Knowledge Management System Of Institute of Oceanology, Chinese Academy of Sciences
|Alternative Title||High-resolution sedimentary records and its significance of environment in the Shandong Peninsula coastal current area during the Late Holocene|
|Place of Conferral||中国科学院海洋研究所|
|Keyword||沉积演化 山东半岛沿岸流 黄河 晚全新世 东亚冬季风|
山东半岛沿岸流海域悬浮体浓度与潮流流速具有明显的正相关关系。近端三角洲海域的悬浮体混合了黄河输入物质和再悬浮物质，其粒度分布通常是多峰态，而远端泥质区的悬浮体粒度分布多为单峰态。表层沉积物粒度空间分布受河流输入、水动力以及海洋锋面等因素控制。山东半岛沿岸流海域沉积物可分为粗粒级端元（< 5 φ）和细粒级端元（> 5 φ）。粗粒级端元只能在冬季强风条件下随着沿岸流向远端泥质楔输运，且受到海洋锋面的阻隔。相比之下，细粒级端元不受海洋锋面限制，常年在潮流和沿岸流的作用下向外扩散。这种沉积物输运模式解释了山东半岛沿岸流海域沉积物粒度分布峰型的变化。
在Bayesian年龄-深度模型基础上获得了山东半岛泥质楔2.6 ka BP以来高分辨率沉积物粒度、主微量元素演化特征。稀土元素配分模式、87Sr/86Sr-εNd图解显示黄河改道南黄海入海期间，渤海废三角洲再悬浮物质在沿岸流下持续供给远端泥质楔。以沉积物粒度粗粒级端元丰度及Zr/Rb比值为指标反演了2.6 ka BP以来东亚冬季风强度。2630 - 900 cal. BP东亚冬季风强度在低水平上旋回变化，900 - 400 cal. BP冬季风强度不断增强，400 cal. BP - 至今冬季风强度在高位振荡。能谱分析和小波分析显示晚全新世冬季风强度演变存在太阳活动周期和PDO周期。在千年时间尺度上，东亚冬季风强度主要受控于太阳活动。而在百年和多年际时间尺度上，东亚冬季风强度与ENSO、PDO等过程关系密切。中世纪暖期（MWP）前，东亚冬季风强度与El Niño发生频率反向变化，MWP - 至今，冬季风强度与PDO具有一致的变化趋势。
The Shandong Peninsula Coastal Current (SPCC) area covering the Yellow River proximal delta and distal mud wedge, is the most significant area of the source-sink system and an important channel for material derived from the Yellow River diffusing outward. In recent decades, the hydrodynamic environment, sediment transport model and sediment characteristics evolution in the SPCC area had been studied extensively, but the spatiotemporal evolution of sediment characteristics from the proximal delta to the distal mud wedge under coastal current was still unclear. In this study, the spatial differentiation characteristics and dynamic mechanism of sediments were studied based on the concentration of suspended particulate matter (SPM), grain size of SPM and surface sediments in the SPCC area. The grain size, Sr-Nd isotopes, content of rare earth elements, TOC\TN, major and trace elements in the core sediments recovered from the SPCC area were analyzed. Combining with AMS14C dating and 210Pb dating, the high-resolution sedimentary records were reconstructed. The environmental significances of the sedimentary records were discussed on centennial and millennial scales.
The concentrations of SPM were related to the tidal current strength in the SPCC area. Generally, the concentrations of SPM in the region with strong tidal current were higher. The grain size distribution of the SPM in the proximal delta of the Yellow River was multi-modal and variable with depth, whereas that in the distal much area was typically unimodal. Such grain size variability of sediments in the SPCC area was controlled by the input of the Yellow River, the coastal currents under East Asian Winter Monsoon (EAWM), local tidal currents and waves, and sea fronts in the water column. The sediments in the SPCC area could be divided into coarse-grained end-member (< 5 φ) and fine-grained end-member (> 5 φ). The coarse-grained end-member of suspended sediments was hindered from further diffusion under fair weather and could be only transported to the distal mud area under strengthened coastal currents in winter. By contrast, the fine-grained end-member was not restricted by ocean fronts and could transported far away under tidal currents and coastal currents all year round. These transport patterns supplied bimodal grains and were responsible for the sediment grain size distribution in the distal mud wedge in the SPCC area.
The temporal and spatial evolution of grain size, major and trace elements, TOC \TN of sediments in the SPCC area was quite different over the past century. The sedimentary environment was relatively stable in the distal mud wedge. And the trend of sediment characteristics evolution of the region was similar, and was mainly affected by the strength of the coastal current caused by the winter monsoon. The temporal variabilities of sediment characteristics in the proximal delta region were more complex than that in the distal mud wedge. On the one hand, the hydrodynamic environment and sediment diffusion process were complicated and changeable with the deltaic progradation to the sea; on the other hand, the shift channel of the Yellow River and changes in sediment load affected the evolution of sediment characteristics in the proximal delta.
Human activities had greatly influenced the sediment characteristics of coastal current area in recent decades. Such activities as reservoir construction and the regulation of large reservoirs not only reduced the sediment load of the Yellow River, but also changed the sediment supply model and transport process, which affected the grain size characteristics of sediments in the proximal delta. In addition, the industrial and agricultural activities in the Shandong Peninsula resulted in the enrichment of As in the sediments of the SPCC area. The accumulation process of heavy metals in sediments was consistent with the process of economic development of China.
Based on the Bayesian age-depth model, the high-resolution sedimentary record on evolution of grain size, major and trace elements in core sediments of the Shandong Peninsula mud wedge since 2.6 ka BP had been obtained. The results the REE partition model and 87Sr/86Sr-εNd analysis showed that erosion material from the proximal delta became the main source of the Shandong Peninsula mud wedge when the Yellow River diverted to the South Yellow Sea. The EAWM intensity since 2.6 ka BP had been retrieved using sediment coarse-grained endmember abundance and Zr/Rb as indices. The EAWM intensity cycled at low level in 2630 - 900 cal. BP, increased continuously in 900 - 400 cal. BP, oscillated at high level since 400 cal. BP. Spectral analysis and wavelet analysis showed that the existence of solar and PDO cycles in the evolution of winter monsoon. The EAWM intensity was controlled by solar radiation on a millennium time scale, while was closely related to ENSO and PDO on centennial and multiannual time scales. The EAWM intensity was inversely related to the frequency of El Niño before the Medieval Warm Period (MWP), while changed with PDO since the MWP.
|MOST Discipline Catalogue||理学::海洋科学|
|Table of Contents|
|杨立建. 晚全新世山东半岛沿岸流海域高分辨率沉积记录及其环境指示意义[D]. 中国科学院海洋研究所. 中国科学院大学,2022.|
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