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This study aims to analyze statistical behavior of the continental shelf wave motions, including continental shelf waves (CSWs) and arrested topographic waves (ATWs), in the northern South China Sea. The baseline consists of tidal gauge data from stations Kanmen, Xiamen, Shanwei, Hongkong, and Zhapo, as well as along-track sea level anomaly (SLA) data derived from multi-satellite altimeters from 1993 to 2020. The subtidal signals propagating along the coast with periods shorter than 40 d and phase speeds of about 10 m s-1 are interpreted as CSWs. The cross-shelf structure of along-track SLA indicates that mode 1 of CSWs is the predominant component trapped in the area shallower than about 200 m. The amplitudes of CSWs reach the maximum 0.6 m during July–September, and minimum 0.2 m during April–June. The inter-seasonal and seasonal signals represent ATWs. The amplitudes of ATWs reach 0.10 m during October–December, twice of that during July–September. These observations are well interpreted by the framework of linear wave theory. The cross-shelf structures of CSWs and ATWs derived from along-track SLA illustrate that the methods are suitable for observing dynamic behavior of the CSWs.

The bottom current is an important component of the three-dimensional ocean circulation, which is of significance for the safeties of ocean bottom engineering and facilities, the research on sediment and pollutant transports, and the ecological environment. Due to the lack of observation data, research on the bottom current in the South China Sea (SCS) has been limited. This study systematically analyzes bottom currents from 0.5 to 5 m above the seafloor based on 20-month-long mooring observations on the shelf slope west of the Dongsha Atoll. The spectral analysis results indicate that currents induced by the internal tides and the internal solitary waves (ISWs) comprise dominant constituents of bottom currents with velocity amplitudes up to O(50–90) cm/s. Dominant internal tide-induced bottom currents of the velocity amplitude of O(50) cm/s occupy 53% of the total horizontal kinetic energy. The pulsating ISW-induced bottom currents reach a maximum amplitude of 93 cm/s, which has intrinsic relation to the amplitude of the ISWs, according to the soliton propagation speed solutions of the Korteweg–De Vries (KdV) equation. The background bottom current is strongest in winter, followed by spring, and weak in summer and autumn, which is closely correlated with the behavior of mesoscale eddies. These results are of significance for understanding the dynamics of the bottom boundary layer.

Using satellite observations from 2003 to 2020 and cruise observations from 2019 and 2021, this study reveals an unexpected minor role of upwelling in seasonal and interannual variations in chlorophyll a (Chl a) concentrations in the coastal upwelling region east of Hainan Island (UEH) in the northwestern South China Sea (NWSCS). The results show strong seasonal and interannual variability in the Chl a concentration in the core upwelling area of the UEH. Different from the strongest upwelling in summer, the Chl a concentration in the UEH area reaches a maximum of 1.18 mg m−3 in autumn and winter, with a minimum value of 0.74 mg m−3 in summer. The Chl a concentration in summer increases to as high as 1.0 mg m−3 with weak upwelling, whereas the maximum Chl a concentration in October increases to 2.5 mg m−3. The analysis of environmental factors shows that, compared to the limited effects of upwelling, the along-shelf coastal current from the northern shelf and the increased precipitation are crucially important to the Chl a concentration variation in the study area. These results provide new insights for predicting marine productivity in upwelling areas, i.e., multiple mechanisms, especially horizontal advection, should be considered in addition to the upwelling process.

With a Phosdac 1000 Digital Color Analyzer, the writer processed the images of the meteorological satellite GMS-1 and NOAA-5 IR band to enhance the information on sea surface temperature (SST), which is then used to plot sea surface isotherms. This paper briefly describes the winter SST pattern in the Yellow Sea and the East China Sea as obtained by application of the above method, in combination with measurements made by some stations in situ, and makes a preliminary discussion on the causes of formation of these patterns.