Observations of internal tides off the coast of Shandong Peninsula, China

Bottom mounted platforms equipped with current profilers/meters, temperature/salinity and turbidity sensors were deployed for about 10 days in August 2017 over an elongated deposit off the coast of Shandong Peninsula, in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer. In total, semidiurnal barotropic tides dominate the measured currents, accounting for 90% of total variance. However, in the cross-shore direction, greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents. Both the Empirical Orthogonal Functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode-1 internal tides, i.e. the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle. Although the bottom slope is subcritical in most area of the deposit, the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0.5, suitable for local internal tide generation. The internal tides generated from the deposit are especially significant considering that the shelf of the Yellow Sea is usually broad and flat. The quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides (6.44ⅹ10−4 m3 s−3) is greater than the internal tides (−0.95ⅹ10−4 m3 s−3), and the total dissipation rate due to bottom drag is 5.49ⅹ10−4 m3 s−3, which is much greater than the interior one due to internal tides (2.69ⅹ10−4 m3 s−3). The internal tidal current alone is not energetic enough to resuspend the local fine-grained sediments. However, in the cross-shore direction, the sediment flux due to internal tides is twice as much as the barotropic component, resulting in a net onshore sediment flux, thus highlighting the advection effect of internal tides in the coastal mass transport.