The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Internal tides off the highly stratified Changjiang River Estuary can have strong ecological effect by modulating diapycnal mixing near the nutricline. Nevertheless, little is known about the generation, propagation, and dissipation of these internal tides, despite numerous observational evidences of vigorous internal wave activity in this region. Therefore, a suite of mooring observations was employed to examine the energetics of M₂ internal tides within ~200 km of the river mouth. Moreover, a high resolution FVCOM model was configured to provide insights about seasonal variability of internal tides over the entire adjacent shelf.

Mooring observations revealed that i) most of the baroclinic energy flux was southeastward; ii) the highest energy flux (up to 180 W m^-1) and baroclinic kinetic energy was located near 20 m isobath; iii) the strength of M₂ internal tides presented strong spring-neap variability and inshore/offshore stations showed stronger/weaker internal tides during spring tide, which is closely related to the dynamics of the Changjiang River plume. Moreover, the baroclinic pressure perturbation and baroclinic velocity were in phase at most stations, suggesting local internal tides behaving as progressive waves. The model results well captured these observed features. In addition, the modelled baroclinic energy showed a strong seasonal cycle, which peaks during summer when the wide-spread river plume greatly enhanced the stratification on the shelf. With energy budget analysis, hotspots of internal tide energy dissipation have been identified, which may result in strong diapycnal mixing and elevated nutrient flux, with important ecological implications.

river plume, internal tides, Changjiang River Estuary