【来访单位Institution】: 台湾中山大学，台湾 National Sun Yat-sen University, Taiwan

【邀请人Host】: 余凤玲， 副教授

【联络人Contact】: 陈敬艳 Chen Jingyan, chenjy@xmu.edu.cn

Abstract:

As the river plume disperses, it interacts with the ambient coastal sea. Physical processes of advection, buoyancy, and mixing largely determine the vertical structures of salinity, temperature, and thus the water density. In this setting, the distribution patterns of suspended particles are additionally affected by the resuspension from the seabed.

Particles carried by the river plume could be terrestrial sourced, or marine sourced. They could be clastic, biogenic, flocs, or organic debris.  There is a great diversity in these particles. However, their identity could be revealed by their grain size, bulk density, and chlorophyll and organic contents, etc.  Since physical processes determine their distribution patterns, there is a strong coupling between the physical processes and the biogeochemical signatures of suspended particles in the river plume regime.

We report findings from two river-plume systems located on the opposite sides of the Taiwan Strait in the summer of 2012.  At the mouth of the Zhuoshui River, through the course of a tidal cycle, the river plume regime was characterized as statistically stable due to stratification; having high SSC (45-64 mg/l) in which large (>153 μm) size class dominated the population. There was presence of flocs and biogenic particles, and non-living organic debris. The plume front regime was unstable; having particles with high bulk density (due to braking of flocs); biogenic and organic particles also appeared. In the unstable ambient seawater regime resuspension by currents of fine-grained (<63 μm) particles were dominant; particles with high bulk density with low biogenic signals were also present.   Off the mouth of Minjiang, nepheloid layers (NLs) at surface, intermediate, and benthic depths (SNL, INL, BNL, respectively) were present. The NL dynamics under two contrasting wind conditions were mainly controlled by (1) the presence of the Minjiang river plume and terrigenous material carried by the river plume; (2) water-column stability affected by wind, current, and waves; (3) current-induced resuspension of seafloor sediment; and (4) physically coupled biological activities. The wind was the major forcing influencing spread of the river plume. Southerly winds enhancing the seaward dispersal of the plume, facilitating water-column stratification, thereby forming 3 NLs. Phytoplankton growth enhanced by terrigenous material supply and sunlight, and suspension of the seafloor sediment were the major sources for suspended particles in these NLs. Conversely, under typhoon-related northerly winds, the plume was restricted. The reduced riverine input and enhanced mixing resulted in the disappearance of the SNL. Elevated turbidity in the INL was largely due to the presence of phytoplankton, while the BNL was comprised of sediment resuspended off the seafloor and from horizontal advection.