Using 0.1°×0.1° high-resolution temperature, salinity, velocity and sea surface height (SSH) data from the ocean general circulation model for the earth simulator (OFES) model, this study analyzes the capability and applicability of the eSQG (effective Surface Quasi-Geostrophy) method in vertical velocity diagnosis in the South China Sea (SCS), as well as the spatiotemporal variation of vertical velocities. The diagnosed vertical velocities ω_eSQG from SSH with the eSQG method are of the same order of 10⁻⁵ m/s as the “true” vertical velocities ω_OFES from the OFES model. ω_eSQG shows spatial variations with higher values in northern basin. The correlation coefficients of the horizontal distribution of ω_eSQG and ω_OFES (r^s) are greater in deep basin than that in the whole SCS, suggesting that the eSQG method is more efficient in vertical velocity diagnosis in deep water far from boundaries. Vertically, the correlation coefficient has maximum values occurring in the subsurface layer at about 150 m. ω_eSQG is stronger in summer and r^s show seasonal variation with higher values in winter, indicating more efficient in eSQG diagnosis in winter. ω_eSQG is reliable in the regions southwest of Taiwan and east of Vietnam, where the temporal correlation coefficients of ω_eSQG and ω_OFES (r^t) exceed 0.6, while ω_eSQG is poorly correlated to ω_OFES in the shelf regions in the southern and northwestern SCS with r^t mostly under 0.2. r^s in the same region is varying at periods of about 18−55 d. ω_eSQG performs better as the distributions of the SSH and the sea surface density are in same phase. ω_eSQG varies little as the temporal resolution of SSH varies, while r^s increases as spatial resolution reduced to 0.25° in mesoscales.

We can discover that there exist storm currents along Yangjiang sea area of western Guangdong waters in spring and summer of 2019 by analyzing materials which measure hydrologic and hydrometeorological along west coast of Guangdong flow Yangjiang sea area from 2018 to 2019. The result of research shows: Firstly, the velocity of 2 m water depth at the observation site reached 164.7 cm/s and 9 m water depth at the observation site reached 127.6 cm/s at 6:00 a.m. on May 5, 2019. The velocity of Yangjiang Shapa sea area 2 m water depth at the observation site reached 161.8 cm/s and 9 m water depth at the observation site reached 156.6 cm/s at 4:00 to 5:00 a.m. on August 1, 2019. Secondly, the suddenly strong currents in spring and summer have typically shock current trait in the Yangjiang 20 m to 30 m sea area along the shore current area of western Guangdong. The strong current happens at the surface of the ocean during the time of rising tide for 2 h to 4 h. Thirdly, during the transition period of southwest wind and northeast wind, the coastal sea area of western Guangdong is prone to form a water convergence zone. The sea level of the coastal sea area rises, and the sea level of the offshore sea area drops. The strong horizontal pressure gradient force from the shore to the outside causes the coastal water to strengthen the westward movement, resulting in shock current.

This study compiled the data of ^239+240Pu specific activity, ²⁴⁰Pu/²³⁹Pu atom ratio and ^239+240Pu flux or inventory in the East China Sea and adjacent waters. Based on the ^239+240Pu concentration in atmospheric fallout, ^239+240Pu in seawater, ^239+240Pu in organisms, ^239+240Pu in sediment trap and ^239+240Pu in sediment, the geochemical behavior of ^239+240Pu were explained in the East China Sea and adjacent waters. The results showed that global fallout and Pacific proving grounds close-in fallout were the two major sources of ^239+240Pu. Under the influence of water masses such as the Changjing River diluted water, Zhejiang-Fujian Coastal Current, Taiwan Warm Current, Kuroshio Current and upwelling current, mixing effect and removal effect, the concentration of ^239+240Pu in coastal waters of the East China Sea showed a trend of removal over time, the burial depth of ^239+240Pu in the near shore sediments was deeper than that in the far sea area. In the northeast of Taiwan Island of China, the ^239+240Pu specific activity and ^239+240Pu inventory in Okinawa Trough increased significantly under the influence of Kuroshio current intrusion and upwelling current. At the same time, this study found that the relationship between ^239+240Pu specific activity and ²⁴⁰Pu/²³⁹Pu atom ratio in surface sediments of the East China Sea, and confirmed the existence of a tributary of the Kuroshio bottom in northeastern Taiwan, and indicated the location where the Taiwan Warm Current and a tributary of the Kuroshio bottom may intersect.

Increasing heat stress due to global warming is the main threat to coral reef regions over the South China Sea islands. Coral reefs bleaching events are most often predicted by heat stress, which will benefit the protection and management coral reefs. Degree heating week (DHW) is used to measure the intensity and duration of heat stress experienced on coral reefs, represents the accumulation of positive sea surface temperature (SST) anomaly at that location over the past 12 week periods. This study utilizes the National Oceanic and Atmospheric Administration-Coral Reef Watch (NOAA-CRW) SST dataset to investigate spatio-temporal in the heat stress of the coral reef regions of the South China Sea islands between 1985 to 2019 and its relevance to El Niño. K-means cluster analysis was performed on the 35-year maximum degree heating week values per pixel, and the coral reefs of the South China Sea islands were divided into 6 regions: Nansha−1, Nansha−2, Nansha−3, Dongsha, Xisha and Zhongsha coral reef region. The main results are as following: (1) The maximum DHW of the coral reef regions of the South China Sea islands is 0−12.9°C-week, and it decreases from high to low in latitude. (2) The linear fitting method was used to analyze the annual maximum DHW from 1985 to 2019. The results showed that the thermal pressure intensity in the coral reef area of the South China Sea islands showed an upward trend, ranging from 0.013°C to 0.174°C per week. The maximum DHW in the coral reef area of the South China Sea islands appeared in 1998, 2010, 2014. (3) The maximum annual DHW might have caused 93.9% of coral reefs to have more than one bleaching risk event, and 19.6% of coral reefs to have at least one risk of death. (4) The cross-wavelet analysis of monthly mean DHW in the coral reef regions of the South China Sea islands and Oceanic Niño index shows that there are time-frequency characteristics and time-lag correlation of multi-period 8−32 months resonance period, which confirms that the thermal pressure of coral reefs in the South China Sea islands increases significantly with the occurrence of El Niño events. The time lag correlation analysis shows that Oceanic Niño index is positively correlated with the thermal pressure in the coral reef regions of the South China Sea islands, and the latter lags behind the former by 7−9 months.

The assimilation fusion or interpolation fusion of the sea surface wind field based on multi-source data is currently restricted by computing power. This paper proposes to train the XGBoost-based machine learning ERA-5 data correction fusion model in the overlapping area of the multi-source satellite data and the ERA-5 reanalysis data, and then use the model to quickly correct (machine learning inference) ERA-5 data, of which the ERA-5 whole area correction fusion it only takes about 2 seconds. Due to the rapidity of machine learning inference, the entire sea surface fusion wind field can be constructed at a lower computational cost. This paper expands on typical wind field variables such as 10 m wind speed, 10 m wind direction, U10 component and V10 component, taking into account the difference in sea and land distribution, using land masks to eliminate land areas, and constructing D_S_A_XGBoost, D_S_O_XGBoost, U_V_A_XGBoost, U_V_O_XGBoost corrections model, and finally generate sea surface fusion wind field. By comparing the ERA-5 reanalysis data before and after the correction with the satellite data, the above four models all reduce the gap between the ERA-5 reanalysis data and the satellite data. Especially in terms of wind speed, both root mean square error (RMSE) and mean absolute error (MAE) are effectively reduced. In terms of wind direction, RMSE_d and MAE_d also show a decreasing trend. Using Tropical Atmosphere Ocean Array (TAO) buoy data to evaluate the four XGBoost models, it is found that the U_V_O_XGBoost model has the best correction results for ERA-5 data, and its correlation reaches 0.893, an increase of about 0.011, and the results show that the fusion speed is greatly improved under the condition of ensuring the accuracy of wind field.

Based on the non-hydrostatic numerical calculation model, this paper systematically studies the wave dissipation characteristics of permeable submerged breakwater under the impact of focused wave. By setting reasonable calculation conditions, the effects of wave height, water depth above the submerged breakwater, spectral peak period, porosity and the crest width of submerged breakwater on the wave dissipation characteristics of permeable submerged breakwater are analyzed in detail. At the same time, the calculation results of permeable submerged breakwater are compared with those of impermeable submerged breakwater. The calculation results show that the attenuation effect of permeable submerged breakwater on focused wave is stronger than that of impermeable submerged breakwater, which shows that permeable submerged breakwater can more effectively reduce the impact of freak wave on coastal infrastructure; wave height and the water depth above the submerged breakwater are important factors affecting the wave dissipation characteristics of submerged breakwater. With the increase of incident wave height and the decrease of the water depth above the submerged breakwater, the wave dissipation effect of permeable submerged breakwater increases gradually. The permeable submerged breakwater has poor wave dissipation effect on large-spectrum peak period waves. Within the range of porosity considered in this paper, as the porosity increases, the wave dissipation effect of permeable submerged breakwater is better; when the porosity is 0.4 and the crest width is 0.6125 m, the permeable submerged breakwater can reduce 54% of the incident wave energy, which is 36.1% higher than that of the impermeable submerged breakwater. The research results of this paper can provide corresponding reference for further understanding the wave dissipation characteristics of permeable submerged breakwater and the design of coastal protection engineering.

In this paper, sediment smear observations, X-ray diffraction analyses, major, trace and rare earth elements analyses, and in situ micro zone geochemical analyses of single minerals were carried out on samples of core GC02 and GC06 from the rare earth-rich deep-sea sediments in the Central Indian Ocean Basin to explore their geochemical characteristics, material sources and enrichment mechanisms of rare earth elements (REY). The results show that the sediment types of core GC02 are calcareous clay and zeolitic clay, and the sediment types of core GC06 are calcareous clay, zeolite-bearing clay and zeolitic clay. Rare earth elements are enriched in zeolite-bearing clays and zeolitic clays. The North American Shale Composite (NASC) Standardized patterns of REY in the sediments indicate a possible seawater origin. Mineralogical and geochemical signatures indicate that the terrestrial fraction of these sediments in the study area should be the eolian dust material originated primarily from Australian. Elemental correlations and CaO/P₂O₅ ratios indicate that the main host mineral of REY in REY-rich deep-sea sediments is bioapatite (fish teeth/bone), followed by Fe-Mn micronodule. This study summarizes and discusses the formation mechanism of REY-rich sediments and improves a conceptual model for the formation process of REY-rich sediments.

The Bering Sea is one of the most obvious areas with reduced winter sea ice in Arctic region. The seasonal and long-term variations of sea ice in this region are closely related to the local climate, hydrological environment and ecosystem, as well as to Chinese weather and climate. In order to identify the long-term variation of winter sea ice in this region, the trend and spatial difference of sea ice extent in Bering Sea from 1960 to 2020 were analyzed by using the sliding t-test and linear regression analysis method based on Hadley Center data, and the effects of atmospheric forcing, such as general circulation, on sea ice change were analyzed. The results showed that the winter sea ice extent of the Bering Sea decreased significantly from 1960 to 2020, and there were significant abrupt changes in the 1970s and around 2000. During these processes, the Aleutian low pressure center and low pressure were strengthened, the core position shifted to the west of Bering Sea and the corresponding wind field distribution changes. Such process has a nearly 20-year cycle of oscillation. At the same time, the phase change of the Pacific Decadal Oscillation can regulate the meridional wind by changing the sea level pressure, and alter the thermal advection into the Bering Sea, thus affecting the winter sea ice extent. Therefore, winter sea ice in the Bering Sea is mainly controlled both by the Aleutian low pressure system and the North Pacific decadal oscillation, as well as the gerneral climate warming.

To analyze the effects of wave height, vegetation density, submerged height of vegetation and current on the bed shear stress at vegetation zones, a three-dimensional wave-current numerical flume is established based on OpenFOAM in this study. The results show that the bed shear stress attenuates along the vegetation zones because of the blocking effect of vegetation, and the decay rate is positively correlated with the wave height, vegetation density and submerged height of vegetation. Compared with pure wave, the amplitude of positive bed shear stress increases and the amplitude of negative bed shear stress decreases under the condition of combined wave-current flows. The weak current has no obvious effect on the size and distribution of the bed shear stress at vegetation zones. In the case of strong current, the bed shear stress increases at vegetation zones and suddenly decreases after the vegetation zones.

Based on the ERA5 reanalysis data and the meteorological observation data obtained during Chinese Arctic Research Expeditions, the temporal and spatial variation characteristics of the key near-surface meteorological parameters that influence ship navigation in the Arctic passages in summer are analyzed. The results show that the weather conditions in July and August are the most suitable for ship navigation in the Arctic passages. The low temperature, strong wind and huge wave weather increase significantly in September, which impacts ship navigation greatly. The weather in October is even worse, posing a quit challenge to ship navigation. Low temperature mainly occurs in the middle of each passage, and strong wind and huge wave are concentrated in the areas at both ends of the passages. Both the strong wind probability and huge wave probability show a decreasing tendency in the entire Arctic passages in summer with large interannual changes except for the Norwegian Sea and Barents Sea in October and the central Arctic in summer. According to the observation data, it is found that the northeast passage has the poorest visibility, the northwest passage has the best visibility, and the trans-Arctic passage has moderate visibility.