Where were the monsoon regions and arid zones in Asiaprior to the Tibetan Plateau uplift?

Te impact of the Tibetan Plateau uplif on the Asian monsoons and inland arid climates is an important but also controversial question in studies of paleoenvironmental change during the Cenozoic. In order to achieve a good understanding of the background for the formation of the Asian monsoons and arid environments, it is necessary to know the characteristics of the distribution of monsoon regions and arid zones in Asia before the plateau uplif. In this study, we discuss in detail the paterns of distribution of the Asian monsoon and arid regions before the plateau uplif on the basis of modeling results without topography from a global coupled atmosphere–ocean general circulation model, compare our results with previous simulation studies and available biogeological data, and review the uncertainties in the current knowledge. Based on what we know at the moment, tropical monsoon climates existed south of 20◦N in South and Southeast Asia before the plateau uplif, while the East Asian monsoon was entirely absent in the extratropics. Tese tropical monsoons mainly resulted from the seasonal shifs of the Inter-Tropical Convergence Zone. Tere may have been a quasi-monsoon region in central-southern Siberia. Most of the arid regions in the Asian continent were limited to the latitudes of 20–40◦N, corresponding to the range of the subtropical high pressure year-around. In the meantime, the present-day arid regions located in the relatively high latitudes in Central Asia were most likely absent before the plateau uplif. Te main results from the above modeling analyses are qualitatively consistent with the available biogeological data. Tese results highlight the importance of the uplif of the Tibetan Plateau in the Cenozoic evolution of the Asian climate patern of dry–wet conditions. Future studies should be focused on effects of the changes in land–sea distribution and atmospheric CO2 concentrations before and afer the plateau uplif, and also on cross-comparisons between numerical simulations and geological evidence, so that a comprehensive understanding of the evolution of the Cenozoic paleoenvironments in Asia can be achieved