|Alternative Title||Seasonal evolution of hydrological structure and its sedimentary environment effects in the South Yellow Sea|
|Place of Conferral||中国科学院海洋研究所|
|Keyword||南黄海 悬浮体 Lisst 黄海冷水团 黄海暖流|
南黄海海区是东亚大陆陆源物质向西太平洋扩散的重要通道，是研究中国东部陆架海区“源-汇”沉积体系的关键海区。作为物质循环的重要载体，悬浮体在海洋动力环境影响下的输运和沉降对陆架海区的“源-汇”过程和生物地球化学循环具有重要意义。黄海冷水团和黄海暖流是暖半年和冬半年南黄海海区最典型的水文现象，主导了研究区的环流结构，对悬浮体的物质输运和沉降过程具有重要影响。然而，陆架海区的悬浮体物质组成及其粒度分布特征存在较大的区域差异性，受调查数据和测量手段限制，目前南黄海海区的水文环境季节变化与悬浮体分布的关系尚不明确，悬浮体的粒度分布特征对现代沉积过程的影响的相关研究值得进一步讨论。本论文利用2012年夏季和秋季，以及2016年冬季三个航次的水体综合调查数据，研究了南黄海海区的水文结构季节演变特征及其影响因素；利用原位激光粒度仪（laser in situ scattering transmissometry，LISST）的现场调查数据讨论了悬浮体平均粒径的计算方法及其适用性，分析了悬浮体的粒度分布特征及其物质组成；探讨了黄海冷水团和黄海暖流主导的夏季和冬季南黄海海区的沉积物输运模式，及其对南黄海中部泥质区形成的启示，所获得的主要结论如下：
阐述了南黄海海区水文结构的季节演变特征。夏季，南黄海海区的水文结构具有典型的层化特征，季节性温盐跃层位于10~30 m左右的深度，底层为典型的黄海冷水团所占据。秋季，受风混合作用影响，上部混合层厚度达50 m，底层是低温高盐的南黄海冷水团残留水，高温高盐的黄海暖流沿西北方向侵入研究区东南部。冬季，风混合作用进一步增强，混合层深度变深至60 m左右深度，南黄海中部60 m以深为黄海冷水团残留水。北向的黄海暖流已进入南黄海中部，形成双分支结构，并与南向的沿岸流（山东半岛沿岸流和黄海沿岸流）共同主导了冬季环流系统。
分析了南黄海冷水团对悬浮体分布和物质组成的影响机制及其对南黄海中部泥质区形成的启示。夏季，南黄海悬浮颗粒中≤128 μm的细颗粒主要是由无机矿物颗粒组成的，而>128 μm的粗颗粒则由有机颗粒主导。再悬浮的海底表层沉积物是海水中无机颗粒的主要来源，潮混合过程是引起再悬浮作用的主要动力因素。潮混合锋阻挡了近岸高浓度无机悬浮颗粒物沿次表层至近底层向远岸扩散，但跨锋面的表层离岸流可以将近岸区的部分无机细颗粒物（<16 μm）输运至南黄海中部。密度跃层阻碍了冷水团内营养盐进一步向海表扩散，导致浮游植物在密度跃层处富集；大量浮游生物及其分泌物与细小的无机颗粒相结合形成絮集体是海水中>128 μm的粗颗粒的主要来源，絮集体的形成促进了表层无机细颗粒向海底沉降。江苏外海的再悬浮颗粒为泥质区的形成提供了物源；跨潮混合锋面的离岸流是携带细颗粒（<16 μm）进入南黄海中部的动力；聚集体的形成是将这些细颗粒带离表层并快速沉降到海底的主要方式，并促进了南黄海中部泥质区的形成。
揭示了冬季南黄海海区的悬浮体输运模式，为黄海暖流向南黄海中部泥质区的物质输运过程提供了现代沉积学证据。冬季，小于256 µm的细颗粒和中等颗粒主要由无机颗粒构成，而大于256 µm的粗颗粒主要与有机物质相关。391 µm的峰值主要是由有机颗粒导致的，反映了黄海暖流的影响，尤其是在表层。黄海暖流增强了冬季南黄海海区的营养和温度条件，在适宜的光照条件下促进了浮游植物的生长。南黄海中部64~159 µm的颗粒迅速减小，反映了研究区南部的悬浮颗粒向南黄海中部的输运。综合证据显示，黄海暖流作为主要的驱动力，在冬季将江苏近岸以及长江来源的悬浮颗粒输运至南黄海中部。
The South Yellow Sea is an important channel for transporting terrigenous materials from the East Asian continent to the western Pacific Ocean. It is also a key area for studying source-to-sink sediment transport systems in East China shelf seas. As the primary channel for material circulation, the fate of suspended particulate matter (SPM) is significant for the source-to-sink process and biogeochemical processes in shelf sea areas. The Yellow Sea Cold Water Mass (YSCWM) and Yellow Sea Warm Current (YSWC) are the most typical hydrological phenomena and exhibit important influence on the transport and sedimentation of SPM. However, the material composition and particle size distribution (PSD) of SPM show obvious spatiotemporal heterogeneity. Due to the limit of observation data and methods, the relationship between the seasonal variation of hydrological structure and SPM distribution in the South Yellow Sea is ambiguous. The influence of PSD on the modern sedimentary process is worthy of further discussion. In this study, integrated surveys from three cruises during summer and autumn of 2012 and winter of 2016 are studied. The seasonal evolutions of hydrological environment and its influencing factors; the calculation of mean size and its application are discussed based on the LISST data, the PSD and composition of SPM are also analyzed; the transport pattern of SPM in summer and winter season and its implication to formation of central South Yellow Sea mud deposits are also discussed as well. Here are the main conclusions:
The seasonal evolution of the hydrological structure in the South Yellow Sea is described. In summer, the hydrologic structure of the South Yellow Sea is characterized by typical stratification. The seasonal thermocline and halocline are located at 10-30 m. The Southern Yellow Sea Cold Water Mass (SYSCWM) dominate the bottom layer under thermocline. In autumn, the depth of upper mixed layer reaches 50 m, due to the influence of northly wind. The residual water of SYSCWM dominate the bottom layer. Warm and salty Yellow Sea Warm Current (YSWC) intrude from the southeast of the study area. In winter, the northly wind enhanced, and the depth of upper mixed layer reaches 60 m. And the residual water of SYSCWM dominate the bottom layer as well. The YSWC intrudes into the central South Yellow Sea and forms double branch structure. The northward YSWC and southward coastal current dominated the circulation of the South Yellow Sea in winter.
The mean size of SPM is calculated based on the LISST data, with moment and mean grain size methods respectively. The applicability of the two methods in continental shelf sea is also compared. The mean size calculated by the moment method are always greater than those obtained by the method of mean grain size method. The calculation difference is negligible above the thermocline both in summer or winter. The difference increases with depth under the thermocline due to the increase of fine particle composition. The calculation differences are closely related to the particle size distribution. The moments method highlights the contribution of coarse particles, while the mean size class method is sensitive to the fine particles. The latter is more suitable for the study of modern deposition environment in continental shelf sea areas.
The underlying mechanism between the southern Yellow Sea Cold Water Mass and the distribution and composition of SPM in summer and autumn seasons are classified. The implication for the formation of central South Yellow Sea mud deposits is also analyzed. In summer, the fine particles (≤128 μm) are mainly composed of inorganic particles, while the coarse particles of (>128 μm) are dominated by organic particles during summer season. The resuspended sea surface sediment is the main source of inorganic particles, and the tidal mixing process is the main driving force of resuspension. The tidal mixing front prevents the coastal inorganic particles from spreading to the offshore area in bottom layer, but some finer particles (<16 µm) can be transported to the central Southern Yellow Sea by surface cross-front currents. The pycnocline obstructs the upward diffusion of nutrients inside the Yellow Sea Cold Water Mass, which lead to the accumulation of phytoplankton in the pycnocline. The coarse particles (>128 µm) are mainly from the plankton or aggregates formed by organic secretion and fine inorganic particles. The formation of aggregates enhances the sedimentation of surface fine inorganic particles. The resuspension of bottom sediments in Jiangsu coast supply the inorganic particles, and the cross-front current transports these fine particles to the central South Yellow Sea. The formation and sedimentation of flocs are the chief way of taking these fine particles into sea bed, which promotes the formation of mud deposits.
The transport pattern of SPMs in the South Yellow Sea during winter season is revealed, and the evidence of modern sedimentology is provided about transportation of SPMs from the southern study area to the central Yellow Sea mud area by the Yellow Sea Warm Current. The fine and medium particles (≤ 256 µm) are mainly inorganic particles, while the coarse particles (>256 µm) include organic materials. The peak at 391 µm is dominated by organic particles and reflects the influence of the Yellow Sea Warm Current in the surface layer. The Yellow Sea Warm Current enhances the nutrient and temperature conditions in the South Yellow Sea, which facilitates phytoplankton growth under appropriate light conditions. The content of inorganic particles with sizes of 64-159 µm decreases sharply in the central South Yellow Sea, which reflects the transport of suspended particulate matter from the southern study area to the central Yellow Sea mud area. The synthesized evidence suggests that the Yellow Sea Warm Current, as the main driving force, transports particles from the Jiangsu coast or the Changjiang River into the central Yellow Sea mud area in winter.
|MOST Discipline Catalogue||理学::海洋科学|
|Table of Contents|
|李文建. 南黄海水文结构季节演变及其沉积环境效应[D]. 中国科学院海洋研究所. 中国科学院大学,2020.|
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