Response of the Yellow and East China Seas ecosystems to two typhoons with different translational speeds in the northwestern Pacific

The Yellow and East China Seas (YECS) are semi-enclosed marginal seas that are one of the most vulnerable regions to typhoons in the world. Frequent typhoons can significantly change the temperature, nutrients, and phytoplankton biomass in the YECS. The oceanic response to typhoons is usually influenced by the features of the typhoon, among which, the translational speed is of critical importance. Using a high-resolution coupled physical-ecological model, we investigated the response of the YECS to two typhoons with different translational speeds, Muifa in August 2011 and Bolaven in August 2012, during their northward translation in the YECS. The results show that the typhoon with slower translational speed uplifts more deep water in the YECS, leading to a more significant response of the ocean. The effects of horizontal convection on ecological elements during typhoons should not be ignored. Horizontal advection caused the flow of nutrients in the surface and bottom layers in opposite directions, but the flow of chla in the same direction. At the same time, the flux of nutrients in the bottom layer is more than that in the surface layer, while the opposite is true for chla. These phenomena are closely related to the spatial distribution of nutrients and chla. Further studies have shown that the degree of ocean response to typhoons is also highly correlated with the initial levels of physical and ecological elements of the ocean before the typhoon, as well as with ocean structure. Pre-typhoon initial levels of ocean physical and ecological elements, mixed layer depth (MLD) and Potential Energy Anomaly (PEA) can all alter the degree of typhoon-induced ocean response. This study emphasizes the important roles of the translational speed of typhoons and the initial oceanic condition in the oceanic response to typhoons.