What controlled Mid–Late Miocene long-term aridification in Central Asia? — Global cooling or Tibetan Plateau uplift: A review

Debate continues over whether global cooling or uplift of the Tibetan Plateau provided the first-order driver for the aridification (moisture levels) of Central Asia throughout the Mid–Late Miocene, between about 17 and 5 Ma. This review attempts to throw new light on the relations between the aridification and these two key factors. This paper examines the evolution of Miocene climate (both moisture and temperature) within five separate regions of Eurasia to help understand the large scale controls of long-term moisture in Central Asia. The five regions include: (1) Europe, (2) high-latitude Asia, (3) the East Asian Monsoon region, (4) the South Asian Monsoon region, and (5) Central Asia itself, because moisture reaching Central Asia has to firstly cross at least one of the other four regions. Temperature proxy data compiled from these five regions correlate with ocean temperatures from the global deep-sea oxygen isotope records. Furthermore, compiled moisture proxy data from the four regions surrounding Central Asia co-vary and correlate with each other. This can be explained by positive feedbacks between drying and cooling, and supports the assumption that global cooling provides a dominant driving factor for the drying of Eurasia: global cooling reduces the amount of water vapor held in the atmosphere and thereby can cause terrestrial drying. However, in Central Asia the moisture evolution shows less similarity with its surroundings. The uplift of the Tibetan Plateau (including the Tianshan Mountains) could provide a possible explanation for this difference. The changing topography resulting from uplift events over time and space strongly influenced the moisture patterns in Central Asia during Miocene times. Future research on the spatial timing and amplitude of Tibetan Plateau uplift should be useful to understand the moisture processes in Central Asia during the Miocene.