Thorium isotopes ((228)~Th,(230)~Th,(232)~Th) and applications in reconstructing the Yangtze and Yellow River floods  

作　　者：Wei-feng YANG Min CHEN Xin-xing ZHANG Zhi-gang GUO Guang-xue LI Qiang MA Jun-hong YANG Yi-pu Huang 

机构地区：[1]State Key Laboratory of Marine Environmental Science,Xiamen University [2]Department of Environmental Science and Engineering,Fudan University [3]College of Marine Geo-Science,Ocean University of China

出　　处：《International Journal of Sediment Research》2013年第4期588-595,共8页国际泥沙研究（英文版）

基　　金：supported by a Chinese COMRA Program(No.DY125-13-E-01);the Chinese National ScienceFoundation(41076043,41125020 and 40606022); a special scientific research project for public welfare supportedby the State Oceanic Administration(201105022-4)

摘　　要：In the past decades, the floods of the Yangtze and Yellow River introduced unexpected changes of the ecological community and sedimentary dynamics in the East China Sea （ECS）. To reconstruct the flood events in the ECS, 228Th, 230Th and 232Th have been examined in a sediment core. The specific activities of three thorium isotopes have good positive relations with fine fractions （〈63 μm）, indicating that Th activity concentrations heavily depend upon the sediment grain size. The size-normalized activities of 228Th, 23-Th and 232Th showed significant variations. Coincidences between the higher Th activities and historical floods of the Yangtze and Yellow River demonstrated that size-normalized Th recorded the two rivers＇ flood events. The activity ratios of thorium isotopes, i.e. 230Th/232Th and 228Th/232Th, also showed similar patterns to the historical river floods. In three periods （1740s, 1840-1860s and 1930-1960s）, characterized by frequent floods, the thorium activity ratios were fairly low and close to the Yangtze and Yellow River estuary sediments, coinciding with the less oceanic 228Th and 230Th contributions during the flooding periods. Accordingly, these results support the size-normalized Th activity and thorium ratios as proxies of the river floods in coastal seas.In the past decades, the floods of the Yangtze and Yellow River introduced unexpected changes of the ecological community and sedimentary dynamics in the East China Sea （ECS）. To reconstruct the flood events in the ECS, 228Th, 230Th and 232Th have been examined in a sediment core. The specific activities of three thorium isotopes have good positive relations with fine fractions （〈63 μm）, indicating that Th activity concentrations heavily depend upon the sediment grain size. The size-normalized activities of 228Th, 23-Th and 232Th showed significant variations. Coincidences between the higher Th activities and historical floods of the Yangtze and Yellow River demonstrated that size-normalized Th recorded the two rivers＇ flood events. The activity ratios of thorium isotopes, i.e. 230Th/232Th and 228Th/232Th, also showed similar patterns to the historical river floods. In three periods （1740s, 1840-1860s and 1930-1960s）, characterized by frequent floods, the thorium activity ratios were fairly low and close to the Yangtze and Yellow River estuary sediments, coinciding with the less oceanic 228Th and 230Th contributions during the flooding periods. Accordingly, these results support the size-normalized Th activity and thorium ratios as proxies of the river floods in coastal seas.

关 键 词：THORIUM Yellow River Yangtze River Flood East China Sea 

分 类 号：P333.2[天文地球—水文科学]