A specimen collected from the Beibu Gulf in October 2016 was identified as Taeniopsetta ocellata (Günther, 1880) belonging to genus Taeniopsetta (Pleuronectiformes: Bothidae). Such genus and species are reported for the first time from the coastal waters of mainland China. Characters of genus Taeniopsetta mainly include the following: body ovate; both eyes on the left side of body; mouth rather small; teeth uniserial on both sides; scales small, lateral line only on ocular side, absent on blind side; one strong rostral and two or three orbital spines present in males, feeble or absent in females; first ray of ventral fins on the blind side opposite to the second ray on the ocular side; base of ventral fins short; and some of the rays of the dorsal and anal fins prolonged into filaments. The diagnostic features of T. ocellata are as follows: pectoral fins unequal on both sides; the 13th to 17th dorsal-fin rays and six anterior rays of anal fins elongated and filamentous in males; 2~4 irregular V-shaped or semicircular hollow blotches within yellow spots on the upper and lower body on the ocular side.

As an omnivorous and widespread fish in tropical coral reefs, Balistapus Undulatus is an important sea urchins predator according to previous observations. However, the accurate food composition and ecological function of B. Undulatus remain unclear due to the lack of food composition information in natural environment. Here, we studied samples of triggerfish collected from the coral reef of Nansha in the summer of 2017. We used the high-throughput sequencing method targeted on the Cytochrome c. Oxidase subunit I (COI) gene and stable isotopes method to analyze the gut content composition of B. Undulatus, and conducted trophic levels analysis. Thirteen species were detected, including Arthropoda, Chordata and Annelida. Crabs of the Xanthidae family were the most important food item, such as Etisus sp., Luniella pubescens and Liomera rugata, accounting for 61.8%, 6.7% and 1.8%, respectively. Fish also made a contribution, accounting for 23.5% of the total food sequence. The isotopic results show that the trophic level was 3.71±0.07, which was consistent with the results of molecular detection. The results show that the main food of triggerfish (B. Undulatus) was small crustaceans and herbivore parrotfish. This study deepens our understanding of the ecological role of triggerfish.

Ecological carrying capacity assessment is the basis and premise for reef organisms of maintaining the health of coral reef ecosystem. Based on the survey data of the fishery resources and ecological environment in 2019, we developed an Ecopath model of the Qilianyu Islands coral reef ecosystem in the South China Sea. The ecological carrying capacities of some functional groups were analyzed by using the Ecopath model. The results show that the coral reef ecosystem was dominated by the grazing pathway, and the proportion of total energy flow originating from primary producers was 57%. Overall, the ratio of total primary productivity to total respiration was 2.54, and the ratio of total primary productivity to total biomass was 19.07. The connectance index and system omnivory index were 0.35 and 0.18, respectively. Outputs of the Ecopath model show that the maturity and stability of the coral reef ecosystem of the Qilianyu Islands were relatively low, and the ecosystem had weak resistance to external disturbances. Under the condition of stable ecosystem construction and sustaining the ecosystem, the ecological carrying capacities of functional groups of coral, bivalve and phytophagous fish were 25.09~53.77 t•km^-2, 2.55~39.95 t•km^-2 and 4.89~17.94 t•km^-2, respectively; their biomass still has a large growth space. The maximum ecological carrying capacity of coral reef fish communities was closely related to the multiplication of coral reef invertebrate communities. In the future of coral reef fishery management, the system design of stock enhancement should be considered from the perspective of the overall structure of the ecosystem.

Quorum sensing (QS) is a process of bacterial cell-cell communication in which bacteria can monitor their population density by detection of extracellular autoinducer. QS allows the bacteria to switch between two kinds of gene expression modes: The program is suitable for individual development at low cell density, while favoring community at high cell density. Presently, there are mainly seven kinds of QS signaling molecules, including oligopeptides, AHL (Acylated Homoserine Lactones), AI-2 (Autoinducer-2), CAI-1 (Cholera Autoinducer-1), PQS (Pseudomonas Quinolone Signal), AI-3 (Autoinducer-3), and DSF (Diffusible Signal Factor). Among them, oligopeptides mainly exist in gram-positive bacteria, and the others are commonly found in gram-negative bacteria. Species of the Vibrio genus are important pathogens for human and aquaculture. Since traditional antibiotic treatment has a strong selection pressure leading to increasing number of drug-resistant Vibrio and increasing serious problems, QS quenching is believed as one alternative strategy of the most potential to combat bacterial infection. Thus, it is necessary to investigate the distribution of QS pathways among the Vibrio genus. Among the 46 whole genome sequenced Vibrio species, we found that only three pathways exist in Vibrio species, including AHL, AI-2 and CAI-1 pathways. Specifically, five Vibrio species contain the above three pathways, and 30 strains contain both AI-2 and CAI-1 pathways. However, none of the 46 Vibrio species have the PQS, AI-3 and DSF pathways. In addition, the distribution of QS pathways in Vibrio is related to their phylogeny, suggesting that species with the same QS pathway(s) are close relatives, which indicates that the genes of this pathway evolved from their common ancestor. This study provides useful information for QS quenching against Vibrio pathogens by targeting the AI-2 and CAI-1 QS pathways.

The C-type lectin superfamily is a class of immune proteins that can recognize and bind to polysaccharides. In this study, a new type C-type lectin gene of Crassostrea hongkongensis was cloned for the first time, and the full-length sequence of the gene was obtained. The results show that the full length of ChPerlucin gene cDNA is 577 bp, including 5′-untranslated region (UTR) in 21 bp, 3′-UTR in 73 bp, and an open reading frame (ORF) in 483 bp open reading that code 160 amino-acid polypeptide. The predicted molecular mass is 18kD, and the isoelectric point is 5.95. Amino acid sequence alignment showed that the Perlucin gene of Crassostrea hongkongensis contains a conserved carbohydrate recognition domain (CLECT). Neighbor-Joining (NJ) evolutionary tree analysis showed that ChPerlucin clustered with Perlucin from other shellfish, indicating that this gene is a new member of the Perlucin family of mollusks. The results of qRT-PCR showed that ChPerlucin was broadly expressed in various tissues and during different stages of the oyster’s embryonic and larval development; the expression of ChPerlucin increased significantly after bacteria stimulation; the recombinant protein ChPerlucin was successfully expressed using Pichia pastoris eukaryotic; and we find that ChPerlucin recombinant protein has antibacterial effect. The above results indicate that ChPerlucin plays an important role in the innate immunity of Crassostrea hongkongensis.

Alliroseovarius sp. Z3 was isolated from guts of Litopenaeus vannamei. In the study, Illumina Hiseq sequencing platform was used for genome sequencing; then, the genome was assembled, annotated by software SOAPdenovo etc., and compared with other five similar type strains. Genome annotation results showed that Z3 genome consists of 3525503 bp with a guanine-cytosine (GC) content of 59.4%, and 3509 protein-coding genes. The results of 16S rRNA sequence alignment, average nucleotide identity (ANI), DNA-DNA hybridization (DDH) and collinearity analysis showed that strain Z3 had the highest 16S rRNA similarity with Aliiroseovarius crassostreae CV919-312^T, at 98.20%, and had the highest DDH and ANI values with Aliiroseovarius sediminilitoris DSM 29439^T, at 26.80% and 84.95%, respectively. It was considered to be a new species of Alliroseovarius, and was named Aliiroseovarius sp. Z3. Comparative genomic analysis displayed that Aliiroseovarius sp. Z3 shared 2005 core orthologous gene clusters with other five similar type strains, and Z3 had 413 specific genes that are related to carbohydrate transport and metabolism, amino acid transport and metabolism, replication, recombination and repair, etc. After functional annotations, we found that Z3 possesses a complete denitrification pathway, indicating that Z3 can utilize nitrate and nitrite in the environment. These results related to the genome features and comparative genome of strain Z3 not only enrich the gene source of Aliiroseovarius genus, but also provide a molecular basis for studying its characteristics of denitrification.

The South China Sea (SCS) is one of the marginal seas with strong turbulent mixing. More attention was paid on turbulent mixing in the upper and middle layers than that in the bottom layer in previous studies of the SCS. Based on the temperature data obtained in the northeastern SCS with high-resolution records at 0.5 m above the seafloor at 22 stations for about 4.4 days in May 2019, we analyzed the time variation characteristics of bottom-water temperature with ocean depth varying from 2216 to 3200 m, and discuss the influence of topographic roughness and internal tides on bottom turbulent mixing. The analysis results show that the bottom temperature fluctuation at each station is 10^-4~10^-3℃, the trend of temperature variation is different from that of barotropic tide elevation, the temperature variation is affected by baroclinic process, mainly modulated by the diurnal and semi-diurnal tides at most stations. The magnitude of the turbulent kinetic energy dissipation rate at the bottom of the continental slope-deep basin transition zone and the deep basin is 10^-10~10^-9m²∙s^-3, and turbulent diffusivity is 10^-4~10^-3 m²∙s^-1. The results, however, cannot reveal the significant positive correlation between the intensity of bottom turbulence mixing and topographic roughness. The spatial distribution of bottom turbulent dissipation is in accord with the north-south asymmetry of internal tides in the deep basin west of the Luzon Strait.

A disaster loss assessment method based on the Dempster-Shafer theory of evidence for storm surge is proposed in this paper. Because of uncertainty of storm surge in the disaster process, we select representative indicators (maximum height of storm surge, significant wave height, disaster prevention and reduction ability) to produce several pieces of evidence. The weight of evidence is calculated by using correlation between indicator and direct economic loss of storm surge disaster. A modified Murphy method is used to fuse evidence from different sources to judge the disaster loss level. An example is used to show that the classification accuracy of the method used in this paper can reach 93.1%, which is better than some existing methods, such as the Naive Bayes, Support Vector Machine, Neural Network, and Decision Tree methods. In addition, the method is simple in computation, and the results of disaster loss assessment can be more detailed with increasing training samples.

The coral δ¹⁸O data can precisely record climate variation and change of the tropical ocean, making up the shortage of deficient instrumental observations and providing us with the possibility of retrieving long-term paleoclimate conditions. The climate modes of the tropical Indian Ocean influence the climate of the surrounding region and even the globe through ocean-atmosphere interaction; so they are of great significance in climate study. In the present study, coral δ¹⁸O data from 1880 to 1999 at four sites located in the tropical Indian Ocean (Kenya, Seychelles, Tanzania, Mentawai) are used to study their ability to reproduce past climate in the tropical Indian Ocean. First, coral δ¹⁸O and SST changes are consistent on the long-term trend. Second, coral δ¹⁸O coincides nicely with local SST in terms of seasonal cycle, and is more sensitive to SST variation in cold seasons. What is more, coral δ¹⁸O at the four sites can describe changes of IOBM (Indian Ocean Basin Mode) and IODM (Indian Ocean Dipole Mode), but the interannual variability of the tropical Indian Ocean recorded by coral δ¹⁸O is modulated by interdecadal variation. This study suggests that the δ¹⁸O data from coral is an essential indicator of paleoclimate in the tropical Indian Ocean. Different sites' information should be taken into account to reflect past climate change in the Indian Ocean.

Using tropical cyclone (TC) data from the Joint Typhoon Warning Center, the Extended Reconstructed Sea Surface Temperature version 5 from the National Oceanic and Atmospheric Administration, the temperature and salinity data from the Global Ocean Data Assimilation System, and the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research, we investigated climatic characteristics and interannual variability of TC rapid intensification (RI) in the South Indian Ocean (SIO) during the period of 1981~2019. The occurrence frequency of RI events in the SIO presents a single peak distribution, which ranges from October to June of the next year. The occurrence of SIO RI events is distributed in the subtropical area in a belt shape, with three high-value centers of RI events located in the northeast of Madagascar, the middle of the SIO and the northwest of Australia. The spatial distribution of SIO RI events is mainly modulated by two large-scale environmental variables: tropical cyclone heat potential (TCHP) and vertical wind shear (VWS). We also found that the influence of El Niño-Southern Oscillation on the occurrence frequency of SIO RI events is asymmetric: the occurrence frequencies of RI events during El Niño and La Niña years are both reduced. During El Niño years, the decrease of RI events is mainly due to higher VWS. During La Niña years, the decrease of RI events is mainly due to lower TCHP, and SST; VWS and RHUM also contribute to the decrease of RI events.

The partial pressure of carbon dioxide (pCO₂) refers to the content of CO₂ gas at the sea surface when the CO₂ exchange between the sea surface and atmosphere is in dynamic equilibrium, which is an important factor to calculate air-sea CO₂ flux. Based on the observations of pCO₂ covering most of the South China Sea (SCS) from 2008 to 2014, combined with in-situ observations of sea-surface temperature (SST), sea-surface salinity (SSS) and Modis-Aqua satellite observations of chlorophyll a (Chla), we construct a regional inversion of sea-surface pCO₂ based on a multi-linear regression method. The root mean square error is estimated to be 5.3 μatm in the area with depth shallower than 30 m, and 10.8 μatm in the remaining sea area, which are consistent with previous results based on cruise observations. Using the equation acquired from our method and combining with the HYbrid Coordinate Ocean Model (HYCOM) reanalysis SST and SSS data and MODIS-Aqua remote sensing Chla data, we obtained monthly sea-surface pCO₂ of the SCS from 2004 to 2016 with spatial resolution of 5'×5'. The data can well reflect the seasonal variation of sea-surface pCO₂ in the SCS under the influence of SST, which is high in spring and summer, and low in autumn and winter. These findings are similar to previous results based on cruise observations, indicating our method has rather high reliability. Further analysis shows the average sea-surface pCO₂ of the SCS and adjacent sea areas has a significant quasi-decadal oscillation: a minimum value appeared around 2011, which first showed a decreasing trend and then an increasing trend. Due to the influence of sea-surface pCO₂, the average air-sea CO₂ flux in the SCS and adjacent areas decreased significantly before 2012, and changed into negative values during winter, then changed slowly since 2012. The variation of SSS in the SCS caused by the Pacific Decadal Oscillation is the main reason for the quasi-decadal oscillation of sea-surface pCO₂ and air-sea CO₂ fluxes. Our results indicate the variation of sea-surface pCO₂ in the northern SCS is the most significant, which plays an important role in the seasonal and quasi-decadal oscillation of pCO₂ in the whole area.

Surface sediment samples were collected from 16 mangrove wetlands in four provinces (Fujian, Guangdong, Guangxi and Hainan) of China and analyzed for polybrominated diphenyl ethers (PBDEs) and five alternative brominated flame retardants (ABFRs), including decabromodiphenyl ethane (DBDPE), 1, 2-bis (2, 4, 6-tribromophenoxy) ethane (BTBPE), hexabromobenzene (HBB), pentabromotoluene (PBT) and pentabromoethylbenzene (PBEB). Results showed that PBDEs, DBDPE and BTBPE were widely detected in the mangrove sediments, while HBB, PBT and PBEB were only observed in some regions. Average concentrations of total PBDEs ranged from 1.39 to 293 ng·g^-1 dry weight (dw), showing an obvious spatial difference (p=0.016), which was significantly positively correlated with the local population and economic levels (p<0.01). BDE 209 was the predominant congener in all mangrove sediments, accounting for 72%~96% of the total PBDEs. DBDPE and BTBPE were the two dominant ABFRs, with average concentrations ranging from 0.489 to 29.4 ng·g^-1 and from 0.0127 to 1.11 ng·g^-1, respectively. There was a significant positive relationship between levels of BDE 209 and its alternative, DBDPE (p<0.01), reflecting their similar regional distributions in the mangrove sediments. This suggests that BDE 209 and DBDPE might have similar pollution resources and/or environmental behaviors. Ratios of DBDPE/BDE 209 were in the range of 0.0839~0.925, which indicates that levels of DBDPE were still lower than those of BDE 209 in the mangrove sediments of China. Still, environmental issues of ABFRs should not be ignored.

The Oxygen Minimum Zone (OMZ) is a stable dissolved oxygen (DO) minimum layer that forms in the mid-ocean water (200~1000 m). High-resolution surveys of DO in the water columns near the continental slope of the northern South China Sea (NSCS) were performed during July-September 2019 using an observation network including seven Sea-Wing Gliders. Our results revealed the existence of a stable basin-scale OMZ in the middle layer of the NSCS. Our data indicated that the depth of the OMZ was about 700 m with minimal DO content of about 80-100 μmol·L^-1. Besides, the DO content remains relatively stable within the depth range of 700-900 m, with an averaged OMZ thickness of about 200 m. The OMZ generally shows a wedge-shaped distribution in the horizontal direction with a gradual decrease of OMZ thickness and intensity from the southwest to the northeast along the continental slope of the NSCS. The OMZ eventually disappears near the Luzon Strait. In addition, we used data of two sections near the Xisha regions with repeated glider surveys to estimate the temporal change of OMZ over time. Our results suggested that the DO concentration within the OMZ core increased by ~0.023 μmol·L^-1 per day in the cross-slope direction but decreased by ~0.034 μmol·L^-1 per day in the along-slope direction. The increase of DO content in the northeastern OMZ can be explained by the intrusion of high-oxygen water through the Luzon Strait. Based on the above observation results, we believe that the distribution and formation of the OMZ be affected by physical processes such as advection, water mass distribution and stratification; it is also related to biological respiratory, organic decomposition, oxidation of reducing substances, and other factors.

Exposure surfaces in shallow-water carbonates are considered to be the faithful archive of paleo sea-level fluctuations, which are important for studying carbonate sequences and development of coral islands. Based on core observations, thin section identifications, and analyses of stable isotopes and mineral compositions, we identified nine main exposure surfaces in the Quaternary reef carbonates from a deep borehole “Well Nanke-1” (NK-1) drilled on Meiji Island, and we discussed their relationship with sea-level change and coral reef evolution in the South China Sea. Exposure surfaces in the Quaternary reef carbonates in Well NK-1 are characterized by heavily dissolved cavities and rich calcareous nodules with reddish-brown or yellowish colors. Weathered carbonates around most exposure surfaces have negative carbon and oxygen isotopes, and higher contents of Al, Th, Fe, and rare earth elements. The AMS¹⁴C and U-Th age data confirm that the Holocene coral reefs have developed during 8.2~4.7 ka on Meiji Island; and its growth period is consistent with that of other coral reefs in the South China Sea. The slow rise in sea level provided a favorable environment for the vertical growth of most coral reefs. Most exposure surfaces within Pleistocene stratum of Well NK-1 correspond to low sea-level stages, and the dated ages of these exposure surfaces by Sr isotopes and paleomagnetic studies are consistent with the records from the Xisha Islands and Yongshu Island.

A number of factors control the evolution of deep-sea currents in the northeastern South China Sea (SCS), but there is still a lack of deep understanding of sensitive indicators, evolution processes and controlling factors of the bottom currents since the Last Glacial Maximum (LGM). We selected the 16ZBS11 core in the deep-sea basin of ??the northeastern SCS to analyze the grain size and age of the terrigenous sediment. The environmental sensitivity factors were extracted by the grain size-standard deviation method; at the same time, the bottom current intensity and transport capacity were calculated. Our results show that the terrigenous debris in the study area are mainly composed of silt and clay; sandy components only appear in a few layers. The deep-sea sedimentary environment evolution in the northern SCS has gone through three stages: stage Ⅰ: 22.39~16.02 ka BP; stage Ⅱ: 16.02~9.58 ka BP; stage Ⅲ: 9.58 ka BP to present. Interestingly, the components of clay and silt in each evolution stage evoluted in reverse phase. The intensity and transport capacity of the bottom current have decreased gradually since the LGM and changed synchronously. At about 16 ka BP and 11.5 ka BP, the SCS was connected with the Indian Ocean and the Taiwan Strait, respectively, which affected the oceanic processes in the northern SCS. In particular, the changes of mixing patterns and intensities in the northern SCS since 9.58ka BP, profoundly affected the deep-sea terrigenous sediment transport and sedimentary evolution. Our results provide a new understanding of the evolution of bottom current activities in the northern SCS, and new evidence for deep-sea processes in the SCS.

Blue holes retain original water, sediments, fossil remains, and intact organic skeletons, which are important natural heritages and geologic miracles and have great scientific values. As the deepest blue hole discovered in the world, the Sansha Yongle Blue Hole (SYBH) has typical cavity structure and hydrochemistrical characteristics; however, its formation process is still a scientific puzzle. Based on the tectonic evolution of the South China Sea, we analyze the development history of carbonate platform in Yongle Atoll. Formation of Yongle Atoll is mainly attributed to the aggradation and backstepping of carbonate platform that could generate escarpment to erosional platform margins and facilitate development of faults/fractures along the banks. According to oxygen isotopes (δ¹⁸O) in carbonate cores from the drilled wells of Yongle Atoll, phreatic dissolution mainly occurred from 14.75 m to 168.60 m in depth, which agrees with collapse of deep voids observed above the cave break at the depth 158m in Yongle Atoll. Compared with other blue holes and caves in the world, we propose that the formation of the SYBH is due to a combined action of fault/fracture of bank margin and collapse of deep voids. Phreatic (fresh water and sea water) dissolution along the fault/fracture formed sub-vertical sinkhole above 158 m in depth through collapse of deep voids, whereas it continued to work along fault/fracture to form a slightly inclined and narrower cave downward below 158m. Then, the SYBH finally evolved into a deep blue hole due to flooding of rising sea level. This study provides important knowledge and reference for exploring other blue holes in the future.

The Hainan Qiongbei volcanic area is a typical Quaternary volcanic area in the coastal area of South China, which has attracted worldwide attention. Previous studies focused more on deep geological structures and the evolution of this volcano, but its surface geological structure is not yet well understood. Horizontal-to-vertical (H/V) spectrum of microtremors has been widely applied to shallow subsurface structures. By using classic full wave field H/V_(full) and the Rayleigh wave ellipticity H/V_(Ray) methods, we obtained spatial variation of peak frequency (F₀) and the amplification (A₀) from a seismic array of 35 short-period seismometers in the Qiongbei volcanic area. The results show that the peak frequency of the H/V curve in the Qiongbei volcanic area is significantly different on both sides of the Changliu-Xiangou fault. Clear F₀ and A₀ can be found at every site on the northeast side of the fault, while they do not exist on the opposite side of the fault. Based on the existing geological data, we believe that the shallow volcanic rocks at the southwest side of the Changliu-Xiangou fault have not undergone significant weathering under the condition of geological depression background, while the northeast side of the fault is located in an uplift area, so the rocks have been weathered seriously. Our results show that the H/V method can be used to evaluate the weathering state of surface volcanic rocks, and the peak frequency and amplification factor of the H/V curve of the outcropping site of the volcanic rocks are more obvious with the increasing of the degree of weathering. Our study provides important information for the weathering state of the volcanic rocks in the shallow and seismic risk assessment of this area.

Active Ocean Bottom Seismometer (OBS) prospecting is taking the leading role in illuminating submarine structures, among which converted shear wave modeling provides precise constrains on seismic structures and lithology. Due to the tedious procedures involved, difficulties in reaching optimal solution and insufficiency in non-uniqueness analysis in the present modeling method, we propose a new modeling method based on model solution space and objective function. Automatic modeling of converted shear waves can be realized using this new method with the aid of computer programming. This method is tested for its utilities in a realistic wide-angle OBS seismic profile, OBS2013-3, traversing the Xisha block, the northwestern South China Sea continental margin. PPS phases from a single station and PSS phases from all stations are employed in the case to model V_p/V_s ratios in sediments and the crust, respectively, where V_p is compressional wave velocity and V_s is shear wave velocity. Capacities of the new method to provide quick and accurate search for optimal models and estimates for modeling non-uniqueness are demonstrated. The new method is expected to promote the efficiency of converted shear wave modeling using OBS data and lay solid foundation for reliability and stability of modeling results.

The northern margin of the South China Sea (SCS) is often regarded as a magma-poor passive continental margin. Many high amplitude anomalies were observed in previous studies on seismic profiles at the northern part of the Continent-Ocean Transition (COT) in the northern SCS, and were interpreted as sills and volcanos. However, further investigation on the properties of these high amplitude anomalies was lacking. In this study, we observed a large anomaly with a thickness of ~1.2 km in two multi-channel seismic profiles (SO1E and SOY) on the northeastern continental slope of the SCS. This provides an opportunity to determine the presence of magmatic activities north of the COT. Velocity analysis and AVO (amplitude variation with offset) analysis were performed for the large-amplitude anomaly. Results show that the high-amplitude anomaly has a higher P wave velocity and Poisson’s ratio than the host strata above. Considering the regional geologic background, the internal reflection characteristics, spatial size and shape of this high-amplitude anomaly, we suggest that the high-amplitude anomaly can be characterized as an igneous rock and further classified as a laccolith. This also indicates that multi-phase magmatism occurred north of the COT since the Miocene.

We apply the FOAGRNN (fruit fly optimization algorithm, FOA; generalized regression neural network, GRNN) method and SODA (simple ocean data assimilation) reanalysis data to construct a global ocean projection relationship model between sea-surface variables (sea surface height, SSH; sea surface temperature, SST; sea surface salinity, SSS) and subsurface thermohaline field. The remote sensing observations are utilized to evaluate the applicability of this global surface-subsurface reconstruction model. First, an ideal reconstruction test is executed using the independent SODA data in 2016. The idealized reconstruction results show that the global mean root mean square error (MRMSE) values of the reconstructed temperature and salinity are 0.36 ℃ and 0.08‰, which are reduced by about 50% and 60% compared to those of the WOA13 (World Ocean Atlas), respectively. Then, the satellite observations (Input field) and Argo profiles (verification field) are inputted to evaluate the practical application performance of the model. The results again indicate that our reconstruction model can reasonably reconstruct the thermohaline structures, and the MRMSE values of the reconstructed temperature and salinity are 0.79 ℃ and 0.16‰, which are 27% and 11% lower than those in the WOA13, respectively. Specifically, the RMSE of temperature is small at the sea surface and in the deep ocean, and the largest value exists in the thermocline layer with a maximum value of 1.35 ℃ at 100 m, and then quickly decreases to 0.81 ℃ at 250 m. The RMSE of salinity mostly decreases as depth increases, and has the largest peak of about 0.25‰ around 25 m. Finally, the analysis of Argo floats’ tracks and the statistics of regional water mass confirm that the reconstructed model can better describe the interior characteristics of the three-dimensional thermohaline field.

We used the continuous in-situ air pressure, temperature, sea-surface wind, sea-surface temperature, salinity, chlorophyll a, current observation data, satellite rainfall data, and moderate resolution imaging spectroradiometer (MODIS) visible band images to analyze the characteristics of sea-surface chlorophyll a in Lingding Bay of the Pearl River Estuary, during the study period of July 5 - 20, 2019. The methods of wavelet analysis and ensemble empirical mode decomposition (EEMD) are used. The results showed that the concentration of chlorophyll a during the observation period varied from 0.44 to 1.75 µg·L^-1, with an average value of 0.80 µg·L^-1. The periods of the signals in the time series of chlorophyll a were 6, 12 and 24 h. It is obvious that there was a phase relationship between chlorophyll a and tidal current, which would be changed by the rainfall over the Pearl River basin. In the study period, chlorophyll a was in an inverse phase relationship with the tidal current, which means that the chlorophyll a concentration reached maximum (minimum) with the maximum flow in the ebb (rising) tide. The difference of chlorophyll a concentration in the ebb and rising tides was about 0.3 µg·L^-1. When rainfall occurred in the Pearl River Basin from July 8 to 13, chlorophyll a concentration increased from 0.02 ~ 0.09 µg·L^-1 to about 0.15 µg·L^-1 at the periods of 6, 12 and 24 h. Furthermore, the chlorophyll a concentration in the Pearl River Estuary increased by about 0.3 µg·L^-1 for 80 h after the rainfall. After the rainfall, the time series of tidal current lagged behind chlorophyll a for about 6 h from July 13 to 20. The concentration of chlorophyll a reached minimum (maximum) with high (low) tide. The results present that rainfall not only increased the chlorophyll a in the estuary, but also induced the transformation of the phase relationship between chlorophyll a and tidal current.

We used the Japan Meteorological Agency (JMA) best track data, tropical rainfall measuring mission (TRMM) 3B42 3-hourly precipitation data and Japanese 55-year reanalysis (JRA-55) 6-hourly data from 1998 to 2017. We selected typhoons, which originated from the Northwest Pacific and had rain belt passing through South China with moving path located to the south of Taiwan Island, as our research objects. The date of the first spiral rain belt of typhoon arriving in South China was manually judged from satellite cloud images and TRMM precipitation data. The influences of typhoons on diurnal variation of precipitation in the study area before the rain belt arriving were then analyzed. The results showed that on the one hand the peripheral circulations of typhoons would transport much water vapor into the region before typhoon landfall, which was beneficial to the precipitation in the region; on the other hand, the downdraft outside of cyclonic divergence field would suppress the convection in the region, which was inconducive to the occurrence of precipitation. When the former played a greater role than the latter, the precipitation in South China would increase. The maximum of atmospheric instability within a day would occur in the afternoon, resulting in an afternoon rainfall peak. These relevant typhoons appeared mostly in July and August, when the western Pacific subtropical high was located easterly and was favorable for the northward movement of typhoon. The typhoon centers were close to the coastal area of South China when their first wave of rainband reached South China. On the contrary, the atmospheric layer over South China was stable and therefore precipitation decreased; the diurnal variation of precipitation peaked in the morning due to radiative cooling and the relevant typhoons mostly appeared in September and October. As the westward extension of the western Pacific subtropical high is not conducive to the northward movement of typhoon, the typhoon centers were far away from the coastal area of South China when their first wave of rain band reached South China. The results are expected to improve the knowledge for impact of cyclonic peripheral circulation on precipitation process in coastal regions before typhoon landfall.

Using satellite altimeter, model and assimilation data, we reveal the spatial and temporal distribution characteristics of the East India Coastal Current (EICC) in the annual cycle, and discuss its possible mechanism, and heat and salt transports. In the annual cycle, the EICC presents three distribution states. Affected by the monsoon, it flows southward (northward) in the early stage (October to December) and late stage (February to May) of the northeast monsoon, while it distributes in three stages from June to August, which is significantly different from the other two periods, showing southward flow in the areas south of 9°N, north of 16°N and northward in the area between 9°N and 16°N. Previous studies suggested that the local wind stress along the east coast of India is the main mechanism of the EICC. In addition to the local wind stress, the Ekman Pumping in the central Bay of Bengal (BOB) plays an important role during the whole year, and drives the northward (southward) flow of the EICC from February to May (October to December), while the local wind stress is conducive to the southward flow of the EICC from October to December. The EICC is a factor for the transport of low-salinity water from the BOB to the Equatorial East Indian Ocean and the Arabian Sea, which plays an important role in the heat and salt exchanges between the basins. The heat transport of the EICC from June to December (February to May) is favorable (unfavorable) to the temperature increase in the BOB; salt transport is conducive to the increase of salinity in the BOB throughout the year. The transport characteristics of the EICC promote the redistributions of heat and salt in the BOB and play an important role in maintaining the heat and salinity budgets in the northern Indian Ocean.

The water level in the estuary area is affected by many factors, such as runoff, tide and topography, resulting in a complex pattern in spatial morphology. Understanding the evolution characteristics of water level distribution is essential for sustainable water resources managements in estuaries. In this study, we use the residual water level data from six gauge stations (Makou, Ganzhu, Jiangmen, Zhuyin, Denglongshan, and Sanzao stations) along the Modaomen estuary of the Pearl River during 1965 to 2016, together with the monthly averaged river discharge data from the Makou hydrological station during the corresponding period. With a bivariate variable linear regression model, we quantitatively identify the influence of human activities on water surface profile dynamics, and attempt to understand the coupling relationship among human activity, dynamic structure and morphological change. The results show that the bulk parameters displaying the shape of water level profile (i.e., curvature) can well indicate the trends of erosion and deposition of river bed, with the positive curvature indicating sedimentation tendency and the negative curvature indicating erosion tendency. In the central part of the Modaomen estuary, such as the Jiangmen-Ganzhu reach, there exists an area where the water level slope is considerably reduced, especially during the dry season when the water level slope even fluctuates negatively in the landward direction. The river-bed deepening caused by human activities such as land reclamation, sand excavation and river dredging are the main reason for the alteration in spatial dynamics of the water surface profiles in the Modaomen estuary. We show that the river-bed deepening causes the water level curvature of the seaward reach (Sanzao to Zhuyin reach) and the upper reach (Ganzhu to Makou reach) decreasing by 0.41×10^-4 m·km^-2 and 1.04×10^-4 m·km^-2, respectively, while the central reach of the estuary (Zhuyin to Ganzhu reach) increasing by 0.21×10^-4 m·km^-2; the water surface shape changes from concave (C>0) - convex (C<0) - concave to convex - concave - convex, and the trends of erosion and deposition of river bed are also adjusted accordingly.

Lingdingyang of the Pearl River Estuary is one of the most important bays in China. The suspended sediment concentration (SSC) there is significantly affected by the tidal processes in the dry season, which makes it an ideal area for studying the influence of tides on SSC variation. The Gaofen-4 (GF-4) satellite is the first geosynchronous orbit satellite with ultra-high spatial and temporal resolution in China. The spatial resolution of visible light bands is 50 m, and the maximum temporal resolution can reach 20 s. It has unique advantages in studying the variation of SSC within one day. In this study, we retrieved the surface SSC of Lingdingyang from the GF-4 satellite L1A data and in-situ data in January 2020, and then analyzed the spatial distribution of SSC in different stages of a tidal cycle. The results showed that the SSC in Lingdingyang was higher nearshore than offshore, and higher in the west than in the east. At flood tide, there were four high SSC areas. The average SSC showed a decreasing trend, and the suspended sediment was transported to the bay. During the initial, middle and last stages of flood tide, the decreased SSC became gradually more significant. At ebb tide, there were seven high SSC areas. The average SSC showed an increasing trend, and the suspended sediment moved toward the sea. During the initial, middle and last stages of ebb tide, the SSC increased significantly first, and then slowed down; it finally showed a negative growth trend. The variation of SSC was jointly affected by sediment transport in the horizontal direction, resuspension process in the vertical direction, and topography.

Phytoplankton are the basis of the marine ecosystem food chain, and affect the variation of CO₂ flux through photosynthesis. In this study, an estimation system of phytoplankton biomass in the South China Sea was established based on an area indicator. We used the empirical orthogonal function decomposition interpolation method (DINEOF) to reconstruct the chlorophyll a concentration field in the South China Sea from long time series of remote sensing data. We studied the space-time distribution of the high biomass water area of the South China Sea and found that the changes of water area with high chlorophyll a concentration had significant seasonal characteristics. The area of waters with high chlorophyll concentration reached the maximum in winter, and the minimum in summer. Conversely, the chlorophyll concentration reached the minimum in winter, and maximum in summer. This feature may be due to the wind-driven dynamic processes that redistribute the chlorophyll concentration near the surface. Moreover, waters with high chlorophyll concentration were found near the coast year round, especially in coastal waters of China, along the coast of Vietnam, the Gulf of Thailand, and near Borneo Island. In the Sunda Shelf and the central basin east of the Mekong estuary, the area of high biomass water showed interannual variation. The East Asian monsoon modulated by the El Niño and Southern Oscillation led to different degrees of cold water invasion from the north to the southeast of the Mekong Estuary in different years, which may be the reason for the increase and decrease of local phytoplankton biomass.

Scatterometers measure the normalized radar cross-section (NRCS) from the sea surface, which is then used to retrieve the wind vector over the sea surface using the geophysical model function (GMF). The GMFs adopted by the wind retrieval of scatterometers generally consider the influence of the radar polarization, radar incident angle, wind speed, and relative direction, but research showed that sea-surface temperature (SST) has a non negligible impact on the wind retrieval of scatterometers in the Ku band. In this study, we use Haiyang-2A scatterometer (HY2A-SCAT) L2A data, European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis wind and SST data to build an SST-dependent GMF (TNGMF) using the artificial neural network. Using the TNGMF, we find that the NRCS increases with SST, and its range affected by SST is related to radar polarization and wind speed. In contrast, we use the same dataset and the same method to build another GMF without considering SST (NGMF); we then use NSCAT2 (NASA scatterometer-2) GMF, NGMF and TNGMF in the wind retrieval of HY2A-SCAT and find that NSCAT2 and NGMF wind speeds are systemically lower at low SST, and systemically higher at high SST. However, the TNGMF can well adjust the wind speed deviation affected by SST to improve the quality of retrieved wind.

The Xuande Atoll is one of the most exploited and utilized area in the South China Sea. Offshore geological hazards around the Xuande Atoll are likely to threaten the construction of reef infrastructure projects and human activities. To meet the needs of sustainable development of islands and reefs in the South China Sea, this study aims to explore the types and spatial distribution of geological hazards in the east sea area of the Xuande Atoll based on single-channel seismic profiles collected by the Guangzhou Marine Geological Survey in 2018. The results show that there are three kinds of geological hazards in the study area, including submarine landslides, seabed scarps and faults. Submarine landslides are the main geological hazard factor in the study area with different scales, and seabed scarps and faults are the secondary geological hazards. Seabed scarps can be divided into reef scarps and landslide scarps according to their genetic mechanisms. The reef scarps were formed under the control of sea-level rise during the formation of the reef, and the landslide scarps were caused by submarine landslide. The tectonic environment in the study area is relatively stable, so we infer that the steep topography and canyon erosion are the main controlling factors for the development of geological hazards. These geological hazards have adverse effects on marine engineering construction and pipeline laying. The results of this study provide basic geological services for infrastructure construction, active disaster prevention and sustainable economic development around the Xuande Atoll and its surrounding areas.

The Bromine (Br) intensity collected by the non-destructive X-ray fluorescence (XRF) core scanner has been used to estimate the content of organic carbon in marine sediment in high speeds. However, the accuracy of this estimation and the effectiveness of various calibration methods need to be carefully evaluated. In this study, two gravity cores from the Arabian Sea and South China Sea, where the organic contents and their source components are different in sediment, are selected to investigate the correlation between the total organic carbon (TOC) content and the Br intensity by the core scanner. This study also analyzes the influence of water content and evaluates the effectiveness of different calibration methods used to estimate the TOC content according to the Br intensity. A good correlation is found between the Br intensity and the TOC in marine sediment with high organic carbon contents, no matter whether the Br intensity is calibrated or not. However, the estimation of sedimentary TOC content should be cautiously used when terrigenous organic matter is high.

Zooplankton were sampled in coral reef waters from three islands (Qilianyu, Yongxing and Dong islands) and five atolls (Langhua, Panshi, Yuzhuo, Huaguang, and North atolls) around the Xisha Islands from May to July, 2015 in order to understand the community structure of zooplanktonin the region. The aims of this study are to analyze the species diversity, abundance distribution and community structure of zooplankton, and to compare the differences in zooplankton community between the lagoon and seaward reef-slope waters among the five atolls. A total of 180 species of zooplankton including 13 groups of planktonic larvae were identified, among which the greatest species number was the copepods with 80 species, followed by the hydromedusae, pelagic mollusca, chaetognaths and pelagic tunicates. The average abundance of zooplankton was 256.4 ± 117.8 ind·m^-3, among which copepods accounted for 51.08% of the total abundance, followed by planktonic larvae (16.30%), pelagic tunicates (13.22%) and chaetognaths (7.70%). Differences in zooplankton species, diversity, evenness index, and abundance between islands and atolls, as well as in the lagoon and seaward reef-slope of five atolls, were observed. The diversity and abundance of zooplankton were relatively high in Dong Island, Yuzhuo Atoll and Huaguang Atoll, but low in Qilianyu and North atolls. They were higher in the seaward reef-slope regions than in the lagoons of the five atolls. Two major assembled groups were distinguished into the atoll lagoon-island and nearshore group, and the seaward reef slope-island and offshore group at the similarity of 85%. A significant difference in the two zooplankton assemblages was observed (r=0.832, p<0.001). The former group was characterized by low values of species richness, diversity index, total abundance, and abundances of main groups such as copepods, chaetognaths and planktonic larvae compared with the latter group. The heterogeneity and ecological environment differences between the atoll lagoon and seaward reef-slope waters may be the main factors determining the zooplankton community structure around the Xisha Islands.

Differences in zooxanthellae density, photosynthetic physiological indicators, and symbiotic fungal communities between healthy and bleaching states of Galaxea fascicularis were investigated in this study. The results showed that the zooxanthellae density and maximum photochemical quantum yield (F_v/F_m) of Galaxea fascicularis in the bleaching state were significantly lower by 75% and 16%, respectively, than those in the healthy corals. The composition of endolithic fungi community was mainly Ascomycota, Basidiomycota, Chytridiomycota, and Mucoromycota. The Shannon diversity index of endolithic fungi in healthy corals was slightly lower than that in bleaching corals, and the endolithic fungi compositions of these two coral groups had some similarity. Zooxanthellae content of healthy corals was significantly reduced due to the threat of heat stress, but it was still within the recommended appropriate symbiont density range. Despite the significant lost of density of symbiotic zooxanthellae from bleached corals, their Photosystem Ⅱ complexes were not completely destroyed. The results showed that there was no significant increase in diversity index, fungal pathogen group and predictive function in bleaching corals. The stability of endolithic fungi community may play an important role in the heat stress response. In the future, we will consider combining traditional isolation and culture techniques, high-throughput sequencing, metagenomics, and other methods to comprehensively study the diversity and ecological functions of coral endolithic fungi.

Jellyfish blooms mostly occur in the Bohai Sea and Yellow Sea as well as in the East China Sea, but rarely in the South China Sea. We conducted morphological observations and molecular identification of blooming jellyfish in many waters of the northern South China Sea, including Haikou, Wenchang and Maoming in May 2019. Morphological results showed that the jellyfish in Haikou and Wenchang were the same species with hemispherical umbrella, pear-shaped protrusion in the lower reproductive point, and the oral arms are covered with filaments and a whip appendage at the end, which are highly similar to the Acromitus flagellatus. The jellyfish in Maoming were different: the umbrella was relatively flat hemispherical, the subgenital pits were milky protrusions and the oral arms had no filaments, which were similar to Catostylus townsendi. Based on the comparison of mitochondrial ribosomal large subunit (16S rRNA) gene sequences, the blooming jellyfish of Haikou and Wenchang were 97.5% and 97.7% similar to A. flagellatus of the eastern Pacific Ocean, and jellyfish of Maoming was 93.5% similar to C. townsendi from the Strait of Malacca. The phylogenetic tree constructed based on mitochondrial COI gene and 16S rRNA gene suggested that the jellyfish of Haikou and Wenchang were the same and belong to the same branch with A. flagellates; the jellyfish of Maoming were close to C. townsendi. Therefore, combined with morphological observations and molecular analyses, we considered Acromitus flagellatus to be the jellyfish in Haikou and Wenchang, and Catostylus sp. in Maoming.

There are a large number of uncultured microbial resources in coral reef environments. Microbial diversity research will help us understand their ecological functions, and also help develop and utilize microbial resources. In this study, a total of 349 pure bacterial strains were obtained by selective isolation media with multiple oligotrophic components, from three samples collected from three coral reef islands in the South China Sea. Based on 16S rRNA gene sequence analysis, we found the cultivable bacteria belong to four phyla of Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes; and they spread into six class, 26 orders, 43 families, 73 genera, and 134 species. There are 18 potential new taxa with 16S rRNA gene sequence similarities less than 97%. The dominant group is Actinobacteria, which accounts for 60% of all isolates. In this study, the improved and optimized oligotrophic media were used, which showed better isolation results including the composition of the microbial community and rare or new taxa in every sample. The results showed that the cultivable microbial resources are rich and diverse in coral reef island environments of the South China Sea, and the microbial community has comprehensive functions for material and energy metabolism; and the proportion is higher to obtain potential new taxa. This research has laid a good foundation for the methods to mine microbial resources in coral reef islands; it also accumulated abundant and rare microbial resources for the deep development and application in the future.

Synechococcus, which is one of the representative groups of picocyanobacteria, is widely distributed in global oceans and estuaries. It has high phenotypic (pigment) and genetic diversity. According to the level of ability to deal with variation in salinity, Synechococcus can be divided into the strictly marine type and euryhaline type. In this study, we compared the growth of Synechococcus sp. K1 (isolated from the Pearl River estuary) and Synechococcus sp. YX02-1 (isolated from the South China Sea oligotrophic water) under a series of salinity gradient conditions. We also conducted phylogenetic analysis of K1 and YX02-1 based on rpoC1 gene sequences. We found that euryhaline Synechococcus sp. K1 could grow in all salinity levels, while strictly marine Synechococcus sp. YX02-1 was unable to survive below 13‰, which is consistent with the distribution characteristics in the estuary. Transcriptome analysis showed that the expression of genes (ggpS, SPS, stpA) that synthesize osmotic pressure regulator molecules in euryhaline Synechococcus were significantly down-regulated, while the gene expression of the membrane channel protein glzT was significantly up-regulated under low-salinity condition. This suggests that the low-salt tolerance mechanism of euryhaline Synechococcus mainly includes reducing the synthesis of small molecules related to intracellular osmotic pressure and increasing membrane channel proteins to improve the efflux of small molecules. In addition, salinity affected the photosynthesis and metabolism levels of euryhaline Synechococcus. The expression of photosynthesis energy-saving genes (ATPF0B, ATPF0A, ATPF1D, ATPF1A) and pigment protein genes (cpcA, cpcB) were significantly down-regulated under low-salinity condition, and the expression of inorganic nitrogen utilization-related genes were up-regulated. Under low-salinity condition, the demand for small molecules related to osmotic pressure is reduced, which can make more carbon sources to support growth. Meanwhile, the absorption of inorganic nitrogen is enhanced. These two reasons may be responsible for the higher growth of Synechococcus under low-salinity condition.

The marine Vibrio HN897 strain is an agarose-producing Vibrio astriarenae. Studies indicated that the absence of the gene Vas1-1339, encoding a β-agarase, significantly reduced the hydrolysis effect of Vibrio HN897 strain on agarose. Herein, we further analyzed the expression and enzymatic characterization of the β-agarase gene in heterologous bacteria, Escherichia coli (E. coli). Vas1-1339 agarase was successfully expressed in E. coli, and the optimal concentration of inducer, IPTG, was at 10 μmol·L^-1. Immunoblotting analysis showed that the C-terminal of the gene expression product might be cleavage in E. coli, suggesting complex maturation process of this protein. Lugol’s iodine staining analysis revealed that E. coli, expressing Vas1-1339 agarase, was highly effective in degrading agarose, and purified protein also had this similar function, which suggests that the β-agarase Vas1-1339 of the HN897 strain can independently play the role on agarolytic degradation. These results lay a preliminary foundation for the functional study and related technology application of β-agarase derived from marine vibrion.

Bacterial enteritis can cause severe damage to seahorse aquaculture, while little is known about the effects of bacterial pathogen infection on intestinal microbiota of seahorses. In the present study, both bacterial pathogen (Edwardsiella tarda YT1) and seahorse research model of bacterial enteritis previously reported by us were employed to explore the role of bacterial pathogen in intestinal microbiota by high-throughput full-length 16S rRNA gene sequencing. The results showed that E. tarda infection significantly altered the composition and abundance, and significantly decreased diversity of intestinal microbiota of lined seahorses (p<0.05); significantly increased the relative abundance of Proteobacteria (p<0.05), and decreased the abundance of Actinobacteria, Firmicutes, and Bacteroidetes (p<0.05); significantly increased the relative abundance of pathogenic Edwardsiella (p<0.01), while decreasing that of Psychrobacter, Rothia, Macrococcus, and Planococcus (p<0.05) at genera level. It indicates that E. tarda infection can reduce the diversity and relative abundance of intestinal autochthonous microbiota and result in dysbiosis in lined seahorses. Based on the results of bacterial function and correlation, increasing relatively abundance of E. tarda may significantly upregulate its activities of bacterial chemotaxis, flagella assembly, ABC transporter, phosphotransferase system, and lipopolysaccharide biosynthesis pathways (p<0.05), cause decrease of the relative abundance of the core intestinal microbiota of Psychrobacter, Planococcus and Glutamicibacter and suppression of their functional activities of ribosome, RNA degradation, nucleotide excision repair, and fatty acid biosynthesis pathways (p<0.05), induce dysbiosis of intestinal microbiota, and finally result in enteritis. These results may be helpful for further revealing pathogenic mechanism of E. tarda-induced enteritis in seahorses by more detailed metagenomic and metabolomics analysis.

We report one newly recorded species of the genus Cuspivolva (Gastropoda, Ovulidae) from the offshore waters off Xiamen, Fujian Province: Cuspivolva bellica (C. N. Cate, 1973). All the specimens were collected near the low-tide line and inhabited on the branches of gorgonian corals; and now they are deposited in the Tropical Marine Biodiversity Collections of the South China Sea Chinese Academy of Sciences (TMBC). The shell morphological features of this species were presented, along with its habitat and distribution. Differences between this species and similar species are compared and discussed. Until now, there are eight Cuspivolva species known from waters off China. The discovery of this new species further enriches the cowries diversity in Chinese waters. A list of Cuspivolva species known from Chinese waters is also given in the paper.

A new species of halocyprid ostracod, Bathyconchoecia nanshaensis sp. nov., from the Nansha Trough (the North-West Borneo Trough), southern South China Sea is illustrated and described in detail. The species is a small one that closely resembles Bathyconchoecia paulula Deevey, 1968 and Bathyconchoecia pacifica Chavtur, 1977 in terms of its carapace length (CL; <1.0 mm) and relative height (~70% CL). However, it can be easily distinguished from these species by the locations of its asymmetrical glands’ opening, by the structure of the coxal toothed edge of the mandible, and by the setation of the sixth limb.

The Jurassic crust is thought to be the oldest existing oceanic crust, with a very sparse distribution on Earth. The fault characteristics and structural deformation of the Jurassic crust remain poorly understood. In this study, we took full advantage of high-resolution reflective seismic profiles to examine the basement of Jurassic oceanic crust, sedimentary stratigraphy, and fault structures in the western Pacific. Our new results revealed three types of faults in the Jurassic crust, namely, basement fault, sedimentary fault, and collapsing fault. Geometric parameters and deformational characteristics of these faults were quantitatively studied in unprecedented detail, such as strike, dip, and displacement. Basement fault is formed by the bending and extending of oceanic crust, which continues to evolve to cut off the overlying sedimentary units and break through the seafloor to form distinct fault scarps during subsequent submarine sedimentation. Sedimentary fault is resulted from the gravity loading of sediment itself, with effect from the material properties of sedimentary layer. Collapsing fault is caused by the lateral movement of sediment above the intrusive magmatic body. The intrusion of magmatic body uplifts the existing oceanic crust and its overlying sediment, causing the existing basement fault and sedimentary fault to reactivate. Inferred strikes of active faults that cut through the basement and sediment are basically in agreement with the orientations of the Jurassic basement undulation, gravity anomaly abrupt-change boundaries, and magnetic lineations, implying that these faults were formed during the seafloor spreading at the Jurassic mid-ocean ridges and had been active till now. These faults developed on such old oceanic crust allow water to enter the lithosphere for a long time and enhance water cycling through plate subduction. Despite being absent of great earthquakes on these normal faults, they have the potential to evolve into giant seismogenic faults on the subducting plate. Here, we call for attention to tectonic evolution and geologic risk of these faults when they approach subduction zone.

Estuarine sediment, as an important carrier of terrestrial and marine ecosystems, is one of the main forms of organic matter occurrence. In this study, we analyzed total organic carbon (TOC) concentration, total nitrogen (TN) concentration, soluble organic matter excitation emission matrix spectroscopy (EEMs), spatial differences and influencing factors in different areas. Carbon stable isotope (δ¹³C) was applied to estimate the contribution of sediment organic matter (SOM) in different regions of the Pearl River Estuary (PRE). The results are as follows. (1) Spatial variations of TOC and TN concentrations are similar. The concentrations of SOM in the inner estuary and mixed areas are significantly higher than those in the estuary mouth. Principal component analysis results show that SOM concentrations in the inner estuary and the mixed area are mainly affected by river flow input, and those in the estuary mouth, by ferric iron. (2) MixSIAR results show that SOM in the inner estuary and the mixed zone is still mainly from terrestrial sources, and that in the estuary mouth is primarily from marine sources. (3) Newly produced organic matter in the sediments, which can be quickly utilized, is highly enriched in the PRE. Terrestrial input induced the higher humification degree of SOM in the inner estuary and mixed areas, which is conducive to organic carbon storage processes. In contrast, low storage capability was implicated in the estuary mouth, due to the influence of marine sources and iron oxide-organic matter complex. This makes it unfavorable for the storage of organic carbon in the PRE. This study provides a supplementary reference for further understanding the biogeochemical process of SOM and carbon storage in estuaries.