Storm surge disasters occur frequently along the Pearl River Estuary and are significantly affected by typhoon. This study analyzed the extreme surge at the Chiwan Station in the Pearl River Estuary during the past 30 years (1990-2019). The results show that the average annual storm surge in this region has not changed significantly recent years, but the extreme storm surge (99.9 quantile) has increased greatly (1.62 cm·a^-1), which means that the extreme storm surge disasters have continued to increase. In the past 30 years, the annual maximum storm surge in 20 years occurred during typhoons (accounting for 66.7%). In 2018, the maximum storm surge caused by super typhoon “mangkhut” reached 254 cm, which was the largest storm surge disaster in the past 30 years. The maximum response distance of storm surge to typhoon is about 500~800 km. Within the influence range of typhoon, the storm surge has an approximate linear relationship with typhoon intensity, and an exponential relationship with the distance from typhoon center. Different indexes of typhoon intensity (minimum pressure, maximum wind speed and maximum wind speed radius of typhoon center) were used to fit the storm surge with the distance from the observation station to the typhoon center, and it was found that the combination of wind speed and distance had the best description effect on storm surge (S_w=3.23e^-0.0036D×Γ_w-3.90)+4.48, R²=0.78, RMSE=9.69 cm). These results can improve the understanding of local storm surge disaster, provide validation data for typhoon storm surge simulation and reference for storm surge disaster risk assessment and response decision.

The El Niño-Southern Oscillation (ENSO) includes both low-frequency ocean-atmosphere coupling and high-frequency processes, yet the nonlinearity in ENSO dynamics prevents any quantitative estimation of the contributions of the two to ENSO development. The online low-frequency filtering technique was proposed in a recent work to exclude the high-frequency part of wind stress during ocean-atmosphere coupling in model, thus can be used to scale the impact of low-frequency ocean-atmosphere interaction on the ENSO dynamics. By comparing model simulations with and without the online low-pass filtering module, we found that removing the high-frequency wind forcing prolongs ENSO period and decreases El Niño diversity. The results confirm that the high-frequency momentum processes play a crucial role in the genesis of El Niño diversity.

Based on the observations and the global climate model simulation outputs of historical run and future warming scenarios from phase 5 and phase 6 of the coupled model intercomparison project (CMIP), we assessed the performance of 23 CMIP6 and 32 CMIP5 models in reproducing El Niño diversity, and then projected the responses of the eastern Pacific (EP) and central Pacific (CP) type of El Niño to global warming. The results show that most CMIP5/6 models can reasonably simulate the characteristics of El Niño diversity, and the simulation performance of CMIP6 models is significantly improved compared with CMIP5 models. Not only do the CMIP6 models weaken the discreteness of the simulated EP El Niño-related spatial patterns, but also significantly improve the simulation ability of the CP El Niño-associated spatial patterns. The CMIP5/6 models can basically simulate the seasonal phase-locking characteristics of the EP and CP El Niño events, however, compared to the observation, the decay time of the simulated CP El Niño is obviously delayed by 3 months. The intensity of EP El Niño simulated by CMIP5/6 is close to the observation, but the counterpart of CP El Niño is stronger than the observation. Under global warming, the frequency of CP El Niño will tend to decrease relative to EP El Niño. The amplitudes of EP and CP El Niño will be enhanced along with the intensification of global warming, and the enhanced amplitude of EP El Niño is greatly stronger than that of CP El Niño.

Calcified macroalgae, an important calcifying group widely distributed in reef ecosystems, plays vital roles in the primary productivity and reef frameworks construction. Furthermore, several species of calcified algae can induce the coral larval settlement, which is closely related to the sustained development of coral reef ecosystem. However, it is not clear how calcified algae will response to ocean acidification and warming. In this study, healthy and bleached Porolithon cf. onkodes were exposed to different pCO₂ (400 µatm, 1200 µatm, 1800 µatm) and temperatures (27 ℃, 30 ℃, 32 ℃) for one month, respectively. The results showed that the growth rate and net calcification rate of living P. onkodes were not significantly affected when the temperature increased from 27 ℃ to 30 ℃, however, these physiological parameters declined significantly at 32 ℃. The net calcification rate decreased from 206.99 nmol·cm^-2·h⁻¹ (400 µatm pCO₂ + 27 ℃) to -42.22 nmol·cm^-2·h⁻¹ (1200 µatm pCO₂ + 32 ℃). Similarly, the enhancement of pCO₂ also significantly inhibited the growth and calcification in living P. onkodes. Additionally, warming and acidification had interactive effects on the chlorophyll a content and net calcification rate. Compared with living P. onkodes, dead or bleached algal skeletons were more susceptible to warming and acidification. When the temperature was 30 ℃ or the pCO₂ was 1200 µatm, the net dissolution rate of dead algal skeletons increased significantly. Furthermore, the adverse effects of warming were exacerbated when high temperatures coincided with acidification. The results revealed that acidification and warming not only affected the growth and calcification rates of living algae, but also accelerated the dissolution rate of calcium carbonate skeleton, which can affect the coral reef ecosystem. The study may contribute to predict the impacts of climate change on reef ecosystem to protect reef ecosystems.

To address the complexity and uncertainty of tropical cyclone disaster, this study proposes a new tropical cyclone disaster risk assessment model based on the Bayesian network and geographic information system (GIS). The model can automatically explore the causal relationships among disaster influencing factors from objective historical data, and express them in the form of probabilities to assess and predict uncertain disaster risks. Based on the historical data of tropical cyclone disaster in three southeastern coastal provinces (Guangdong, Fujian, and Zhejiang) of China from 1980 to 2016 for risk assessment experiments, a total of 12 assessment indicators in three aspects, i.e., hazard of disaster-causing factors, sensitivity of disaster-inducing environment, and vulnerability of disaster-bearing bodies, were selected as model inputs, and direct economic losses were quantified as disaster risk levels as model outputs to construct a Bayesian network-based risk assessment model. The model was then tested against cyclone disaster data from 2017 to 2021, and the accuracy of the assessment prediction was 80.75%. The relative errors of very low, low, medium, high and very high risks predicted by the model were 27.72%, 8.45%, 18.58%, 16.52%and 19.12%, respectively, and the zonal results of risk prediction values were highly consistent with the actual disaster loss distribution in terms of spatial patterns. In addition, the assessment construction method was applied to the risk assessment of individual cases of Typhoon “Meranti”. The results showed that the high and very high risk areas assessed by the model were basically consistent with the actual disaster reports. Thus, the tropical cyclone disaster risk assessment model established in this study has high accuracy and credibility, and provides a new methodological approach and technical support for tropical cyclone disaster risk assessment.

Based on the data of the comprehensive scientific cruise survey in eastern Indian Ocean from 2010 to 2019, Argo (array for real-time geostrophic oceanography) and SODA (simple ocean data assimilation), the interannual variability of subsurface high salinity water (SHSW) in eastern equatorial Indian Ocean was studied and its formation mechanisms was explored. The observation results limited to spring show that the high salinity water from Arabian Sea is distributed in 70~130m in eastern Indian Ocean equatorial section and exhibits significant interannual variations. And the result based on monthly SODA reveals that the trend of anomalous salinity of SHSW varies significantly in different periods, with a relatively stable trend from 2010 to 2015 and an obvious increasing trend from 2016 to 2019. Wind field and subsurface zonal current are dominant factors that control the interannual variability of the high salinity water by regression analysis of SHSW. Further analysis indicates that the anomalous easterly wind in equatorial Indian Ocean leads to the westward accumulation of water masses, then generates an eastward pressure gradient force, which in turn stimulates the anomalous subsurface eastward flow, and causes the increases of anomalous salinity of SHSW eventually. The dynamical connection is particularly remarkable in Indian Ocean Dipole, which further indicates that the interannual variability of SHSW is modulated by Indian Ocean Dipole.

The tropical ocean-atmosphere system in spring may simultaneously respond to the El Niño-Southern Oscillation (ENSO) in the Pacific ocean. At the same time, it can affect the ENSO development through coupled regional ocean-atmosphere interactions. Based on the joint empirical orthogonal function and open-source datasets, we identify two major global climate modes. The first EOF mode presents the ENSO pattern along with the spring meridional mode in the Atlantic and asymmetric mode in the Indian Ocean, in which the sea surface temperature warms up and precipitation increases in the tropical central and eastern Pacific ocean, accompanied by the equator-asymmetric pattern of precipitation in the tropical Atlantic and Indian Oceans as well as anomalous sea surface temperature gradient in the trans-equatorial. Further analyses suggest that the ENSO influences the intertropical convergence zone by adjusting atmospheric circulation during its mature phase and then induces regional ocean-atmosphere feedback resulting in the spring meridional modes. The differences in spring asymmetric modes of precipitation in the tropical Atlantic and the Indian Ocean are determined by the different positions of the intertropical convergence zone in winter and spring. The second mode shows a meridional sea surface temperature and precipitation anomalies in the tropical Pacific, i.e., the Pacific meridional mode. The warm pole of the spring Pacific meridional mode extends over the equator, causing westerly wind anomalies that favor the El Niño development. This study reveals the relationship between the Pacific ENSO and the global spring meridional mode, contributing to a better understanding of the seasonal 'footprint' of tropical climate modes.

As the unique deep channel that connects the South China Sea (SCS) with the western Pacific Ocean, Luzon Strait is also the key oceanic passage that modulates the SCS circulation and its thermodynamic characteristics. Influenced by large-scale western boundary current, meso-scale eddies, tropical cyclones and other factors, Luzon Strait transport (LST) exhibits significant multi timescale variability. Tropical cyclones are strong and localized low-pressure weather systems that occur frequently in the area, therefore, understanding the dynamic connection between tropical cyclones and LST is one of the most essential topics in oceanography research. This study reviews the research progress in the characteristics of tropical cyclones near the Luzon Strait and its impact on the Kuroshio, ocean circulation and LST, and reveals their recent development. We further suggest that the future study should focus on the modulating mechanisms of the tropical cyclones on the LST and evaluate their contributions to the interannual variations of LST.

Based on the satellite observations and model outputs, the statistical characteristics of eddy, eddy-induced heat transport and the influences from two winter circulation patterns and wind stress are discussed in this study. The results show that the climatological mean of eddy statistics in the study area has characteristics of strong rotation speed, large radius and amplitude that are slightly higher than the average in the whole SCS, among which cyclonic eddy (CE) accounts for 56.8%. The formation and extinction of eddies mainly occur in winter/spring, while the amplitude, radius and rotation speed of eddy reach their peak values in summer/autumn. On the interannual time scale, the annual mean meridional wind stress has a good correlation with anticyclonic eddy (AE) including its amplitude, radius, rotation speed and extinction, but the correlations with CE are weak. In the “O” pattern, the western boundary current and winter wind stress are significantly weakened, and the easterly branches of winter circulation occur along the coast of Vietnam. By absorbing mean flow energy, the eddy in this study area developed rapidly in “O” pattern, generating strong eddy-induced heat transport (EHT) in the east of the Vietnam coast. In the meantime, the rotation speed of eddy and the number of AE decrease. The above situation is opposite under the “U” winter circulation pattern.

The change of river inflow sediment is an important content in the study of estuarine delta evolution. Against the backdrop of increased frequency and intensity of extreme weather caused by global warming, it is of great practical significance to study the variability of sediment fluxes in rivers entering the sea under the influence of extreme weather for understanding the environmental evolution of estuarine deltas. This paper takes the Nanliu River, a small and medium-sized river flowing into the sea, as an example. Based on the measured data of water, sediment and floods from 1966 to 2020, the variation coefficient of variation and mathematical statistics are used to analyze the variation law of water and sediment under the influence of extreme weather. The research results show that: 1) the multi-year average daily flow during the transit of tropical cyclones is 7.72×10² m³·s^-1, which is 4.73 times that of normal weather of 1.63×10² m³·s^-1. The multi-year average of the average daily sediment transport of tropical cyclones was 2.55×10⁴ t, which is 13.42 times that of 0.19×10⁴ t in normal weather. During the tropical cyclone, the amount of sediment entering the sea is large, and it has the characteristics of "rich water and sand"; 2) the multi-year average daily flow and sediment load during the flood period were 8.53×10² m³·s^-1 and 3.07×10⁴ t, respectively, which were the average daily flow (1.56×10² m³·s^-1) and sediment load (0.17×10⁴ t) 5.46 times and 18.18 times. During floods, the greater the amount of incoming sediment, the greater the flux of sediment into the sea, showing the typical feature of “more incoming and more transportation”; 3) extreme weather has an important contribution to the sediment flux of the Nanliu River into the sea. The multi-year average contribution rates of tropical cyclones to runoff and sediment transport were 6.78%and 19.31%, respectively, while the multi-year average contribution rates of floods to runoff and sediment transport were 14.33%and 36.21%, respectively.

The material and energy exchange at the air-sea interface is an important cause of global climate and ecological environment change. As the largest shelf margin sea in China and the Northwest Pacific Ocean, atmospheric deposition plays an important role in the exogenous input of the South China Sea. With the continuous and rapid economic and social development of the surrounding countries in the South China Sea, the transport of anthropogenic pollutants to ocean through atmospheric deposition is increasingly enhanced, which is bound to have a non-negligible impact on the ecological environment of the South China Sea. Based on the research reports of atmospheric deposition of biogenic elements, micro-trace elements and new pollutants microplastics in the South China Sea in the past nearly 30 years, this paper systematically summarized the concentrations, fluxes and influencing factors of atmospheric dry and wet deposition in the South China Sea, and analyzed the eco-environmental effects of atmospheric deposition in the South China Sea. The results show that 1) The concentration of atmospheric particulates in the South China Sea is lower than that in the east coast of China, and there is almost no acid rain deposition. However, the atmospheric carbonaceous aerosol component concentration and deposition in the South China Sea are at a high level due to the influence of biomass burning in Southeast Asia and fossil fuel combustion emissions in China. 2) Nitrogen is the dominant nutrient in the atmospheric dry and wet deposition in the South China Sea, and the proportion of nitrogen species varies greatly in different sea areas, resulting in strong imbalance of nutrient structure in atmospheric deposition. 3) The solubility of anthropogenic metal elements in aerosols is high, and most of them in the form of wet deposition. Aerosol microplastics mostly exist in the form of fiber. Meteorological conditions (precipitation, wind speed, etc.) and source emission intensity are the main factors controlling atmospheric component concentration and deposition flux. 4) Atmospheric nitrogen deposition accounts for about 20% of the total nitrogen input in the sea surface of South China Sea. The addition of nitrogen will aggravate the hypoxia and acidification of the offshore, and nutrient deposition plays an important role in the explosive proliferation of phytoplankton. Atmospheric deposition will have multiple and complex impacts on South China Sea, an oligotrophic ecosystem, which is closely related to hydrologic conditions, initial nutrient status, phytoplankton groups, atmospheric composition and deposition characteristics. In the future, it is suggested that the researchers should pay more attentions to the depth and breadth of the research, focus on the precise and regular monitoring of the dry and wet deposition of various atmospheric components, especially organic nitrogen and phosphorus species and new pollutants, and fully explore the influence and feedback mechanism between the atmospheric deposition of biogenic elements and micro-trace elements and the South China Sea ecosystem from the perspective of interdisciplinarity. Atmospheric deposition is an important part of biogeochemical cycle in the South China Sea, and its impact on the ecological environment is a "double-edged sword". With the continuous enhancement of atmospheric deposition of terrigenous species in the South China Sea in the future, this effect will become more complex and far-reaching.

El Niño and South Oscillation (ENSO) asymmetry between El Niño and La Niña events in the positive and negative Pacific Decadal Oscillation (PDO) phases is examined using HadISST and ORAS3 ocean reanalysis products. It is found that ENSO asymmetry in the equatorial eastern Pacific is significantly weaker in the negative PDO phase than that in the positive PDO phase. It is found that the eastern Pacific's subsurface nonlinear dynamical heating (NDH) is likewise greatly affected by the various PDO phases, and it is much stronger during the PDO positive phase than that during the PDO negative phase through heat budget analysis of the ocean subsurface layer. The subsurface NDH is largely contributed by NDHx. A larger gap between the El Niño event and the La Niña event Subsurface Temperature Anomaly (SubTA) during the positive phase of the PDO is caused by the stronger subsurface NDHx in the East Pacific, which causes the asymmetry of the SSTA, and results in a stronger ENSO asymmetry in the East Pacific during the positive phase of the PDO than that during the negative phase of the PDO.

This study systematically investigates the evolution and energy characteristics of the climatic Sri Lanka Dome (SLD) using hybrid coordinate ocean model (HYCOM) and National Centers for Environmental Prediction (NCEP) reanalysis datasets. The results show that the SLD undergoes two peaks of intensity and eddy kinetic energy (EKE) during its lifecycle. During the first development stage (May 23 to June 10), SLD shifts from the southeast to the east of Sri Lanka, and its area gets wider while its intensity gets stronger. The strengthening of the SLD is attributed to a combination of wind stress work, eddy-mean flow interaction, and advection of the southwest monsoon current (SMC). During the mature stage (June 11 to 22), when the SLD is located to the east of Sri Lanka, the EKE and eddy available potential energy (EPE) in the SLD region reaches its first peak due to enhanced wind stress work and eddy-mean flow interaction. During the weakening stage (June 23 to July 20), the SLD moves northwestward and loses EKE and EPE due to the dissipation of the advection term, reduction of wind stress work and baroclinic instability. During the stable stage (July 21 to August 14), the SLD shifts to the northeast of Sri Lanka, with weaker wind stress work, pressure work, and eddy-mean flow interaction, which keeps the strength of the SLD at a weak level. During the second development stage (August 15 to 25), the SLD moves northward with increased intensity, mainly due to enhanced wind stress and pressure work. During the decay stage (August 26 to September 5), the process of ocean internal instability transforms EKE and EPE into mean flow energy, weakening the SLD. In summary, wind stress work, eddy-mean flow interaction, pressure work, and the advection of SMC are all essential factors in the evolution of SLD.

Storm surges caused by typhoon seriously affect life and business in coastal areas, which is one of the most serious marine disasters that cause economic losses. Shenzhen is located on the edge of the northern South China Sea, which is vulnerable to typhoon induced storm surges. The study of Shenzhen offshore storm surges can not only promote understanding of the physical mechanisms of storm surges, but also has an important significance for the effective disaster prevention and reduction warning of coastal cities. In the process of storm surge modelling studies, a typhoon meteorological field is the key factor for the accuracy of storm surge model simulations. Based on the FVCOM (finite volume community ocean model) current model and SWAN (simulation wave nearshore) wave model, a regional storm surge and wave coupling model is established for the offshore area of Shenzhen. We use reanalysis of meteorological data (European center for medium weather forecasting, ECMWF), ideal typhoon model (Holland) and atmospheric model (weather research and forecast, WRF) as driving field conditions to simulate the storm surge process during Typhoon Mangkhut. The main conclusions are as follows: the low resolution ECMWF reanalysis meteorological data is difficult to accurately reflect the horizontal structures of typhoon, which leads to simulation errors. Overall, Holland meteorological field can accurately simulate Typhoon Mankhut, but it cannot reproduce the structural deformation of typhoon in the coastal region, which results in high simulated storm surge water levels in and around Shekou (Shenzhen Bay, inside the Pearl River Estuary). WRF has a good simulation effect on wind speeds, air pressure fields, water levels and waves as a whole. WRF is a good solution to the problem of high storm surge levels in Holland near the typhoon landfall. The quantitative improvement of WRF in the Pearl River Estuary and Shenzhen Bay area can reach about 20%~30%. In the future storm surge study, if the Holland meteorological field is used, care should be taken into simulation results of the above areas. In addition, both Holland and WRF have good wave simulation results.