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.