East Asian monsoon evolution during the Eemian, as recorded in the western Chinese Loess Plateau

摘要

We present a high resolution environmental magnetic record of the East Asian summer monsoon spanning paleosol S1, corresponding to Marine Oxygen Isotope (MIS) 5, from the Jiuzhoutai (JZT) loess section in Lanzhou, on the northwestern edge of the Chinese Loess Plateau. We use a chronology based on a sediment grain-size age model frequently used for Chinese loess. The Eemian is dated to 127.37 - 121.31 ka BP and can be divided into three sub-stages based on variations in summer monsoon intensity: early Eemian (127.37 - 125.67 ka BP) with an intermediate summer monsoon intensity; mid Eemian (125.67 - 124.24 ka BP) with weakest summer monsoon intensity, and late Eemian (124.24 - 121.31 ka BP) with the strongest summer monsoon intensity. Contrasting, the winter monsoon weakened at the beginning of MIS5e, reached its weakest intensity during the late Eemian (similar to 121 ka BP), and then commenced an irreversible strengthening trend. Furthermore, the Eemian exhibits a similar climatic trend to the Holocene optimum, since both are divided into two parts by an intervening arid interval and the most humid period occurs in the secondary pedogenic stage. Therefore we suggest that the climate evolution during Eemian and later may provide useful information about climate forecast in the future. (C) 2015 Elsevier Ltd and INQUA.