Recent field observations and theoretical analysis have revealed that submesoscale activities are ubiquitous in the upper ocean, and that their formation is closely related to frontogenesis and mixed layer instability. Based on high-resolution numerical simulations and diagnostic analysis, we investigate the seasonal variability of submesoscale activities in the upper ocean of the Kuroshio Extension. The results suggest that the submesoscale behaviors in the Kuroshio Extension have significant seasonal variation. Although the mesoscale eddy energy of the Kuroshio Extension is weak in winter, the submesoscale activities are the most active on the seasonal scale, which is likely due to the contribution of the mixed layer baroclinic instabilities in the upper ocean. The mixed layer is shallow in summer with weak submesoscale activities, but the mesoscale eddies are active. The diagnosis of frontal tendency suggests that the frontogenesis caused by the deformation of mesoscale flows be the main contributor to the submesoscale activities in summer. Also, the energy transformation from mesoscale to submesoscale has significant seasonal variation with the conversion rates of available potential energy and kinetic energy in winter much higher than those in summer, which contributes to richer submesoscale activities in winter than in summer. These results can improve our understanding of the seasonal variation of submesoscale activities and their dynamical mechanisms in the Kuroshio Extension.

Using the measured wave data in 2017 in the central Taiwan Strait, we analyze the basic features of wave, including spectral features, and their relationships with wind. The regression relationship among important characteristic wave parameters and the appropriate wave spectrum form are also investigated. The results are as follows. 1) The most frequently occurring wave direction is NE, and the strong wave direction is NNE. The monthly average significant wave height varies from 0.87 to 2.98 m. The wave height is the smallest in July and the highest in December. The wave period has similar inter-month change to wave height. 2) Mixed waves dominated by wind wave and single-peaked spectra make up the majority. The wave height is positively correlated with the wind speed as a whole. Strong wave is mainly generated by typhoons and strong northeast monsoon. 3) There are good linear correlations between mean wave period and most characteristic period parameters. The significant wave height and its corresponding wave period are strongly linearly related in the directions of NNE and NE. 4) Compared with the Jonswap spectrum, the Code spectrum 1 is more reasonable for the fitting of sea wave spectrum in this area. A spectrum in the form of Code spectrum 1 is given, which is fitted by significant wave height and spectral peak period. These results can provide references for ocean engineering design and numerical simulation of wave.

As one of the three high nutrient and low chlorophyll (HNLC) regions in the global oceans, the growth of phytoplankton in the subarctic North Pacific Ocean is restricted by the trace element iron, which plays an important role in nitrogen fixation, photosynthesis and metabolism of phytoplankton. For an open ocean, atmospheric deposition (atmospheric pollutants produced by human activities as well as dust) is an important source of iron, which can impact biological activities in the upper layer of the ocean. In this study, we use the daily-averaged atmospheric deposition model outputs from the Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) for the period between December 1997 and November 2017, to quantify the flux of atmospheric deposition in the North Pacific Ocean and the corresponding spatial and temporal variability. The results show that the annual flux of atmospheric deposition into the North Pacific Ocean is 26.81 Tg·a^-1, with clear seasonal variation: high flux of atmospheric deposition flux happens during spring and peaks in May, and low values occur in winter. The spatial distribution of atmospheric deposition shows a prominent increasing from the Northwest Pacific Ocean to Northeast Pacific Ocean. In this study, we analysis the response of Particulate Organic Carbon (POC; Aug. 2010) and chlorophyll (Apr. 2001, Apr. 2008 and Aug. 2010) at station K2 (47°N, 160°E) in the Northwest Pacific Ocean to strong dust events, which are defined as the times when high flux of atmospheric decomposition happens. The results show that the POC flux and chlorophyll increase obviously after each dust event because the iron from atmospheric deposition can regulate the growth of phytoplankton and biological pump Thus, the dust events can stimulate the responses of marine ecosystem by promoting ocean primary production.

More frequent and persistent marine heatwaves (MHWs) under global warming have exerted severe ecological and socioeconomic impacts. However, there are still limited studies on the air-sea interaction related to MHWs and how MHWs modulate regional climate. Spatiotemporal distribution of summer MHWs in the Northwest Pacific (NWP) and associated air-sea interaction were systematically studied based on daily Optimum Interpolation Sea Surface Temperature (OI SST) dataset from the National Oceanic and Atmospheric Administration (NOAA) and reanalysis dataset from the National Centers for Environmental Prediction (NCEP) during the period of 1982-2017. Empirical orthogonal function (EOF) analysis of MHWs' frequency shows a linear increasing trend in the first mode except for the Kuroshio extension region, while a north-south “dipole” pattern appears in the second mode, with characteristic of inter-decadal oscillation. Maximum intensity, duration, and cumulative intensity of MHWs all show a linear increasing trend. Maximum intensity and cumulative intensity rise most in the high latitudes, and the duration of MHWs varies significantly in the Kuroshio extension region. Analysis of air-sea interaction illustrates that, when MHWs occur in the mid or low latitudes, latent heat and sensible heat fluxes from the ocean to the overlying atmosphere play a dominant role, which impacts atmospheric circulation in the surrounding area. The atmospheric forcing is more significant when MHWs occur in the high latitudes, including longwave radiation and sensible heat fluxes.

Based on the Pre-industrial Control (picontrol) experiments from 24 Coupled Model Intercomparison Project (CMIP5) models, we assessed these models’ capability in simulating the eastern Pacific ITCZ dipole (EPID) mode and its linkage with models’ climatological simulation capability. The main results are as follows. (1) Most of the CMIP5 models cannot well reproduce the spatial pattern of the EPID mode in February-April (FMA), because of the common biases of modeled Intertropical Convergence Zone (ITCZ), which is mainly located south of the equator during FMA. (2) After seasonal adjustment according to the highest skillscore of EPID mode, the spatial distribution of the EPID mode in most models is more consistent with that in observations. The models with skillscore above 0.7 can simulate the "double ITCZ" climatological precipitation feature during the EPID season. Additionally, the error of the multi-model ensemble (MME) is smaller than that of most CMIP5 models.

Field spectra and water quality measurements were performed in Zhongshan City and its adjacent river network in the Guangdong-Hong Kong-Macao Greater Bay Area. The hyperspectral reflectance characteristic of the river network and its correlation with the concentration of two non-optical activity parameters Chemical Oxygen Demand (COD_Cr) and Total Phosphorus (TP) were analyzed. The results showed that the spectral reflectance of the river network was mainly affected by suspended particulate matter and chlorophyll-a. In the range of 500~680 nm, the spectral reflectance of the water had negative correlations with the concentrations of COD_Cr and TP. Compared with the single band, the reflectance ratio of the specific band had higher correlations with COD_Cr and TP concentrations. The reflectance ratio band combinations with the highest correlations with COD_Cr and TP concentrations are R₆₇₅/R₇₉₄ and R₆₉₀/R₈₁₅, respectively. The water quality retrieval models that depend on the band combination show good estimation accuracy, with 27.2% and 32.1% of the average relative errors, indicating that the hyperspectral technology has good potential application for non-optical activity parameters (COD_Cr and TP) retrieval in the river network of the Pearl River estuary.

In bivalve mollusks, circulating hemocytes phagocytosis is one basic way to eliminate invading pathogens. In this study, we identi?ed a novel Leucine-rich repeat (LRR) domain containing gene (i.e., CgLRRC69) in the Pacific oyster, Crassostrea gigas, which plays an important role in recognizing bacteria and promoting hemocyte phagocytosis. Tissue distribution analysis showed its constitutive expression in various tissues, including hemocytes, gills, muscles, mantle, heart, digestive glands, and gonads. Moreover, CgLRRC69 mRNA was signi?cantly increased and peaked at six hours of post-infection with V. parahaemolyticus in hemocytes. Furthermore, functional assay revealed that recombinant CgLRRC69 protein can specifically bind lipopolysaccharide (LPS), indicating its function in immune defense. Meanwhile, CgLRRC69 protein can also significantly promote phagocytosis of hemocytes. Finally, CgLRRC69 depletion via RNAi in vivo resulted in obvious reduction of bacterial clearance in hemocytes. Therefore, our study demonstrates that CgLRRC69 may function as a pattern recognition receptor for Vibrio spp. and promotes hemocyte phagocytosis. This study contributes to our better understanding of the mechanism of immune defense and disease management in the Paci?c oyster.

Quorum Sensing Inhibitors (QSIs) are promising alternatives to antibiotics, which can reduce the infectivity and virulence of pathogenic bacteria by interruption of quorum sensing (QS) pathways. The strategy aimed at disarming rather than at eradicating bacterial pathogens, and imposed no strong selective pressure on bacteria that can lead to the development of resistance mechanisms. Marine microorganism is one of the most potential sources of novel QSIs. In the present study, actinomycetes strains, isolated from the deep-sea sediment samples obtained from the South China Sea and Indian Ocean, were tested by Chromobacterium violaceum 026 (CV026) model, for screening for QS inhibitory strains. Strain SCSIO 53717 showed inhibitory activity against quorum sensing of CV026. The extract of SCSIO 53717 significantly reduced the production of CV026 violacein, and the extract of the strain showed no inhibitory effects on the growth of CV026 strain within the concentration range from 0 to 1000 mg·mL^-1. This strain was assigned to the genus Kocuria based on morphological characteristics and 16S rRNA gene sequence analysis. To the best of our knowledge, this is the first time that Kocuria is reported to be QS inhibitory active. This result indicates that strain SCSIO 53717 is worthy further studying.

Pyropia haitanensis is an economically important seaweed species, usually cultured by means of raft suspension. The thallus are periodically exposed to air and face desiccation when the tide is low. In this study, we investigated the effects of physicochemical properties of surface water film and desiccation on chlorophyll fluorescence characteristics in emersed thallus of Pyropia haitanensis. The results showed that the increase of the pH value of the thallus surface water film had no significant effect on the maximum quantum yield (Fv/Fm) of Photosystem Ⅱ(PSⅡ), photochemical quenching (qP) and non-photochemical quenching (NPQ), as well as the light utilize efficiency (α) and relative maximum photosynthetic electron transport rate (ETRm). The Fv/Fm, qP, NPQ, ETRm, and α remained stable over the salinity range of 0~75‰. However, when the salinity reached 75‰~150‰, Fv/Fm, NPQ, ETRm, and α declined significantly. High salinity in the thallus surface water film reduced Fv/Fm, NPQ, α, and ETRm by 66%, 84%, 70%, and 60%, respectively. This suggests that the activity of PSII reaction center was inhibited by high salinity in the thallus surface water film. The thallus photosynthetic activity remained stable during the initial stage of water loss. When the thallus surface water film thickness dropped to 0, water was lost within the thallus cells and the photosynthetic activity decreased progressively. Severe dehydration of 75% reduced the Fv/Fm, NPQ, α and ETRm by 41%, 69%, 38% and 43%, respectively. The results showed that the thallus surface water film thickness decreased linearly with the increase of initial water loss. With further water loss, the thallus photosynthetic activity and heat dissipation capacity were negatively affected, and the heat dissipation capacity was more sensitive to the change of water content of algal bodies.

Large-scale cultivation of seaweed Gracilaria lemaneiformis has important economic and environmental benefits. However, the litter decomposition of the seaweed may affect water quality in the cultivation area and its adjacent waters. To investigate the effects of the decomposition of G. lemaneiformis on water quality, a decomposition experiment was carried out for 45 days. The results showed that the concentration of dissolved oxygen (DO) reduced 82.81% in the dried seaweed group compared with the control group, and the concentrations of total nitrogen and phosphorus increased 161.78% and 759.93%, respectively. While DO concentrations in the treatment of fresh seaweed+seawater+sediment (FWS) continuously decreased from 5.56mg·L^-1 to 0.26mg·L^-1 from Day 0 to 21, and then gradually recovered to the control level at the end of the experiment. Significantly increase of nitrogen (36.65%) and phosphorus (177.80%) concentrations in water bodies were also observed in FWS treatment in the mid-late period of the experiment. Meanwhile, the change curves of nitrogen and phosphorus in fresh seaweed treatment were slower and gentler than those of the dried seaweed treatment. The nutrients release rates of fresh seaweed were lower than those of dried seaweed during the litter decomposition process. Sediment promoted the decomposition of fresh seaweed and the release rates of carbon, nitrogen and phosphorus, but had opposite effects on dried seaweed. The weight loss rate and the decomposition rate and the nutrients release rates of G. lemaneiformis followed a descending order of dried seaweed+seawater treatment (DW), dried seaweed+seawater+sediment treatment (DWS), fresh seaweed+seawater+sediment treatment (FWS), and fresh seaweed+seawater treatment (FW). To avoid secondary pollution to the sea water, we suggest that shedding or senescent algae be removed in time during the large-scale cultivation period, and the harvested seaweed should be properly deposed.

Hypnea as one of the raw materials for carrageenan has significant economic value. Due to its wide geographical distribution, strong phenotypic plasticity and lack of detailed anatomical features, the species identification has always been controversial. Using morphological and anatomical methods, we carried out a taxonomic study on genus Hypnea using samples from Shantou, eastern Guangdong province from 2013 to 2014. According to the identification, there are four species, namely Hypnea boergesenii, H. chordacea, H. charoides and H. japonica. We provide the internal and external structural characteristics and geographical distributions of these species, and discuss the division of the family-level taxonomy of Hypnea (Hypneaceae/Cystocloniaceae), including whether H.boergesenii is an independent species.

Cyclic steps caused by supercritical turbidity currents are distributed widely along the West Penghu Canyon in the Taixinan Basin of the northeastern South China Sea. Turbidity currents occur frequently in this area due to high tectonic activities, marine factors such as typhoon and delivery of large sediments from rivers. Using high-resolution bathymetric data, we conduct quantitative analysis on the morphology of 23 net-erosional cyclic steps and 10 net-depositional cyclic steps along the West Penghu Canyon, and compute flow velocity of turbidity currents flowing through these cyclic steps. We find that the flow velocity of turbidity currents has an abrupt change in the transition of net-erosional cyclic steps, while the velocity decreases significantly in the transition from net-erosional to net-depositional cyclic steps. The former is mainly caused by the slope break in the canyon, while the latter is caused by the change from confined to unconfined environment. In addition, the net-depositional cyclic steps are located closer to the southwestern flank of the West Penghu Canyon; and we propose that this phenomenon should be mainly caused by turbidity currents affected by the Coriolis force. Investigating the evolution and controlling factors of cyclic steps in this area can help us better understand the interaction of submarine bedforms and turbidity currents, which plays a significant role in the geomorphological evolution along submarine canyons.

The Kyushu subduction zone is a unique region on the convergent boundary between the Philippine Sea Plate and Eurasian Plate. The zone is an ideal place to study plate interaction within the subduction zone. To understand the stress state and interaction characteristics between plates in the subduction zone in this region, we use 97251 earthquake events beneath 20-km depth in the region to delineate the upper surface of the subduction plate and the section of the vertical trench direction by detailing b-value. We found that the b-value in this area has significant spatial variation, which gradually increases from the northeast to the southwest along the Nankai Trough and Ryukyu Trench. There is also a significant low b-value zone on the subducted Kyushu-Palau Ridge. It is inferred from the negative correlation between the b-value and stress that the ridge has entered the subduction zone, and that the Shikoku Basin ocean crust on the northeast side of the ridge is strongly coupled with the overlying slab of the subduction zone, while the coupling effect of the convergent plates in the subduction zone on the southwest side of the ridge is relatively weak. We believe that the formation times and convergence rates of subduction ocean crusts on both sides of the Kyushu-Palau Ridge played important roles. For the Kyushu-Palau Ridge, the low b-value zone in the shallow part of the subduction zone is mainly due to enhanced coupling between the towering ridge and overlying plate. With the increase of the subduction depth and the steepening of the inclination of the subducting plate, a plate tear along the ridge may occur, thereby releasing the compression-shear stress between the ridge and overlying plate, and causing the degree of coupling to be greatly weakened.

Coral reef limestone is a kind of rock with complex pore structure and large density variation. The relationships between P-wave velocity and pore structure of coral reef limestone and the influencing factors on acoustic properties, however, are not well studied. The P-wave velocity, porosity, and density of coral reef limestone were measured and analyzed in this study. The results exhibited that the P-wave velocity of coral reef limestone varies between 5104 and 5958 m·s^-1, its porosity varies between 1.47% and 17.7%, and its density varies between 2.07 and 2.72 g·cm^-3. We showed that the porosity and density in coral reef limestone were determined by compaction and recrystallization. In addition, the porosity and pore structure also had an effect on P-wave velocity in coral reef limestone. More importantly, the structure and stability of coral reef limestone can be determined by the ratio of S-wave and P-wave velocities. The acoustic properties of coral reef limestone can provide important support for the stability of engineering.

Mariculture has become a major source of pollution in offshore waters. Chlorophyll-a, as a parameter of primary productivity, is an important indicator of water quality evaluation. We took Zhelin Bay of Guangdong Province as our study area. Using Sentinel-2 spectral image on September 4, 2018 and in-situ measured chlorophyll-a concentration, we constructed an estimation model of chlorophyll-a concentration to obtain the spatial distribution of chlorophyll-a concentration. In the chlorophyll-a concentration inversion model, we selected a linear regression model, a three-band model and the Normalized Difference Chlorophyll Index (NDCI) for comparative analysis. Through comparison and evaluation, a model with high inversion accuracy was used to estimate the chlorophyll-a concentration in multiple months of 2018 and analyze its distribution characteristics. The results showed that the inversion accuracy of the NDCI model was significantly higher than that of the other models. The decision coefficient R² of the NDCI model was 0.8, the root mean square error (RMSE) was 9.7, and the mean absolute percentage error (MAPE) was 0.99. The time applicability of the NDCI model was tested by the measured data, which showed that the NDCI model could more accurately and effectively estimated the spatial distribution characteristics of chlorophyll-a concentration. The chlorophyll-a concentration showed a trend of decreasing from nearshore to the outside of the bay. The overall trend of chlorophyll-a concentration in the aquaculture area was as follows: pond breeding area > tidal flat breeding area > cage culture area > floating raft breeding area. Under the influence of water exchange, rainfall and culture activities, the concentration of chlorophyll-a in the culture area of the fish pond was the lowest in February when the fish was in the seedling stage, and its change trend was February < April < June < December. This study provides a valuable reference for environmental monitoring of marine aquaculture waters in Zhelin Bay.

The drag coefficient and aerodynamic roughness length of the sea surface are essential in calculating momentum, heat and water-vapor exchanges between the air and sea. With the observations collected by eddy covariance systems during typhoons Hagupit and Chanthu, we investigated parameterization relationships of 10-m wind speed with friction velocity, drag coefficient, and aerodynamic roughness length of the sea surface. Results show parabolic relationships between drag coefficient and friction velocity, and between drag coefficient and 10-m wind speed; results also show exponential relationships between aerodynamic roughness length and friction velocity, and between aerodynamic roughness and 10-m wind speed. We found that the critical friction velocity is 0.83 m·s^-1 and critical 10m wind speed is 23.69 m·s^-1.

The Mozambique Strait and its adjacent coastal area are one of the areas with the strongest tidal current and energy dissipation in the world. In this study, the high-resolution MIT general circulation model (MITgcm) is used to simulate the barotropic current in this area, and the characteristics of tidal energy flux and dissipation are analyzed. The results show that the tidal waves in the Mozambique Strait and its adjacent coastal area are dominated by the semidiurnal tide while the diurnal tide can be ignored. The M₂ barotropic tide forms an anticlockwise rotary tidal system and a clockwise rotary system, and the S₂ barotropic tide forms an anticlockwise rotary tidal system only. The M₂ and S₂ barotropic tidal currents in the Mozambique Strait and the southern part of Madagascar are counter-clockwise, and those north of Madagascar and other local areas are clockwise. The current velocity is large in the strait and over rough topography. The tidal energy mainly divergences at the east boundary while most of that convergences at the Mozambique Strait along the northern part of Madagascar Island. The tidal energy flux of M₂ (S₂) barotropic tide passing through the northern part of Madagascar Island and the Mozambique Strait is 156.86 GW (40.53 GW) and 148.07 GW (36.05 GW), respectively. The dissipation induced by bottom friction mainly occurs in the Mozambique Strait and the south and north of Madagascar Island. The bottom friction dissipation of M₂ (S₂) barotropic tide is 1.762 GW (0.460 GW) in the Mozambique Strait, accounting for 43.74% (39.72%) of the total dissipation in the water column.

We compare four observations and reanalysis datasets (SSM/I&SSMIS, RSS V7R01, ERA5, and MERRA-2) in terms of climate states of global water vapor. The variation and long-term trend of total column water vapor (TCWV) of different scales are also explored. The results indicate that the spatial distribution, seasonal cycle and interannual variability of the four datasets are consistent. From 1988 to 2018, the TCWV had an increasing trend in the tropical oceans. The interannual changes of the TCWV are significant and highly correlated with the El Ni?o-Southern Oscillation (ENSO). The datasets of ERA5 and MERRA-2 should be used with caution when analyzing TCWV trend in a short period (e.g., 1991—1997). When studying the long-term water vapor trend in the tropical regions, MERRA-2 data should be used carefully because the long-term trend is different from other datasets.

Epsilon-proteobacteria is widely distributed, from deep-sea hydrothermal vent to surface sea water, from free-living environment to host-associated one. Chemotaxis plays an important role in bacteria survival through sensing and responding to environmental changes. Thus, some bacteria have evolved into many complex and diverse chemotaxis systems. Epsilon-proteobacteria can adapt to different environments; especially, some species can survive in the deep-sea extreme environments including hydrothermal vent and cold seep, whose chemotaxis system may have special characteristics. Bioinformatics analyses by BlastP and MIST database revealed that most Epsilon-proteobacteria species in the deep-sea hydrothermal vent have F3 type chemotaxis system. They all contain a single copy of CheV, which is a double domain fusion protein. Besides, a unique domain, CZB (C-terminal Zinc-Binding) domain, exists in chemoreceptors of deep-sea Epsilon- proteobacteria. A CZB-like domain is also identified in Epsilon-proteobacteria. Using the model strain Campylobacter jejuni 81-176, we confirmed that CheV can interact with all chemoreceptors with MA domain by bacterial two-hybrid experiments. Additionally, we demonstrated that CZB-like domain cannot bind Zn by ICP-Mass, but it can promote the interaction between chemoreceptor Tlp9 and CheV.

(R)-1-phenylethanol is a key chiral building block in the synthesis of chiral drugs, and plays important roles in the synthesis of many chiral compounds and in the industrial production of medicines and spices. The strain Bacillus sp. DL-2 screened from the deep-sea sediments of the western Pacific Ocean was broke, and the obtained intracellular proteases can asymmetrically hydrolyze (±)-1-phenylethyl acetate to obtain (R)-1-phenylethanol. Three different ways, namely, surfactant, lysozyme and ultrasonic, were utilized to crush Bacillus sp. DL-2. After the optimizations of the surfactant and lysozyme crushing methods, the optimal working conditions were found to be 0.5% TritonX-100, 35 ℃ and pH 7.0 for 2 h. After process optimization, (R)-1-phenylethanol was obtained with an enantiomeric excess of 96% and a conversion of 23%, which provide reference for using intracellular proteases to produce chiral chemicals.

Daya Bay is experiencing ecological problems such as eutrophication and frequent algal bloom under the pressure of intense anthropogenic activities. The Dan’ao River is the largest rive entering Daya Bay. We found the concentrations of total dissolved nitrogen and phosphorus at the Dan’ao River estuary reached 85.3 and 1.5 μmol·L^-1, respectively. In situ enrichment experiments were conducted to explore the effect of estuary water from the Dan’ao River on phytoplankton community. Our results showed filtered water (0.2 μm) from the Dan’ao River estuary promoted total Chlorophyll a (Chl a) and phytoplankton abundance, and shifted the dominated Chl a size structure to smaller size (0.7 ~ 20 μm), and also increased the relative abundance of dinoflagellates (Scrippsiella trochoidea and Prorocentrum spp.). The phytoplankton size structure and species composition changed in the same pattern under the addition of dissolved organic nitrogen (DON) of urea. Although combined addition of dissolved inorganic nitrogen and phosphorus increased total Chl a and abundance, the phytoplankton size structure and dinoflagellate abundance did not show significant changes. Our results demonstrate that DON may be the causative nutrient component that leads to miniaturization of the phytoplankton community and promotes the growth of dinoflagellate by comparing the enrichment results of estuary water to N and P nutrient enrichments. These results indicate the significance of DON for eutrophication and harmful algal blooms in Daya Bay, which should be included in management strategies of coastal water eutrophication.

Based on the vertically stratified sampling of zooplankton in the continental slope of the northeastern South China Sea (SCS) in March and September 2016, the seasonal and vertical variations in zooplankton species composition, abundance, and biomass were analyzed and compared to explore the factors affecting their differences. A total of 225 species of zooplankton was identified; 150 species appeared in March, and 169 species, in September. There were 132 species of copepods, followed by 18 species of chaetognaths and siphonophores, respectively. The number of zooplankton species was the highest in the 50 ~ 100 m water layer and generally decreased with the increase of water depth. The abundance and biomass of zooplankton were mainly concentrated in the range of 0 ~ 100 m, and both of them decreased with the increase of depth in the deeper water layer. However, above 60% of the biomass concentrated within the layers between 100 and 1000 m. The abundance of dominant species had obvious seasonal and vertical variation. In March, the abundance of coastal species such as Undinula vulgaris and Canthocalanus pauper was higher above the depth of 100 m. In September, the abundance of oceanic species such as Cosmocalanus darwinii and Lucicutia flavicornis was high in the upper layer of 100 m. Calanoides carinatus showed higher abundance and average body length in March than in September, and the larger body length appeared mainly in deep layers. The zooplankton community could be divided into three groups of 0 ~ 100 m, 100 ~ 400 m, and 400 ~ 1000 m, which was mainly caused by the differences in the composition and abundance of different water layers. Zooplankton abundance and biomass were significantly positively correlated with temperature and chlorophyll a concentration. The seasonal and vertical variations in zooplankton abundance and biomass were driven by monsoon, coastal currents, and mesoscale eddies in the continental slope of the northeastern SCS.

In this study, Sargassum fusiforme was treated at 27 ℃ and 32 ℃, and Sargassum fusiforme grown at 22 ℃ was used as control. Air bladders were collected at 0, 1, 3, 5, and 7 days of the treatment, respectively, to explore the effects of high temperature stress on membrane damage, osmotic regulation and antioxidant protection of Sargassum fusiforme. The results showed that the membrane system of Sargassum fusiforme was damaged by high temperature stress, which resulted in ion extravasation in vivo, and membrane lipid peroxidation; and the relative conductivity and Malondialdehyde (MDA) content of cells increased. Soluble protein, soluble sugar and proline were accumulated in the cells. Soluble protein was always higher than the control under high temperature stress, and reached the maximum value at 7 days. Soluble sugar and proline increased first and then decreased in the high temperature stress group, but they were always higher than those in the control group. Soluble sugar reached the maximum value at 3 days under high temperature stress, and proline reached the maximum value at 5 days under high temperature stress. After high temperature stress, Sargassum fusiforme can reduce the damage of high temperature stress mainly by increasing the activity of antioxidant enzyme Superoxide dismutase (SOD), while the activities of Peroxidase (POD) and Catalase (CAT) decreased in the process of high temperature stress. In a word, Sargassum fusiforme is more sensitive to high temperature stress. The higher the temperature is, the longer the treatment time is, the greater the damage to Sargassum fusiforme is.

To identify the immunity function of Aquaporin of Pinctada fucata martensii (PfAQP4), the mRNA expression patterns of PfAQP4 and immune-related genes were detected by qPCR after immunostimulation and RNA interference. The results showed that the mRNA expression of PfAQP4 in the mantle was significantly up-regulated at 24 h (p < 0.05), while that in the digestive gland was significantly down-regulated at 12 h, and increased at 24 h, 36 h and 48 h after LPS injection (p < 0.05). After poly (I : C) injection, the expression of PfAQP4 was significantly up-regulated in the mantle at 36 h and 48 h (p < 0.05), and up-regulated at 48 h in the digestive gland (p < 0.05). When PfAQP4 was knocked down by RNA interference, the mRNA expression of CuZn-SOD in the mantle was significantly down-regulated (p < 0.05); a significant positive correlation of expression level between CuZn-SOD and PfAQP4 was found (r = 0.818, p < 0.001). We showed that PfAQP4 plays an important role in the immune response of P. f. martensii, which provide new data for the innate immunity of P. f. martensii.

The study of fault activities since the late Miocene in the shelf area of the Qiongdongnan Basin helps us understand its tectonic evolution. Such study plays an important role for the safety evaluation of drilling platform, oceaneering and regional stability evaluation. In this paper, the fault characteristics in the Qiongdongnan Basin are analyzed with statistics and the throw-depth (T-Z plots) to quantitatively analyze the fault activities in the region, and to discuss the causes of fault activity change. The faults in the study area were growth faults, the strike was mainly concentrated in the NWW, and most faults ceased in the Late Miocene period. Our quantitative results show that the fault activities changed in the Late Miocene period (5.5 Ma). The value of fault throw in the south part of the study area was much larger than that in the north. Based on the above results, we propose that the faults have been affected by tectonic stress in the process of growth, and the fault activities changed at the end of the late Miocene, from inverse fault to positive fault. The Red River Fault Zone played an important role in the tectonic evolution of the Qiongdongnan Basin, and the controlling factor of this change may be due to the tectonic reversal of the Red River Fault Zone. The reversal of the strike-slip motion of the Red River Fault Zone in 5.5 Ma was coupled with the change of the fault activities and the reverse of the faults in the study area.

Based on ocean surface currents observed by the High Frequency Ground Wave Radars (HFSWRs) from April 2019 to May 2020, the characteristics of tidal and residual currents in the central eastern sea area of Hainan Island were studied. The results show that the tide in the central eastern sea area of Hainan Island mainly belongs to the irregular semidiurnal tide. The movements of the semidiurnal tidal currents M₂ and S₂ are mainly in the form of reciprocating current, and the movements of the diurnal tidal currents O₁ and K₁ are mainly the form of clockwise rotary current. The spatially averaged amplitudes of M₂, S₂, O₁, and K₁ have a ratio of 1 : 0.51 : 0.60 : 0.65; and the semidiurnal tidal current M₂ is dominant among the four tidal current constituents. The probable maximum current velocities increase gradually from southwest to northeast, and the maximum is 35 cm·s^-1. Due to the influence of the East Asian monsoon, the residual currents have significant seasonal variation, with summer (from June to August), winter (from September to February of the following year) and transitional (from March to May) types. For the summer type, the directions of the residual currents are basically northeast, and the average velocity is 29 cm·s^-1. The residual currents of the winter type flow toward the southwest, and the average velocity is 36 cm·s^-1. Note that the residual currents of the winter type are greater than those of the summer type. The residual currents of the transitional type have complex directions, and the average velocity of 13 cm·s^-1. Overall, the southwest residual currents have the largest velocity and last the longest time during the year, and therefore the material transport in surface sea water is from northeast to southwest in the central eastern sea area of Hainan Island.

In view of different wave height and period in the South China Sea, the design of Wave Glider wing parameters is studied to obtain greater thrust. Based on the reanalysis data set of ERA5, we provide statistics on the wave height and wave period of different seasons and induced by one typhoon in the South China Sea. In addition, the software FLUENT is used to study the influence of the maximum limit angle, the position of rotating axis and the spacing of the wings. The simulation results show that the larger the wave height, the larger the maximum limit angle should be in order to ensure that the wings can get more thrust. Under the conditions of wave height and period in the South China Sea, it is better to select 1/5 of the front of the wing as the position of rotating axis. Increasing the spacing of the wings properly can improve the thrust. By simulating the flapping wings, the thrust generated by the wings under different parameters is obtained, which provides a reference for the design of the wings.

Island ecological Internet of things (marine IoT) is a new technology, which combines island ecological environment monitoring with the IoT and plays a positive role in integration and sharing of ecological environment monitoring information, disaster prevention of marine ecosystem, and scientific exploitation of coastal and marine resources. We developed the ecological and environmental IoT for typical uninhabited island, according to the practical application requirements of coral ecological restoration and humanity environment characteristics in Miaowan Island of Zhuhai. We also studied in detail the key technologies of ecological IoT such as ecological environment parameter sensing technology of underwater, communication relay and power supply remote control technology on the offshore, large capacity data transmission and remote work control based on wired local area network (LAN) and wireless wide area network (WAN), and the ecological information management technology on the terminal server in the laboratory. These technologies provide a useful reference for the development of marine IoT in island ecosystem, and provide a technical support for island ecological restoration and health assessment.

A new type of underwater acoustic buoy platform with target detection capability has been developed by combining vector hydrophone with profile buoys. The acoustic buoy can achieve multiple floating and diving, and has the characteristics of long in-position time, high concealing performance and low cost. The use of multiple underwater acoustic buoys can quickly form a large area coverage. To verify the underwater acoustic buoy’s detection performance on ocean targets, a large scale underwater acoustic buoy platform trial was carried out in the South China Sea in August 2019. The results are as follows: under the typical sound velocity profile of the South China Sea, the acoustic buoy has a maximum detection distance of 13.8 km to the surface vessel with a length of 42 m and a speed of 8.4 kn. The root mean square error (RMSE) of target estimated azimuth can reach 5°, and the standard deviation will be up to 2° when the distance between the acoustic buoy and surface vessel is less than 1.9 km.

Microbe-mediated nitrification is an essential part of global nitrogen cycle; and nitrite-oxidizing bacteria (NOB), which catalyze the second step of nitrification, have received more and more attention recently. Up to date, those isolated NOB have been identified as four phyla, belonging to seven genera. Among them, Nitrospira bacteria become a hotspot for research due to the high diversity and wide ecological distribution. In this paper, we reviewed the composition, phylogenetic relationship, nitrite oxidizing and carbon fixation pathways of NOB. We also emphasized the functional importance on global nitrogen and carbon of NOB, and highlighted research prospect for NOB.

Mangroves are salt-tolerant plants of tropical and subtropical intertidal regions distributed mainly between latitudes 25°S and 25°N globally. They have high productivity, high return rate, high decomposition rate, and high resistance, which cover roughly 60%-75% of the world’s tropical coastlines. Mangroves are distributed over more than 118 countries with a total area near 17 million hectares in the world, and their net primary productivity is up to 2000 gC·m^-2·a^-1. They form a widespread ecosystem and also play an important role in the process of global change. Global climate change has aroused great concerns in the last three decades. Mangroves are a vulnerable and eco-sensitive ecosystem along tropical and subtropical intertidal shores that are regulated by both lands and oceans. They are one of the typical marine ecosystems that can be affected by global climate change. As an important ecological barrier along the coast, global climate change will also affect the survival and distribution of mangroves in the world. The present paper briefly reviews the impacts of global climate change on mangroves in terms of global warming, sea-level rise, atmospheric CO₂ concentration increase, and extreme weather. The ongoing global climate change will bring great challenges and opportunities to research, maintenance, and development of mangroves in the future.

As the largest marginal sea in the western Pacific, the South China Sea (SCS) plays an important role in the global ocean and the global oceanographic research. In the past 40 years, chemical oceanographic research in the SCS achieved systematic new discoveries and new understandings; researchers put forward many new theoretical viewpoints, making important contributions to the development of oceanography. A subsurface layer was revealed in the SCS, maximum values of ecological environmental parameters represented by nitrite are present; and the depth ranges of water layers for different parameters are different, forming a thermocline ecosystem that has significantly different characteristics from the other ecosystems. The carbon cycle process in the SCS is very complex, and changes of the biological pump controlled by biological activities, and the regional and seasonal changes of carbon sources and sinks, are all great. The characteristics and intensity of carbon sources and sinks in the SCS are unique in different regions at different times. Annually, the SCS is a weak source of atmospheric carbon dioxide. The characteristics of ecological environment and the cycling process of chemical material in the Pearl River Estuary and deep-sea basins were found not only closely related to but also significantly different from that in shelf marginal seas and coral reefs, as the dissolved oxygen concentration is low in the bottom, and the Pearl River Estuary is basically an ecologically fragile area characterized by hypoxia. Based on the systematic understanding of the rapid material circulation and vertical transfer of chemical substances controlled by biological processes in the Nansha coral reef ecosystem, a new mechanism - “resembling drift-net theory” - was proposed to explain how the coral reef ecosystem could maintain high productivity. Systematic studies on the sedimentary chemistry of the SCS show that there is a close coupling between the sediments and chemical cycling of water bodies. The distribution of chemical substances in coral reefs or in sediment cores of the SCS can be used to retrieve historical environment changes. The paleo productivity of surface seawater in the SCS during the glacial period was 1.6 times higher than that of the interglacial period. A "biological explosion event" occurred in the southern SCS in the late Miocene. The productivity in that period was mainly affected by the monsoon and terrigenous nutrients input, while the influences of northeast monsoon and southwest monsoon differed in different regions. These new discoveries and new understandings in chemical oceanography of the SCS in the past 40 years have laid a strong foundation for further systematic and in-depth understanding of the oceanographic processes in the region. In the future, chemical oceanographic research will definitely provide scientific support for the sustainable utilization of resources and environment in the SCS.

The key project of "Deep Structure survey and study on the Manila subduction zone in the eastern South China Sea (SCS)" was funded from the major research program "Deep Sea Processes and Evolution of the SCS" of the National Natural Science Foundation of China (NSFC) during 2015-2018. This project focuses on the Manila subduction zone to resolve the formation and evolution of the SCS using geological and geophysical methods. Five comprehensive geophysical surveys were successively carried out during the project period with the help of NSFC open cruises. A total of 73 Ocean Bottom Seismometer (OBS) stations and five Ocean Bottom ElectroMagnetometers (OBEM) have been deployed; and 13,872 airgun shots were fired. Totally 60 OBSs and five OBEMs have been recovered, and a large amount of data have been acquired. At the same time, a series of innovative results have been obtained. (1) The crust of the northeastern SCS has been determined as a 12-15 km thinned continental crust affected by volcanic activities after post-rifting phase based on the results of active seismic and earthquake tomography; and its continent-ocean boundary (COB) was also determined. (2) According to the multi-channel seismic reflection profile, the detailed structure of the accretionary wedge front of the northern Manila subduction zone was delineated. (3) The SCS oceanic crust domain when the seafloor spreading stopped has been outlined. (4) The tectonic evolution model of the SCS and the Philippine Sea Plate (PSP) was constructed. This project not only contributes substantially to the key scientific question (age and process of seafloor spreading) of the major research program "Deep Sea Processes and Evolution of the SCS," but also provides important basic data for the "skeleton" of the tectonic evolution and life history of the SCS from seafloor spreading to plate subduction, which has a far-reaching scientific significance.

As an important expression of Earth’s movement and a migration way for fluid-rich materials from substrates to the surface, mud volcanism and the entrained materials carry with ample information that is important for understanding the geodynamics, stratigraphic lithology, resources, and environment. Featuring thin (~1 km) Cenozoic Erathem and considerably thick (>5 km) Mesozoic Erathem, the Dongsha Waters is deemed as the best but unproven prospect for petroleum sourced from the Mesozoic Erathem. It is also rich with seamounts and submarine hills that are believed as magmatic volcanoes, a potential risk factor for petroleum accumulation. However, it is revealed from recent geophysical surveys that many of the seamounts and hills have developed with remarkable diapiric deformation and faults, fluid infill-led blank reflection zone, fluid seepage, and emission. By sampling with box dredges over tens of seamount and hill, plentiful authigenic carbonate nodules and deep-water corals, sponges, etc., have been collected, which feature them mud volcanoes. Discovery of the mud volcanoes shows favorable conditions for petroleum source and migration over the waters, and provides excellent lines to explore the petroleum and gas hydrates sourced from the Mesozoic Erathem. Abundance of deep-sea coral, sponge and others implies the Dongsha mud volcanoes as potential province for deep-sea coral and sponge reefs, meaningful to study the relationship among petroleum seepage, growth of chemosynthetic community and marine environment.

The coasts of coral reefs and islands are characterized with very complex wave-current dynamics, unique morphology and largely unknown engineering responses, where wave transformation and wave-induced currents have significant impacts on the infrastructure safety, morphological evolution, disaster prevention, and eco-environmental protection. Recent research advances on these topics are reviewed with respect to three spatial scales, e.g., the large-scale long-wave guiding and trapping, the medium-scale hydrodynamics in a reef-lagoon-channel system, and the local wave-structure interaction. This paper includes the descriptions of, specifically, theoretical findings of guided and trapped waves over ocean ridges and around reef islands, two-dimensional horizontal wave basin experiment of a reef-lagoon-channel system, and new methods to estimate wave overtopping and forces on the seawall based on a large-scale wave flume experiment. Further research prospects are also suggested.

The air-sea turbulent heat fluxes (THFs), including the evaporative latent heat flux and convective sensible heat flux, are key components in air-sea interaction and ocean circulation, which are important for our understanding of the global energy balance, water cycle and climate change. Due to the limitations of observations and numerical simulations, the diurnal variations in THFs are however not accurately known. In this paper, we propose a future research plan toward identifying the mechanisms behind diurnal variations in THFs. With the recent development of traditional buoy observations, new observations (e.g., glider) and newly released atmospheric reanalysis, it is helpful to research the diurnal variations in THFs. Using the combined observations and reanalysis, we investigate the key scientific issues on diurnal variations in THFs under different boundary layer stability based on the bulk formulas and turbulence methods. In the future, we will demonstrate the global basic structures and dominant factors for diurnal variations in THFs, as well as the strength of the diurnal variation associated with the extreme weather processes and climate events. To evaluate accurate magnitudes of THFs for better understanding of diurnal variations, high-frequency surface currents and height-dependent air-sea physical variables will be incorporated into the estimates of THFs in terms of bulk formulas. Innovatively, this study transfers the multi-scale THF variations into the space of boundary layer stability to concentrate on the diurnal variations, which help study the mixed-layer dynamics, upper-ocean ecosystems, energy balance, and climate change.

Mangrove is one of the most important ecological and environmental resources in the world, which can have significant effects including reservation of the organic carbon, accretion of the tidal flat, and protection from ocean hazards. In this study, we reviewed studies of the mangrove tidal flat (MTF) sedimentary dynamics, which involve damp energy and sediment trapping of the MTF, bio-geomorphological behavior of the MTF, and response of the MTF to storm and sea-level rise. We stress that understanding of the MTF sedimentary dynamics should focus on the following scientific questions: attenuation of the coupled dynamics between wave and tidal current along MTF, coupling processes among hydrological dynamics, deposition, geomorphology, and vegetation. Moreover, it is urgent that the study of regional-scale sedimentation processes and driving mechanics of MTF should be intensified in future.

Anaerobic oxidation of methane (AOM) by archaea in marine sediments is gradually recognized by scientists and is regarded as an important biogeochemical process performed by both methanotrophic archaea and sulfate-reducing bacteria. Our analysis of 16S rRNA showed that multiple kinds of Methanoarchaea including AEME-1, AEME-2 and AEME-3 were the players in the AOM process, and these Methanoarchaea were distributed widely in the oxygen minimum zone of the open ocean. Furthermore, AOM process is related to the global environmental change closely. Most methane leaked from cold seeps of deep sea was consummated by Methanoarchaea in the course of penetrating the deposition layer of anoxic zone; so emission of strong greenhouse methane was reduced greatly. The studies of AOM biogeochemical process should be significant for understanding the formation mechanism of clod seep carbonate, controlling the leaking methane from seafloor, exploitation of combustible ice, and so on.

We use bibliometrics to analyze journal articles with related themes published in and before 2019, to comprehensively evaluate ocean remote sensing applications in the South China Sea (SCS), especially in terms of its U-boundary. We employed CNKI (China National Knowledge Infrastructure) and WOSCC (Web of Science Core Collection) as the representatives of journal article databases in Chinese and in foreign languages, respectively. The classifying selection results are as follows: 10150 articles in Chinese and 10130 in foreign languages were published on natural sciences of SCS, 560 in Chinese and 1296 in foreign languages on remote sensing of SCS, and 303 in Chinese and 33 in foreign languages on the U-boundary of SCS. The bibliometric analysis shows that the country with the most articles in all kinds of languages was China (18253), where the top publishing institutions (such as No. 1 South China Sea Institute of Oceanology, Chinese Academy of Sciences) and the journals (such as No. 1 Journal of Tropical Oceanography) were primarily from. The annual article qualities on SCS natural sciences experienced four stages (slow start, slow growth, fast growth, and fallback), those on SCS remote sensing experienced two stages (slow start and fast growth), while those on the U-boundary experienced three stages (slow start, fast growth and fallback). The research hotspots of SCS natural sciences were monsoon, gas hydrate and typhoon, while the research hotspots of SCS remote sensing were sea surface temperature, chlorophyll and typhoon, and those of the U-boundary were SCS disputes and geologic features. Our study finds that it was in 1974 that remote sensing data were first applied to the research of SCS typhoons, and it was in 2019 that remote sensing data were first used on ecological environment research of the U-boundary. It is of great significance to develop comprehensive scientific research on the U-boundary corridor in SCS by developing remote sensing technology.

Offshore wind power is a clean renewable energy source. In this paper, the development history of offshore wind power is briefly reviewed, the current offshore wind power projects under construction in Guangdong Province in the northern South China Sea are introduced, and some typical marine hydrodynamic processes and their existing problems in in-situ observations are described. Finally, a view on constructing synchronous real-time in-situ observational system of marine hydrology in the northern South China Sea based on the offshore wind power field is put forward, and the advantage of using these synchronous real-time network in-situ observational data on the study of oceanic meso- and small-scale dynamic processes is noted. This paper would be significant and valuable to the integrated development of offshore wind power and marine science study.