Chinese Coastal Sediment Transport In The Bohai Sea, Yellow Sea And East China Sea

The observations of bottom sediment distribution in the Bohai Sea, Yellow Seaand East China Sea (BYECS) show that beside the mud patches in the Huanghe River(Yellow River), the Old Huanghe Delta and the Changjiang River (Yangtze River),fine-grain mud patches are also found in the Yellow Sea Trough, the Zhejiang andFujian Provinces Costal Area (ZFPCA), the South West of Cheju Island (SWCI) andin the Okinawa Trough. The sources and transport mechanisms of these mud patcheshave been widely studied over the past decades and lots of plausible sedimenttransport mechanisms have been proposed to explain the existence of these mudpatches. However, due to the lack of enough field data, the sediment transportmechanisms are still unclear, especially in the outer seas. The observed temperature,salinity and turbidity data and the Regional Ocean Modeling System (ROMS) modelare used to study the Chinese coastal sediment transport processes in the BYECS.The source and transport mechanisms of land-derived sediments transport in theBYECS were studied using the field data (2006-2007) of temperature, salinity andturbidity in the East China Seas. The results suggest that the highest suspendedsediment concentration (SSC) distributes in the coastal areas while the outer sea areascan hardly observe turbid water; the surface layer SSC is much lower than the bottomlayer SSC; the winter time SSC is higher than the summer time SSC. The HuangheRiver sediment can be transported to the Northern Yellow Sea by the Bohai SeaCoastal Current and it also seems can be carried to the Southern Yellow Sea.However, the Huanghe River sediment can be hardly transported to the south of35°N.The Old Huanghe River and Changjiang River sediment can be transported to theouter shelf area by the Taiwan Warm Current. Suspended particulate matter is unableto get through the barrier of the Kuroshio Current under normal conditions.Eventhough the observed turbidity data can reflect the basic sediment transportpaths and mechanisms, it is still hard to reveal the presice sediment transport pathsand the exactly sediment transport mechanisms. The ROMS model is used to simulatethe Chinese land-derived sediment transport in the BYECS. The model combines the effect of currents, tides and waves on the sediment transport processes. The modelresults show that the sediment transport paths in the BYECS are generally wellrepresented by the ROMS model. The dynamic mechanisms of the fine-grainsediment transport from the Huanghe River, the Old Huanghe Delta and theChangjiang River are studied in this article. The seasonal variability of the sedimenttransport in the BYECS and the formation mechanisms of the Yellow Sea Troughmud patch, the mud patch southwest of Cheju Island and the Okinawa Trough mudpatch are discussed. The results show that the Huanghe River sediment can betransported to the Yellow Sea Trough, but little makes it to the outer shelf while theOld Huanghe Delta sediment is mainly transported to the Yellow Sea Trough. Thesediment from the Changjiang River mouth is carried to the mud patch off the coast ofthe Zhejiang and Fujian provinces but with part of this sediment also transported tothe Yellow Sea Trough. The front between the coastal water and the Taiwan WarmCurrent blocks the seaward sediment transport, but the Taiwan Warm Current alsotransports the Changjiang River sediment from the Taiwan Strait to the outer shelfand part of the sediment can be directly transported to the Okinawa Trough.According to the model results, a plausible picture of sediment transport in theBYECS, which would be difficult to obtain from observations, is achieved using themodel. Some contentious views are also verified in this study, such as:(1)The Huanghe River sediment not only can be transported to the Bohai Sea andNorthern Yellow Sea but also can be transported to the Southern Yellow Sea.(2)The sediment which is transported to the Cheju Island by the Subei Shoal CoastalCurrent not only includes the Old Huanghe River sediment but also includes theChangjiang River sediment.(3)The Changjiang River sediment can be transported to the north in summer andarrives at Yellow Sea Trough mud patch in winter.(4)The Taiwan Warm Current blocks the coastal turbid water transported to thecontinental shelf. However, it can transport the Taiwan Strait sand to the outer shelf.(5)The winter time wind-drive bottow off-shore flows cannot transport the coastalarea sediment to the outer shelf. It only transports the sediment100Km away fromthe shore.(6)Under normal condition, there are two paths for the sediment transport to theOkinawa Trough. The Changjiang River sediment is transported to the OkinawaTrough by the Taiwan Warm Current in spring and transported to the shelf edge area by the Subei Shoal Coastal Current in winter. The episodic water exchanges betweenthe shelf and the Kuroshio Current transport the shelf edge areas sediment into theOkinawa Trough. The sediment cannot be transported to the Okinawa Trough due tothe strong block effect of the Kuroshio Current under normal conditions. However, itcould be carried to the Okinawa Trough by episodic events, such as winter storm,typhoon and turbidity flows.(7) Under normal condition, the tide is the main agency for sediment re-suspension,and the wave have more important influence on the sediment resuspension only in thevery nearshore area in the East China Sea; the tide and the wind-wave are the themain force for the sediment vertical movement.