The severe drought event of 2009–2010 over southwest China as recorded by a cave stalagmite from southeast Yunnan: Implication for stalagmite δ18O interpretation in the Asian monsoon region

It is still debated whether the stalagmite δ18O in the East Asian monsoon region indicates the intensity of the summer monsoon or the precipitation of the summer monsoon season on an annual scale. One key reason for this debate is the lack of accurate comparison between stalagmite δ18O and instrumental records. To better decipher the stalagmite δ18O in the Asian monsoon region on an annual scale, stalagmite PL1 from Pailong Cave, southeast of Yunnan, was selected. The calcite deposited from 2004 to 2019 within stalagmite PL1 was determined by laminar counting, 210Pb dating and seasonal variations in δ13C values. Seasonal scale δ18O, δ13C and Mg/Ca ratios were found to record the severe drought over Southwest China that occurred in 2009–2010. In 2009, when the severe drought was the most intense, the stalagmite δ18O, δ13C, and Mg/Ca ratios changed significantly, reflecting the hydrological response caused by climate change (decrease in precipitation). However, distinct from the δ13C and Mg/Ca ratios, the highest δ18O value was found in 2010, which reflects the influence of the evaporation in the soil and epikarst. On the annual scale, the stalagmites/precipitation δ18O in both Yunnan and eastern China are dominated by El Niño-Southern Oscillation (ENSO) activity. During the El Niño/La Niña phase, reduced/enhanced convective activities but strong/weak water vapor flux transportation occurred in the Bay of Bengal and the South China Sea, and weaker/stronger water vapor flux transportation in the Arabian Sea induced enriched/depleted precipitation δ18O and hence stalagmite δ18O in Yunnan and eastern China. On the interannual scale, the stalagmite δ18O of Yunnan is mainly affected by the strength of the South Asian summer monsoon and water vapor flux transportation from the Arabian Sea. The stronger (weaker) South Asian summer monsoon intensity will induce more (less) water vapor flux transported from the Arabian Sea and depleted (enriched) stalagmite δ18O in Yunnan. Distinct from stalagmite δ18O in Yunnan, the precipitation/stalagmite δ18O in eastern China is significantly correlated with ENSO indices on the interannual scale. Precipitation/stalagmite δ18O in eastern China is dominated by convective activities in the source area (Bay of Bengal-South China Sea).