Fig. 4. Spatial-temporal comparison of speleothem δ¹⁸O records from mainland Southeast Asia over the past 40 ka.

The records obtained from the CBoB and Mawmluh (21, 26) (site 1), CM (site 2), and SEY (site 3) caves are shown in red, pink, and purple, respectively. Note that the δ¹⁸O in those records from locations other than CBoB has been corrected for temperature effect during calcite precipitation (see details in Materials and Methods). We further smoothed each record using 1000-year averages (thick lines). The shaded envelopes indicate the range of 1σ uncertainty of the δ¹⁸O values. The comparison shows a broad ¹⁸O-depletion trend from coastal sites to inland, associated with the progressive rainout effect on water isotopes. In addition, the isotopic gradient was larger during the LGM compared with today.