Storm surge is a complex ocean phenomenon which is sensitive to many factors and has attracted much attention. In this paper, based on covariance localization method of ensemble Kalman filter(EnKF), the storm surge data of different sources, different error and different spatial and temporal resolution calculated by tide gauge stations and FVCOM model were assimilated and fused for the first time. Taking the storm surge process of typhoon 201810 landing in Shanghai for example, the optimal solution of 72-hourly storm surge in the Shanghai offshore areas was obtained and verified, the setting range of set sample number and Schur radius were given. The results show that the root mean square error of storm surge calculated by the observed stations and the model is 0.20 m, while calculated by the observed stations and assimilation is 0.07 m, which is improved by 65%, the root mean square error calculated by independent observation and assimilation is 0.09 m, the ratio of set dispersion to root mean square error is 0.90, the assimilation effect is better and credible. The assimilated storm water increment field can clearly and accurately depict the characteristics of double peaks storm surge, typhone eye surge and frontal surge which can be better used for the research of storm surge, correction of numerical simulation and marine disaster prevention.

Since 1950, the sediment load of the Changjiang River entering the sea has been stepwise decreasing. As the distal mud of the Changjiang River, whether the signal of “sediment load reduction” was recorded in the Zhe-Min coastal mud? If so, how to extract and interpret these sedimentary information? In order to discussing this scientific problem, 5 sediment cores were collected in the Zhe-Min coastal mud; in addition, high resolution grain size analysis (2 mm) was conducted, and four end members were obtained through end-member (EM) model decomposing. Combined with the analysis of the spatial discrepancy in provenance and hydrodynamics of the study area, the specific indicative significance of each EM was revealed: EM1 (with the modal grain size about 2 μm) is originated from extremely fine-grained sediment of the Changjiang River; EM2’s (with the modal grain size about 10 μm) origin is predominated by the Changjiang River, and small part is contributed by the middle and small sized rivers of Zhe-Min coast; EM3 (with the modal grain size about 80 μm) mainly consists of coarse-grain sediment might be provided by Taiwan Warm Current; EM4 (with the modal grain size about 200 μm) is also characterized by coarse-grain sediment, and may be contributed by the Changjiang River. Further analysis indicated that, the EM1 variation was in agreement with the sediment stepwise reduction of the Changjiang River; however, the response intensity gradually decreased from the north to the south. In addition, the hysteresis existed in response time, and the retardation time increased from 4−6 years in the north to 10−14 years in the south. In general, fine-grained sediment could better reflect the Changjiang River catchment change information, and response intensity exhibited significant difference in different areas of the Zhe-Min coastal mud.

Based on the one-layer Boussinesq model with highest spatial derivative being 3, a numerical model is established for focused wave group. The numerical model is solved with predictor-corrector scheme in finite differential method. For time integration, a third-order Adams-Bashforth scheme and a fourth-order Adams-Moulton scheme are separately used in predicting stage and correcting stage. Firstly, the numerical simulations are carried out upon nonlinear regular wave evolution over a constant water-depth in a flume, and the computed results are compared with the semi-analytical solutions. The results demonstrate that the simulated surface elevations, the horizontal velocity and vertical velocity on the free surface can well match the related analytical solutions, while the agreement of the horizontal velocity profile under the crest becomes worse with the increase of water-depth, and the range of the model with respect to nonlinear horizontal velocity profile is for kh<3.5, which is similar to the range of the related linear model with respect to horizontal velocity profile. Secondly, the numerical simulations are conducted upon the nonlinear focused wave group evolution in deep-water. The linear wave groups are used as incident wave conditions. The laboratory experiments conducted by Baldock and Swan (1996) are used to examine the present model. Both the computed surface elevations and the horizontal velocity profile at the focused position are compared with the related experimental data. The results show that the agreement of the surface elevations is pretty good, while the agreement of the horizontal velocity profile is moderate. Finally, with the middle frequency being kept unchanged, the numerical simulations upon the maximum surface elevation and horizontal velocity under the crest are conducted with the variation of the range of focused wave period, the results show that both the crest and the horizontal velocity increase with the increase of the range of the wave periods.

A series of laboratory experiments is carried out in a wave flume to study the influence of rough reef surface on solitary wave transformation and run-up over coral reefs. The cylinder array is used to model the reef surface with large roughness. The results show that the rough reef surface significantly reduces the leading solitary wave and the secondary wave due to beach-reef beach reflection, as well as the wave speed on the reef flat. The relative cross-shore wave height decreases with the increase of dimensionless incident wave height along the reef. It also increases with the increase of reef-flat wave level. The cross-shore wave height attenuation is more evident with the rough reef surface. The variation of dimensionless reflected wave height with the dimensionless incident wave height depends on the reef-flat wave level. The dimensionless reflected wave height approaches to a constant when the incident wave height is sufficient large. The rough reef surface slightly enhances the wave reflection from the fore-reef slope. The dimensionless transmitted wave height as well as wave run-up decline with the increasing dimensionless incident wave height, particularly for the large reef-flat water level. The dimensionless wave run-up on the back-reef beach with the rough reef surface reduces by an average of 46% compared to that with the smooth surface. An empirical formula is obtained by a regression analysis to predict the wave run-up with both smooth and rough reefs.

The formation and evolution of the South China Sea is well recorded in the northern continental margin. But the discrepancies of the tectonic and sedimentary evolution between the west and east of the northern margin are still enigmatic. Several drilling and simulation wells with analogous geological setting are chosen from the deep water areas of the Zhujiang River Estuary Basin and the Qiongdongnan Basin. Based on backstripping and previous studies, high resolution sedimentation rates and subsidence rates are constructed. Results show that both two basins are characterized by analogous sedimentation rates and subsidence rates in the syn-rift stage, but significant discrepancies are revealed in the post-rift stage. Episodic sedimentary and tectonic evolution characteristics are revealed in the Zhujiang River Estuary Basin, sedimentation rates are characterized by “two rapid sedimentation periods and three slow sedimentation periods” and subsidence rates are characterized by “two rapid subsidence periods and one slow subsidence period”. But the sedimentation rates are characterized by “graben” style evolution, and the subsidence rates are characterized by “step-up” style evolution in the Qiongdongnan Basin. The “step-up” subsidence rates in the Qiongdongnan Basin might be controlled by activities of the Hainan mantle plume which moved northwestward derived from the dextral strike-slip of the Red River Fault. And it coincided with the magmatism and the subsidence rate in the northwest margin of the South China Sea. The distribution of the rapid deposition and accelerated subsidence in the Qiongdongnan Basin after 1.8 Ma BP could be mainly controlled by the meanwhile dextral strike-slip of the Red River Fault.

It is of great significance to quickly acquire spatiotemporal change in the information of waterline of remote sensing image. The extraction of the waterline of tidal flat on the remote sensing image has always been a difficult problem in the application of remote sensing technology. There are unique spatial relationships and spectral characteristics on the remote sensing image of waterline. The research area is the Chongming Dongtan of the Changjiang River Estuary. By integrating methods of color model transformation, information entropy calculation, maximum variance and edge detection, we explored how to enhance the contrast of land and sea on the Landsat-5 satellite image, and the edge extraction at different scales was studied. The calculation method of the spatial and spectral characteristics of the waterline using the thermal infrared band was given. A fast extraction method of waterline of sensory image taking the spatial relationship and spectral characteristics into account under the framework of object-oriented technology was proposed. Results show that: (1) The local threshold segmentation method based on the maximum between-class variance method can automatically extract the waterline of band 6. The waterline is continuous, complete, and rich in spatial information. (2) The combination of the optimum index factor method, the dispersion method and the color model transformation method can effectively enhance the contrast between land and sea. The local adaptive Canny operator based on the maximum between-class variance method can automatically detect the high precision edge of the enhanced remote sensing image. (3) Using the spatial relationship and spectral characteristic of waterline, the computer can recognize and connect waterline automatically. (4) The waterline extraction method proposed in this paper is fast and automated, inheriting strong continuity of the threshold segmentation method and high positioning accuracy and strong ability to present details of Canny operator. The results have significant value for researches on the dynamic changes in the coastal zone, the mechanism of land-sea interaction, the protection and development of coastal zone resources, and offshore engineering management.

In recent years, several deep-water gas fields of Yinggehai Formation have been discovered in ultra-deep water area of Qiongdongnan Basin, showing a broad exploration prospect. However, the reservoir physical property prediction of the Member 2 of Neogene Yinggehai Formation have become increasingly prominent which seriously restricts the further exploration of oil and gas. Based on the regional geological data summarized by predecessors, combined with core, logging and three-dimensional seismic data, the third-order sequence framework of the Member 2 of Neogene Yinggehai Formation is established, and the provenance systems in the sequence framework and the sedimentary characteristics of gravity flow under its control are comprehensively analyzed. The results show that gravity flow sedimentary system mainly developed in Ⅱ2-ygh2c and Ⅱ2-ygh2b, and include three major provenance systems which are the south, the north and the axis. Different rovenance systems control the spatial distribution and sedimentary characteristics of gravity flow reservoirs. (1)The submarine canyons controlled by the south provenance are mainly filled by abyssal mudstone, while the canyons controlled by the north provenance are mainly filled with thick turbidite channel sandstone with fine porosity and permeability, which is a good reservoir. (2) The flood plain deposit affected by axial provenance can also be a good oil and gas reservoir because of its good physical properties. (3) The submarine fans controlled by the south provenance is characterized by thin sandstone with fine grain size and high argillaceous content. While the submarine canyons and fans controlled by the north and the axis provenance formed large scale sandstone with big thickness, coarse grain size and good reservoir physical properties, which are the most important high-quality gas-producing reservoirs of deep water area.

In order to study the wave characteristics in the Sanmen Bay, field observation based on AWAC data acquisition equipment was continued for one year, and the statistical analysis, linear regression analysis was done. Moreover, statistics and spectral variations of waves during the typhoon occurrence were investigated, and the reason for the variations was determined on the basis of wave data collected. The results show that the dominant wave direction and the strong wave direction are both E due to the topography of coastal areas; during the wave observation period, H_1/10 is mainly under 0.8 m, and H_max is 2.71 m; the distribution of wave characteristics is a typical Rayleigh distribution in this region; the wave spectra estimated during Typhoon Talim is double-peaked, and the total wave is a combination of swell and wind sea, when the low frequency swell about 0.08 Hz is in a dominant position and the high frequency wind sea about 0.25 Hz is relatively weak. This study will be important as reference in the design of offshore structures as well as for disaster prevention and mitigation.

In order to study the relationship between the open South China Sea Sthenoteuthis oualaniensis fishing ground and the marine environmental factors, this article is based on the data of fishing net fishing boat production and remote sensing of marine environment from 2013 to 2018 in Beihai, Guangxi Zhuang Autonomous Redion. The relationship between the spatiotemporal distribution of the fishing ground of Sthenoteuthis oualaniensis and sea surface temperature (SST), sea surface height (SSH) and sea surface chlorophyll a (Chl a) concentration were studied. The results showed that in the sea areas of 5°−20°N and 108°−118°E, the three environmental factors of SST, SSH and Chl a concentration had a great influence on the spatial and temporal distribution of the fishing ground of Sthenoteuthis oualaniensis. The suitable values of SST, SSH and Chl a concentration within the fishing Sthenoteuthis oualaniensis ground of oualaniensis were: 25−31℃, 46−80 cm, 0.05−0.27 mg/m³, and the center of gravity of the fishing ground shifts from south to north. In addition, the K-S test was performed on the relationship between CPUE values and marine environmental factors from January to December 2013−2018, and the results showed that there was no significant difference between the CPUE values and marine environmental factors.Therefore, the three environmental indicators SST, SSH and Chl a concentration can effectively characterize the resource density of the Sthenoteuthis oualaniensis and the distribution of the central fishing ground.

Yellowfin tuna (Thunnus albacares) is an important fishing target for offshore fisheries worldwide. Stock assessment is essential for its fishery management of sustainable exploitation. According to catch and catch per unit effort (CPUE) data from the International Commission for Conservation of Atlantic Tunas (ICCAT), the Bayesian state space model was conducted to make stock assessment in an open environment (Just Another Bayesian Biomass Assessment) and to compare the effects of different surplus production forms and CPUE data on the assessment. The results showed that the model performed best with the Fox surplus production form and CPUE data of four fleets (United States, Venezuela, Japan and Chinese Taipei). The median and 95% confidence intervals for carrying capacity, intrinsic growth rate were 178 (140, 229)×10⁴ t and 0.210 (0.159, 0.274), respectively. The current stock was not overfished (B/B_MSY=1.109) and was not subject to overfishing (F/F_MSY=0.893). Sensitivity analysis revealed that when the rates of reported catch divided by the actual catch were 70%, 80%, 90%, 110%, 120%, and 130%, the current biomass assessment results were higher with lower fishing rate, but the stock was still in a healthy status. When the total allowable catch (TAC) was set at 11×10⁴ t, the stock would remain basically healthy until 2024. The results from this stock assessment is generally consistent with ICCAT's current stock assessment results, so it is recommended to set a TAC of 11×10⁴ t to keep the stock status healthy and sustainable exploitation of this important fishery.