Characteristics and transport mechanism of suspended particles in offshore area of Zhoushan Islands

The transportation and dispersal of suspended particles play a key role in the deposition and evolution of offshore muddy deposits. In order to reveal the characteristics and transport mechanism of suspended particles in the offshore of Zhoushan Islands, field survey had been carried out during the spring tides in the summer of 2018, which include the observations of temperature, salinity, hydrodynamics, contents of suspended particles, and samples of sea water and seafloor surface sediment, etc. The results show that the suspended particles could be divided into three types: micro-flocs above thermocline with higher effective density formed by low-degree flocculation; larger flocs with lower effective density below thermocline aggregated by high degree of flocculation; and larger biological particles around the thermocline with the lowest effective density. During one diurnal tidal cycle, more than 3 000 kg·m⁻¹ suspended matters were transported southwards, controlled by Stokes drift, tidal pumping and gravitational circulation. In conclusion, the southward transport of suspended particles by continental circulation and tidal asymmetry played a positive role in the evolution of Zhejiang-Fujian muddy system. Nevertheless, the northward transport caused by uneven vertical distribution of velocity and suspended particle weakened the process to certain extent.