Stepwise expansions of C-4 biomass and enhanced seasonal precipitation and regional aridity during the Quaternary on the southern Chinese Loess Plateau

The expansion of C-4 plants is one of the most prominent vegetation changes in the global ecosystem during the Cenozoic Era. Although C-4 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 delta C-13 values indicate stepwise C-4 plant expansions initiated at similar to 1.6 and at similar to 0.43 Ma, respectively. We conclude that such tectonic time scale C-4 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 C-4 plants, while the latter appears phase-locked with cyclical changes of summer monsoon circulations.</p

Effect of aridification on carbon isotopic variation and ecologic evolution at 5.3 Ma in the Asian interior

The Cenozoic era is marked by dramatic climatic and ecological changes. The timing of the emergence and the subsequent expansions of C-4 grasses are prominent biological events on Earth. In China, thick Cenozoic deposits in the Tarim and Junggar Basins, which are located in the Asian interior, provide important geological archives for studying paleoenvironmental changes. Here we use carbon isotope compositions of organic matter to reconstruct the history of ecologic evolution during the late Cenozoic in the Tarim and Junggar Basins. The results show that there is a shift to slightly higher delta C-13 values at 5.3 Ma indicating a change in terrestrial ecosystems in the Asian interior driven by an increased regional aridity rather than decreasing atmospheric pCO(2) levels. The weakened water vapor transportation related to the retreat of Paratethys Ocean and the enhanced rain shadow effect of mountain uplift during the latest Miocene mostly triggered this event.</p