Sediment resuspension in winter in an exceptional low suspended sediment concentration area off Qinhuangdao in the Bohai Sea. (30th October 2020)

• Record Type: Journal Article
• Authors: Jiang, Man; Pang, Chongguang; Liu, Zhiliang; Jiang, Jingbo
• Is Part Of: Estuarine, coastal and shelf science. Volume 245(2020)
• Publication Date: 2020-10-30
• Subjects: Turbulent resuspension event -- High turbulent kinetic energy -- Wave-dominated bed shear stress -- Bottom-mooring observation system -- Bohai sea; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2020.106859
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: Seawater with low suspended sediment concentration (SSC) and high salinity dominates the sea area off Qinhuangdao all year round, especially in winter, which is an exceptional case since most of the coastal waters in the Bohai Sea are turbid. Being one of the most famous coastal tourist resorts in the area, it is crucial to keep the seawater around Qinhuangdao clear and unpolluted. Three bottom-mooring systems were deployed in the low SSC region from February to March 2017 for up to 22 days to reveal the processes and mechanisms of local sediment resuspension. The observation results showed that during the strongest wind of the whole deployment period, the sediment resuspension process included a turbulent resuspension event that occurred in the high turbulent kinetic energy period, and a continuous resuspension event when the bed shear stress (BSS) was larger than critical. The turbulent resuspension event was characterised by high-turbidity resuspension of sediments near the bed in the form of pulsation, with a depth of influence not more than the thickness of the bottom boundary layer. It was found to be triggered by strong turbulence driven by storm winds. In contrast the continuous resuspension could be attributed to high wave-dominated BSS. During storm winds, high concentrations of suspended sediment in the upper and middle layers appeared to lag the wind speed by about 8–10 h. In contrast, the turbulent resuspension event occurred at the same time as the strong winds. In-situ measurements from all three moorings indicate that it is the local weak sediment resuspension, even under the influence of storm winds in winter, that causes the formation of the low SSC area off Qinhuangdao. Highlights: Seawater with low SSC dominates the sea area off Qinhuangdao all year round. Turbulent resuspension was followed by continuous resuspension under storm winds. Turbulent resuspension was induced by high turbulent kinetic energy. Weak sediment resuspension is the local cause of the formation of the low SSC area.