Upstream rainout processes govern tree-ring oxygen isotopes with implications for monsoon and tropical hydroclimate reconstruction

Abstract

Abstract The interpretation of oxygen isotope ratios (δ18O) in proxy records over the Asian monsoon region remains a significant debate, particularly regarding the importance of the local "amount effect" versus upstream rainout processes. Here, we present a precisely dated annual-resolution network of tree-ring oxygen isotopes (δ18Otr) encompassing various tree species and local climates. We demonstrate that δ18Otr is a reliable proxy for δ18O in precipitation (δ18Opr) and that upstream rainout processes, rather than the local amount effect, predominantly govern the δ18Otr variations. The El Niño-Southern Oscillation and the associated Walker Circulation play a crucial role in modulating upstream atmospheric convective activity, which in turn influences δ18Otr. By elucidating the spatial coherence between climate observations and δ18Opr proxies, our research marks a pivotal advancement in δ18Otr network development, which is set to advance the interpretation of monsoon dynamics and the reconstruction of tropical hydroclimates.