Response of the Yellow and East China seas low-trophic ecosystems to two typhoons at different translational speeds

Frequent typhoons can significantly change the temperature, nutrient availability, and phytoplankton biomass in marginal seas. The oceanic response to typhoons is usually influenced by the features of the typhoon, among which the translational speed is critically important. By using a highresolution coupled physical-biological model, we investigated the response of the Yellow and East China seas (YECS) to two typhoons at different translational speeds, Muifa in August 2011 and Bolaven in August 2012. The model well reproduced the spatial and temporal variations of temperature, chlorophyll-a concentration over the YECS. Results show that typhoons with slower translational speeds uplift more deep water, leading to a more significant oceanic response. Divergence and convergence caused nutrient fluxes in opposite directions in the surface and bottom layers. Moreover, the nutrient flux in the bottom layer was greater than that in the surface layer. These phenomena are closely related to the spatial distribution of nutrients. Further studies show that the degree of ocean response to typhoons is highly correlated with the initial conditions of physical and biological elements of the upper ocean before the typhoon, as well as with ocean structure. Pretyphoon initial conditions of oceanic physical and ecological elements, mixed layer depth, and potential energy anomalies can all alter the degree of typhoon-induced oceanic response. This study emphasizes the important roles of the translational speed of typhoons and the initial oceanic conditions in the oceanic response to typhoons.