Progress has been made in the study of the evolution of the global monsoon system

Recently, Hu Yongyun, a professor in the Department of Atmospheric and Oceanic Sciences at the School of Physics at Peking University, and Guo Zhengtang, an academician from the Institute of Geology and Geophysics of the Chinese Academy of Sciences, published a paper entitled “The Rise of the Pangia Super Monsoon in a Modern Global Monsoon System Dominated by Continental Evolution” in Nature Earth Sciences. Combined with geological records and a series of simulation experiments, this paper studies the relationship between the global monsoon and the continental area, continental position and continental cracking degree since the Pankia supercontinent, and makes new progress in the relationship between the supercontinental cycle and the supermonsoon cycle.

Changes in the area of the global terrestrial monsoon region (blue line) and the intensity of monsoon precipitation (orange line) over the past 250 million years. The left vertical coordinate is the percentage of the terrestrial monsoon region to the earth’s surface area, and the right vertical coordinate is the average annual precipitation of the terrestrial monsoon region. The solid line represents the results of the control test, and the dotted line represents the results of the fixed CO2 concentration and solar constant test. (Photo courtesy of the research group)

These results provide new insights for future studies of paleomonsoons in different geological periods. Since the regulation of the evolution of the monsoon system by continental evolution not only affects the regional climate, but also the changes in the monsoon region have an important impact on the evolution of ecosystems in different geological periods, the relationship between chemical weathering and the global carbon cycle, and the formation of exogenous deposits. Hu Yongyun, the corresponding author of the paper, told China Science Daily.

The monsoon is driven by the difference between land and sea temperatures. When summer arrives, because the land heats up faster than the ocean, the moist air from the ocean blows to the land, forming precipitation on the continent. As summer ends, the temperature difference between land and sea reverses, the wind direction also reverses, and the rainy season ends. This seasonal phenomenon of precipitation and reversal of wind direction is known as the monsoon. China has a typical monsoon climate, and precipitation is mainly concentrated in summer.

The modern global monsoon system consists of six regional monsoons, which have their own characteristics, but also share common spatiotemporal variation properties. This is where the concept of the “global monsoon” comes into play. It is one of the important entry points for earth system scientific research to reveal the similarities, differences and dynamics of the evolution of monsoon systems in different regions from the perspective of global monsoon.

Over the past 250 million years, continental evolution has undergone a process of disintegration and reconvergence of the Pangia supercontinent (United Continent) (right). With the movement of plates and changes in sea level, the area of the continent has also undergone a process of decreasing and re-expanding. How does continental evolution affect the evolution of the global monsoon system, and how is the current regional monsoon related to the supermonsoon cycle caused by continental evolution, which is the core scientific question of this study.

Using the air-sea coupled Earth system model (CESM1.2.2), the team conducted a series of climate equilibrium simulations (one every 10 million years) over the past 250 million years, revealing that the evolution of the global monsoon since the Pankia union can be divided into three main stages: (1) during the Pangia supercontinent, the global terrestrial monsoon area was large (i.e., the Pangia “supermonsoon”) (2) In the Cretaceous period, the continental fragmentation was the fullest, and the continental area reached the minimum due to the rise of sea level, and the area of the continental monsoon region was smaller, but the intensity of monsoon precipitation was larger; (3) During the Cenozoic, the continental plates began to converge again and the area increased, and the area of the continental monsoon region became larger, but the intensity of monsoon precipitation decreased.

These results show that, firstly, the evolution of the global monsoon system at the tectonic scale is not only related to the tectonic uplift and other factors, but also plays a very key role in the evolution of the global monsoon in the supercontinental cycle. Finally, the modern global monsoon system is closely related to the new continental convergence since the Cenozoic, rather than directly originating from the super monsoon in the Pangia era.

This research was supported by the National Natural Science Foundation of China (NSFC) Basic Science Center project “Continental Evolution and Monsoon System Evolution”. (Source: Cui Xueqin, China Science News)

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