Evolution of Suspended Particles in the Autumnal North Yellow Sea: Grain-Size Distributions Measured by Laser In Situ Scattering and Transmissometry

Mud deposits in cold water masses (CWMs) on continental shelves represent distinct units of suspended particulate matter (SPM); however, the generative mechanism and variation in SPM during source–sink processes remain unresolved. In this study, we measured the properties of SPM during transport among water masses into a CWM in the Nort in situ scattering and transmissometry (LISST). Our results show that this CWM is an important sink for SPM from the Bohai Sea and Chengshan Cape. The SPM in these source areas mainly consists of fine aggregates or flocs. Particles may bond to form coarse flocs when they pass through a high-temperature water mass (HTWM), as the weak turbulent shear in these water masses facilitates flocculation. The subsequent transport of such coarse flocs into the marginal waters around the CWM, where temperatures are lower and turbulent shear is stronger, causes the coarse flocs to disaggregate into fine aggregates/flocs. These low-density fine flocs, which are mainly composed of organic matter (OM), are subsequently transported toward the upper water body by upwelling; meanwhile, high-density fine aggregates, which are mainly inorganic, are transported toward a northern CWM, where they are deposited due to the quiescent near-bottom water. The results of our model provide new insights into the generative mechanisms of muddy deposits subject to cold vortices on continental shelves.