Intrusion Pattern of the Offshore Kuroshio Branch Current and Its Effects on Nutrient Contributions in the East China Sea

• Published in: Journal of geophysical research. Oceans 2018-03, Vol.123 (3), p.2116-2128
• Main Authors: Wang, Wentao, Yu, Zhiming, Song, Xiuxian, Yuan, Yongquan, Wu, Zaixing, Zhou, Peng, Cao, Xihua
• Format: Article
• Language: English
• Subjects: Autumn; Biogeochemistry; branch current intrusion; Continental shelves; East China Sea; Geophysics; Haloclines; Intrusion; Kuroshio; Mineral nutrients; Nitrogen; Nutrients; nutrients cycles; Oceanic vortices; Offshore; Oxygen; Oxygen isotopes; phosphate; Phosphorus; Physical properties; Pycnoclines; Seasonal variation; Seasonal variations; Spring; Spring (season); Subsurface water; Water circulation; Water column; Water masses
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2017JC013538

During the autumn season of 2014 (October–November), nutrient samples and nitrogen and oxygen isotope samples from the East China Sea (ECS) were collected and analyzed, and auxiliary physical parameters were determined. Distinctive high‐salinity water column conditions with significant haloclines and pycnoclines similar to those observed during the spring were detected at the bottom of the ECS during the autumn. These water column conditions were attributed to the intrusion of the Kuroshio Subsurface Water (KSSW), which then separated into two currents, including the Offshore Kuroshio Branch Current (OKBC). Compared with spring, this intrusion transported higher phosphorus (P) concentrations onto the ECS continental shelf in autumn. However, according to multiple analyses, biogeochemical nitrogen processes are unable to explain the variations in the P concentrations (increase) while assuming that each distinctive water column is consistent. Identifying the water columns by their salinities and P concentrations revealed that the northern ECS water column was similar to the deep KSSW while the southern ECS water column was similar to the shallow KSSW. Therefore, we speculate that the distinctions among the seasonal variations of P‐enriched water masses were attributable to the different intrusion positions of the Kuroshio. The shift of the KSSW intrusion location moved toward the northeast during the autumn relative to the spring. This shift, which was proved by the oceanic vortex data, caused the deeper KSSW water upwelled to the ECS and formed the OKBC, thereby supplying additional P during the autumn. Key Points An obvious difference of P concentration gradient was observed in the Offshore Kuroshio Branch on ECS shelf in autumn The higher concentrations of P likely came from deeper layer of Kuroshio subsurface water This phenomenon might be attributed to the location change of Kuroshio Branch intrusion to ECS shelf