Abstract Based on mooring observations carried out in the southern Yellow Sea during late summer 2017, this study focuses on the characteristics of the internal tide-induced turbulent mixing and the influences on the vertical transport of nitrates. We observe clear semidiurnal pycnocline displacements with an amplitude of ~3.5 m during 25 h. The baroclinic velocity and velocity shear are mainly controlled by the low-mode semidiurnal internal tide. The turbulence profiling measurements reveal that the measured turbulent kinetic energy dissipation rates e are largely enhanced at the thermocline ( e ~2.0 × 10−8 Wkg−1) where the maximum displacements occur. The depth of the enhanced e and velocity shear coincide with each other which all follow the displacements of isopycnals induced by the internal tide, indicating the role of local velocity shear in generating the strong turbulence. Further analysis shows that the observed interior e is in good agreement with the MacKinnon-Gregg parametrization model which is formulated based on the wave-wave interaction theory. The strong turbulence has induced large vertical turbulent diffusivity ( K ρ ~1.0 × 10−5 m2s−1) in the nitracline. The estimated vertical nitrate fluxes across the nitracline are 0.07–0.44 mmolNm−2d−1. Considering the fact that the temporal variation of vertical nitrate fluxes is mainly determined by the trend of K ρ , our results suggest that the internal tides which have generated large nitracline K ρ may play an important role in transporting nitrates upward, supporting the growth of phytoplankton in the summer subsurface chlorophyll maximum zone at least near our measurement location where internal tides may prevail.

中文翻译：

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黄海南部半日内潮引起的湍流混合和硝酸盐垂直通量

摘要 基于2017年夏末在黄海南部进行的系泊观测，重点研究了内部潮汐引起的湍流混合特征及其对硝酸盐垂直输运的影响。我们在 25 小时内观察到清晰的半日倾角位移，幅度为~3.5 m。斜压速度和速度切变主要受低模半日内潮汐控制。湍流剖面测量表明，测量的湍流动能耗散率 e 在发生最大位移的温跃层 (e ~2.0 × 10-8 Wkg-1) 处大大增强。增强的 e 和速度切变的深度彼此重合，都遵循内部潮汐引起的等密线位移，表明局部速度剪切在产生强湍流中的作用。进一步分析表明，观测到的内部 e 与基于波波相互作用理论建立的 MacKinnon-Gregg 参数化模型非常吻合。强烈的湍流在硝酸盐中引起了大的垂直湍流扩散系数 (K ρ ~1.0 × 10−5 m2s−1)。估计穿过硝胺的垂直硝酸盐通量为 0.07–0.44 mmolNm-2d-1。考虑到硝酸盐垂直通量的时间变化主要由K ρ 的趋势决定，我们的结果表明产生大硝酸盐K ρ 的内部潮汐可能在向上输送硝酸盐中起重要作用，