Summer Monsoon Rainfall Variability in Central China over the Past 4700 Years and Its Possible Link to Solar Activity

Based on 467 pairs ofδ^(18)O andδ^(13)C records and 8230 Th dates from a stalagmite(BF4)from Xiniu Cave,central China,we present a reconstruction of 9-yr resolution monsoon rainfall record for the past 4700 years.Ourδ^(18)O record shows good coherence with East Asian summer monsoon(EASM)rainfall proxies from adjacent regions during the overlapping intervals,suggesting thatδ^(18)O signal in BF4 can be interpreted as a monsoon rainfall proxy.Theδ^(13) C variations are related to changes in local processes at the cave site,and regional rainfall and temperature changes.Based on theδ18 O record,a series of dry periods can be identified at 4500-4200,3500-3200,2800-2500,1900-1600,1400-1200,700-500,and 400-200 yr BP,while a series of wet periods can be identified at 4200-3600,2400-2200,3200-2800,1100-900,600-400,and 200-100 yr BP.Power spectrum analysis on ourδ^(18) O record reveals significant cycles at 470 and 80 yr,coinciding with the typical solar periodic variations.This result suggests that changes in solar activity play a dominant role in driving centennial-decadal monsoon rainfall variation in central China.Due to minor changes in solar irradiance(less than 1.5 W m^(-2))over the past 4700 years,our record was further compared to the El Nino-Southern Oscillation(ENSO)and Pacific Decadal Oscillation(PDO)proxies,confirming that solar forcing on monsoon rainfall changes might be amplified by the ENSO and PDO variations.From 600 to 150 yr BP(the Little Ice Age,LIA),a positive shift of 2‰can be revealed in both theδ^(18)O andδ^(13)C records,indicating a cold/dry climatic pattern.By comparing ourδ^(18)O andδ^(13)C records with historical documents,we suggest that the climatic deteriorations between 450 and 250 yr BP may have caused serious social unrest at the end of the Ming Dynasty.