Based on the NOAA optimal interpolated sea surface temperature and other data from 1982 to 2021, seasonal variability of marine heatwave in the Bay of Bengal and associated formation mechanism were analyzed in this study. The results show that, bounded by the connection between Sri Lanka Island and the mouth of the Irrawaddy river in Myanmar, the frequency and days marine heatwave show different seasonal variation characteristics in the northwest and southeast of the Bay of Bengal. In the northwestern of the bay, both the frequency and the number of days of marine heatwaves are the largest in summer followed by spring and autumn, and the least in winter. In the southeastern of the bay, the seasonal variation of both is relatively weak. According to the cumulative intensity of marine heatwave, marine heatwaves are divided into four categories from weak to strong: I−IV. The analysis shows that the weak marine heatwave of category I and II mainly occurred in western or northwestern of the bay in summer and autumn; severe marine heatwaves of category 3 and above are mostly found in the Andaman Sea and the southeastern of the bay in spring and off southwestern Myanmar in summer. Further analysis shows that in most active areas of marine heatwaves in spring, summer and autumn, the change of net surface heat flux and the shallow mixed layer depth play a major role in these areas, while the formation and maintenance of marine heatwave in the southern of bay may be related to the remote forcing from the equator.

Compared with the fast and intermediate spreading mid-ocean ridges, the hydrothermal fields forming at slow and ultra-slow mid-ocean ridges usually contain abundant metal sulfide resources. Previously statistical results suggested the gold concentrations in massive sulfide deposits decreases with the increase of spreading rate, and the hydrothermal fields, located in ultra-slow mid-ocean ridges, have the highest gold concentrations. Previous studies carried out detailed research on the tectonic environment and sulfide assemblage of the Longqi hydrothermal field, but the occurrence and precipitation mechanism of gold in the Longqi hydrothermal field still need further research. In this paper, the texture and trace element concentration of sulfides in the Longqi hydrothermal field are analyzed in order to investigate the occurrence and precipitation mechanism of gold. The sulfides in the Longqi hydrothermal field are mainly pyrite, along with chalcopyrite (isocubanite) and sphalerite. Minerals such as ferronatrite and native gold have also been observed. According to the mineral texture and morphology, pyrite is divided into two types the first type (Py1) is fine-grained or colloidal, while the other type (Py2) shows subhedral-euhedral with coarse grain. Py1 usually exists in Py2 or is surrounded by Py2 as inclusions, and Py2 coexists with euhedral-subhedral chalcopyrite and sphalerite. Native gold mainly exists in the internal pores of Py1, and minor grains exist between Py2 and other sulfides. Compared with Py2, Py1 contains higher trace element contents of Ni, Zn, Pb, Ba, Mn, V, Mg, U, Au, Ag, Cd, and lower contents of Co, Se, As, Sb. Under the physico-chemical conditions of the Longqi hydrothermal field, Au(HS) is the main existing form of Au. The decrease of HS⁻ concentration and the increase of pH value will promote the precipitation of gold. The mixing of hydrothermal fluids with seawater in the Longqi hydrothermal field results in an increase in pH values and a decrease in temperature, which can lead to pyrite crystallization and consequently decrease of sulfur fugacity of hydrothermal fluid. An increase in pH and decrease of sulfur fugacity both contributed to the precipitation of gold.

The relative contents of clay minerals in 34 surface sediment samples were analyzed by X-ray diffraction. The results showed that the content of clay minerals in the surface sediments was illite (35%), palygorskite (20%), smectite (20%), kaolinite (16%) and chlorite (10%). Q-cluster analysis using SPSS software shows that clay minerals can be divided into two provinces (Province I and Province II). Province I covers most of the northern area, and the source is mainly the dust influx from the deserts of Arabian Peninsula, western India and Somali coast; Province II is located at the southwest of the study area, mainly receiving the weathering matters from the granite bedrock of Seychelles Plateau. A comprehensive analysis of the sources of fine particulate matter in the study area and the regional dynamical environment reveals that the southward transport of the aeolian dust from the Arabian Peninsula, western India and the Somali coastal deserts by the South Asian summer monsoon controls the composition of clay minerals in the Province I. The south equatorial low latitude ocean current system promotes the meridional diffusion of fine particles in the study area. The southern Equatorial Counter Current drives the eastward diffusion of kaolinite and chlorite-rich fine materials from Seychelles Plateau.

To identify abalone species effectively for better management and protection of abalone germplasm resources, we have obtained the complete mitochondrial genome of juvenile green abalone (Haliotis fulgens) through high-throughput sequencing, and its sequences and structural characteristics are analyzed accordingly. The results show that the mitogenome of H. fulgens is 17 041 bp in total length and encoded 37 genes, including 13 protein coding genes, 22 transfer RNA (tRNA) genes and 2 ribosomal RNA (rRNA) genes. The 13 protein coding genes used AUG as the starting codon and UAA or UAG as the termination codon. Twenty-one tRNA genes other than tRNA-Ser^(AGN) could be folded into a typical cloverleaf structure. There is a rich A+T non-coding region between tRNA-Glu and COX3, with two hairpin structures containing palindromes in it. A phylogenetic tree was constructed based on the reported complete mitochondrial genome sequences of Haliotis genus species, and phylogenetic analysis shows that H. fulgens is clustered with H. discus hannai, H. rufescens and H. cracherodii. Comparing the domains of 13 proteins of mitogenome of H. fulgens and H. discus hannai, we found the number of transmembrane domains of ND2 or ND4 dehydrogenase subunits were different in them. Whether this is related to the difference of high temperature tolerance between them needs further study. In brief, the first acquisition and analysis of the complete mitochondrial genome of H. fulgens has enriched the abalone cellular genetic information, and provided basic data and references for abalone species classification, germplasm identification, and protection of germplasm resources of H. fulgens as well.

Beibu Gulf is located in the northwestern part of the South China Sea and is experiencing a significant increase in the frequency, duration and extent of harmful algal blooms (HABs) outbreaks in the last 30 years. To characterize phytoplankton and bacterial communities during the massive Noctiluca scintillans bloom in the Beibu Gulf, seawater samples were collected from the area of a massive N. scintillans outbreak west from Weizhou Island on February 21, 2021, and environmental factors, along with phytoplankton and bacterial communities were analyzed. The results showed that the sea water quality of this area met the standards of Chinese Class I seawater quality, mainly in the absolute phosphate limit state. In recent years, other studies reported low nutrient content and limited phosphorus in waters adjacent to Weizhou Island and in the central part of Beibu Gulf during the non-harmful algal bloom (HAB) period. Therefore, N. scintillans bloom investigated in this study belonged to a non-eutrophication HAB event. Two phyla, five genera, and five species of phytoplankton were identified in seawater, among which N. scintillans was the absolute dominant species, with a cell density of 2.00×10³–3.75×10³ cells/L. The red discoloration of the sea water was caused by the red heterotrophic N. scintillans. Both phylogenetic and genetic distance analyses demonstrated that the causative N. scintillans in the Beibu Gulf was similar to N. scintillans along the coast of China. High-throughput sequencing of the V3–V4 region of the 16S rRNA gene in seawater samples revealed that the number of OTUs (operational taxonomic units) in bacterial community ranged from 294 to 414, with Alphaproteobacteria and Gammaproteobacteria as the dominant groups. The bacterial community structure was affected by various environmental factors, including COD, DO, DIN, ${\rm{PO}}_4^{3-} $-P, and N/P, among which COD was predominant. This research provides new insights into the environmental characteristics and microbial composition of sea water during a massive N. scintillans bloom and will aid bloom management in the Beibu Gulf.

Combined with hydrometeorological data, a six-day tracking survey was carried out in the coastal waters of Changhua Town, Changjiang County, western Hainan Island on March 10 to 15, 2022. And this study analyzed the variation characteristics of environmental factors and influencing factors in the process of Phaeocystis globose bloom. During the peak of the bloom, the abundance of Phaeocystis globosa and COD_Mn were as high as 3.10×10⁸ cells/L and 35 mg/L, which were much higher than those reported in other areas. The rainfall and wind wave disturbance before the bloom promoted the terrestrial runoff and the release of sedimentary nutrients, which provided material conditions for the bloom. The sudden rise of temperature induces the bloom, and the larger tidal range and lower wind speed create favorable external conditions for the accumulation along the colony. During the elimination of the bloom, the concentrations of DIN, PO₄-P, DO, COD_Mn and Mn decreased significantly, in which DIN and PO₄-P were the limiting factors, and DO, COD_Mn and Mn were important characteristic factors. After the yellow colony broken, the concentrations of Chl a and SiO₃-Si also decreased rapidly, and then slowly increased or even higher than the peak concentration level, when the diatom abundance represented by Chaetoceros curvisetus gradually increased. The study also preliminarily explores the basic generation and elimination process of the bloom, which provides an important reference for the further study of the bloom mechanism of P. globosa in this area.

Implementation of the artificial sandbar is a typical measure for the beach nourishment. Research on the morphological evolution of the artificial sandbar meets the important need for coastal protection and restoration. Domestic and international research on morphological evolution of nearshore artificial sandbar and underlying sediment transport mechanisms are summarized in this paper, focusing on the theoretical aspects, e.g. cross-shore migration, morphology evolution, morphology coupling and mechanisms of sediment transport of the artificial sandbar. In the methodology perspective, the description of the equilibrium profile and numerical modelling of morphology evolution of the artificial sandbar are also highlighted. It is also proposed that future research should focus on the deepening of mechanisms of key processes, the improvement of simulation and prediction methods and the application of practical beach nourishment projects.

Carrying out researches on marine sediments’ source can help to better understand the mechanism of material transport and the process of regional and global material circulation. A sediment provenance study has been conducted by analyzing the rare earth element and Sr-Nd isotopes of the ANT36-C4-05 core sediment in the Cosmonaut Sea, Antarctic. The results show that the average content of rare earth element (REE) in the sediment is relatively high, with an obvious fractionation between light REE (LREE) and heavy REE (HREE); and the average ⁸⁷Sr/⁸⁶Sr value of the sediment is relatively high, while the average εNd(0) value is significantly negative. The REE and Sr-Nd isotopic characteristics indicate that since the late Middle-Holocene, the sediment is mainly originated from high-grade metamorphic rocks in the vicinity of the Prydz Bay and Enderby Land, East Antarctic. These detrital materials are partly introduced into the Cosmonaut Sea under the ice-sea interaction, with the Antarctic Coastal Current and Antarctic Slope Current playing important roles in the transportation; simultaneously, it may also rely on katabatic winds originating from the Antarctic interior plateau to complete the transport process from source areas to the study area. The results of the provenance end member mixing model show that the sediment is mainly originated from metamorphic rocks in the Prydz Bay area (>70%), while the contribution from Enderby Land is relatively small. The significant difference in the contribution of two source areas is related to the differences in glaciers, ocean currents, and wind forces between two areas: compared to Enderby Land, the glacier in the Prydz Bay area is larger in scale and moves at a faster speed, with a stronger erosive and transport capacity for the bedrock; in the meanwhile, the Antarctic Bottom Water originating from the bottom of the Prydz Bay area may play an important role during the westward transportation; and the Prydz Bay area is one of the stronger wind force regions of katabatic winds, which can contribute more bedrock debris to downwind areas, for example the Cosmonaut Sea. These factors result in the characteristic of the ANT36-C4-05 core sediment in the Cosmonaut Sea which is mainly from the Prydz Bay area.

Quantitative analysis on the properties of marine phytoplankton bloom events is helpful to understand the marine ecology, environment, and dynamic processes. In the South China Sea, remote sensing is vulnerable to clouds. Previous studies were mostly conducted with discontinuous observation or remote sensing data, which failed to comprehensively understand the characteristics and controlling factors of marine bloom events in the South China Sea. This study applied the statistical framework for defining marine heat waves, based on previously reconstructed daily full coverage remotely sensed chlorophyll a product from 2005 to 2019, to extract marine bloom events in two representative subregions, i.e., the northwestern Luzon in winter and southeastern Vietnam in summer. The duration, intensity, and corresponding long-term trends of marine bloom events in the two representative sea areas were analyzed. The results showed that the bloom frequency in the Luzon Strait has decreased, while the intensity has increased. These trends were significant in most areas for the winter Luzon Strait, while the trends for most of the summer Vietnam coasts were not significant. We further analyzed the influencing factors of marine bloom events and found that the winds (positive correlation) and sea surface temperature (negative correlation) had the greatest impacts on the bloom events. In both two representative sea areas, the marine bloom events were mainly dominated by upwelling, and the wind was the most important influencing factor. Analysis on the precursor conditions of marine bloom events found that the sub-mesoscale activity represented by the temperature front is also an important influencing factor. The study applied in South China Sea as a case study, as well can provide a new perspective to study marine ecosystem and environment.

Flow velocity is one of the key environmental factors for deep sea aquaculture. In order to further understand the molecular regulation mechanism of golden pompano (T. ovatus) under flow velocity stress, the fishes were stressed under the static water, medium flow velocity (54 cm/s) and high flow velocity (90 cm/s), and the LC/MS metabolomics technology was used to explore the changes of endogenous metabolites in the liver to look for differential metabolites and related metabolic pathways. The results show that 51 metabolites in the medium flow velocity group have significant difference with which in the static water and are enriched in 40 pathways, mainly including galactose metabolism, gluconeogenesis, biosynthesis of unsaturated fatty acids, arachidonic acid metabolism, etc. Forty metabolites in the high flow velocity group have significant difference with which in the static water and are enriched in 22 pathways, mainly including biosynthesis of unsaturated fatty acids, pantothenate and CoA biosynthesis, lysine degradation, arachidonic acid metabolism, linoleic acid metabolism, etc. Compared with the medium flow velocity group, 31 metabolites in the high flow velocity group have significant difference and are enriched in 12 pathways, mainly including arachidonic acid metabolism, adipocytokine signaling pathway, cysteine and methionine metabolism, etc. Pathway analysis shows that both medium and high flow velocity stress promoted unsaturated fatty acid metabolism, arachidonic acid metabolism and pantothenic acid synthesis. The ability of swimming is improved to against the stress of flow velocity by strengthening metabolism. The medium flow velocity group mainly significantly affected the metabolism of galactose, cysteine and methionine. At this time, more and more energy produced by fish is used for exercise. The high flow velocity group mainly significantly affect the metabolism of L-lysine and retinoic acid, which reveals that the swimming ability of fish may be decreased and some immune functions may be triggered under the high flow velocity stress.