The influence of physical processes on the physical and biogeochemical properties of suspended particles along the river-dominated northern South China Sea Shelf
Jay Lee
Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan R.O.C.
The continental margin is considered the land-sea boundary and receives abundant terrestrial and marine substances delivered by rivers or coastal currents. In one of the largest continental margins, the northern South China Sea (NSCS), the sources for the suspended sediment (SS) are complex because various water regimes occupy the water column in the coastal region. A 5-day shipboard observation at a fixed station in summer was conducted to investigate the transport of SS on the NSCS. Hourly hydrographic profiling (e.g. salinity etc.) was carried out. Every 2 hours, water samples were taken at 3 m on the surface and 3 mab for nutrients, chlorophyll-a (Chl-a), particulate organic carbon (POC), and stable carbon isotope (δ13CPOC) measurements. Our results showed two regimes at the surface and bottom water. The surface water was occupied by the ZRP with low salinity, high N/P ratio, and high fluorescence, in which the SS was dominant by sizes <153 μm. In this regime, POCs were mainly composed of in-situ marine phytoplankton according to a low POC/Chl-a (PC) ratio and heavier δ 13CPOC. In the bottom water, previous works suggested the observed cold-water temperature was related to wind-induced upwellings. The observed decreasing water temperature was accompanied by the increasing SiO4 and Chl-a. However, the PC ratio and δ 13CPOC indicate POCs in the bottom water were mainly degraded terrestrial materials. Furthermore, the grain-size composition of SS varied semi-diurnally. Those preliminary findings suggest diurnal tides might have entrained POCs in the bottom water from reworked terrestrial materials on the seabed.
Keywords: Continental shelf, river plume, worked sediment, suspended particles, particular organic matters, Chl-a, δ 13CPO
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