The history and variability of the East Asian paleomonsoon climate

Changes in the East Asian paleomonsoon reflect interactions between the glo bal atmosphere, ocean, land and ice systems, and are also an expression of their combined effect within the boundary conditions imposed by the East As ian continent and solar radiation. The history of the East Asian monsoon is an alternation between dominance by the dry-cold winter and warm-humid sum mer monsoons. High-resolution eolian sequences preserved in the Chinese Loe ss Plateau reveal that the East Asian monsoon may have commenced at least 7 .2 Ma ago. They also provide evidence indicating that the pulsed uplift of the Tibetan Plateau at about 3.4 and 7.2 Ma may have played an important ro le in inducing climate change. The palaeoclimatic records of the last glaci al cycle show high-frequency variability on time scales of 1000-year or eve n shorter, and instability of the East Asian paleomonsoon system. The high- frequency variability could be due to a non-linear response to orbital forc ing, or a result of the coupling processes between different components of the global system. Cold air activity in northern high latitudes, the trans- equatorial air streams from the Southern Hemisphere and, possibly, ENSO may have played an important role in East Asian monsoon variability. The synch roneity of all the palaeoclimatic events along the polar-equator-polar (PEP ) transect is still an open question. Correlation of limited palaeoclimatic records for the last 30 kyr obtained from East Asia and Australia suggests that the trans-equatorial air streams driven by the monsoon and trade wind s may have had an influence on opposite hemispheres. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.