Pollen evidence from Baode of the northern Loess Plateau of China and strong East Asian summer monsoons during the Early Pliocene

The red clay eolian sequence on the Chinese Loess Plateau (CLP) is an important archive for paleoclimate change from the late Miocene to Pliocene, and can provide significant information for the controversial problems of East Asian monsoon evolution and its forcing mechanism. In this study, we present a pollen record from Baode, northern CLP. The record shows four stages of paleoecological evolution. From 5.6-4.4 Ma, a forest steppe ecosystem developed under an extremely warm period with high seasonal precipitation. Since 4.4 Ma, a drier episode occurred, which prompted parkland landscapes to develop. During 3.5-3.05 Ma, the environment changed to a rather open steppe ecosystem with a much cooler and drier climate. After 3.05 Ma, the vegetation evolved to forest steppe. Using the percentages of arboreal plants to mirror precipitation, and comparing with other published pollen data from the CLP, we find the existence of S-N directionality of the precipitation change and high percentage of arboreal plants in the entire CLP during the Early Pliocene, which suggest the CLP was characterized by a strong East Asian summer monsoon. The strong summer monsoon corresponds well to the low global ice volume, which may illuminate global climate mechanism for the summer monsoon evolution in the early Pliocene.