17:15 〜 18:30
[AOS11-P07] Elevated nutrient supply caused by the approaching Kuroshio to the southern coast of Japan
キーワード：Nutrient injection, Hyuganada Sea
Although the Kuroshio Current has been known for being nutrient poor in its upper layers, it supports a great fishery industry in Japan due to the great biodiversity it presents. Previous studies reported that the Kuroshio carries a large amount of nutrients in dark subsurface layers, but the mechanisms of how these nutrients from dark subsurface layers are brought to the sunlit layers are still unclear. In a previous observational study by the authors, it is showed that the Kuroshio flowing on the continental shelf can induce very strong turbulent dissipation rates O(10-7 W kg-1) associated with trapped near-inertial internal waves in this region, leading to the generation of a large diffusive nitrate flux of >O(1 mmol N m-2 day-1). Nevertheless, since this previous study was conducted for just one transect survey, questions remain of how long this enhanced turbulent diffusive nitrate flux extends further to the downstream and how the Kuroshio path modulations can influence on this nutrient injection.
In this study, using a high-resolution nested simulation coupled with a N2PZD2 ecosystem model, observed features were reproduced, showing that when the model Kuroshio flows closer to the coast, it hits the small bump in the upstream region of the Hyuganada Sea producing negative potential vorticity. At the same time, it is observed that near-inertial internal waves are trapped in the streak of lowered lowest internal wave frequencies, producing the strong turbulence and vertical mixing. As a result, the elevated mixing diffuses up the nitrate from dark subsurface layers to sunlit shallow layers. The results of this study can improve our understanding of the role of the Kuroshio in providing nutrients and enhancing biological productions including fish abundances, providing a better predicting of the ecosystem responses to the Kuroshio path modulations.
In this study, using a high-resolution nested simulation coupled with a N2PZD2 ecosystem model, observed features were reproduced, showing that when the model Kuroshio flows closer to the coast, it hits the small bump in the upstream region of the Hyuganada Sea producing negative potential vorticity. At the same time, it is observed that near-inertial internal waves are trapped in the streak of lowered lowest internal wave frequencies, producing the strong turbulence and vertical mixing. As a result, the elevated mixing diffuses up the nitrate from dark subsurface layers to sunlit shallow layers. The results of this study can improve our understanding of the role of the Kuroshio in providing nutrients and enhancing biological productions including fish abundances, providing a better predicting of the ecosystem responses to the Kuroshio path modulations.