Early-Holocene monsoon instability and climatic optimum recorded by Chinese stalagmites

The timing and duration of the Holocene East Asian summer monsoon (EASM) maximum and the interpretation of Chinese stalagmite delta O-18 records have long been disputed. Notably, interpretations of Holocene EASM variations are frequently based on a single record or study area and are often contradictory. In this study, we conducted stable isotope analyses of four Holocene stalagmites from Chongqing, southwest China. The results reveal differences in the timing of the Holocene EASM maximum and to try to resolve the inconsistency we analyzed and statistically integrated a total of 16 Holocene stalagmite records from 14 caves in the EASM region. The resulting synthesized Holocene stalagmite delta O-18 (delta O-18(syn)) record is in agreement with other EASM records and confirms that stalagmite delta O-18 records are a valid indicator of EASM intensity, rather of local precipitation amount. The delta O-18(syn) record shows that the EASM intensified rapidly from the onset of the early Holocene; notably, however, there were distinct EASM oscillations in the early Holocene, consisting of three abrupt millennial-scale events. This indicates that, contrary to several previous interpretations, the early Holocene EASM was unstable. Subsequently, during 8-6 kyr BP, the EASM was relatively stable and strong, with the strongest monsoon occurring during 8-7 kyr BP. This evidence of a stable and strong mid-Holocene EASM in eastern China is in accord with the classical view of a mid-Holocene Optimum in China.