百年尺度东海内陆架风暴事件重建:器测记录与沉积记录耦合

A 100-year reconstruction of typhoon events on the inner shelf of the East China Sea:Coupling of meteorological observations and sedimentary records

未来全球变化可能带来极端事件的强度增加、频度提高,加之海面上升加快,给海岸带防灾减灾工作带来更新防护标准的课题。由于台风的器测记录时间较短,需要从其他载体寻找替代指标以延长台风记录的时间跨度,这样才能更好地估计极端事件的强度一频率关系。陆架泥质区的风暴事件沉积记录和历史文献中的有关灾害记录,是拓展台风记录的两个方向。本文试图通过台风观测记录与沉积记录的耦合,重建百年尺度东海内陆架泥质区的风暴事件沉积记录,并与气象灾害记载的台风暴潮成灾事件相印证,以期探讨陆架泥对台风事件的保存潜力,及其可能反映的台风信息(如路径和强度)。2018年在浙江温岭近海采集了2 m长的柱样沉积物(J1),通过多指标(粒径分布、D90、Zr/Fe、Sr/Al、Ca)综合识别出台风沉积事件;采用放射性同位素210Pb定年法确定沉积物的年代序列,将识别的台风沉积记录与器测台风记录通过时间标尺进行耦合分析。结果显示,J1的沉积速率约为1.1 cm/a,年代跨度大约是1836年至2018年;整根柱样共识别出25次台风沉积事件,其中气象观测时期(1950-2018年)有10次台风事件留下了沉积记录,这10次台风的平均风速与影响J1的所有台风平均风速比较接近,且大多数属于登陆浙闽、成灾较严重的Ⅲ型和Ⅳ型台风。通过多变量综合分析,发现就J1而言,沉积记录中台风事件的保存潜力约为30%;另外,历史文献中记载的台风事件可能偏重于登陆、成灾的较强台风,因而文献记录的台风数量显著少于实际产生影响的台风数量。这些认识有助于更好地利用沉积记录中保存的台风事件拓展台风记录的时间跨度,也有助于指导未来的采样地点,以尽可能多地获得保存更完整的台风沉积记录。

Future global changes may increase the intensity and frequency of extreme events,coupled with the rapid rise in sea level,bringing the issue of updated protection standards to the coastal areas.Due to the short length of observational records,it is necessary to find other alternative records to extend typhoon records other than meteorological observations.The sedimentary records and historical documents provide alternative approaches to extend typhoon records.This study attempts to reconstruct typhoon events on a 100-year scale on the inner shelf of the East China Sea through coupling of meteorological observations and sedimentary records.This reconstruction is compared with the meteorological disaster records to explore the preservation potential,path and intensity of typhoon events in the shelf mud area.In May 2018,a 2 m Core J1 was collected in the offshore area of Zhejiang Province.Typhoon events were comprehensively identified by multiple indicators(grain size distribution,D90,Zr/Fe,Sr/Al and Ca).The radioisotope 210Pb dating method was used to determine the age model of Core J1.The results show that the sedimentation rate of Core J1 is about 1.1 cm/a,and the time span is about 1836 to 2018.25typhoon events are identified in Core J1 and 10 of which match the meteorological observation period(1950-2018).The average wind speed of the 10 typhoons is close to the one of all typhoons affecting Core J1,and most of them belong to the strong typhoons of type III and IV landing on Zhejiang Province and Fujian Province.Through multivariate comprehensive analysis,it is found that the preservation potential of typhoon events in sedimentary records is close to 30%for Core J1.In addition,the typhoon events recorded in historical documents may be biased towards stronger landing typhoons,thus the number of typhoons recorded in literatures is significantly less than that actually affected.The knowledge obtained here helps to not only make better use of sedimentary records to expand the time span of typhoon records,but also guide future sampling to obtain more complete typhoon sedimentary records.