Typhoon Rainfall Impact On Drip Water?¹⁸O In Xianyun Cave,West Of Fujian

The southeast coastal area of China is one of the areas with the most landfall and the most serious disasters in the world.Typhoon is the strongest rain making system in nature.Several torrential rains in China's history are basically caused by typhoon.Therefore,more and more attention has been paid to the study of typhoon rainstorm and its impact.Due to the complex relationship between the earth's various systems,which limits the understanding of the frequency and intensity of typhoon,there is still great uncertainty in the prediction of typhoon.Therefore,it is very important to identify and quantify the typhoon events in the geological carrier,to verify the basic process of typhoon occurrence and to obtain a longer time range of typhoon records.Precisely dated high-resolution speleothems may record past typhoon events,however,the state of the artcave monitoring is a prerequisite to identify suitable stalagmites for the reconstruction of such events.With this motivation,from December 2018 to December 2019,we examined the isotopic composition(?¹⁸O and?²H)of rainfall,river water,cave drip water and meteorological factors at monthly to bi-monthly scale in the Xianyun cave system,located in southeastern Fujian to explore the transmission mechanism of typhoon signals in the cave system.In the one year,a typhoon event was included(Typhoon Bailu,Typhoon 11,2019,August 24,2019 to August 26,2019).At monthly scale,the?¹⁸O of rainfall samples over the cave ranged from-9.7‰to-1.9‰and the?¹⁸O of outside river samples ranged from-8.2‰to-6.3‰while the?¹⁸O of Typhoon Bailu rainfall ranged from-19.6‰to-6.3‰and the the?¹⁸O of outside river samples ranged from-10.4‰to-7.7‰during Typhoon Typhoon Bailu-induced rainfall showed distinctly negative?¹⁸O values as compared to those of the monthly and bi-monthly rainfall,exhibiting a three-stage inverted U-shaped variation characteristic.At monthly scale,four drip water monitoring sites and underground river inside the cave revealed low variations during the studied period with average values of-7.8‰,-8.0‰,-8.0‰,-8.1‰and-8.0‰.However,during the typhoon,the drip water?¹⁸O values exhibited similar characteristic as outside rainfall but with just0.2‰negative deviation owing to precipitation amount and drip water source reservoir.The integration of rainfall amount with drip water source reservoir determines the degree to which a typhoon isotopic signature gets diluted during epikarst infiltration.Our results imply that the?¹⁸O of drip water in Xianyun cave can instantaneously respond to typhoon rainfall,but the 0.2‰shift in drip water?¹⁸O is difficult to be recorded by speleothems.This study provides the first instrumental evidence of typhoon signal in karst system in southeastern China We suggest multi-year monitoring to ascertain fully if the stalagmites could be used as paleotyhoon proxy.