Fig. 2: Plots of δ18O versus Δ′17O for water and carbonate samples.

Group I is meteoric water in the Asian monsoon region and parent water of speleothem carbonates. Group II is speleothem carbonates. As expected, the calculated δ18O-Δ′17O values of the parent water of speleothems (Group I) are similar to the meteoric water9, 17, 37. All data are in VSMOW-SLAP, and the Δ′17O values of speleothem samples are normalized to Wostbrock et al.61. The error is based on the standard deviation (1σ SD) for each sample.