Stepwise expansions of C4 biomass and enhanced seasonal precipitation and regional aridity during the Quaternary on the southern Chinese Loess Plateau

The expansion of C4 plants is one of the most prominent vegetation changes in the global ecosystem during the Cenozoic Era. Although C4 plant expansions in the latest Miocene have been widely reported, factors driving the expansions are still in debate, and the details of vegetation changes during the Quaternary have not been well studied. Here we present high-resolution carbon isotope time series of both organic matter and bulk carbonates, covering the past 2.58 Ma, derived from the loess–soil successions on the southern Chinese Loess Plateau. The organic matter δ13C values indicate stepwise C4 plant expansions initiated at ∼1.6 and at ∼0.43 Ma, respectively. We conclude that such tectonic time scale C4 plant expansions are controlled by enhanced seasonality of precipitation (relatively more precipitation in the warm growing season) as well as regional aridity, and this long-term fluctuation superimposes on the orbital scale variations of C4 plants, while the latter appears phase-locked with cyclical changes of summer monsoon circulations.

► Constructing high-resolution δ13C record covering the past 2.6 Ma.
► Stepwise C4 plant expansions initiated at 1.6 and 0.43 Ma.
► Enhanced seasonal precipitation and regional aridity driving these events.