Cruise observation and numerical modeling of turbulent mixing in the Pearl River estuary in summer

• Bottom stress is responsible for the mixing in the Pearl River estuary (PRE).
• Internal shear instability plays a key role in mixing of the Pearl River plume bulge.
• Wind induces the surface mixing in the Pearl River plume far-field.
• Estuary mixing is controlled by tidal strength.
• Wind stirring reinforces the internal shear instability mixing.

The turbulent mixing in the Pearl River estuary and plume area is analyzed by using cruise data and simulation results of the Regional Ocean Model System (ROMS). The cruise observations reveal that strong mixing appeared in the bottom layer on larger ebb in the estuary. Modeling simulations are consistent with the observation results, and suggest that inside the estuary and in the near-shore water, the mixing is stronger on ebb than on flood. The mixing generation mechanism analysis based on modeling data reveals that bottom stress is responsible for the generation of turbulence in the estuary, for the re-circulating plume area, internal shear instability plays an important role in the mixing, and wind may induce the surface mixing in the plume far-field. The estuary mixing is controlled by the tidal strength, and in the re-circulating plume bulge, the wind stirring may reinforce the internal shear instability mixing.