High resolution flood records in the Yangtze subaqueous delta during the past century and control mechanism

Summer flood hazards have a strong influence on the social economy of the Yangtze River Basin, so it is in dire need of investigating multiple spatiotemporal variations in floods and control mechanisms, but this is handled by short time extent of instrumental flood data and lack of effective research methods for palaeoflood deposition records.A sediment core (YEC1701)collected from the Yangtze subaqueous delta was studied in detail with its top 100 cm through using high-resolution XRF core scanner (XRFCS), and measurements of grain size, organic carbon and nitrogen, stable carbon isotope (δ¹³C), and²¹⁰Pb compositions.The above study results were compared with the observing instruments or documental flood data to establish an effective proxy for paleo-flood depositions by comparison with instrumental or documental flood data.The results show that the peak value of Zr/Rb in the subaqueous delta sediments of the Yangtze River usually corresponds to the high value of coarse grain composition, the high value of C/N, and the negative value of δ¹³C.The sedimentary age of the strata in the delta corresponds well to the year of flood events in the basin.Therefore, the Zr/Rb ratio can be used as an important proxy index for the identification of palaeo-flood sediments in the Yangtze River.Totally, 22 flood events occurred in the period 1930-2017 in the Yangtze River basin, 11 and 18 of which were identified by the XRFCS Zr/Rb data in terms of 10 mm and 2 mm measurement intervals with effective recognition rates of 50% and 80% respectively.It is therefore recommended to perform XRFCS measurement with a smaller interval than half of sedimentation rates for better recognition rates of flood events.Multiple source data of river floods and precipitations were analyzed to show that river floods in Yangtze River basin are majorly influenced by ENSO (El Niño-Southern Oscillation), EASM (East Asian summer monsoon) and SASM (South Asian summer monsoon) over different time scales from multiple years to millennium.However, the time resolution for earlier flood records is very low, and it can be greatly improved by employing XRFCS mm-scaled Zr/Rb ratio of continuous flood depositions in the Yangtze subaqueous delta.This will also improve our understanding of controlling mechanisms of flood events and then better prediction of flood variation in response to global climate change.