Shapes of freak waves are strongly related to the characteristics of their surrounding sea state. The most probable shape of rogue waves obeys NewWave theory under the narrow band assumption in the linear process. Based on the NewWave theory, the largest wave is located in the center of a wave group and the adjacent waves are symmetrical. However, wide spectral widths containing various frequency components are more common in the ocean. There is still a lack of systematic understanding of the shapes of in-situ measured freak waves and the surrounding waves. Furthermore, key parameters that affect the shapes are not clear. In the present study, shapes of 112 freak waves and the related influence factors from the ocean weather station in the Norwegian Sea are investigated. Merely 52% of freak waves are located in the center of the group, and the possibility of other freak waves occurring towards the front of the wave groups is higher. Besides, shapes of the adjacent prior and following waves of freak waves are asymmetry. Generally, the amplitude of the following wave is larger than that of the preceding one. By quantitatively comparing shapes of the averaged measured rogue waves and based on the NewWave theory, it is found that the spectral width is a key parameter for affecting shapes of freak waves. With the spectral width wider, the difference of profiles of sea surface elevations around the freak waves between the measured and using the NewWave theory is exponentially increasing.

Deep water breaking wave is usually generated by the wave focusing method in laboratory. A wave with a significantly increased height can be generated by the superposition of components so that wave breaks when the steepness exceeds the limit value. However, using this method, the number of wave breaking is usually not unique leading to less obvious field characteristics after breaking and it’s hard to set research cases due to the difficulty in selecting wave-making parameters. As a result, the effect and efficiency of elaborate deep water wave breaking experiments is affected directly. Theoretical wave surface was calculated by the theory of wave focusing method and theoretical wave steepness was calculated using the wave height and wavelength defined by up-cross-zero method in this paper. On the other hand, wave breaking times and intensity were obtained from the physical experiments. The JONSWAP spectrum was used as the input spectrum and the effects of wave-making parameters, such as focusing amplitude, spectrum peak frequency, frequency bandwidth, on wave breaking were discussed so as to establish an approximate quantitative relationship between breaking times and input parameters. The research conclusions can provide a reference for selection of wave-making parameters so that the efficiency of the experiment can be improved.

The free-dropping acoustic Doppler current profile (FADCP) samples in a “free-fall” manner, which can observe the full depth current without relying on the cable traction of the ship, and its stability is greatly improved compared with lowered acoustic doppler current profiler (LADCP), effectively reducing the irregular motion in the observations. The FADCP observation experiments conducted in April and September 2021 at Xisha waters in the South China Sea obtained current and CTD data from two sections containing 16 stations. Based on the real bottom current observation during the resting period, the full-depth current profiles at each station were obtained by shear method, and the average deviation of the station profile near a mooring compared with the mooring profile was 3 cm/s. The observation section captured the cyclonic eddies of two periods at Xisha waters with more precise vertical structures than the HYCOM simulation, and the surface flows fitted with the absolute geostrophic currents. This research shows that the FADCP has low vessel requirements, high data quality, easy post-processing and good results, but cannot perform supplementary observations for specific water layers.

Estuarine bay is a special geomorphological system, which is often charactered with the combination of shoals and channels. Its evolution and shifting balance of shoal-channel structure are not only the frontier hotspots of estuarine and coastal researches, but also the theoretical cornerstone of estuarine management and port waterway construction. Based on the nautical bathymetry data of different historical ages, using geomorphological information entropy and other analytical methods, this paper studies the phylogenetic evolution characteristics and shifting balance mechanism of the shoal-channel structure in Huangmaohai Estuary Bay (HEB), and the main findings include: (1) The geomorphological evolution of HEB has undergone a transition from siltation to erosion during 1940 to 2007. The average annual siltation rate was 1.4 cm/a. From then on, till 2015, the bay had shifted to erosion period and the average annual erosion rate was 1.2 cm/a. (2) The structure of shoal and channel in HEB was converted, and the structure of "three shoals and two channels" was transformed into the structure of "two shoals and one channel" between 2003 and 2007, and the elevation differentiation between shoals and channels tended to be enlarged due to the impact of reclamation in the shallow coasts and dredging projects in channels. As a result, the shallow shoals became shallower and the channels were deeper. (3) The entropy value of geomorphological information of HEB decreased first and then increased, indicating HEB it changed from the relatively stable mode of slow siltation to the abrupt changing mode, in which the uncertainty of the shoal-channel evolution was induced by human intervention; moreover, the steady states of the shoal and channel are different. The shoals showed higher uncertainty than the deep channel. (4) Human activities disturbed the original steady state of the shoal-channel structure, and the dredging project will enhance the vitality of the East Channel and promote the adaptive reconstruction in the deep channel to evolve in an orderly direction. The West Shoal and the East Shoal have undergone a disturbance balance of human activities such as reclamation, and the shoal instability has shown a disorderly evolution.

To explore the source of platinum group elements (PGE) in cobalt-rich crusts, the samples from Caiwei Seamounts in western Pacific were chosen as the research object, for which XRD, ICP-OES and ICP-MS were used to analyze the mineral composition, major elements contents and PGE contents in cobalt-rich crusts. The results showed that, the main crystalline minerals were vernadites in cobalt-rich crusts, and the minor minerals included quartz, plagioclase, potassium feldspar and carbon fluoride apatite. Also many amorphous ferric minerals were contained in cobalt-rich crusts. In addition, Mn and Fe contents were the highest in cobalt-rich crusts, and PGE were enriched in cobalt-rich crusts. PGE contents were 142−1352 ng/g, and Pt contents were 114−1268 ng/g, in which Pt accounted for more than 80%. PGE contents in the old layers were higher than that in the new layers. And the phosphatization appeared in the old crust layers. Moreover, there was an obvious contrast in PGE of cobalt-rich crusts, Pd group (PPGE) contents were more than Ir group (IPGE). PGE diagrams showed the positive Pt anomalies and negative Pd anomalies. And Pt was enriched and Pd was poor in cobalt-rich crusts. Meanwhile, PGE in cobalt-rich crusts were probably derived from the reaction between seamount basalt and seawater during the oceanic shell erosion process. PGE had positive correlation with CaO, P₂O₅, Ba and Cu, so PGE were probably enriched in the phosphate phase. In addition, the growth profile of cobalt-rich crust was from top to bottom and from new to old, PGE contents increased gradually. Therefore, oxidative marine environment and high marine productivity had a positive impact on phosphatization, which further promoted the enrichment of PGE. This study provided a certain reference value for revealing the source of PGE in cobalt-rich crusts.

In order to improve the success rate and accuracy of species identification of fish eggs and larvae, fish eggs and larvae samples collected from the Zhujiang River Estuary in spring were identified by DNA barcoding technology based on the mitochondrial COⅠand 12S rRNA genes. A total of 391 samples were amplified and 60 species in 7 orders, 25 families, 42 genera were successfully identified (2 species were not identified). Among them, Perciformes had the most species and quantity accounting for 51.6% and 47.91% respectively, followed by Clupeiformes with 25% and 34.56% respectively. There were 10 dominant species, among which Coilia mystus had the highest dominance of 0.071, Collichthys lucidus had the lowest dominance of 0.014. The amplification results of COⅠand 12S rRNA gene fragments showed that the success rate of 12S rRNA gene amplification in eggs and larvae (95.60%) was significantly higher than that of COⅠgene (43.22%). Genetic distance and ABGD analysis showed that the intraspecies genetic distance of COⅠ gene was 0−0.005 (average was 0.003), and the interspecific genetic distance was 0.061−0.376 (average was 0.253), and there was an obvious “barcode gap” between them. The intraspecific genetic distance of 12S rRNA gene was 0−0.011 (average was 0.007), and the interspecific genetic distance was 0.007−0.487(average was 0.283). which do not form a “barcode gap” between the interspecific and intraspecies genetic distances. The Bayesian phylogenetic tree based on COⅠ and 12S rRNA genes showed that all species could be clustered into independent branches and can be effectively distinguished. The above results show that both COⅠ gene and 12S rRNA gene can be used for the identification of most fish eggs and larvae, but the success rate of COⅠ gene amplification is low, and it is difficult to distinguish some closely related species of 12S rRNA gene. The combined use of the two genes can improve the success rate and accuracy of species identification of fish eggs and larvae.

Mangroves forests, as a coastal zone ecosystem dominated by mangrove plants in the tropics and subtropics, are one of the important coastal wetland types. In this paper, multi-source and multi-phase satellite data were used to form a data atlas of shoreline, reclamation, aquaculture area, mangrove distribution in the Guangdong-Hong Kong-Macao Greater Bay Area from 1969 to 2020, and the time series analysis of the evolution of mangroves in the Greater Bay Area was obtained by using the combine mangrove recognition index (CMRI). The results show that the existing mangrove forests data set can be obtained by interpreting the multi-source remote sensing data, and the CMRI time series data can establish the history of the existing mangrove forest change, and then effectively estimate the mangrove forest age. The temporal and spatial distribution of mangroves in the Guangdong-Hong Kong-Macao Greater Bay Area has undergone obvious changes, with the existing mangroves being about 3 316 hm², and the existing forest age in various regions in the Greater Bay Area is quite different, and the overall average forest age is 20 a. In the past 50 years, the shoreline as a whole has moved towards the sea, and the changes in shoreline, reclamation, and breeding areas have significantly affected the area, spatial distribution, and age of mangroves. Artificial cultivation has been the main reason for the restoration of mangroves in the past 20 years.

Bacteria play an important role in the aquatic ecosystem. In our work, bacterial community structure and assembly mechanisms were studied in Sansha Bay in Fujian Province based on DNA and RNA high-throughput sequencing. Our results revealed that: (1) A total of 1476 operational taxonomic units (OTUs) were detected, and γ-proteobacteria, α-proteobacteria, cyanobacteriia and bacteroidia were the most diverse bacterial groups. (2) γ-proteobacteria, α-proteobacteria, cyanobacteriia and bacteroidia were also the most abundant groups in Sansha Bay both in the DNA and RNA high-throughput sequencing results. The metabolic activities of these four dominant groups were different, and their metabolic activities were mainly regulated by salinity, total nitrogen, nitrite nitrogen and inorganic phosphate concentrations. (3) The bacterial community structure in Sansha Bay was different in spatial scale, and the closer the geographical location was, the more similar the bacterial community structure was. Neutral process was the main assembly mechanism affecting the construction of bacterial community in Sansha Bay. Our results were useful for the understanding the bacterial community structure and assembly mechanism in Sansha Bay, Fujian.

Diurnal observation is necessary for grasping the variability of carbonate system in coastal waters and sea-air CO₂ exchange process and is helpful to reduce the uncertainty of assessments for carbon source/sink. Surface carbonate system and related parameters were obtained during twice 24 hours fixed sampling and observation conducted in April and August 2018 in the Yingluo Bay-Anpu Harbor, located in the northeastern Beibu Gulf. In this paper, we analyzed the hourly variations of partial pressure of CO₂ in surface sea water (pCO₂) and discussed the corresponding environment factors controlling pCO₂ in both seasons. The pCO₂ values ranged from 530−628 μatm in spring to 427−748 μatm in summer, with the average sea-air CO₂ flux in spring and summer for (1.7±0.8) mmol/(m²·d) and (1.2±0.8) mmol/(m²·d), respectively. The study area acted as a weak CO₂ source during both seasons. The hourly changes of pCO₂ in spring were more significantly affected by temperature effects than in summer. During summertime, pCO₂ had more sensibly response to tidal action, enhanced biological production and respiration with inflow of coastal freshwater such as rivers and submarine groundwater discharge. Water warming dominated the formation of high pCO₂ in spring. The enhanced biological production during the physical mixing of saline and fresh water played a role in the drawdown of surface dissolved inorganic carbon (DIC) and the mangroves and salt marshes ecosystems along the bay had a certain contribution to the addition of DIC on the freshwater end-member in summer. The variations of the ratio of DIC concentration and total alkalinity (TA) in the water masses could imply the overall distribution pattern adjacent to the Yingluo Bay-Anpu Harbor that high values exists in the bay and lower values exists in offshore water.

According to the data of four voyages of zooplankton survey in the southwest of Bohai Sea from August 2020 to May 2021, the community structure and seasonal variation of small medusae were analyzed, and the effects of environmental factors on the abundance of small medusae were discussed. There were seasonal variations in species composition and abundance distribution of small medusae in the southwest of Bohai Sea, a total of 13 species of small medusae were found throughout the year, including 11 species of hydromedusae and 2 species of ctenophores. The number of medusae species in spring, summer, autumn and winter were 4, 9, 7 and 2 species respectively. The mean abundance values were 30.74 ind./m³, 30.78 ind./m³, 12.08 ind./m³ and 0.57 ind./m³ respectively. The dominant species were Sugiura chengshanense, Rathkea octopunctata, Eirene ceylonensis, Clytia hemisphaerica, Pleurobrachia globosa. The average seasonal replacement rate of dominant species was 91.67%, showing obvious seasonal succession. Water temperature and salinity were main environmental factor affecting the seasonal variation of total abundance of small medusae in the southwest of Bohai Sea. The increase of water temperature and nutrients in spring promote the growth and reproduction of small medusae. In summer, copepods provided rich bait for small medusae to promote its growth, the community was mainly affected by salinity in autumn. According to the risk species of small medusae in the southwest of Bohai Sea, it was speculated that the peak of risk species in summer and autumn was a risk to the planned nuclear power.