Innovation and Development

Ecological Shift and the Enhanced Aridification in the Asian Interior

There have been many different opinions about the causes, timing and mechanisms of C4 plants expansion in the world. Prof. Sun Jimin with his colleagues, from the Cenozoic Geology and Environment Division, Institute of Geology and Geophysics, CAS, studied the organic carbon isotopes of the Cenozoic deposits in the Junggar and Tarim Basins in the northwest China. The new results obatained indicate that: (1) there is a shift to higher delta 13C values at 5.3 Ma indicating a change in terrestrial ecosystems in the Asian interior since the end of the Miocene; (2) such changes can be attributed to the expansion of C4 grasses, the changes in C3 species as a response to regional aridity or both of them; (3) the ecological shift at 5.3 Ma was driven by regional aridity rather than the previous views of either decreasing atmospheric pCO2 levels or enhanced Asian summer monsoon circulation. Although enhanced regional aridity is regarded as the main factor of the ecological shift, the primary forcing mechanism is associated with the weakened water vapor transportation related to the retreat of Paratethys Ocean controlled by both the global eustatic sea level decrease and the northward tectonic convergence of India, Arabia, and African plates with Eurasia. In this sense, the ecological shift and aridification initiated 5.3 million years ago in the Junggar and Tarim basins were ultimately forced by tectonics and global cooling. This relevant result published in a geoscience journal of Earth and Planetary Science Letters（Sun et al. Effect of aridification on carbon isotopic variation and ecologic evolution at 5.3 Ma in the Asian interior. Earth and Planetary Science Letters, 2013, 380: 1–11）.