Western Pacific Ocean influences on monsoon precipitation in the southwestern Chinese Loess Plateau since the mid-Holocene

Numerous paleoclimate records on reconstructed monsoon precipitation isotopes (delta D-p and delta O-18(p)) have been published to infer past hydroclimate changes in Asian monsoon region. However, there are still debates on whether or not these reconstructed delta D-p or delta O-18(p) can represent changes of monsoon precipitation. In this study, we report a similar to 5000 year record of leafwax hydrogen isotope (delta D-wax) from a 6.67-m-long sediment core collected in Beilianchi (BLC) Lake in the southwestern Chinese Loess Plateau. Based on analyses of the instrumental precipitation isotopes, precipitation amounts, and moisture sources, we find that delta D-p in the southwestern Chinese Loess Plateau shows distinct negative correlation with amounts of summer (from April to September) monsoon precipitation at inter-annual scales. This is further supported by the observed negative relation between precipitation amounts and regional lake-sediments and speleothems inferred delta D-p (or delta O-18(p)) values at decadal scales over the past 60 years. Therefore, our reconstructed similar to 35-year resolution monsoon precipitation, inferred from delta D-wax, reveals a long-term decrease since the mid-Holocene. Superimposed on this trend, there are several multi-centennial to millennial-scale fluctuations for increased monsoon precipitation at 4500-4000 years BP, 2900-2400 years BP and 1200-700 years BP and decreased precipitation at 3900-3000 years BP, 2200-1300 years BP, and 500-0 years BP. Reanalyses of instrumental data and Kiel Climate Model on regional atmosphere circulations show that moisture of this region is mainly derived from the western Pacific Ocean through the East Asian summer monsoon circulation at inter-annual to inter-decadal, and millennial timescales. We conclude that monsoon rainfall in the southwestern Chinese Loess Plateau is likely connected with changes in sea surface temperatures and migrations of the ITCZ in the western Pacific Ocean.