Synchronous decadal changes between Asian monsoon and Greenland climates during the last glacial maximum

An annually laminated stalagmite from Hulu Cave in Southern China grew for about 3000 years starting at 21345 aBP (±85 a) as determined by lamina counting and U-Th dating. The stalagmite δ 18O time series provides a continuous history of the Asian monsoon precipitation and δ 13C may reflect the soil biogenic production, which is linked to climatic factors such as temperature and humidity. The annual layer thickness (LT) from this stalagmite can not be regarded as a direct indicator of precipitation. LT and gray level (GL) may indicate the changes in the relative humidity of the cave environment. The δ 18O record with average 3.7-year resolution precisely anchored the timing of IS2 event which was well expressed in the Greenland ice core δ 18O records. The timing of IS2 in GISP2 is close to the chronology of the stalagmite records within the uncertainty of U/Th dates. Our record, in combination with the previously-published record between 17 and 15 kaBP also from Hulu Cave, indicated that the monsoon events (H1 and H2), in terms of their structure, are quite different from the cold events in North Atlantic, which were well presented in the Greenland ice core δ 18O records. For both of the H1 and H2, the monsoon precipitation records show a rapid transition from dry to wet conditions, followed by a stepwise increasing trend, with a total duration of more than 600 years. In contrast, the Greenland δ 18O records display abrupt changes either into or out of the events. The H98 δ 18O record shows a teleconnection between the density of East Asia monsoon and polar temperature on centennial to multi-decade scales during the LGM. However, the different structure of climatic events between the low and high latitude areas also suggests that changes of East Asian monsoon were triggered not only by the North Atlantic themorhaline circulation but also by some other factors. The coupled oceanic- atmospheric circulation from tropical Pacific may be a possible forcing, it may through ENSO-PDO influences the Asian monsoon rainfall on decadal scale during the LGM.