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.
Bibliographical noteFunding Information:
This work was funded by the National Research Foundation of Singapore under its NRF Fellowship scheme (award no. NRF-NRFF2011-08 to X.W.), the EOS, the National Research Foundation and the Singapore Ministry of Education under the Research Centers of Excellence initiative, an NSFC grant (no. 41888101 to H.-W.C.), an NRF-NSFC joint grant (no. NRF2017NRFNSFC001-047 to X.W.), and a DPST research grant (award no. 042/2558 to S.C.).
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