Under summer monsoon, upwelling develops around the Zhoushan Islands (ZSI) in the East China Sea, strongly influencing regional primary production and fisheries. Using a high-resolution circulation model, we investigated the general flow patterns and examined the respective roles of tides and winds in modulating the intensity and pathways of upwelling around the ZSI. The simulations showed that summer flows were primarily tide-driven, characterized by a strong horizontal along-front jet and vertical cross-front secondary circulation. The along-front jet enhanced the cross-shore velocity gradient within the interior of water column, thereby strengthening the horizontal flow convergence and resulting in farther-upward increase of vertical velocity, namely, deviation of the upwelling pathway to the interior. Moreover, the tide-induced uplifting also occurred with weakened bottom stress and increased Slope Burger number. Nevertheless, influence of weak summer monsoon was also significant and varied with depth. Specifically, weak northeastward winds reduced both barotropic and baroclinic pressure gradients, further weakening the horizontal flows throughout the water column and suppressing the upwelling in the upper layer. However, winds enhanced the upwelling in the deep layer, for the addition of wind-induced upwelling peaking near the top of the thin bottom boundary layer. Furthermore, upwelling locations and intensities inferred from SST differed substantially from those diagnosed from hydrodynamic processes, likely for intense tidal mixing over very shallow regions and energetic jets within narrow channels. Therefore, the integrated upward transport over a specified area or vertical velocity away from islands may provide a more robust metric for quantifying changes in coastal upwelling.
 

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