末次冰消期以来长江口沉积环境演化及沿岸流变化

Sedimentary Evolution and Coastal Currents Variations of the Yangtze River Mouth(East China Sea) since Last Deglaciation

长江口附近的沿岸流和水团变化对研究长江三角洲沉积物的"源-汇"机制具有重要意义.对HZK2孔沉积物的粒度、年龄和有孔虫分布特征进行了研究分析.结果表明:HZK2孔52.5 m以上有孔虫均有分布,底栖有孔虫丰度在12 m以上和26.0~52.5 m含量超过40枚/g,代表不同沿岸流和水团的有孔虫属种含量在垂向上呈现明显的分带性.HZK2孔全新世以来经历了河口湾和水下三角洲两大沉积体系,并在全新世早期发育潮流沙脊.末次冰消期,钻孔所在位置受长江冲淡水和苏北沿岸流共同影响.全新世早期,则受苏北沿岸流影响为主;在此之后,长江口冲淡水的作用减弱,苏北、黄海沿岸流影响较强.全新世中晚期,苏北沿岸流、长江冲淡水、江浙沿岸流和东海外海水团多种水体共同作用钻孔所在海域,全新世晚期长江冲淡水作用占绝对优势.

The study of coastal currents variations in the Yangtze River mouth has significance for the understanding of riverine sediment‘source to sink’processes in this region.The post-glacial core sediments from the northern Yangtze River mouth,along with sedimentary structures and distributions of grain size and benthic foraminifera,show an estuarine depositional system characterized by tidal sand ridge in Early Holocene and a deltaic system consists of prodelta,delta front slope and delta front.Based on changes in the dominant microfauna species,two main current patterns prevailed in this region during most of the Holocene:one is the Yellow Sea coastal current(YSCC)and the other is the Yangtze dilute water(YDW).in Early Holocene,the YSCC dominated this area and the effect of YDW gradually strengthened.The YDW clearly weakened due to the sea level rise in early Middle Holocene.Then the East China Sea water mass(ESWM)penetrated the area dominated by mixed water mass consists of YDW,YSCC,Zhe-Min coastal current(ZMCC)and Yellow Sea cold water(YSCW),yet the Yangtze plume prevailed due to the rapid seaward migration of the Yangtze mouth.The YDW dominated this area again in Late Holocene.