Variability and Dynamics of Wave Effects on Upwelling Circulation off the Pearl River Estuary

We employed a coupled wave-circulation model to investigate the variability and dynamics of surface gravity wave effects on the upwelling circulation within the estuary-shelf system of the Pearl River Estuary and its adjacent shelf. Our analyses demonstrated that waves produce shoreward Stokes transports, cumulatively raising the surface elevation in nearshore regions and reducing the surface elevation in offshore regions even though the anti-Stokes current due to the Stokes Coriolis force partially counteracts this effect. Subsequently, changes in the cross-isobath barotropic pressure gradient force (PGF) weaken the along-isobath flow and the upwelling. Meanwhile, wave-induced shoreward advection of the river plume notably alters the cross-isobath density gradients, modulating the baroclinic geostrophic flow. Wave effects on the alongshore flow are dominated by competing these barotropic and baroclinic effects of the geostrophic adjustment. Wave affects the cross-isobath flow governed intricately by Stokes forces, geostrophic adjustment, and weakened turbulent stress in the surface, interior, and bottom layers of the water column, respectively. A more pronounced reduction in the upwelling circulation occurs east of the continental shelf compared to the region west of the shelf and offshore compared to nearshore with reductions in depth-integrated along-isobath and cross-isobath Lagrangian transports. This spatial variation is primarily associated with wave-modulated PGF over different topography.