technical support for the protection and management of mangrove ecosystem.

In order to investigate the contents and sources of heavy metals in the Xisha waters in the South China Sea, 24 seawater samples at six sites were collected in December of 2021. Vertical profiles of temperature, salinity, turbidity, dissolved oxygen, colored soluble organic matter and chlorophyll were determined by Conductivity-Temperature-Depth instrument. Inductively coupled plasma mass spectrometry was used to measure the contents of heavy metals in seawater samples, and the average Cu, Pb, Zn, Cd, Ni, Cr, As, Fe and Mn contents were 0.22~20.79 µg·L^-1, n.d. (not detected) ~0.25 µg·L^-1, 1.90~15.90 µg·L^-1, 0.13~0.17 µg·L^-1, 0.54~1.31 µg·L^-1, 0.29~0.33 µg·L^-1, 2.93~3.17 µg·L^-1, 0.39~1.23 µg·L^-1 and 0.35~1.14 µg·L^-1, respectively; Hg was not detected. Only Cu or Zn contents in 5m-depth seawater at D2~D4 sites exceeded Class I requirement of National Seawater Quality Standard (GB 3097-1997), and the spatial distribution of heavy metals was influenced by terrestrial inputs, environmental factors and human activities. Principal component analysis indicated that the heavy metals in the Xisha waters are mainly from three sources: ship emission, terrestrial agricultural runoff, as well as terrestrial debris and industrial inputs. The measurements in this study are generally within the range of heavy metal contents previously reported in the South China Sea. However, compared with the background values of the South China Sea in 1998, the contents of Cu, Pb, Zn and Cd in surface seawater have increased by one order of magnitude, reflecting the impact of recent intense human activities in this region.

Sea Cucumbers play an important role in marine ecological system and have edible and medicinal values. At present, wild resources of sea cucumbers are greatly depleted in China, and artificial breeding of sea cucumbers provides an essential way to restore the population resources. Understanding the hormones that regulate spawning behaviors of sea cucumbers has great significance for the development of artificial injection hormone. We reviewed the hormones found in sea cucumbers that can regulate their spawning behaviors, and we also provide some new perceptions for the future research. The review can provide some valuable references for revealing the key spawning mechanism of sea cucumbers and developing the artificial spawning induction by injecting hormones.

Human-induced emissions of greenhouse gases such as carbon dioxide (CO₂) are the main drivers of global warming. Global warming poses a serious threat to the security of food, water resources, energy, economy, and other fields. Alleviating global warming is imperative. Not only does it require massive greenhouse gas emissions reduction, but also large-scale deployment of carbon dioxide removal (CDR) or negative emissions techniques to intentionally remove CO₂ from the air and sequestrate it for a long period so that to decrease global net CO₂ emissions to zero as soon as possible, and achieve "carbon neutrality". The ocean accounts for 70% of the earth's surface area and is the largest active carbon pool. It has a huge potential to absorb CO₂. Ocean-based CDR is necessary to achieve carbon neutrality. The research on the theory, method, and technology of ocean CDR has become a hot spot and frontier field. At present, the knowledge of ocean CDR is still relatively limited, and there is a large space for development. The urgent need to mitigate global warming is promoting the rapid development of the basic theory of marine carbon sinks and ocean CDR research, and original progress is emerging. This paper mainly summarizes the theoretical basis of the Iron-Aluminum Hypothesis and discusses the potential of ocean aluminum fertilization as a CDR strategy. The iron-aluminum hypothesis indicates that aluminum can enhance carbon fixation by phytoplankton in the upper ocean, reduce the decomposition rate of biogenic carbon, improve the efficiency of the biological pump, increase carbon export and sequestration to the deep sea, regulate marine carbon sinks, and affect the concentration of CO₂ in the atmosphere. Thereby, as well as iron, aluminum may be a key factor in influencing historical and modern climate changes. Aluminum improves the efficiency of iron use and carbon export to the deep ocean, which can make up for the shortage of artificial ocean iron fertilization, and endow ocean aluminum fertilization with the potential to become a new CDR method and technology based on natural carbon sinks. Despite its potential high efficiency, ocean aluminum fertilization as a CDR method is still nascent. We suggest further study on the mechanisms underlying the roles of aluminum in enhancing marine carbon sinks from the three aspects 1) carbon fixation by marine phytoplankton in the upper ocean, 2) biogenic carbon export to the deep ocean, and 3) long-term carbon sequestration, and thus to strengthen the theoretical basis of iron-aluminum hypothesis and ocean aluminum fertilization. We also propose to verify the CDR efficacy of ocean aluminum fertilization and its potential environmental impacts at different temporal and spatial scales. The above two works are expected to provide basic scientific knowledge for the development and application of ocean aluminum fertilization as a CDR strategy.

The material and energy exchange at the air-sea interface is an important cause of global climate and ecological environment change. As the largest shelf margin sea in China and the Northwest Pacific Ocean, atmospheric deposition plays an important role in the exogenous input of the South China Sea. With the continuous and rapid economic and social development of the surrounding countries in the South China Sea, the transport of anthropogenic pollutants to ocean through atmospheric deposition is increasingly enhanced, which is bound to have a non-negligible impact on the ecological environment of the South China Sea. Based on the research reports of atmospheric deposition of biogenic elements, micro-trace elements and new pollutants microplastics in the South China Sea in the past nearly 30 years, this paper systematically summarized the concentrations, fluxes and influencing factors of atmospheric dry and wet deposition in the South China Sea, and analyzed the eco-environmental effects of atmospheric deposition in the South China Sea. The results show that 1) The concentration of atmospheric particulates in the South China Sea is lower than that in the east coast of China, and there is almost no acid rain deposition. However, the atmospheric carbonaceous aerosol component concentration and deposition in the South China Sea are at a high level due to the influence of biomass burning in Southeast Asia and fossil fuel combustion emissions in China. 2) Nitrogen is the dominant nutrient in the atmospheric dry and wet deposition in the South China Sea, and the proportion of nitrogen species varies greatly in different sea areas, resulting in strong imbalance of nutrient structure in atmospheric deposition. 3) The solubility of anthropogenic metal elements in aerosols is high, and most of them in the form of wet deposition. Aerosol microplastics mostly exist in the form of fiber. Meteorological conditions (precipitation, wind speed, etc.) and source emission intensity are the main factors controlling atmospheric component concentration and deposition flux. 4) Atmospheric nitrogen deposition accounts for about 20% of the total nitrogen input in the sea surface of South China Sea. The addition of nitrogen will aggravate the hypoxia and acidification of the offshore, and nutrient deposition plays an important role in the explosive proliferation of phytoplankton. Atmospheric deposition will have multiple and complex impacts on South China Sea, an oligotrophic ecosystem, which is closely related to hydrologic conditions, initial nutrient status, phytoplankton groups, atmospheric composition and deposition characteristics. In the future, it is suggested that the researchers should pay more attentions to the depth and breadth of the research, focus on the precise and regular monitoring of the dry and wet deposition of various atmospheric components, especially organic nitrogen and phosphorus species and new pollutants, and fully explore the influence and feedback mechanism between the atmospheric deposition of biogenic elements and micro-trace elements and the South China Sea ecosystem from the perspective of interdisciplinarity. Atmospheric deposition is an important part of biogeochemical cycle in the South China Sea, and its impact on the ecological environment is a "double-edged sword". With the continuous enhancement of atmospheric deposition of terrigenous species in the South China Sea in the future, this effect will become more complex and far-reaching.

As the unique deep channel that connects the South China Sea (SCS) with the western Pacific Ocean, Luzon Strait is also the key oceanic passage that modulates the SCS circulation and its thermodynamic characteristics. Influenced by large-scale western boundary current, meso-scale eddies, tropical cyclones and other factors, Luzon Strait transport (LST) exhibits significant multi timescale variability. Tropical cyclones are strong and localized low-pressure weather systems that occur frequently in the area, therefore, understanding the dynamic connection between tropical cyclones and LST is one of the most essential topics in oceanography research. This study reviews the research progress in the characteristics of tropical cyclones near the Luzon Strait and its impact on the Kuroshio, ocean circulation and LST, and reveals their recent development. We further suggest that the future study should focus on the modulating mechanisms of the tropical cyclones on the LST and evaluate their contributions to the interannual variations of LST.

Based on the satellite observations and model outputs, the statistical characteristics of eddy, eddy-induced heat transport and the influences from two winter circulation patterns and wind stress are discussed in this study. The results show that the climatological mean of eddy statistics in the study area has characteristics of strong rotation speed, large radius and amplitude that are slightly higher than the average in the whole SCS, among which cyclonic eddy (CE) accounts for 56.8%. The formation and extinction of eddies mainly occur in winter/spring, while the amplitude, radius and rotation speed of eddy reach their peak values in summer/autumn. On the interannual time scale, the annual mean meridional wind stress has a good correlation with anticyclonic eddy (AE) including its amplitude, radius, rotation speed and extinction, but the correlations with CE are weak. In the “O” pattern, the western boundary current and winter wind stress are significantly weakened, and the easterly branches of winter circulation occur along the coast of Vietnam. By absorbing mean flow energy, the eddy in this study area developed rapidly in “O” pattern, generating strong eddy-induced heat transport (EHT) in the east of the Vietnam coast. In the meantime, the rotation speed of eddy and the number of AE decrease. The above situation is opposite under the “U” winter circulation pattern.

The influence mechanism of the typical topography in the Bay of Bengal on the tide has not been fully understood. Therefore, this study sets up a group of controlled experiments and three groups of comparative experiments based on FVCOM (finite-volume community ocean model) to study the influence mechanism of the north, west and east continental shelf topography, as well as the influence of the most visible canyon topography in the continental shelf area on the tide. The results show that the Ganga Trough can reduce the amplitude of tidal wave near the canyon, but has little effect on the tidal range at the head of the bay; the width of the top shelf is helpful to increase the amplitude of tidal wave and the tidal range at the head of the bay; the eastern continental shelf helps to enhance Kelvin wave and increase the tidal range at the top of the bay, but the impact is not as significant as that on the top shelf; and the western continental shelf only has an impact on the western region, but has little impact on the co-tidal distribution of the whole area.