Sediment settling process revealed by a bottom-tethered sediment trap at the east tip of the Shandong Peninsula

This paper investigates sediment settling process during summer seasons based on in-situ observation and sediment analysis at the east tip of the Shandong Peninsula, which is a pathway for sediments from the Bohai Sea and the North Yellow Sea to enter the South Yellow Sea in China. Bottom-tethered sediment traps, together with platforms equipped with current profilers/meters and temperature/salinity and turbidity sensors, were deployed for approximately 10 days in August 2017 over an elongated deposit off the coast of the Shandong Peninsula. A computed tomography (CT) scan and grain size and 210Pb analyses of trap sediment were carried out to determine the settling process of suspensions at the study site. Twenty-three couplets were found in the CT images of the trap, the time series of which was established using intervalometer disks. Quantitative characterization of rhythmites using a hounsfield unit indicates that the period of couplets is approximately quarter-diurnal, and the settling process could be divided into three stages during Aug. 21st – 27th. Current, wave, wind, and SSC data illustrate that the diversion of the bottom current leads to the formation of couplets, and the thickness of the couplet is controlled by the vertical current velocity and wind direction. Northerly winds enhance the difference in settlement between flood and ebb tides, whereas southerly winds smoothen the difference. The gale event inhibited the settlement of the suspended matter, and the source of the suspensions was converted from local to remote after the event, as evidenced by 210Pb data. No evident erosion can be detected in the sediment traps. The results are of significance to better understand the sedimentary dynamics near the Shandong clinoform and inspire the practical efficiency of bottom-tethered sediment traps in the settling process in coastal areas.