[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

*堤 英輔^1,3,2、松野 健²、伊藤 幸彦³、張 勁⁴、千手 智晴²、酒井 秋絵⁵、Lee Keunjong^6,3、柳本 大吾³、安田 一郎³、小川 浩史³、Villanoy Cesar⁷ (1.鹿児島大学水産学部、2.九州大学応用力学研究所、3.東京大学大気海洋研究所、4.富山大学学術研究部理学系、5.九州大学大学院総合理工学府、6.Korean Institute of Ocean Science and Technology、7.Marine Science Institute, University of the Philippines)

キーワード：乱流硝酸塩フラックス、ルソン海峡、クロロフィルブルーム、鉛直渦拡散

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.