Asian summer monsoon instability during the past 60,000 years: magnetic susceptibility and pedogenic evidence from the western Chinese Loess Plateau

The 28 m high-resolution Shajinping loess section in Lanzhou on the western Chinese Loess Plateau records a 60 ka, millennial summer monsoon variation . The record shows that Asian summer monsoons have rapid episodic pulse enh ancements spanning only ca. 1-2 ka in high-frequency domain and having sub- Milankovitch cycles of progressive weakening in low frequency domain in the last glaciation. Soil formation seems to occur with a surprisingly fast re sponse to these summer monsoon enhancements, resulting in weakly or moderat ely developed paleosol sequences. Both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm ( Dansgaard-Oeschger) episodes and long-term cooling (Bond) cycles of the Nor th Atlantic climatic records, indicating a possible teleconnection between tropic oceanic air masses and the North Atlantic climatic system. But diffe rences exist for the transition of MTS 2/3 and the Holocene, when extraordi narily heavy dust-input events and fairly variable climatic fluctuations oc cur for the former and latter, respectively. A westerlies-swing model is pr oposed to interpret this link. (C) 1999 Elsevier Science B.V. All rights re served.