10:45 AM - 12:15 PM
[ACG31-P03] Nutrient supply associated with tropical cyclone passage in the continental shelf of the East China Sea
Keywords:Tropical cyclone , Nutrient supply, East China Sea, Near-inertial internal wave
Several tropical cyclones (TC) pass over the East China Sea every year. Nutrient in the lower layer is supplied to the surface layer due to vertical mixing and upwelling by strong winds of TC, and then chlorophyll-a concentration increases a few days later. These phenomena are well-known from satellite ocean color data analysis. In the continental shelf, the 1st mode of near-inertial internal wave (NIIW) is dominant after TC passage; the opposite direction of currents in the upper and lower layers are dominant and upwelling and downwelling flows occur periodically. The 1st mode of NIIW might supply nutrients from the lower layer to the upper layer due to advection and diffusion. As a result, chlorophyll-a (chl-a) concentration in the sub-surface layer might increase for a relatively long time. In order to demonstrate the phenomenon, we carried out numerical experiments using a physical-ecosystem coupled model. We conducted 2 cases of numerical experiments: one with TC wind stress and another without it. In the TC wind case, the kinetic energy of NIIW was larger on the continental shelf and the NIIW lasted for about 20 days. The chl-a concentration in the sub-surface layer was much higher in the TC wind case than in the no TC wind case. At the interface between the upper and lower layers, nutrient was continually supplied from the lower layer to the upper layer by mainly vertical advection related to NIIW. In the surface layer, chl-a concentration differences between the two cases were the largest a few days after TC passage and gradually decreased later. On the contrary, chl-a concentration differences in the sub-surface layer reached a maximum a week later, and large differences continued for approximately one month.