Tidal characteristics of the gulf of Tonkin

• The Gulf of Tonkin is one of the few basins with a mesotidal diurnal regime.
• A new data set of unprecedented spatial coverage is proposed.
• The gulf׳s resonance spectrum contradicts previous assumptions.
• Lagrangian residuals are weaker than Eulerian residuals.
• Tidal and wind mixing explain summer frontogenesis.

The Gulf of Tonkin, situated in the South China Sea, is a zone of strong ecological, touristic and economic interest. Improving our knowledge of its hydro-sedimentary processes is of great importance to the sustainable development of the area. The scientific objective of this study is to revisit the dominant physical processes that characterize tidal dynamics in the Gulf of Tonkin using a high-resolution model and combination of all available data. Particular attention is thus given to model-data cross-examination using tidal gauges and coastal satellite altimetry and to model calibration derived from a set of sensitivity experiments to model parameters. The tidal energy budget of the gulf (energy flux and dissipation) is then analyzed and its resonance properties are evaluated and compared with idealized models and observations. Then, the tidal residual flow in both Eulerian and Lagrangian frameworks is evaluated. Finally, the problem of tidal frontogenesis is addressed to explain the observed summer frontal structures in chlorophyll concentrations.