Nagai Takeyoshi, Hasegawa Daisuke, Tanaka Takahiro, Nakamura Hirohiko, Tsutsumi Eisuke, Inoue Ryuichiro, Yamashiro Toru
Tokyo University of Marine Science and Technology, Department of Ocean Sciences, Tokyo, 108-8477, Japan.
Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency, Fisheries Oceanography and Resources Department, Shiogama, Miyagi, 985-0001, Japan.
Sci Rep. 2017 Nov 6;7(1):14555. doi: 10.1038/s41598-017-15167-1.
The upstream Kuroshio flows through Okinawa Trough and the Tokara island chain, the region near the continental shelf of the East China Sea and shallow seamounts, where the Kuroshio can induce strong mixing over the shallow topography. Also, tidal currents over the rough topography may produce internal tides, and associated turbulence. The previous observations show energetic high vertical wavenumber near-inertial wave shear in the Kuroshio thermocline, which implies strong turbulent mixing. However, direct turbulence measurements in this region are very scarce. Using high lateral resolution (1-2 km) direct turbulence measurements, we show here, for the first time, that strong turbulent layers form spatially coherent banded structures with lateral scales of >O(10 km), associated with bands of near-inertial wave/diurnal internal tide shear of high vertical wavenumber in the upstream Kuroshio. The turbulent kinetic energy dissipation rates within these turbulent layers are >O(10 W kg), and estimated vertical eddy diffusivity shows >O(10 m s) on average. These results suggest that the high vertical wavenumber near-inertial waves propagating in the upstream Kuroshio could have large impacts on the watermass modifications, momentum mixing, nutrient supply, and associated biogeochemical responses in its downstream.
黑潮上游流经冲绳海槽和吐噶喇列岛链，即东海大陆架附近区域以及浅海山，在这些地方黑潮能够在浅地形上引发强烈混合。此外，粗糙地形上的潮流可能会产生内潮及相关湍流。先前的观测显示，在黑潮温跃层存在能量较高的高垂直波数近惯性波切变，这意味着存在强烈的湍流混合。然而，该区域的直接湍流测量非常稀少。利用高横向分辨率（1 - 2千米）的直接湍流测量，我们首次在此表明，强烈的湍流层形成了横向尺度大于O(10千米)的空间连贯带状结构，这与黑潮上游高垂直波数的近惯性波/日内潮切变带相关。这些湍流层内的湍动能耗散率大于O(10瓦/千克)，并且估计的垂直涡动扩散率平均显示大于O(10米²/秒)。这些结果表明，在黑潮上游传播的高垂直波数近惯性波可能会对其下游的水体改造、动量混合、营养物质供应以及相关的生物地球化学响应产生重大影响。
