Spatial variation of and the factors influencing the floc size distribution in the North Yellow Sea during the winter season

Abstract Suspended particulate matter (SPM) usually exists in the ocean as floc, the behavior of which is believed to be significant for the source to sink sedimentary systems. However, the spatial variation of floc size distributions on the shelf scale is not fully understood. In this study, the SPM floc size distribution and the corresponding hydrological conditions in the North Yellow Sea are delineated to examine the spatial variation of floc size and the influencing factors based on a comprehensive investigation conducted during January 2017. The results indicate that the fine primary particles and microflocs display high volume concentration (Cv) around the tip of the Shandong Peninsula both in surface and bottom layers, while the macroflocs dominate the western North Yellow Sea. The primary particles ( 219 μm) are dominated by phytoplankton and mucus-bound organic aggregates. The higher Cv of primary particles and microflocs around the tip of Shandong Peninsula mainly results from the resuspension of bottom sediments. Temperature fronts limit the spread of SPM from the coastal area to the offshore area in surface layer, while the bottom sediments tend to cross the temperature front and spread seaward. In the western North Yellow Sea, flocculation is enhanced by plankton which accounts for the dominance of macroflocs, especially in surface layer. The Yellow Sea Warm Current may transport sediments that cross the temperature front in the bottom layer back to the central North Yellow Sea or South Yellow Sea in the winter season. Until the summer season, the deposition of macroflocs may contribute to the formation of mud deposits in the Yellow Sea.