Program     Marine Carbon Sequestration (MARCO): Multiscale Regulation and Response to Global Change       Poster The modulation of nonlinear circulation to the biological productivity in the summer Vietnam upwelling system P-SPS5-03 Wenfang Lu* , Fuzhou University; Xiamen University; University of Delaware Enhui Liao, Princeton University Xiao-Hai Yan, University of Delaware;Xiamen University Lie-Yauw Oey, Princeton University Wei Zhuang, Yuwu Jiang, Xiamen University Presenter Email: luwf@fzu.edu.cn Biological productivity in the summer Vietnam boundary upwelling system in the western South China Sea, as in many coastal upwelling systems, is strongly modulated by winds. However, the role of ocean circulation and mesoscale eddies has not been elucidated. Here we show a close spatiotemporal covariability between primary production and kinetic energy. High productivity is associated with high kinetic energy, which accounts for ~15% of the production variability. Results from a physical-biological coupled model reveal that the elevated kinetic energy is linked to the strength of the current separation from the coast. The separated current forms an eastward jet into the interior South China Sea, and the associated southern recirculation traps nutrient and favors productivity. When separation is absent, the model shows weakened circulation and eddy activity, with ~21% less nitrate inventory and ~16% weaker primary productivity.