Variations in regional hydrological environment and human activities inferred from δ18O and δ2H of stalagmite fluid inclusions in southwest China

The interpretation of δ¹⁸Oc and δ¹³Cc values of stalagmites within China is still complex, although numerous cave archives have been reported in this region. Present challenges include distinguishing between natural and anthropogenic influences on regional hydrological and environmental changes, in particular due to the increasing human activities during the mid-to late Holocene. Here, we report for the first time the δ¹⁸O_fi and δ²H_fi records of fluids entombed as inclusions during the Holocene (6290 to 690 yr BP) from a stalagmite from southwest China. We excluded measurement-induced artefacts using Rayleigh fractionation models and improved measurement methods, producing reliable results. We observed very high δ¹⁸O_fi and δ²H_fi values during a weak Asian summer monsoon (ASM). Our record reveals six drought events during the mid- and late-Holocene (~950, 1360, 2260, 3450, and 5600 yr BP), which coincide with the weakening of ASM intensity and variations in low latitude forcing, such as tropical sea surface temperature, El Niño/Southern Oscillation, and intertropical convergence zone. In 950-1100 A.D., the dramatic enrichment of δ¹⁸O_fi (magnitude ~7‰) corresponds with the increase in regional population density due to large-scale population migration at this time (historically known as the Jingkang event). The overall coefficient of variation (C.V = standard deviation/mean) of the δ¹⁸O_fi sequence is 125% compared to only 5% for δ¹⁸Oc. Hence, δ¹⁸O_fi seems to exhibit a greater sensitivity to regional environment wet/dry variations than traditional carbonate isotope proxies.