Global abnormal precipitation 18O depletion during late/post monsoon season

Previous studies found depletion of precipitation 18O (18Op) during the late or post Asian monsoon season when precipitation amount is much lower. This is inconsistent with the amount effect of precipitation isotopes commonly found in tropical regions. It is still unclear whether this late/post season abnormal 18Op depletion also occurs in other monsoon regions, and what are the possible underlying mechanisms. In this paper, we examined seasonal variations of observed and modeled isotopic composition in precipitation (δ18Op) across the global monsoon regions, and their relationship with atmospheric circulations. We found that this abnormal 18Op depletion occurs in all monsoon regions globally, and it is largely caused by strong rainout along the global trade wind moisture transport pathway. The finding suggests that tropical cyclones are not the only mechanism to deplete 18Op during the late or post monsoon seasons, as suggested by previous studies. We should interpret such low δ18O values in the high-resolution paleoclimate records with more caution.