In this study a novel synthetic aperture radar (SAR) scattering model for sea surface with breaking waves is proposed. Compared with existing models, the proposed model considers an empirical relationship between wind speed and wave breaking scattering to present the contribution of wave breaking. Moreover, the scattering weight factor p, and wave breaking rate q, are performed to present the contribution of the quasi-specular scattering term, Bragg scattering term, and wave breaking scattering term to the total scattering from the sea surface. To explore the modeling accuracy of sea-surface scattering, a simulated normalized radar cross-section (NRCS) and measured NRCS are compared. The proposed model generated the simulated NRCS and a matching GF-3 dataset was used for the measured NRCS. It was revealed that the performance of the VV polarization of our model was much better than that of HH polarization, with a correlation of 0.91, bias of −0.14 dB, root mean square error (RMSE) of 1.26 dB, and scattering index (SI) of −0.11. In addition, the novel model is explored and compared with the geophysical model of CMODs and satellite-measured NRCS from GF-3 SAR wave mode imagery. For an incidence angle 40°–41°, the relationship between the NRCS and wind speed, relative wind direction is proposed. As with the SAR-measured NRCS, the performance of VV polarization was much better than HH polarization, with a correlation of 0.99, bias of −0.25 dB, RMSE of 0.64 dB, and SI of −0.04.

The horizontally variable density stratification and background currents are taken into the variable-coefficent extended Korteweg-de Vries (evKdV) theory to obtain the geographical and seasonal distribution of kinematic parameters of internal solitary waves in the Andaman Sea (AS). The kinematic parameters include phase speed, dispersion parameter, quadratic and cubic nonlinear parameters. It shows that the phase speed and dispersion parameter are mainly determined by the topographic feature and have limited seasonal variation. The maximum phase speed is 2.6 m/s, which occurs in the cool season (November) in the middle of the AS, while the phase speed in the cool season is slightly larger than those in other seasons, up to 11.4% larger than that in the rainy season (July) in the southern AS. The dispersion parameter in the cool season can be 22.3% larger than that in the hot season. The nonlinear parameters have significant seasonal variation, and they can even change their signs at the continental slope in the north of the AS, from season to season. Meanwhile, the algebraic solitons dominate in the AS with minimum amplitudes (a_al) ranging from 0.1 m to 102 m, and the maximum a_al occurs in the cool season in the southern AS. The effect of the background flow on the parameters is also studied. The background flow has a great influence on the nonlinear parameters, e.g., the value of cubic nonlinear parameter can be reduced by 1/3 when the background flow is not considered.

Satellite altimetry observations, including the upcoming Surface Water and Ocean Topography mission, provide snapshots of the global sea surface high anomaly field. The common practice in analyzing these surface elevation data is to convert them into surface velocity based on the geostrophic approximation. With increasing horizontal resolution in satellite observations, sea surface elevation data will contain many dynamical signals other than the geostrophic velocity. A new physical quantity, the available surface potential energy, is conceptually introduced in this study defined as the density multiplied by half of the squared deviation from the local mean reference surface elevation. This gravitational potential energy is an intrinsic property of the sea surface height field and it is an important component of ocean circulation energetics, especially near the sea surface. In connection with other energetic terms, this new variable may help us better understand the dynamics of oceanic circulation, in particular the processes in connection with the free surface data collected through satellite altimetry. The preliminary application of this concept to the numerically generated monthly mean Global Ocean Data Assimilation System data and Archiving, Validation, and Interpretation of Satellite Oceanographic altimeter data shows that the available surface potential energy is potentially linked to other dynamic variables, such as the total kinetic energy, eddy kinetic energy and available potential energy.

In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo (2004 to 2020) and RAMA (2007 to 2020) profiles data in the Bay of Bengal and eastern equatorial Indian Ocean (EEIO). Temperature inversion exists (17.5% of the total 39 293 Argo and 51.6% of the 28 894 RAMA profiles) throughout the year in the entire study area. It shows strong seasonal variation, with the highest occurrences in winter and the lowest in spring. Besides winter inversion in the northern Bay of Bengal, two other regions with frequent temperature inversion are identified in this study for the first time: the northeastern part of the Bay of Bengal and the eastern part of the EEIO during summer and autumn. Driving processes of temperature inversion for different subregions are revealed in the current study. Penetration of heat (mean ~25 W/m²) below the haline-stratified shallow mixed layer leads to a relatively warmer subsurface layer along with the simultaneous cooling tendency in mixed layer, which controls more occurrence of temperature inversion in the northern Bay of Bengal throughout the year. Comparatively lower cooling tendency due to net surface heat loss and higher mixed layer salinity leaves the southern part of the bay less supportive to the formation of temperature inversion than the northern bay. In the EEIO, slightly cooling tendency in the mixed layer along with the subduction of warm-salty Arabian Sea water beneath the cold-fresher Bay of Bengal water, and downwelling of thermocline creates a favorable environment for forming temperature inversion mainly during summer and autumn. Deeper isothermal layer depth, and thicker barrier layer thickness intensify the temperature inversion both in the Bay of Bengal and EEIO.

Marine microorganisms were considered to be important sources of marine bioactive compounds. The major objective of the study was to isolate and characterize bacteria with antimicrobial activities from the various marine environment of Egypt. In this respect, thirty-five bacterial isolates were recovered from sediment samples collected from different spots along the Egyptian Red Sea coastline and Alexandria coastline during the summer season of 2017 and 2018. According to the morphological, physiological, and biochemical characteristics, the bacterial isolates were clustered into 13 groups designated as A, B, ···, M. And, 14 Gram-negative and 21 Gram-positive bacteria were determined. The isolated bacterial strains were screened for their potentiality for antimicrobial agent(s) production against ten indicator strains. Strain Mo13 was showed high antimicrobial activity against all empirical strains. Subsequently, the most promising marine bacterial isolate with code MO13 was identified as Bacillus zhangzhouensis OMER4 according to the phenotypic characterization through morphological, physiological, and biochemical tests as well as genotypic characterization through the 16S rDNA technique. The bioactive components were extracted with ethyl acetate, then analyzed using GC-MS and the substantial component was recognized as phenol, 2, 4-bis(1, 1-dimethyl ethyl).

It has been widely recognized that biological invasion has become one of the greatest threats to the ecosystem. Codium fragile is an invasive species which exhibits a variety of attributes like parthenogenesis, winter fragment, and vegetative reproduction; and therefore, it has become a successful invader, colonizing most subtropical regions. In China’s southeast coastal aquaculture waters, the green algal bloom caused by C. fragile will probably become a serious problem. In order to understand more details about the species, an experiment focused on its reproductive characteristics was conducted using culture established from a sample collected in the aquaculture raft of the Nan’ao Island in the South China Sea. The results showed that there were two types of gametes resembling aplanospores and zoospores respectively, both of which were able to germinate. During the gametes liberation, a long mucilage tube was formed out of the mouth of the gametangium assisting dispersal of gametes away from the parent plant. This tube was adapted not only to its surrounding flowing water environment but also to its parent plant’s outer gelatinous structure. In general, the optimum temperature for gametes release and germination was 15−20°C and 15°C, respectively, which corresponded to the local offshore marine water. The plant was observed to produce vegetative buds under favourable reproductive conditions which were called propagules. They were capable of developing into filamentous thalli. The results will provide some scientific evidences for revealing the biological mechanism of bloom and control strategies of invasive green algae.

The size-spectrum model has been considered a useful tool for understanding the structures of marine ecosystems and examining management implications for fisheries. Based on Chinese tuna longline observer data from the central and eastern tropical Pacific Ocean and published data, we developed and calibrated a multispecies size-spectrum model of twenty common and commercially important species in this area. We then use the model to project the status of the species from 2016 to 2050 under five constant-fishing-mortality management scenarios: (1) F=0; (2) F=F _recent, the average fishing mortality from 2013 to 2015; (3) F=0.5F _recent; (4) F=2F _recent and (5) F=3F _recent. Several ecological indicators were used to track the dynamics of the community structure under different levels of fishing, including the mean body weight, slope of community size spectra (Slope), and total biomass. The validation demonstrated that size-at-age data of nine main catch species between our model predictions and those empirical data from assessments by the Western and Central Pacific Fisheries Commission matched well, with the R ²>0.9. The direct effect of fishing was the decreasing abundance of large-sized individuals. The mean body weight in the community decreased by ~1 500 g (21%) by 2050 when F doubled from F _recent to 2F _recent. The higher the fishing mortality, the steeper the Slope was. The projection also indicated that fishing impacts reflected by the total biomass did not increase proportionally with the increasing fishing mortality. The biomass of the main target tuna species was still abundant over the projection period under the recent fishing mortality, except Albacore tuna (Thunnus alalunga). For sharks and billfishes, their biomass remained at relatively higher levels only under the F=0 scenario. The results can serve as a scientific reference for alternative management strategies in the tropical Pacific Ocean.

The diversity, community composition and 16S rRNA gene abundance of bacterioplankton along a transect across an upwelling area off the eastern coast of Hainan Island (the Qiongdong upwelling) were investigated in August of 2016 using high throughput sequencing and quantitative PCR assay of 16S rRNA genes. Compared with the offshore stations, the inner-shelf stations had higher bacterial gene abundance (up to 3 fold) and operational taxonomic unit richness, a result of the influence of upwelled and fresher waters. Overall, a majority of the reads were affiliated with Gammaproteobacteria (11%–74%) and Alphaproteobacteria (14%–43%). The structure of the bacterial community was significantly affected by salinity, dissolved oxygen, ${\rm{NO}}_3^-$ and ${\rm{NH}}_4^+ $, which also defined the physicochemical features of the upwelled waters. Horizontally, the relative abundances and gene abundances of Rhodobacteraceae, SAR86, Cyanobacteria and Bacteroidetes in eutrophic zone decreased from the inner to outer shelves and slope, whereas Alteromonas, Vibrio and Oceanospirillaceae exhibited an opposite trend. This study stresses the riverine influence on the oceanographic condition and spatial variability of bacterioplankton diversity and distribution in the Qiongdong upwelling.

The identity of Rostraria bierii, originally described as a larval amphinomid from Cape Setozaki, Pacific coast of Japan, is investigated. Based on the original description and illustrations, reinterpretations conclude the “larva” to represent a partial juvenile or adult magelonid specimen, broken after the first chaetiger. The original figures are compared with several known magelonid species to justify the new placement. The authors suggest the supposed amphinomid larva is a Magelonidae taxon inquirendum. The identity of the species is discussed in line with the current knowledge of the Magelonidae in the western Pacific and a key to all known species within the region is provided to aid identifications. Current gaps in our taxonomic knowledge of the Magelonidae of the western Pacific are highlighted and discussed.