[A-OS15] [EE] 海洋混合に関わる諸問題

[AOS15-07] How the Tokara strait cultivates the Kuroshio

*長谷川 大介¹、松野 健²、堤 英輔²、千手 智晴²、中村 啓彦³、小針 統³、仁科 文子³、吉江 直樹⁴、郭 新宇⁴、中川 美和⁴、長井 健容⁵、田中 雄大⁶、安田 一郎⁶ (1.国立研究開発法人 水産研究・教育機構　東北区水産研究所、2.九州大学応用力学研究所、3.鹿児島大学水産学部、4.愛媛大学沿岸環境科学研究センター、5.東京海洋大学、6.東京大学大気海洋研究所)

キーワード：Turbulence, Mixing, Topography, Nutrient, Nitrate, Flux

Previous studies have reported clear signs of vigorous turbulent mixing in the Kuroshio due to the presences of shallow and steep topographies in its path (e.g., Hasegawa et al., 2004 and 2008, Chang et al., 2016). Turbulent mixing is one of the most important processes supplying nutrients to the surface euphotic zone from the deep water; however, a quantitative understanding of the turbulent vertical nutrient flux is still limited. On November 2016, we have conducted intensive survey around the Tokara strait by drifting the T/V Kagoshima-maru with the Kuroshio's stream and passed across the shallow (∼100 m) sill while deploying a submersible ultraviolet nitrate analyzer (Deep SUNA by Satlantic) attached on a turbulence ocean microstructure profiler (TurboMAP-L by JAC). Occurrence of a flow separation and a hydraulic jump on the sill have been identified from a high resolution velocity survey. The rate of dissipation of kinetic energy reaches O(10^-5 W kg^-1), and the turbulent vertical nitrate flux reaches O(1 mmol m^-2 day^-1), which is the highest value ever reported for the open ocean.