Jet-induced rainfall seasonality and C4 migration over East Asia

Abstract

Abstract The Neogene expansion of C 4 grasslands transformed terrestrial ecosystems with marked influence on mammalian evolution, including hominins. However, the asynchronous C 4 expansion on different continents makes it difficult to identify the environmental drivers, especially for higher latitudes. Here we show that rainfall seasonality governed extratropical Plio-Pleistocene C 4 distributions in East Asia. Rainfall oxygen isotope ratios and clumped isotope soil temperatures exhibit coupled variations on the Chinese Loess Plateau (CLP) from 7 to 2.5 million years ago, indicating more spring rain during warmer times when the subtropical westerly jet was further poleward, and more concentrated summer rain under cooler climates. We attribute these changes to meridional shifts of a summer rain band on orbital and longer timescales. The most C 4 -rich ecosystems, as identified by organic carbon δ 13 C records, tracked this summer rain band, eventually eclipsing the southern CLP margin during the late Pleistocene cooling. Our model refines the East Asian paleomonsoon concept and explains the equatorward migration of extratropical C 4 ecosystems, highlighting the tight coupling between regional rainfall seasonality and vegetation.