In the past decades,the Hoods of the Yangtze and Yellow River introduced unexpected changes of the ecological community and sedimentary dynamics in the Fast China Sea(KCS).To reconstruct the flood events in the ECS,^(228)Th,^(230)Th and^(232)Th have been examined in a sediment core.The specific activities of three thorium isotopes have good positive relations with line fractions(<63 urn),indicating that Th activity concentrations heavily depend upon the sediment grain size.The size-normalized activities of ^(228)Th,^(230)Th and ^(232)Th showed significant variations.Coincidences between the higher Th activities and historical Hoods 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.^(230)Th/^(232)Th and ^(228)Th/^(232)Th,also showed similar patterns to the historical river floods.In three periods(1740s,[840—1860s and1930- 1960s),characterized by frequent Hoods,the thorium activity ratios were fairly low and close to the Yangtze and Yellow River estuary sediments,coinciding with the less oceanic ^(228)Th and ^(230)Th 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.
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