Analysis of tidal characteristics in the coastal waters of Zhanjiang

Abstract Tide currents are important for mixing in ocean, especially they flow through straits, generating turbulence that facilitates the mixing of surface and deep waters. To further investigate the tidal current distribution patterns in the coastal waters of Zhanjiang and study the effect of Qiongzhou Strait (QS) on the features of tidal current, a quasiharmonic analysis method was employed to analyze the measured ocean current data collected during the periods of spring and neap tides in both the winter and the summer of 2018 in the study area. The analysis aimed to explore the tidal nature, tidal movement characteristics, and residual current distribution features of this region. The research results indicate that topography influence is dominant factor for tidal current variations in the study area. The northern stations C1, C2, C3, and C7 exhibit irregular semidiurnal tides, whereas southern stations C4, C5, C6, C8, and C9 display irregular diurnal tides. The dominant tidal constituents at all the stations are M 2 , K 1 , and O 1 . The tidal currents mainly flow in a reciprocating manner, with the dominant current direction during both flooding and ebbing tides being southwest-northeast at most stations. The vertically averaged current speeds during spring tides are significantly higher than those during neap tides. The tidally averaged current speeds decrease from the surface to the bottom. Southern stations C4, C5, C6, C8, and C9, which are located close to the QS, present relatively high tidally averaged current speeds. The directions of the residual currents at various depths are similar and are mainly southern biased. In summer, the residual currents are less affected by wind stress, whereas in winter, during neap tides, the residual currents are significantly influenced by northeasterly winds, resulting in velocities that are notably greater than those during spring tides.