Turbulent mixing and vertical nitrate flux induced by the semidiurnal internal tides in the southern Yellow Sea

Intermittent Intense Thermocline Shear Associated With Wind‐Forced Near‐Inertial Internal Waves in a Summer Stratified Temperate Shelf Sea

“…Based on the one‐day measurements of currents and microstructure at a nearby location (36°N, 122.3°E) at the end of August 2017, Xu et al. (2020) showed that the semidiurnal internal tides effectively trigger large velocity shear and turbulence in the weak secondary thermocline further altering the vertical nitrate flux. Z. Y. Liu et al.…”

“…The observed shear spikes were demonstrated to be able to induce shear instabilities and further alter diapycnal mixing and thus vertical nutrient fluxes. Based on the one-day measurements of currents and microstructure at a nearby location (36°N, 122.3°E) at the end of August 2017, Xu et al (2020) showed that the semidiurnal internal tides effectively trigger large velocity shear and turbulence in the weak secondary thermocline further altering the vertical nitrate flux. Z. Y.…”

“…In temperate shelf seas, often present is the seasonal thermocline that acts as a physical barrier separating the euphotic zone from the light‐limited deep water. The processes which interact to determine the stability at the thermocline are key determinants of heat, nutrient, and gas fluxes across the thermocline, controlling the occurrence of many ecological phenomena, such as the development of subsurface chlorophyll maximum and bottom hypoxia (Xu et al., 2020; H. Zhang et al., 2017; W. Zhang et al., 2019). Understanding the physical processes that impact the stability at thermocline is therefore a critical issue in shelf sea dynamics (Dzwonkowski et al., 2018; Yang, Wei, Zhao, & Zhang, 2020).…”

“…Limited observations have revealed potential impacts of internal waves of different types on dynamical instabilities in the thermocline of the YS, including internal solitary waves (Hsu et al., 2000; Z. Y. Liu et al., 2009; Zhao et al., 2014) and semidiurnal internal tides (K. Liu et al., 2019; Xu et al., 2020). Studies of the NIWs in the YS are rare due to a lack of observations, although the existence of near‐inertial current variability was pointed out more than three decades ago (Fang et al., 1989; Li et al., 2016).…”

Widespread Intensified Pycnocline Turbulence in the Summer Stratified Yellow Sea

“…The TKE dissipation rate $$\varepsilon $$ was estimated by fitting the empirical Nasmyth spectrum to the measured shear spectra over consecutive segments of 2 m with a 50% overlap (Figure 2a). As a result, vertical profiles of $$\varepsilon $$ with a vertical resolution of 1 m were obtained (for details of the estimation method we refer to Yang et al., 2020; Xu et al., 2020). With the assumption of isotropy for small‐scale turbulence, $$\chi $$ was calculated from the FP07 thermistor data following $$$\chi =6{\kappa }_{T}\left\langle {\left(\partial {T}^{\prime }/\partial z\right)}^{2}\right\rangle ,$$$ where $${\kappa }_{T}$$ is the molecular thermal diffusivity, $$\left\langle {\left(\partial {T}^{\prime }/\partial z\right)}^{2}\right\rangle $$ is the variance of the thermal gradient over the same consecutive segments of 2 m with a 50% overlap.…”