This study mainly uses the GECCO2 reanalysis data from 1958 to 2016 to analyze the spatiotemporal characteristics of the southern Indian Ocean sea surface temperature anomalies (SSTA) winter-to-winter recurrence through lag correlation analysis, and investigate the roles of oceanic reemergence mechanism and atmospheric forcing. The results show that the winter-to-winter recurrence of SSTA occurs south of 15ºS in the southern Indian Ocean, especially between Madagascar and southwestern Australia (15º–45ºS, 70º–100ºE). The recurrence mainly occurs in the winter of the following year, but there are also some areas where the recurrence occurs in the following fall and continue to the subsequent winter. Further analysis shows that the difference between the deep winter mixed layer and shallow summer mixed layer, known as the oceanic reemergence mechanism, is the main cause of the recurrence of SSTA in the southern Indian Ocean. In addition, the net heat flux also directly contributes to the recurrence of SSTA in southern Madagascar and southwestern Australia.

Affected by fluvial sediment discharge, wind waves and tides, etc., suspended sediment in estuaries and adjacent waters has significant temporal and spatial changes. Based on the GOCI remote sensing images at hourly resolution, this paper uses the optimal remote sensing inversion algorithm, combined with spatial analysis and statistical methods to deeply study the temporal and spatial dynamic characteristics and driving mechanism of suspended sediment in the Yellow River Estuary and adjacent waters. The results show that the impact of fluvial sediment discharge on the concentration of suspended sediment is concentrated in the nearshore area of the estuary. The impact of high fluvial sediment discharge on the distribution of suspended sediment concentration can reach about 20 km offshore and spread to the Gudong nearshore area. Strong winds can cause intensive resuspension of sediment near the old river mouth of Qingshuigou, forming a high-concentration suspended sediment area. The flood and ebb tides have a significant impact on the hourly-scale suspended sediment concentration, and affect the dispersal of suspended sediment from north to south. The variation and dispersal range of the suspended sediment concentration in the spring tide are larger than that of the neap tide due to different tidal flow velocities. There is an obvious negative correlation between water depth and suspended sediment concentration. According to the difference of driving factors, the suspended sediment concentration present exponential, power function, and linear relationships with the increase of water depth.

The coastal current presents complex changes in spatiotemporal scale due to various dynamic processes and shoreline islands. High frequency surface wave radar has become an effective method to solve these problems because of its wide coverage area and high temporal resolution. Several years ocean current data was collected in Zhoushan sea area, the dynamic processes of the ocean in tide cycle, extreme events, intermonth and interannual time scales in this area were interpreted by using tidal current harmonic analysis, low pass filtering and correlation analysis. The results depicted that the Zhoushan sea area is a regular semi-diurnal tide area, and the current movement is mainly in the form of rotating current. The distribution of current velocity in investigation area illustrated a decreasing trend from northeast to southwest. Interannual variation of residual current in the Zhoushan sea area is not significant, however the obvious intermonth variation characteristic of the residual current was detected. In winter, the flow is southward, and its larger near shore than outside sea. On the contrary, the flow velocity is stronger and the spatial distribution is more uniform in summer. The correlation between wind and residual current was analyzed, during strong winds, the correlation coefficient between wind speed and residual current velocity ranged from 0.48 to 0.90, and the correlation coefficient between wind direction and residual current direction ranged from 0.55 to 0.68. When extreme events occur, the correlation coefficients of velocity and direction are 0.92 and 0.91, respectively. By way of conclusion, the analysis of high frequency surface wave radar data can well reflect the temporal and spatial characteristics of ocean currents in Zhoushan sea area, which provide a basis for marine disaster monitoring, pollutants and algal bloom transport research.

Through the analysis of the δ¹³C, δ¹⁸O, δ¹¹B, δ³⁷Cl isotopes and Cl⁻, ${\rm{SO}}_4^{2-} $, K⁺, and Na⁺ ion index in the sediment pore water of the core GSW1 in the East China Sea outer Slope-Okinawa Trough, the changes of early diagenesis, fluid sources, migration and oxidation environment of sediments were discussed. The results show that the pore water dissolved inorganic carbon of the core GSW1 mainly comes from sea water and organic matter, the concentration of ${\rm{SO}}_4^{2-} $ decreases more gently with depth, and the concentration of Cl⁻ is much lower than seawater. The sulfate consumption in the surface sediments of this pore is mainly caused by organoclastic sulfate reduction (OSR) controlled, anaerobic oxidation of methane (AOM) occurs in deeper layers below 4 m. The H₂S produced by OSR diffuses upwards and is enriched and oxidized, which is the main factor that causes the 110−360 cm ${\rm{SO}}_4^{2-} $ content to not significantly decrease. The overall trend of pore water ${\rm{SO}}_4^{2-} $ concentration decreases with depth, indicating that the deposition environment of core GSW1 has gradually changed from an oxidizing and sub-oxidizing environment to a reducing environment. The vertical changes of δ¹¹B and δ³⁷Cl fluctuate greatly. On the one hand, they are affected by the degradation of organic matter in the early diagenesis stage, and they may also be related to the diffusion of pore fluid and sediment/pore water interaction.

As one of the most important water quality parameters, chlorophyll a is an important indicator to evaluate the degree of eutrophication of water bodies and also the main factors of primary productivity state of the oceans. The coastal zone imager (CZI) onboard the Chinese Haiyang-1C (HY-1C) satellite has an advantage observation in high temporal and spatial resolution. In this study, a chlorophyll a concentration retrieval model for CZI onboard the HY-1C satellite is developed from the in-situ measurements in the East China Sea and the South China Sea. The chlorophyll a concentration is retrieved by the model in the measured waters and compared with MODIS chlorophyll a concentration. The chlorophyll a concentration also retrieved in the Zhujiang River Estuary, Changjiang River Estuary and Bohai Bay. The correlation coefficient between the predicted value of the model and the in-situ chlorophyll a concentration is 0.774 3, the average relative error is 24.58%. The accuracy of the model is verified with the in-situ measurements with the correlation coefficient of 0.993 9 and the average relative error of 18.49%. The distribution of chlorophyll a concentration retrieved from CZI is nearly the same as that of MODIS. The chlorophyll a concentration decreases gradually from northwest to southeast and the peak value locates on the west bank of the Zhujiang River Estuary. The inversion of chlorophyll a concentration in Changjiang River Estuary and Bohai Bay accords with the actual situation. The work in this study indicates that HY-1C satellite coastal zone imager data are useful for the monitoring of coastal ocean color in China.

To understand the internal physical mechanism of wave breaking, it is important to study the distribution characteristics of the particle velocity field under breaking wave. In addition, a comparative study of the evolution characteristics of the gas-liquid mixing zone caused by different types of breaking is beneficial to the improvement of the whitecap coverage model. In the laboratory wave flume, a critical wave, a single spilling wave, and a single plunging wave are generated in deep water based on the linear phase focusing theory. The velocity fields below the wave surface and the velocity fields in the gas-liquid mixing zone are measured using particle image velocimetry (PIV) and bubble image velocimetry (BIV), respectively. The distribution characteristics of the velocity field at the extreme state of different breaking types are compared and discussed. The results show that the horizontal velocity u and vertical velocity v of the spilling wave are extremely asymmetrical in the front part and back part of the wave crest. In addition, the maximum horizontal velocity u_max is not at the top of the wave peak, but at the pre-peak position about 0.7$\eta_{\max} $ front part and back part of the wave crest. In addition, the maximum horizontal velocity of the peak. For plunging wave, the maximum horizontal velocity u_max appears at the top and very front of the wave peak with a very small region, and the velocity gradient between this area and the surrounding area is very large. The development characteristics of the gas-liquid mixing zone produced by different wave breaking also have differences. For spilling wave, the gas-liquid mixing zone generated by breaking has high horizontal movement speed, long influencing area, short influence time at each location, and small thickness. For plunging wave, the gas-liquid mixing zone has relatively slow horizontal movement speed and larger vertical input, shorter affected area, longer affected time at each location, and greater thickness.small thickness. However, for plunging wave, these characteristic parameters are in contrast with those of the spilling wave.

As China’s first operational ocean color sensor, the coastal zone imager (CZI) carried by Haiyang-1C (HY-1C) satellite is playing an increasingly significant role in offshore ocean environmental monitoring. After the launch of HY-1D satellite, the combination of CZI sensors can provide two observations in three days for coastal zone through dual-satellite system. CZI sensors have demonstrated prominent application advantages for monitoring marine floating algae, oil spill and so on. Since the high spatial resolution optical data contains abundant information about the marine environment, it also brings some distraction to the identification and extraction of specific ocean targets. In this work, a novel CZI algorithm was developed based on cooperation of scaled algae index (SAI) and virtual baseline floating macroalgae height (VB-FAH) to extract floating green tide information in the Yellow Sea from HY-1C satellite CZI measurements. VB-FAH method can be used to enhance the difference between floating algae and sea water, especially for satellite’s sensors with no short-wave infrared bands. After that, the algorithm efficiently rejects the complex interference information in the ocean high spatial resolution optical data by SAI sliding window. The algorithm has high accuracy and time efficiency in the extraction of floating green tide from CZI measurements. Moreover, the study carried out an uncertainty analysis for the area of algae-containing pixels between HY-1C satellite CZI data with 50 m spatial resolution and GF-1 satellite WFV1 data with 16 m spatial resolution. The result indicates that the uncertainty in the inversion results of CZI data mainly comes from the over estimation of small patches of floating algae. The study also pointed out that the uncertainty of optical data for floating algae monitoring is not only from the difference of spatial resolution between two sensors, but also related to the spatial variability of the morphological size of floating algae. Exploring the morphological spatial variability of floating algae will help improve the accuracy of optical data inversion results and clarify the uncertainty.

The dramatic change of sea ice in the Beaufort Sea has an important impact on the regional ecosystem and economic activities. Based on the sea ice concentration released by the National Ice and Snow Center of the United States, the mechanism of extremely low summer sea ice in the Beaufort Sea in 2019 is discussed. The sea ice area in the melt season (May–September) of 2019 is 1.38×10⁵ km², far lower than the average of 2.28×10⁵ km² from 1998 to 2020. According to the statistics of the sea ice area in the preceding autumn (October–December 2018) and winter (January–April 2019) of 2019, there is no significant difference between the 2019 and the average results of 1998–2019, so it is not the main reason for the extremely low ice event. Combining the data of sea ice drift field, sea ice thickness, 10 m wind field, and net sea surface heat flux, it is found that the sea ice in May of 2019 decreased by 2.33×10⁵ km², which is the largest of sea ice loss in May since 1998, accounting for 62% of the loss of sea ice area in the melt season. Different from the mechanism of extremely low summer sea ice area in 1998, 2008, 2012, and 2016, decreasing sea ice thickness and abnormally strong wind field in May 2019 contribute to the rapid sea ice export, resulting in the formation of open water in the south of Beaufort Sea on May 16, 2019. The abnormally high sea surface net heat flux makes the sea ice melt more, resulting in the abnormal phenomenon of sea ice in the summer of 2019. With the continuous thinning of sea ice thickness, the response of sea ice to wind field is stronger and stronger, and the time of sea ice retreat is advanced, the phenomenon of extremely low summer ice condition in the Beaufort Sea may appear more frequently.

Based on the long-term observation obtained from two sets of submarine mooring system deployed at Niulang Seamount in the western Pacific, the vertical distribution of the deep currents and the temporal variation characteristics were analyzed in the paper. The results show that: (1) The annual mean ocean currents and the variations were the largest in the upper layer, the second in the middle and deep layers, and the smallest in the middle-deep layers. (2) The subtropical countercurrent was at the depth shallower than 150 m, and the northward current was at depth deeper than 150 m and at the middle layers; the near bottom current was weak southward at the summit of the seamount, but southwestward at the bottom of the seamount. (3) Both at the summit and bottom of the seamount, the currents showed a seasonal oscillation with the most energetic oscillation at a period of about 100 d throughout the water column; at depth above 2 000 m, currents showed a synchronous oscillation in the throughout the water column, with the oscillation amplitude decreasing with depth; current oscillation at deep layers (below 2 000 m) were in opposite phase with that at the upper layers, and the oscillation amplitude was the strongest at 4 000 m.

When oil spill occurs and the large scale covering on the sea surface has not been formed, it is hard to find oil film by existing oil spill detection technology. To solve this problem, a novel method for discriminating of oil spill by monitoring the area of oil film is presented based on thermal infrared video image, which combined with the diffusion characteristic of oil spill. Firstly, foreground regions (real oil film region and look-alikes interference region) on the sea surface are extracted and the actual physical area of each region is calculated based on single-frame thermal infrared image processing (i.e., the pixel area calculation method from the previous research). According to the video image processing, the change of the actual physical area of each region is tracked in real-time. The area change rate threshold is set to discriminate whether oil film on the foreground regions, then whether oil spill happened can be determined. The experimental results show that the proposed method can effectively discriminate oil film formed by different viscosity of oil and maintain good identification accuracy under sea surface with waves and floating objects. This strategy is suitable for specific scenes such as wharves and ships, and also can provide technical support for pollution control of oil spill.