Asian Summer Monsoon Changes Inferred From a Stalagmite delta O-18 Record in Central China During the Last Glacial Period

The reconstruction of Asian summer monsoon (ASM) changes during the last glacial period is of great significance for better understanding monsoon dynamics. The phase relationship between the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) subsystems on different timescales is still unclear. The comparative analysis of speleothem records in the ISM region, EASM region, and central China helps to clarify the relationship between the ISM and EASM. Based on the well-dated isotope records of stalagmite DDH-B15 from the Didonghe (DDH) Cave in Hanzhong, Shaanxi, we reconstructed ASM changes during the past 34-13 thousand years before the present (kyr BP). The small average error (61 years) of 18 uranium-series ages enables a precise comparison of the stalagmite delta O-18 record with other well-dated records from the orbital to the millennial timescales. The delta O-18 signal of the DDH-B15 stalagmite is controlled by changes of the low latitude northern hemisphere summer insolation (NHSI) on the orbital timescale. It records cold Heinrich Stadial (HS) and Dansgaard-Oeschger (DO) cycles which are originated from the northern high latitude on the millennial time scale. The delta O-18 changes of stalagmites from the three regions are similar on the millennial and centennial timescales. But on the orbital-suborbital timescale, stalagmite delta O-18 changes during the last glacial cycle have different characteristics. The stalagmite delta O-18 values in eastern China became gradually negative, and the stalagmite delta O-18 values in the Indian monsoon domain showed a increasing trend, but the stalagmite delta O-18 values in Central China adopted an intermediate state between the EASM and ISM. Then we argued that the delta O-18 value of stalagmites in Central China is a mixed signal of the ISM and EASM, which indicates a change of the water vapor source as an important influence on the Chinese stalagmite delta O-18 record.