Abstract
Evolutions of Asian and Australian monsoons have important significance for understanding the past global change but are still a controversial subject. Here, we explore systematically the effects of plate movement and plateau uplift on the formation and evolution of the Asian and Australian monsoons by numerical simulations based on land-sea distributions and topographic conditions for five typical geological periods during the Cenozoic. Our results suggest that the timings and causes of formation of the monsoons in South Asia, East Asia and northern Australia are different. The Indian Subcontinent, which was located in the tropical Southern Hemisphere in the Paleocene, was influenced by the austral monsoon system simulated at that time. Once it moved to the tropical Northern Hemisphere in the Eocene, the South Asian monsoon established and remained persistently thereafter. However, the monsoons of East Asia and northern Australia did not appear until the Miocene. The establishment of the simulated low-latitude South Asian (northern Australian) monsoon appeared to have strongly depended on the location of mainland India (Australia), associated with northward plate motion, without much relation to the plateau uplift. On the contrary, the establishment of the mid-latitude East Asian monsoon was mainly controlled by the uplift of Tibetan plateau.
Highlights
Asian and Australian monsoons are a prominent component of atmospheric circulation and exert a significant influence on the global climate[1,2,3]
In December-January-February (DJF), a segment of the Intertropical Convergence Zone (ITCZ) shifted southward to central India, so that northern India was dominated by the northwesterly winds as the Northern Hemisphere (NH) northeasterly trade winds crossed the equator into the Southern Hemisphere (SH), while central India experienced its rainy season (Figs 1f and 2f)
This suggests that when India was located in the tropical SH, the monsoon climate there was mainly due to the seasonal shift of the ITCZ (Figs 1a and 2a,f) with the wet season in DJF and March-April-May (MAM) and the dry season in JJA and September-October-November (SON) (Fig. 1f)
Summary
Asian and Australian monsoons are a prominent component of atmospheric circulation and exert a significant influence on the global climate[1,2,3]. Given the geological facts that the significant movement of the Indian-Australian plate[14,15,16] and the large-scale uplift of the Tibetan Plateau (TP)[17,18,19,20] occurred during the Cenozoic, we designed a series of numerical experiments using a coupled atmospheric-oceanic general circulation model (AOGCM)[28] to systematically examine the origins and evolution of the Asian and Australian monsoons as well as the relative roles and combined effects of plate motion and topography in 5 typical Cenozoic geological periods: mid-Paleocene (MP: ~60 Ma), late-Eocene (LE: ~40 Ma), late-Oligocene (LO: ~25 Ma), late-Miocene (LM: ~10 Ma), and present day (PD: 0 Ma) (See Methods and Supplementary Information for details of the model and design of experiments)
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