Tree-ring δ18O from Southeast China reveals monsoon precipitation and ENSO variability

Considerable advances have been made in use of tree-ring delta O-18 for climate reconstructions in Southeast China, the East Asian summer monsoon region. However, the relationships among tree-ring cellulose delta O-18 (delta O-18(cell)), local hydroclimate, precipitation delta O-18 (delta O-18(pre)) and El Nino-Southern Oscillation (ENSO) have not yet been fully resolved. The usual interpretation has been that local hydroclimate influences delta O-18(cell) through both the amount effect on delta O-18(pre) and evaporative enrichment, but it cannot fully explain the high inter-site correlation of delta O-18(cell) chronologies or their response pattern to ENSO. In this study, we use a newly-developed delta O-18(cell) chronology of Pinus massoniana from a water-stressed site in Zhejiang province, in combination with another three delta O-18(cell) chronologies in Southeast China, to investigate their climatic implications from a regional perspective. The results show that besides local hydroclimate, delta O-18(pre) is also significantly correlated with delta O-18(cell) but with different effects. Spatially homogeneous delta O-18(pre) variation causes high spatial correlations among delta(18)O(cell )from different sites. Analyses show that ENSO variations are responsible for the large-scale common signals in delta O-18(cell) by modulating delta O-18(pre). Therefore, combining delta O-18(cell) chronologies from different locations can enhance ENSO signals, which provides us new opportunities to reconstruct paleo-ENSO activities. Furthermore, eliminating the part of ENSO signal that is not related to the growing season hydroclimate from delta O-18(cell) can increase the explained variance of observed values. These findings provide a guide for future optimized ENSO and local paleoclimate reconstructions using delta O-18(cell).