Reinterpreting precipitation isotope records from Asian monsoon region through the hidden role of atmospheric updraft.

Speleothem oxygen isotope records (δ18Os) from the Asian monsoon region provide valuable insights into past hydroclimate variability, yet their interpretation relies on understanding the controls on modern precipitation isotopes (δ18Op). Although numerous explanations for the spatiotemporal variability of δ18Op across this region have been proposed, the primary controls remain unresolved. Here we propose a hypothesis to explain δ18Op variability from δ18Op records at 46 sites along a transect spanning the Asian monsoon region. Our results show that seasonally low δ18Op values migrate gradually westward along the east-west transect. We further demonstrate that the corresponding westward migration of atmospheric updraft, particularly convection, controls δ18Op variations along the transect. In contrast to previous interpretations emphasizing monsoon moisture advection, our findings highlight atmospheric updraft as an important control on δ18Op variations across the Asian monsoon region. These findings provide an alternative perspective on interpreting the climate signals preserved in Asian δ18Os records.