Physical Modulation to the Biological Productivity in the Summer Vietnam Upwelling System, Western South China Sea

Wenfang Lu, Fuzhou University & Xiamen University, Sirc, Fuzhou, China, Lie-Yauw Oey, NCU National Central University of Taiwan, Jhongli, Taiwan, Enhui Liao, Princeton University, Department of Geosciences, Princeton, NJ, United States, Wei Zhuang, Xiamen University, State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen, China, Xiao-Hai Yan, Univ Delaware, Newark, DE, United States and Yuwu Jiang, Xiamen University, Xiamen, China
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 wind. 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. In the low production scenario, the circulation is not only weaker but also shows weak separation. In the higher production case, 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.