Pedogenic response to millennial summer monsoon enhancements on the Tibetan Plateau

The Asian summer monsoons experienced both rapid, episodic enhancement and long-term evolution with the uplift of Tibet. The response of pedogenesis to those events on the Tibetan Plateau at mean elevations of 4000-5000 m is of great interest and significance in deciphering the history of Asian and Tibetan summer monsoons, and in understanding soil development, deterioration and management. The over 22 m loess-paleosol sequence at Hezuo on the eastern Tibetan Plateau, extending back through the last interglaciation and the thickest late Pleistocene sequence identified thus far on the Plateau, provides a unique opportunity to tackle the above topics. Detailed chronology and soil development determined by field pedofeatures and soil proxies have revealed a millennial fluctuation of the Asian and Tibetan summer monsoons resembling the late Pleistocene North Atlantic climatic record. The end of each Heinrich event is closely followed by formation of a stronger paleosol and then some much weaker thin soil horizons-weathered loess or loess. The episodes of stronger soil development (or paleosol events) correspond without exception to strongest summer monsoon enhancement at the beginning or in the early part of each Bond cycle recorded in the North Atlantic. The strongest pedogenesis and summer monsoon enhancement is observed to occur during 43-36 ka BP, which is not observed in climatic records outside Tibet, probably indicating a coherent enhancement of Asian and Tibetan summer monsoons in the last mega-interstadial (MIS3). Increase of organic matter excluding decomposition and change of soil types from last interglacial calcic cambisols to Holocene chernozems suggests an increase of relative humidity, implying partially an increase of elevation due to late Pleistocene rapid uplift of the Tibetan Plateau. (C) 2002 Published by Elsevier Science Ltd.