Monsoon‐Facilitated Off‐Shelf Transport of Dissolved Aluminum Across the East China Sea During Summer.

The continental shelf pump is believed to be important in transporting terrestrial materials across the East China Sea (ECS). More than 300 water samples collected from the ECS and a numerical model were used to identify the cross‐shelf exchanges of dissolved aluminum (Al) in the ECS in summer. The results indicated that dissolved Al concentrations ranged from <1.0 to 242 nM, with the highest concentrations observed in the Zhe‐Min coastal waters, while the lowest concentrations were determined to be in Kuroshio deep waters. The Kuroshio surface waters receive additional dissolved Al from the ECS continental shelf through a cross‐shelf exchange process. By using dissolved Al as a tracer, evidence was found about the cross‐shelf transport of Al in the ECS. Cross‐shelf transport of dissolved Al was associated with fluctuations in the Taiwan Strait Warm Water, and the driving mechanisms were analyzed using a momentum equation. Ekman transport promoted by the summer monsoon was the key physical mechanism controlling the off‐shelf transport of dissolved Al. Quantitative calculations showed that the ECS was a net source of dissolved Al to adjacent waters, of which almost 65% of the output entered the East/Japan Sea, while the remaining 35% entered the Kuroshio currents. Our results highlight the importance of cross‐shelf transport processes to the distribution and cycling of biogenic elements within the marginal seas of China, and highlight the wider implications for biogeochemical cycles throughout the western Pacific Ocean. Plain Language Summary: In this paper, we combined field observations with numerical models to study the transport of Al‐rich coastal waters to the adjacent oligotrophic offshore waters across the ECS continental shelf during summer 2013. Evidence was found about the cross‐shelf transport behavior of dissolved Al within the ECS, and the physical mechanisms controlling the off‐shelf transport of dissolved Al across the ECS continental shelf were investigated. The results indicated that the larger cross‐shelf transport was mainly driven by the summer monsoon. The primary objective of this study was to determine the forces driving off‐shelf transport of dissolved Al from the ECS continental shelf. Calculation of the exchange fluxes of dissolved Al along the 100 and 200 m isobaths indicated that the ECS continental shelf was a net source of dissolved Al to adjacent waters. Our results show the importance of cross‐shelf transport processes in the distribution and cycling of biogenic elements within the marginal seas of China, and highlight the potential wider implications for biogeochemical cycles throughout the western Pacific Ocean. Key Points: Combined field observations and numerical simulations were used to investigate the behavior of dissolved aluminum in the East China Sea (ECS)Knowledge of processes and physical mechanisms underlying off‐shelf transport of dissolved aluminum in the ECS was acquiredQuantitative study the off‐shelf and on‐shelf exchange fluxes of dissolved aluminum across the isobaths in the ECS [ABSTRACT FROM AUTHOR]