Seven million years of wind and precipitation variability on the Chinese Loess Plateau

Recent studies of the eolian deposits in northern China have extended the East Asian monsoon history back to the early Miocene. However, the relative intensities of monsoonal winds and precipitation and the extent of their coupling prior to the Pleistocene epoch remain poorly constrained, mainly due to uncertainties in the interpretation of proxy indices generated from the Mio-Pliocene Red Clay sequences. Here we reconstruct East Asian monsoon oscillations over the past 7 Ma using magnetic susceptibility and carbonate content as summer monsoon (precipitation) proxies, and quartz grain size as a winter monsoon (wind intensity) index. Our results suggest that precipitation and wind intensity exhibited significant orbital-scale variations prior to 4.2 Ma, followed by slightly damped variability between 4.2 and 2.75 Ma. Subsequently, East Asian monsoon circulation experienced two large shifts at about 2.75 and 1.25 Ma, characterized by stepwise strengthening of glacial wind and interglacial precipitation. A remarkable change in East Asian monsoon seasonality occurred around 3.15-2.75 Ma. Prior to 3.15 Ma, strong winds were positively correlated with high effective precipitation, whereas after 2.75 Ma strong winds were negatively correlated with heavy precipitation. This shift was probably induced by a change from an insolation-forced system to one strongly influenced by the combined effects of the phased uplift of the Himalaya Tibetan Plateau and the simultaneous development of the Northern Hemisphere ice sheets. (C) 2010 Elsevier B.V. All rights reserved.