Circulation, hydrographic features and associated transports in the Pearl River Estuary (PRE) as well as over the adjacent shelf are controlled by multi-forcing of the river discharge, tides, and winds. Data from in situ measurements and from a validated three-dimensional, high resolution numerical model have been utilized to investigate the sub-tidal and intra-tidal hydrodynamics in the PRE and the estuary-shelf interaction in different seasons. Our observation results indicate that in summer, freshwater from Pearl River covers the entire estuary in the surface and upper estuary in the bottom. The river plume is formed after the freshwater spreads to eastern part of the shelf by the southwesterly wind-driven coastal current. In winter, discharge from a relative small runoff fro...[ Read more ]

Circulation, hydrographic features and associated transports in the Pearl River Estuary (PRE) as well as over the adjacent shelf are controlled by multi-forcing of the river discharge, tides, and winds. Data from in situ measurements and from a validated three-dimensional, high resolution numerical model have been utilized to investigate the sub-tidal and intra-tidal hydrodynamics in the PRE and the estuary-shelf interaction in different seasons. Our observation results indicate that in summer, freshwater from Pearl River covers the entire estuary in the surface and upper estuary in the bottom. The river plume is formed after the freshwater spreads to eastern part of the shelf by the southwesterly wind-driven coastal current. In winter, discharge from a relative small runoff from the river flows along the west bank of the estuary under Coriolis effect and northeasterly wind forcing. Tidally-driven currents dominate axial circulation in the estuary and greatly modify the transports between the estuary and adjacent shelf. It is found that flood current starts from the bottom at the eastern side of estuary while the ebb current exists at the western side. The strongest stratification occurs in the lower estuary where the river water encounters sea water and the tidal straining effect intensifies during the ebb tides when tidal mixing is relatively weak.

Both the model and observation show that the circulation in the PRE is a salt-wedge estuary with a typical two-layer estuarine circulation in summer, and a partially mixed estuary in winter, as a result of seasonal variation of the river discharge. Our analyses based on the process-oriented modeling study show that the heat transport between the estuary and adjacent shelf is mainly determined by the volume transport due to small cross-shore temperature gradient, while the salt flux is controlled by both the transport and the cross-shore salinity gradient. Tidal prism varies considerably, due to highly variable ratio of river discharge to tidal volume, which affects strongly the exchanges between the estuary and the adjacent shelf, especially in winter. It is shown that there is an obvious spring-neap variation in the volume, heat and salt transports between the estuary and shelf. The stronger transports occur during neaps. Numerical sensitivity studies indicate that the river discharge plays an important role in controlling the net volume and heat transports between the estuary and the shelf, while the tidal forcing has the largest effect on salt transport in both summer and winter. Monsoonal wind forcing modulates the shelf circulation and affects the seasonal transports between the estuary and shelf as a result of the interaction between the estuarine and shelf dynamic regime.