Modulation of Shelf Circulations Under Multiple River Discharges in the East China Sea

East Asian Marginal Seas are a continuum receiving multiple large rivers including the Changjiang, the Yellow, and the Pearl Rivers. Fates of these river discharges are strongly influenced by the energetic shelf circulation system. Meanwhile, the massive freshwater discharge from these rivers also modulate the density structure and dynamic height of receiving seas, which could affect the shelf circulation as well. In this study, we developed a numerical model covering the East Asian Marginal Seas based on the Regional Ocean Modeling System to assess the influence of river plumes on the circulation over the entire shelf. The East China Sea was selected as a focus due to the massive freshwater influence and the strong and complicated shelf circulation therein. The model results suggested that both local (e.g., the Changjiang River) and remote (e.g., the Pearl River) rivers were important in regulating the shelf circulation. Overall, the riverine freshwater elevated the adjacent sea level and changed the density field, which weakened the Taiwan Warm Current (TWC), strengthened the southward coastal current, and even disturbed the Kuroshio. In the vertical direction, the TWC turned from surface-intensified to bottom-intensified under the river plume influences. In the cross-shelf direction, the cross-shelf exchange was enhanced and the Kuroshio subsurface water could more easily intrude to the coastal region, due to the enhanced bottom Ekman transport. The fundamental mechanism is the barotropic and baroclinic adjustments under the riverine influences, which could be considered as a shelf-version of the estuarine circulation.

Automated summary

This study used a numerical model to investigate the influence of river plumes on the circulation of East Asian Marginal Seas, finding that riverine freshwater discharge can alter density structure and dynamic height of the receiving seas, thus affecting shelf circulation. Both the Changjiang and Pearl Rivers play important roles in regulating the East China Sea shelf circulation, particularly in modifying the coastal current and the Taiwan Warm Current.