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

Considerable advances have been made in use of tree-ring δ¹⁸O for climate reconstructions in Southeast China, the East Asian summer monsoon region. However, the relationships among tree-ring cellulose δ¹⁸O (δ¹⁸O_cell), local hydroclimate, precipitation δ¹⁸O (δ¹⁸O_pre) and El Niño–Southern Oscillation (ENSO) have not yet been fully resolved. The usual interpretation has been that local hydroclimate influences δ¹⁸O_cell through both the “amount effect” on δ¹⁸O_pre and evaporative enrichment, but it cannot fully explain the high inter-site correlation of δ¹⁸O_cell chronologies or their response pattern to ENSO. In this study, we use a newly-developed δ¹⁸O_cell chronology of Pinus massoniana from a water-stressed site in Zhejiang province, in combination with another three δ¹⁸O_cell chronologies in Southeast China, to investigate their climatic implications from a regional perspective. The results show that besides local hydroclimate, δ¹⁸O_pre is also significantly correlated with δ¹⁸O_cell, but with different effects. Spatially homogeneous δ¹⁸O_pre variation causes high spatial correlations among δ¹⁸O_cell from different sites. Analyses show that ENSO variations are responsible for the large-scale common signals in δ¹⁸O_cell by modulating δ¹⁸O_pre. Therefore, combining δ¹⁸O_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 δ¹⁸O_cell can increase the explained variance of observed values. These findings provide a guide for future optimized ENSO and local paleoclimate reconstructions using δ¹⁸O_cell.