Rip currents are narrow and concentrated seaward-directed flows and play an important role on coastal morphodynamics, mass transport and swimmer safety. As the intersecting wave field caused by wave reflection of coastal structures is not uniform alongshore, the flow characteristics and spatial distribution of rip currents are different from those of uniform intersecting waves on an open coast. The reflection of waves on cross-shore coastal structures will lead to longshore standing waves, and rip currents will occur in the area of standing wave nodes because of the small wave height, which is one of the generation mechanisms for rip currents. In this study, the characteristics of rip current systems near a coastal structure on a barred beach are given by a laboratory experiment. The influence of the longshore variation of wave height on the flow balance of each rip current unit is discussed. The results showed that the existence of structure drives a longshore current away from the structure and causes the water exchange between each rip current unit. The lateral currents between rip current units are found to make contributions to the rip current transport of each rip current unit and the contributions mainly depend on the relative position of the unit to the structure.

Airborne Laser Bathymetry (ALB) as an established surveying procedure is certainly operated in blue-green region (532 nm) for penetrating the water column to collect depth. Alongside geometric information accepted widely, ALB typically record the radiometric properties (backscattering intensity) about sensed targets and assist with accurate strips registration, fine ground (sediment) cover classification, and advanced geometric modelling. However, due to the design limitations of Automatic Gain Control (AGC), there is a delay in gain value adjustment, particularly prominent in island and coastal areas with more high-return and low-return targets such as exposed rocks and water, which throws the issue of intensity compensation abnormality into stark relief. In response to this issue, a local weighted intensity correction method based on bidirectional movement is designed. Firstly, effective intensity is extracted by index sharing and elevation information. Then, the emission angles are used to divide the scan line and serve as the judgment unit, and the Kolmogorov-Smirnov test is used to identify the abnormal area. Finally, intensity correction is performed by joint weighting of adjacent scan lines and neighborhood intensity, where the joint weighting can ensure the intensity details while eliminating the deviation from the neighborhood intensity. In addition, a unique bidirectional moving strategy is introduced to weaken the decline of strength correction accuracy caused by insufficient correction accumulation. Experiments have illustrated that this approach can effectively solve the AGC compensation anomaly problem, and compared to the pre-correction, the average absolute percentage error of the corrected intensity data decreased by about 0.27, the root mean square error decreased by about 693, and the intensity deviation of the abnormal area was controlled within 26 DN (Digital Number), thus obtaining a high-quality intensity image.

Random errors between systems are not correlated is a necessary assumption for Triple Collocation (TC) analysis, but this assumption does not always hold in practice. The least squares-based Extended Collocation (EC) method can estimate random error in the presence of error correlation, but it cannot accurately estimate standard deviation (SD) of the random error as error correlation is weak. This paper proposes an error estimation method for the fourth system using three error-independent systems, which can estimate the SD of the system error more accurately in case of weak correlation by considering both error correlation and representative error. The SD of the errors of the scatterometer, radiometer and altimeter are 0.600 m/s, 0.742 m/s and 0.533 m/s respectively, as assumed that random errors of three HY-2B wind speed products are independent. The SD of error of ERA5 reanalysis wind speed is also estimated to be 0.810 m/s, the correlation coefficient of the errors of wind speed between HY-2B scatterometer and the ERA5 is 0.231, the correlation coefficient of the errors of wind speed between HY-2B radiometer and the ERA5 is 0.105. This paper proposes a method to estimate random errors and their correlation with the fourth dataset using three known error independent datasets, which achieves a more precise estimation for the SD of the random error in the case of weak correlation, and it helps to use these data better in assimilation and fusion.

The observation and exploration of the seabed urgently requires the appearance of large-scale and long-term observation platforms. The subsea AUV has three main points: a structure that suitable for the mobility in the seabed, an intelligent motion performance that adapts to the complex environment of the seabed, and the underwater acoustic communication and positioning technology that adapts to the seabed. In this paper, the development and evolution of subsea AUV is analyzed, the key technical challenges of underwater AUVs are summarized, and corresponding solutions for underwater AUV hydrodynamic shape optimization technology, intelligent motion control technology, underwater acoustic communication and positioning navigation technology, and underwater connection and charging technology are provided. Finally, a study case of Autonomous Underwater Helicopter is given, to provide a solution for subsea AUV. This paper provides guidance for the development of subsea AUV, as well as ocean observation and exploration technology.

The phenomenon of seabed liquefaction is widely distributed in the underwater delta of the Huanghe River, which poses a great threat to submarine engineering facilities. The determination of liquefaction depth can provide a reference for offshore engineering construction, which has great theoretical significance and application value. The columnar sediments were obtained by drilling in the liquefaction disturbance area of Chengdao sea area in the north of the Huanghe River Delta, and the profile image scanning, radionuclide and particle size composition testing were carried out to obtain the image stratification characteristics, ²¹⁰Pb, ¹³⁷Cs activity and particle size profile, and the deposition rate was calculated on this basis. The results show that the Chengdao sea area was significantly affected by the change of the Huanghe River from the Diaokou channel in 1976, and the sedimentation rate decreased significantly during this period and showed a phased character. During the rapid deposition period, the sand layer produced by frequent liquefaction of surface sediments accumulated continuously, thus forming the dense sand layer. By analyzing ²¹⁰Pb_ex and ¹³⁷Cs activity profiles, the sedimentary records of liquefaction history in the study area were obtained, and the historical liquefaction depth was determined to be at least 5 m, which is similar to previous studies. It is feasible to use the activity of ²¹⁰Pb and ¹³⁷Cs as tools to judge the history and depth of sediment liquefaction, which has great development potential.

fruitless (fru) gene plays an important role in courtship, mating behavior and reproductive development of insectsand crustaceans. Artemia is not only the crucial live food in fish and crustacean larviculture, but also an ideal experimental organism for biological study. In this experiment, the open reading frame (ORF) of fru gene was obtained from the transcriptome of Artemia franciscana and analyzed bioinformatically. qPCR was used to study the expression characteristics of this gene at different stages of gonad development in the Artemia, and its function was explored by RNAi microinjection. Bioinformatics analysis showed that the ORF length of fru gene was 1 215 bp, which contains 404 amino acids, while its molecular weight and isoelectric point were 45.19 kDa and 5.28, and it was an acidic hydrophilic protein with no signal peptide or transmembrane structure; structural domain prediction showed that there are two structural domains of fru, BTB_POZ and HTH. The secondary structure is dominated by α-helix and irregular coil, and the tertiary structure corresponds to it. The qPCR results showed that the expression of fru gene showed a significant increase in late embryos stage, and its expression was significantly higher than that of early oocyte, later oocyte and early embryo stages in the ovary (P < 0.01); while the expression of fru gene also increased in immature stage of the testis, and its expression was significantly higher than that of early, middle and late maturation stages (P < 0.01). After RNA interference, we found that there was a significant decrease in the expression of the fru gene (P < 0.01), and all the offspring produced were cysts. This suggests that the fru gene has an important effect on reproduction and development of A. franciscana, and may be a key factor influencing the reproductive mode of Artemia. Through this study, we obtained important information about the role of fru gene in the reproductive development of Artemia and their related molecular mechanisms, which can help us better understand this important biological process.

17β-hydroxysteroid dehydrogenases (17β-HSDs) are the oxidoreductases in the last step of sex steroid hormone synthesis process, and play important roles in animal gonadal development and reproductive regulation. In this study, on the basis of the genome data of the razor clam Sinonovacula constricta, 17β-HSD genes were cloned and identified, and their chromosome distributions, phylogenetic relationships and gene expression patterns in different tissues and under different gonadal developmental stages were analyzed. The results showed that 17β-HSD6, 17β-HSD10, 17β-HSD12 and 17β-HSD14 genes of S. constricta were located on four different chromosomes, and the encoded proteins all contained the conserved SDR superfamily domains. The four 17β-HSD proteins were clearly differentiated and clustered into four independent branches in the phylogenetic trees. The results of qRT-PCR showed that 17β-HSD genes were all expressed in testes tissues, and possessed higher expression levels in gonads and hepatopancreas. During the gonadal development of S. constricta, 17β-HSD6 gene was expressed higher in testis and ovary at the spawning stage. The expression levels of 17β-HSD10, 17β-HSD12 and 17β-HSD14 genes showed a trend of increasing first and then decreasing during the development cycle of testis and ovary, which were all expressed higher at the mature stage. At the mature stage, 17β-HSD10 gene was expressed significantly higher in testis than in ovary (p < 0.05) , while the expression levels of 17β-HSD12 and 17β-HSD14 genes were all significantly higher in ovary than in testis (p < 0.05). Therefore, 17β-HSD6 gene might not be involved in regulating gonadal development process, while the expressions of 17β-HSD10, 17β-HSD12 and 17β-HSD14 genes were closely related to the gonadal development, suggesting that they might affect the gonadal development by regulating the synthesis and metabolism of sex steroid hormones in S. constricta. These findings laid theoretical foundations for further study on mechanism of 17β-HSD genes in regulating gonadal development and reproductive endocrine of mollusks.

Using reanalysis sea surface data and in-situ high-resolution observations in spring, summer 2018, and summer 2019, this study analyzes the 3D structure and seasonal variation of temperature fronts in the shelf sea west of Guangdong. The results show that the sea surface temperature (SST) fronts reach the strongest intensity up to 0.049°C/km in winter, with the largest occurrence probability of 75% and coverage of 66 km. The SST fronts weaken in spring and summer, and almost disappear in autumn. The average offshore distance of the front is 50 km in winter and 23.1 km in summer. The in-situ observations show a strong thermal front in coastal areas shallower than 20 m in both spring and summer. The front gets weaker and closer to the coast in deeper layers and is associated with warm coastal water and cold shelf water. In shelf areas deeper than 20 m, the fronts in the subsurface layer are stronger than in the surface layer and shift shoreward in deeper layers. The correlation coefficient and information flow between the surface wind and frontal parameters reveal that the surface wind stress curl and along-coast wind are the most important factors affecting the surface thermal front. These thermal fronts also have interannual variations, with maximum intensity in La Niña years with negative PDO and minimum intensity in El Niño years with positive PDO.

Rossby normal mode as a solution of the boundary problem is a key part of the dynamics in the South China Sea. With the usage of multiscale window transform, a recently developed decomposition tool for multiscale processes, mesoscale-eddy fields analogous to Rossby normal modes are separated from the satellite observation of the South China Sea. The eddies are dominated by a group with lifetime of 3 months, which belongs to an oscillating mode with period of 6 months and wavelength of 250 km. To explore the external influence on this mode, we apply an information flow-based causality analysis that has been rigorously established from first principles in physics. It is found that both the Kuroshio intrusion and monsoon, believed to be two primary forcings of the South China Sea circulations, are causal to the Rossby normal mode within one period. Specifically, the Kuroshio intrusion mainly affects the 1/2π and 3/2π phases, while the monsoon the 3/4π phase. Further analysis reveals that the transition between penetration and leaping of the Kuroshio at the Luzon Strait is key to the mode development. Under this circumstance, the leaking and looping branches are almost of equal intensity, facilitating the generation of cyclonic and anticyclonic eddies west of the Luzon Strait, and hence the Rossby normal mode. The monsoon over the South China Sea, on the other hand, shows the greatest influence at its mature phases. The Gulf of Thailand is a key region for the monsoon to affect the Rossby normal mode in the South China Sea, indicating that local forcing plays an important role in exciting a global mode.

Using Tropical Rainfall Measurement Mission 3B42 rainfall data, this study tracks pathways of Tropical Intraseasonal Oscillations (MJO) from a Lagrange perspective, analyses their distribution in the Maritime Continent (100°−120°E) and further discusses its mechanism. Identifying a raining area with above 12 mm in 24 hours precipitation as a MJO convective region and using its centroid as MJO convective center, pathways of MJO are tracked and a set of pathways is given. Because eastward propagating MJO events happen mostly in boreal winter, this study focuses on the distribution of pathways of MJO events in boreal winter. The results show that if measured by precipitation MJO moves through the Maritime Continent mostly near the equator (5°S−5°N), which is different from past research results that MJO detours to the south of the Maritime Continent measured by using outgoing long wave radiation (OLR) as a index. Besides, the conclusion that the precipitation associated with MJO moves through the Maritime Continent mostly near the equator is independent of background climate patterns like ENSO or IOD. The analysis of the mechanism shows that pathways of the precipitation associated with MJO through the Maritime Continent are mostly regulated by strong latent heat flux anomalies and are inconsistent with regions with warm sea surface temperature anomalies, which leads to different pathways of MJO moving through the Maritime Continent from different perspectives of precipitation and OLR.