HIGH-RESOLUTION STABLE ISOTOPE RECORD OF ATMOSPHERIC PRECIPITATION IN GUILIN

This study investigated the factors controlling the δ18O composition of the precipitation in Guilin.Daily precipitation samples for stable isotope analysis were collected in Guilin during 2010.The stable isotope(δD and δ18O) in precipitation displayed obvious spatial and temporal variation,and thus could be used for providing:(1)the best natural tracer for studying the hydrological cycle;(2)the ambient temperature and amount at time of precipitation;(3)the ground surface elevation;(4)the distance between precipitation event and its water vapor source region in the ocean;(5)water vapor source migration pathway.Empirical relations between isotope of precipitation and climate were used in numerous studied aimed to reconstructing past climate from various environmental archives.δD and δ18O in atmospheric precipitation were tested and analyzed,and the results showed:the values of δD distribution ranged from 29.05‰ to 96.27‰;δ18O values distribution ranged from-0.2‰ to-12.96‰.The tested result of stable isotope showed significantly seasonal variability.The research results indicated that there was a significant relationship between δ18O values and the types of monsoon winds.δ18O values of the researched area were mainly affected by summer monsoon of east and southeast area in summer.During the transportation of atmospheric precipitation,the δD and δ18O in vapor caused by intense precipitation became more negative.Thus,δD and δ18O values of precipitation in summer were more negative excursion than that in winter.The Local Meteoric Water Line:δD=8.87δ18O+15.49 was established by using the relationship between δD and δ18O.This result reflected climate character of Guilin:the warm and rainy.In addition,Deuterium Excess(d=δD-8δ18O)presented different characters during summer and winter.At the same time,the equation showed that in the researched area,the vapor source of atmospheric precipitation were mainly from ocean of low latitude in summer,while in winter the vapor source of atmospheric precipitation were mainly from the evaparation of inland and part areas and the transportation of winter monsoon(westerlies).In 2010,the δ18O value of atmospheric precipitation in September was more negative than that in June.This result indicated summer monsoon was extremely strong in September.But the total precipitation in September was far less than that in June.The reason might be that summer wind was strong and caused atmospheric precipitation zone reached to monsoon marginal zone.All of this contributed to the relatively decrease of atmospheric precipitation in the researched area.This study provides significant information to understand present-day seasonality of precipitation and its isotopic composition in Guilin,and strong scientific basis for constructing environment temperature with the use of stalagmites and dripping water.