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

The importance of solar insolation on the temperature variations for the past 110 kyr on the Chinese Loess Plateau

The late Quaternary temperature history on the Chinese Loess Plateau (CLP) is little known due to the absence of suitable paleothermometers. Here, we present a quantitative temperature record for the last 110 kyr from Lantian county, southern CLP, based on the distributions of bacterial tetraethers. Lantian loess temperature variations display significant correlation with the Northern Hemisphere insolation (35 degrees N) as well as the cave monsoon records at the precession band. We attribute such correlation to both the latent heat release from the East Asian summer monsoon and the direct influence of Sun&#39;s sensible heat over the semi-arid landscape. The long term cooling during the Marine Isotope Stage (MIS) 3 and the modest temperature drop of similar to 5 degrees C from 79 to 65 ka are best explained by interactions among multiple climate ford ngs including insolation, atmospheric CO2 concentration, global ice volume, and regional glacier activities. The cold and modestly wet climate during MIS 3 may have promoted maximum regional glacial advances, whereas the minimal temperature during local LGM reduced moisture transfer and led to glacial recession. The unusually early deglacial warming at similar to 22.5 ka highlights the importance of regional climate records to decipher the complex continental climate dynamics.</p

Late Miocene episodic lakes in the arid Tarim Basin, western China

The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (delta O-18) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (delta B-11) and delta O-18 records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at similar to 4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.</p