Nutrient Supply Caused by Submesoscale and Microscale Mixing Processes in the Upstream Kuroshio

Takeyoshi Nagai1, Daisuke Hasegawa2, Eisuke Tsutsumi3, Hirohiko Nakamura4, Tomoharu Senjyu5, Takahiro Endoh6, Takeshi Matsuno7, Ryuichiro Inoue8, Amit Tandon9, Naoki Yoshie10, Kazuki Ohgi11, Ayako Nishina4, Toru Kobari4, Gloria Silvana Duran Gomez12 and Diego Andre Otero13, (1)Tokyo University of Marine Science and Technology, Tokyo, Japan, (2)Tohoku National Fisheries Research Institute, Shiogama, Japan, (3)Atmosphere and Ocean Research Institute University of Tokyo, Kashiwa, Japan, (4)Fac. Fisheries, Kagoshima University, Kagoshima, Japan, (5)Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan, (6)RIAM, Kyushu University, Fukuoka, Japan, (7)Kyushu Univ, Fukuoka, Japan, (8)JAMSTEC Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (9)University of Massachusetts, Dartmouth, Mechanical Engineering, Dartmouth, United States, (10)CMES, Ehime University, Matsuyama, Japan, (11)Center for Marine Environmental Studies, Ehime University, Kashiwa, Japan, (12)La Molina National Agrarian University, Lima, Peru, (13)National Agrarian University La Molina, Lima, Peru
Abstract:
The Kuroshio carries a large amount of nutrients in dark subsurface layer along the southern coast of Japan. However, it has been unclear whether and how the subsurface nutrients are injected to sunlit layers on the continental shelf. This is due to lack of sufficient multidisciplinary high resolution observations. In this study, using in-situ observation data obtained by a state-of-the-art tow-yo microstructure profiler, nitrate measurements, and numerical simulations, it is shown that a large amount of subsurface nitrate in the Kuroshio nutrient stream can be injected through topography induced submesoscale mixing processes in the Tokara Strait. Furthermore, near-lowest frequency internal waves trapped in between the Kuroshio and the continental slopes are found to cause strong turbulence and associated nitrate flux near the continental slope in the Hyuganada Sea, southeast of Kyushu. These results imply that the Kuroshio nutrient stream enriches not only the farther downstream regions, Kuroshio Extension and subpolar regions, but also supplies nutrients to the sunlit layers along the southern coast of Japan.
Back to: (Sub)mesoscale Physical/Biogeochemical Interactions II