Institutional Repository of Key Laboratory of Marine Ecology & Environmental Sciences, CAS
|Place of Conferral||北京|
|Other Abstract|| 悬沙输运是研究海洋沉积过程的重要内容，也是现代海洋环境研究的热点。海洋中各种不同的水动力条件会使泥沙进行起动、搬运、沉降、再悬浮、再搬运的循环运动。这对海洋生态环境变化、海底地形演变以及人类的生产和生活都有重要的影响。悬沙输运的研究是泥沙运动研究的主要内容，研究悬沙输运是研究沉积物输运的一条重要途径。本文利用多年月平均的悬浮物通量对黄东海悬浮物的季节变化和净沉积进行了研究，探讨了陆架环流控制下悬浮物的输运、沉积和黄东海典型泥质沉积区的形成机制。还利用了最新的现场观测数据重点分析了冬季南黄海悬沙跨陆架通道区域的悬沙输运过程。|
黄东海悬浮物沉积和侵蚀的计算结果表明，其具有明显的季节变化。冬季，显著沉积可以从沿岸区域延伸至离岸100m水深区域，如济州岛西南泥区，它被认为是黄东海唯一一个全新世中陆架沉积中心。悬浮物沉积和侵蚀具有年际循环已经被大家认同，黄东海夏季河水带来的悬浮物主要聚集在内陆架特别是毗邻河口的区域，到了冬季这些悬浮物会被输运到中陆架和外陆架区域。通过对悬浮物通量矢量场的分析结果表明，悬浮物长期输运过程和济州岛西南泥形成的主要原因都是受陆架环流的影响。冬季，携带高悬浮物浓度的黄海沿岸流水沿着长江堆向东南流动，和黄海暖流在长江堆东南端相遇，二者相互剪切形成了东海冷涡，从而加剧了悬浮物的聚集，最终形成了济州岛西南泥。由悬浮物通量场计算得到的陆架环流控制的悬浮物沉积速率在济州岛西南泥区域为0.51mm a-1，在跨陆架通道为0.45 mm a-1，在黄海中央泥区域为0.04mm a-1，在长江口区域为3.62 mm a-1，在浙江外海海域为3.83 mm a-1，这些计算结果都与各自的实际测量结果相吻合，由此可以说明悬浮物长期输运主要是由陆架环流控制。
根据CS2站（位于南黄海跨路架输运通道区域）2015年1月连续21天的座底ADCP现场观测资料，进行低通滤波后计算得到冬季南黄海跨陆架环流的垂向结构及其悬浮物通量。冬季，北向季风对CS2站海域的余流影响显著，表明冬季风对跨陆架通道区域的悬沙输运过程也有重要作用。运用悬沙通量分解机制法对悬沙通量进行分解，发现CS2站海域的悬沙输运主要由T1和T3项组成，其中以T1项最大，说明环流对该海域悬沙输运起主导作用。比较平流输运项T1+T2和潮泵输运项T3+T4+T5,平流输运项全为负值而潮泵效应项有正值也有负值，说明潮泵输运项比平流输运项变化大。计算得到CS2站单宽净悬浮物通量为74.76 g/s，月输运量约为200ton/m，假设该通道的宽度约100km，则月净送量约为20百万吨，完全可以满足东海冷涡泥的生长沉积需求。; Sediment transport is the constant topic in the Modern Sea Environment studies. The rates and pathways of sediment transport in the Yellow and East Chins Seas(YECSs) are important to coastal sea communities as a fundamental component of the sediment budget for use in coastal projects, seafloor habitat, and commercial and recreational marine navigation. The understanding of sediment transport processes will lead to more successful management of sediment and coastal resources. However, in the YECSs the accurate pattern of sediment transport is still uncertain and requires further investigation. The seasonal transfer and net accumulation of suspended sediment, especially the forming mechanism of the Southwestern Cheju island Mud(SWCIM) are investigated using multi-year monthly mean suspended sediment flux to establish the linkages between sediment transport and hydrodynamic conditions and to determine the dominant long-term sediment transport process in the YECSs. The more accurate suspended sediment flux, and net deposition or erosion driven by shelf circulation in the YECSs are attained using 10-year time series data on surface suspended sediment concentration and more reliable numerically simulated circulation velocity. Furthermore, the suspended sediment transport process in the across-shelf pathway in winter is studied using the latest field data.
The calculated net deposition or erosion of suspended sediment with distinct seasonal variability in the YECSs demonstrate that during the wintertime significant deposition occurs not only along the coast, but also offshore areas with water depth of about 100 m, such as the SWCIM, which is acknowledged as the only mid-shelf Holocene depocenter in the YECSs. The annual cycle of net deposition or erosion verifies the widely accepted viewpoint, that riverine suspended sediment is stored in the inner shelf, especially adjacent to the estuary in summer and transported to middle or outer shelf in winter in the YECSs. Active sediment-transport process and the forming of the SWCIM mainly influenced by shelf circulation have been reproduced using the vector field analysis on suspended sediment flux. In winter, the Yellow Sea Coastal Current with high suspended sediment concentration flows southeastward along the Changjiang Bank, and interface with the Yellow Sea Warm Current to drive the East China Sea Cold Eddy at the end of the Changjiang Bank, which contributes to the convergency of suspended sediment, eventually generating the SWCIM. The circulation-driven accumulation rates in the YECSs are 0.51 mm a-1 in the SWCIM area, 0.45 mm a-1 at the cross-shelf pathway, 0.04 mm a-1 in the Central Yellow Sea Mud area, 3.62 mm a-1 in the Changjiang Estuary, and 3.83 mm a-1 off the Zhejiang Coast, respectively, which agree with the measured ones reasonably well, and further reveal that shelf circulation dominates long term sediment transport.
The cross-shelf circulation and flux of suspended sediment are calculated with the low-pass filter using the data on current velocity and echo intensity measured continuously by a bottom-mounted ADCP at the CS2 site located at the cross-shelf pathway in the South Yellow Sea for 21 days from Dec. 30, 2014 to Jan.20, 2015.In the South Yellow Sea northerly winter monsoon have a notable effect on residual currents, as well as the cross-shelf process of suspended sediment transport. The main components of suspended sediment flux computed by the sediment flux decomposition mechanism at the CS2 site are T1 and T3terms, indicating that during the wintertime circulation-driven transport is the main part of suspended sediment transport. The capacity of entraining the suspended sediment likely changes with the ebbs and floods since not all the tidal pumping items T3+T4+T5 are positive. The calculated result displays that the net flux of suspended sediment per unit width is 74.76g/s at the CS2 site, the monthly flux is about 200 ton/mon. The monthly net flux will be about 20 million tones given the pathway width of 100km., which is sufficient for the forming of the SWCIM.
|First Author Affilication||Institute of Oceanology, Chinese Academy of Sciences|
|李坤. 黄东海陆架环流控制的悬浮物输运[D]. 北京. 中国科学院大学,2016.|
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