AbstractA combined hydrodynamic and geological analysis of sedimentary and dynamical processes associated with the mud deposits on the continental shelves of Yellow Sea is carried out to synthesize a diverse set of measurements and information, and to identify dominant factors that contribute significantly to the formation of these deposits. The geological analysis makes use of available data, especially those recently collected cold water mass and deep core data while the hydrodynamic and sediment transport processes are quantified using a 3D hydrodynamics model that incorporates the effects of tides, waves and wind. The model study helps to infer from modern shelf sea processes the pathways and control mechanisms of fine sediment transport and check against the deposition rate determined from the core analysis so as to establish the links between sediment supply, accumulation, and dynamics for the deposits.
It is found that the fine sediments discharged from Huanghe River and Changjiang River and the resuspended sediments of Old Huanghe Delta are the main source for the mud deposit at the Southern Yellow Sea (SYS), which is supported by all sedimentological, mineralogical, and geochemical and fluid flow evidence. The tidal current flow is the main agent for transporting the fine sediment to the mud deposit in the central South Yellow Sea. But tidal action alone is insufficient to account for the volume of the deposit. Wind waves play an important role in maintaining suspension concentration and causing sediment resuspension, particularly from the Old Huanghe Delta where strong winter storms, mainly caused by Asian Monsoon, combined with strong current circulation can transport a large quantity of fine sediments from Old Huanghe Delta to the central SYS in winter. The existence of Yellow Sea Cold Water Mass circulation caused by density difference at SYS provide favourable environment for suspended sediment to be trapped and deposited near the front between YSCWM and the coastal water in the Subei coast in summer.
The average deposit of Central Yellow Sea Mud (CYSM) is 3.6 ×107t a-1 based on high-resolution Chirp sonar profiles combined with cores information. Under present hydrodynamic condition, the numerical model showed that approximately 16% (1.33×108t a-1) of the Huanghe River derived sediment is transported out of Bohai Strait and nearly 7% (5.72×107t a-1) will finally transported to the South Yellow Sea, quite close to the budget estimated by Alexander et al. (1991), that 9-15% of the annual Huanghe discharge is accumulating in the Yellow Sea based on 210Pb sediment accumulation rate data.
The tidal fields and wave distribution in the Yellow Sea had changed significantly during the rapid sea-level rise over the 12, 000 years. The number of amphidromic points of M2 and S2 increased from 2 to 4 while that of K1 and O1 increased from 1 to 2 as the sea level rose from -60m, -30m to -15m. The amplitudes of M2 and S2 in the Yellow Sea and Bohai Sea enlarged and co-phase line rotated anti-clockwise as sea-level increased from -60m to 0m. The wave height also increased because the water depth increased with rising sea level. When the sea level was low, the shoreline and shallow region were closer to the CYSM area, therefore, the Huanghe River derived sediments and the resuspended sediments only need travel shorter distance to reach CYSM, which was favourable for the sediment deposited in the CYSM area.
|Date of Award||2014|
|Supervisor||Ping Dong (Supervisor)|