While Asian monsoon (AM) changes have been clearly captured in Chinese speleothem oxygen isotope (δ18O) records, the lack of glacial-interglacial variability in the records remains puzzling. Here, we report speleothem δ18O records from three locations along the trajectory of the Indian summer monsoon (ISM), a major branch of the AM, and characterize AM rainfall over the past 180,000 years. We have found that the records close to the monsoon moisture source show large glacial-interglacial variability, which then decreases landward. These changes likely reflect a stronger oxygen isotope fractionation associated with progressive rainout of AM moisture during glacial periods, possibly due to a larger temperature gradient and suppressed plant transpiration. We term this effect, which counteracts the forcing of glacial boundary conditions, the moisture transport pathway effect.

Water stable isotopes (δ 18 O and δ 2 H) are considered as natural tracers of hydrological cycles because water isotopes fractionate (through equilibrium and kinetic fractionations) during phases change and diffusive processes. Precipitation δ 18 O and δ 2 H have been related to local environmental or climatic conditions at sampling sites, for example, a positive correlation between precipitation isotope values and temperature at midlatitudes to high latitudes (temperature effect), and an anticorrelation between precipitation amount and isotope values in subtropical and tropical regions (amount effect). These isotope-climate relationships have been applied to interpret paleoclimate records, such as ice cores and speleothems, and help us to understand past climate change (e.g.,

No abstract

No abstract