[A-CG31] Nutrient footprint of primary production in the coastal and marginal seas of East and Southeast Asia

[ACG31-P02] Vertical fluxes of nutrients enhanced by strong turbulence and phytoplankton bloom around the ocean ridge in the Luzon Strait

*Eisuke Tsutsumi^1,3,2, Takeshi Matsuno², Sachihiko Itoh³, JING ZHANG⁴, Tomoharu Senjyu², Akie Sakai⁵, Keunjong Lee^6,3, Daigo Yanagimoto³, Ichiro Yasuda³, Hiroshi Ogawa³, Cesar Villanoy⁷ (1.Faculty of Fisheries, Kagoshima University, 2.Research Institute for Applied Mechanics, Kyushu University, 3.Atmosphere and Ocean Research Institute, University of Tokyo, 4.Faculty of Science, University of Toyama, 5.Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6.Korean Institute of Ocean Science and Technology, 7.Marine Science Institute, University of the Philippines)

Keywords:Turbulent nitrate flux, Luzon Strait, Chlorophyll-a bloom, Vertical eddy diffusivity

Steep ridges and tidal currents of the Luzon Strait create some of the strongest turbulent mixing in the world. To assess the impacts of this active turbulence on the marine ecosystems, we conducted a survey of microstructure turbulence, tidal currents, and biogeochemical hydrography along a transect at 21 deg. N of the Luzon Strait in November 2017. We obtained turbulent kinetic energy dissipation rates and vertical eddy diffusion rates above O(10-7) W kg^-1 and O(10^-3) m² s^-1, respectively, over a shallow sill on the eastern ridge of the strait, which are two orders of magnitude higher than in the open ocean. Interestingly, above this sill, in situ and satellite chlorophyll exhibited a clear bloom in the surface. The high diffusive fluxes of nitrate (4.7 mmol N m^-2 d^-1) and phosphate (0.33 mmol P m^-2 d^-1) estimated near the base of the surface chlorophyll-a bloom suggest that enhanced turbulent mixing contributes to nutrient supply to the euphotic zone and new production, leading to the quasi-permanent surface chlorophyll-a bloom.