Sedimentary evolution of the Yangtze River mouth (East China Sea) over the past 19,000 years, with emphasis on the Holocene variations in coastal currents
Sedimentary evolution of the Yangtze River mouth (East China Sea) over the past 19,000 years, with emphasis on the Holocene variations in coastal currents
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长江口（东海）近19000年沉积演化，重点关注全新世沿岸流变化
DOI：
10.1016/j.palaeo.2017.11.023
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Li Xiao
中科院分区：
文献类型：
--
作者：
Zhao Baocheng;Yan Xuexin;Wang Zhanghua;Shi Yujin;Chen Zhongyuan;Xie Jianlei;Chen Jing;He Zhongfa;Zhan Qing;Li Xiao
长江口早期冰期后海侵过程中的水团变化尚未得到深入研究。这一研究空白阻碍了对该地区河流沉积物“源汇”过程的理解。本文通过对长江口北部H5孔的粒度、孢粉-孢子-沟囊组合、底栖有孔虫和介形类的综合分析，研究了19世纪以来沿岸流的完整沉积历史和相关变化。在核心处，大约19-11.3年间发育了河流泛滥平原，而在全新世的大部分时间里，河口到陆架再到水下三角洲占主导地位。根据主要由中国近岸水域种类组成的优势微型动物种类的变化，划分出两种主流格局：一种是7.9 ka以前以黄海沿岸流(YSCC)为主的格局，另一种是以长江冲淡水(YDW)为主的格局。外海盐生物种显著增加，包括玻利维纳罗布斯塔，以及分层水体恐囊物种，刺藻和刺藻。分别被解释为台湾暖流(TWWC)的侵占和YDW的加强。YDW和TWWC在7.9 ka前进入YSCC主导区域，可能与黑潮和亚洲夏季风的强度变化有关。在最大ASM和KC条件下，上升流是由TWWC的加强入侵引起的，从7.9-6.3ka的玻利维亚根茎开花就可以看出。约6世纪后，由于ASM的减弱，YDW明显减弱，但由于长江口的快速向海迁移，扬子羽流占上风。考虑到全新世早期YSCC的优势，黄河泥沙很可能占到长江口早期输运物质的很大比例。
Water mass variations in the early Yangtze estuary during the postglacial transgression have not been thoroughly studied. This research gap has hampered the understanding of riverine sediment ‘source to sink’ processes in this region. This study presents the results of integrated analyses of grain size, pollen-spore-dinocyst assemblages, benthic foraminifera and ostracods from a borehole, H5, located at the northern Yangtze mouth, to investigate the complete sedimentary history and associated variations in coastal currents since 19 ka. At the core site, a fluvial floodplain developed from ca. 19–11.3 ka, whereas an estuary to shelf to subaqueous delta prevailed during most of the Holocene. Based on changes in the dominant microfauna species, which mainly consist of Chinese coastal water species, two main current patterns were distinguished: one dominated by the Yellow Sea coastal current (YSCC) before ca. 7.9 ka and one dominated by the Yangtze dilute water (YDW). Marked increases in open-sea saline species, includingBolivina robusta, and stratified water dinocyst speciesSpiniferites ramousandSpiniferitesspp. were interpreted as the encroachment of the Taiwan warm current (TWWC) and the intensification of the YDW, respectively. The YDW and TWWC penetrated the area dominated by the YSCC before 7.9 ka, which was likely related to intensity variations in the Kuroshio Current (KC) and Asian summer monsoon (ASM). Under maximal ASM and KC conditions, upwelling resulted from the intensified intrusion of the TWWC, as indicated by the blooming ofBolivina robustafrom 7.9–6.3 ka. After ca. 6 ka, the YDW clearly weakened due to the decline of the ASM, yet the Yangtze plume prevailed due to the rapid seaward migration of the Yangtze mouth. Considering the dominance of the YSCC in the early Holocene, Yellow River-derived sediment likely represented a large proportion of the material delivered to the early Yangtze estuary.