Continental drift and plateau uplift control origination and evolution of Asian and Australian monsoons

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.

Figure 1. Simulated monsoon regions over eastern hemisphere and seasonal mean precipitation over North China, India, and northern Australia during the 5 geological periods.

(a) mid-Paleocene (MP: ~60 Ma), (b) late-Eocene (LE: ~40 Ma), (c) late-Oligocene (LO: ~25 Ma), (d) late-Miocene (LM: ~10 Ma), and (e) present day (PD: ~0 Ma). The light-dark green (yellow-orange) areas indicate monsoon regions with the rainy season in JJA (DJF), in which the darker shades represent the typical monsoon regions. In the light (dark) green areas, the rainfall difference between boreal summer (JJA) and boreal winter (DJF) is greater than 200 (400) mm and JJA rainfall is more than 40% of the annual total. In the yellow (orange) areas, the rainfall difference between austral summer (DJF) and austral winter (JJA) is greater than 200 (400) mm and DJF rainfall is more than 40% of the annual total. Red boxes indicate North China, India, and northern Australia where seasonal (DJF, MAM, JJA and SON) mean precipitations are shown in (f ). Note that the geographic coordinates of these regions were changing over time, but their relative positions corresponding to the specific land masses remained the same. Maps were created using GrADS (Version 1.9b4, http://cola.gmu.edu/grads/).

Figure 2. Simulated 850 wind vector (m s⁻¹) and precipitation (mm) fields in JJA (top) and DJF (bottom) during the 5 geological periods.

(a) MP in JJA, (b) LE in JJA, (c) LO in JJA, (d) LM in JJA, (e) PD in JJA, (f) MP in DJF, (g) LE in DJF, (h) LO in DJF, (i) LM in DJF, (j) PD in DJF. Regions where seasonal precipitation greater than 300 mm are shaded. Blue lines are coast lines and red lines outline regions where orography is higher than 1500 m. Maps were created using GrADS (Version 1.9b4, http://cola.gmu.edu/grads/).

Figure 3. Northern boundary of the East Asian summer (JJA) monsoon circulation and meridional distribution of mean summer rainfall during the 5 geological periods.

(a) Northern limits of the East Asian monsoon overlaid on the 850 hPa streamline field of PD. (b) summer rainfall rates (mm day⁻¹) averaged over 105°–120°E. The corresponding ages are labeled for each period in both (a) and (b). Longitudes 105°–120°E cover the conventional range of the present-day East Asian monsoon region. Maps were created using GrADS (Version 1.9b4, http://cola.gmu.edu/grads/).

Figure 4. Simulated monsoon regions over eastern hemisphere for experiments without orography during the 4 geological periods.

(a) LE, (b) LO, (c) LM, and (d) PD. The light-dark green (yellow-orange) areas indicate monsoon regions with the rainy season in JJA (DJF) where summer-winter rainfall difference is greater than 200 mm and summer rainfall is more than 40% of the annual total. Darker shades represent the typical monsoon regions where summer-winter rainfall difference is greater than 400 mm. Maps were created using GrADS (Version 1.9b4, http://cola.gmu.edu/grads/).