HR: 1340h
AN: OS23C-1319    [Abstracts]
TI: Sediment Flux and Fate of the Yangtze River Sediments Delivered to the East China Sea
AU: * Liu, P
EM: jpliu@ncsu.edu
AF: North Carolina State University, MEAS, CB: 8208, Raleigh, NC 27695 United States
AU: Li, A
EM: acli@ms.qdio.ac.cn
AF: Inst. of Oceanology, Chinese Academy of Sciences, 7 Nahai Rd, Qingdao, 266071 China
AU: Yang, Z
EM: zshyang@mail.ouc.edu.cn
AF: Ocean University of China, 5 Yushan Rd, Qingdao, 266003 China
AU: Xu, K
EM: kxu@vims.edu
AF: Virginia Inst. of Marine Science, VIMS, Gloucester pt, VA 23062 United States
AU: Milliman, J D
EM: milliman@vims.edu
AF: Virginia Inst. of Marine Science, VIMS, Gloucester pt, VA 23062 United States
AB: The continental shelf of the East China Sea (ECS), together with the Yellow Sea and Bohai Sea, forms a contiguous shelf of about 0.75\times 10$^{12}$ m$^{2}$ in area. This wide( $>$ 500 km) and shallow ( $<$ 130 m) shelf also receives a large amount of terrigenous materials from two of the largest rivers in the world, the Yangtze River (Changjiang) and the Yellow River (Huanghe). The Yangtze River's annual sediment load has been about 480 million tons historically, combined with the adjacent Yellow River, equals more than 10% of the global total sediment flux to the ocean. Except for the part depositing in the river mouth, most fine sediment of the Yangtze River is believed to transport farther southward and accumulated offshore of Zhejiang and Fujian Provinces, which is commonly referred to as the "Mud belt deposit on the inner shelf of the ECS". However, for a long time, we have had no knowledge of the distribution, thickness, and sedimentary processes of this recent fine-grained deposit. In order to quantitatively define the Yangtze River's sediment transport and fate to the ocean, we conducted two geological and geophysical cruises in the summer of 2003 and 2004, with over 1000 km high-resolution Chirp sonar data, 8 gravity and box cores. The seismic profiles reveal a huge clinoform deposit off the coast of Zhejiang and Fujian Provinces, with a thickest ($\sim$ 40 m) depocenter nearshore between the 20-30 m isobaths and progressively thins offshore (less than 100 km across the shelf) reaching water depths up 60 to 70 meters in the ECS. However, this Yangtze-derived mud wedge has also been found to transport southward at least 800 km from the river mouth, extending all the way into the middle of the Taiwan Strait where it possibly meets the Taiwan rivers-derived hyperpycnal mudflow. The total volume of this mud wedge is estimated to be about 1.2\times 10$^{12}$ m$^{3}$, which is about 1.4\times 10$^{12}$ tons in total. Preliminary analysis of our seismic profiles and core data suggests that the Yangtze derived mud began to accumulate there only after the rapid sea-level rise of MWP-1B at around 11,000 yrs BP, when the sea level rose from -60 m to -40 m, together with the re-intensified Asian summer monsoon. But AMS C-14 dating suggest that major part of this mud has been transported southward along the shore since only about 7000 yrs BP by the newly formed Chinese coastal current after sea level reached its mid-Holocene highstand. This suggests that 2\times 10$^{8}$ tons of sediment could be discharged annually southward from the river to the inner shelf, mainly in the winter season, which equals to nearly 50% of the current annual Yangtze's sediment discharge. The other half has been believed to be trapped in its estuary. The existing Taiwan Warm Current in the middle shelf and Kuroshio Current in the outer-middle shelf are also believed to play critical roles in blocking any Yangtze and Yellow-derived materials from being delivered further into the deep ocean.
DE: 4211 Benthic boundary layers
DE: 4267 Paleoceanography
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 1719 Hydrology
DE: 1724 Ocean sciences
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting