Continental drift, plateau uplift, and the evolutions of monsoon and arid regions in Asia, Africa, and Australia during the Cenozoic

Abstract

Monsoon and arid regions in the Asia-Africa-Australia (A-A-A) realm occupy more than 60% of the total area of these continents. Geological evidence showed that significant changes occurred to the A-A-A environments of the monsoon and arid regions, the land-ocean configuration in the Eastern Hemisphere, and the topography of the Tibetan Plateau in the Cenozoic. Motivated by this background, numerical experiments for 5 typical geological periods during the Cenozoic were conducted using a coupled ocean-atmosphere general circulation model to systemically explore the formations and evolutionary histories of the Cenozoic A-A-A monsoon and arid regions under the influences of continental drift and plateau uplift. Results of the numerical experiments indicate that the timings and causes of the formations of monsoon and arid regions in the A-A-A realm were very different. The northern and southern African monsoons existed during the mid-Paleocene, while the South Asian monsoon appeared in the Eocene after the Indian Subcontinent moved into the tropical Northern Hemisphere. In contrast, the East Asian monsoon and northern Australian monsoon were established much later in the Miocene. The establishment of the tropical monsoons in northern and southern Africa, South Asia, and Australia were determined by both the continental drift and seasonal migration of the Inter-Tropical Convergence Zone (ITCZ), while the position and height of the Tibetan Plateau were the key factor for the establishment of the East Asian monsoon. The presence of the subtropical arid regions in northern and southern Africa, Asia, and Australia depended on the positions of the continents and the control of the planetary scale subtropical high pressure zones, while the arid regions in the Arabian Peninsula and West Asia were closely related to the retreat of the Paratethys Sea. The formation of the mid-latitude arid region in the Asian interior, on the other hand, was the consequence of the uplift of the Tibetan Plateau. These results from this study provide insight to the important roles played by the earth's tectonic boundary conditions in the formations and evolutions of regional climates during geological times.

Bridging the knowledge gap on the evolution of the Asian monsoon during 26–16 Ma

“…The precipitation in central Tibet was dominated by the paleo-Asian monsoon during 26–16 Ma, possibly because the plateau was farther south during that time period. 8 , 19 Today, westerlies control the modern climate in the Lunpola Basin. The Lunpola Basin in central Tibet is situated at 32.1° N and has obvious seasonality in the variations in surface air temperature and precipitation, i.e., cold and dry from December to February in winter and warm and rainy from June to August in summer.…”

“…The uplift of the Tibetan Plateau 20 likely coincided with plate movements 8,21 during this period, thereby enhancing the strength of the Asian monsoon. Central Tibet may not have reached its present elevation before the Middle Miocene, 13,19 implying that uplift occurred in this region before this time.…”

“… 6 Others have speculated that the modern East Asian monsoon was initiated in the Miocene and was triggered by the uplift of the Tibetan Plateau, based on geological evidence from loess deposits 7 and models. 8 The South Asian monsoon seems to have appeared in the Eocene, 9 with controversy regarding its driving force. The thermal effects 10 and dynamic consequences 11 resulting from the uplift of the Tibetan Plateau and changes in the paleogeography 8 were interpreted as the potential driving forces, based on different models.…”

“… 8 The South Asian monsoon seems to have appeared in the Eocene, 9 with controversy regarding its driving force. The thermal effects 10 and dynamic consequences 11 resulting from the uplift of the Tibetan Plateau and changes in the paleogeography 8 were interpreted as the potential driving forces, based on different models.…”

“…Simulated annual precipitation in the Pan-Tibetan plateau regions at25 Ma The blue to orange lines display the simulated annual precipitation (mm); the green shaded area indicates the Asian monsoon domain; the yellow shaded area indicates the arid region; the black line is the topographic contour at 1,500 masl; the violet point is the studied section at 25 Ma. Please refer to Wang and Ding 2 and Liu et al8 for definitions of the monsoon domains and arid areas.…”