Multiple expansions of [C.sub.4] plant biomass in East Asia since 7 Ma coupled with strengthened monsoon circulation

The expansion of plants using the [C.sub.4] photosynthetic pathway is one of the most prominent changes in the global ecosystem during the Cenozoic Era. A significant late Miocene expansion is well documented. However, the existence and cause of subsequent expansions are still not clear, owing in part to the lack of long, continuous climate-vegetation records. Here we present two high-resolution carbon isotope time series, covering the past 7 m.y., derived from eolian deposits on the Chinese Loess Plateau. The data indicate three intervals of significant [C.sub.4] plant expansions within the semiarid monsoonal region of East Asia (ca. 2.9-2.7 Ma, 1.3-0.9 Ma, and 0.6 Ma-present). These expansions covary with strengthened East Asian summer monsoon circulation. We conclude that in East Asia, large-scale late Miocene [C.sub.4]/[C.sub.3] vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation. Keywords: [C.sub.4] plant expansion, carbon isotope, summer monsoon, Chinese Loess Plateau, Miocene.