On February 27, the research team of Nanjing University, aiming at the research on the non-linear evolution of dune landform in arid area, published on science advanced online with the title of critical transitions in Chinese dunes during the past 12000 years. The first and corresponding author of the paper are Xu Zhiwei, associate professor of the school of geography, Nanjing University. Professor Xu Chi, Yi shuangwen, senior engineer and Professor Lu Huayu of Nanjing University participated in the study. In addition, Professor Joe Mason of the University of Wisconsin in the United States and other domestic and foreign co authors, such as Wageningen University in the Netherlands, Ben Gurion University in Israel, Shaanxi Normal University and Nanjing University of information engineering, participated in the paper work.
More than a third of the world's population lives in arid and semi-arid areas, which account for 40% of the world's land area. Sand dunes are widely distributed in arid and semi-arid areas and become a unique natural landscape. The formation and evolution mechanism of sand dunes has always been a hot scientific issue in the field of earth and environmental science. In people 's impression, sand dunes are usually barren and flowing. In the semi-arid area, sand dunes can show different states of flow or fixation. The vegetation coverage and mobility of mobile sand dunes and fixed sand dunes are very different, but they can coexist in the same surface environment for a long time. The coexisting mechanism is a pending scientific problem in the study of dune landform and environment. In recent years, the study of dune bistability (the coexistence of mobile dunes and fixed dunes) shows that complex systems such as landform, ecology and climate may have the characteristics of "alternative stable states". Mobile sand dunes and fixed sand dunes coexist in the same environmental conditions, which indicates that the formation and development of sand dunes may also have the characteristics of multistability. According to the prediction of multi steady state theory, with the gradual change of external environment conditions, weak disturbance may make sand dunes evolve from one stable state to another. This system behavior called "critical transition" usually shows nonlinear characteristics such as delay and sudden change at critical point. At present, limited by the lack of field evidence, the understanding of the formation mechanism of dune multistability and the long-term evolution track of this unique ecological landscape is very limited. Whether there is a steady-state transition in the development and evolution of sand dunes is a fundamental issue, which is also hotly debated in academia. Because the rapid change of sand dunes will have a significant impact on the local ecological environment, and the characteristics of multi steady state delay mean that once activated, it will be difficult to restore the sand dunes. Therefore, the study of multi steady state of sand dunes is of great significance for the prevention and control of sand and the construction of regional ecological civilization in arid and semi-arid areas, especially in clarifying the trigger conditions of rapid land degradation in arid areas and early warning Aspects can play a key role. The research team of Professor Lu Huayu, School of geography, Nanjing University, has carried out 20 years' research work in the desert and sandy land of northern China. In recent years, with the support of the key R & D plan of the Ministry of science and technology and the National Natural Science Foundation, they have carried out "dragnet" investigation and a large number of sample collection, test and Analysis on a number of desert sand, constructed nearly 100 aeolian sand deposition records (paleoenvironmental archives) with precise age control, and achieved a series of scientific research results. "Archives of ancient environment": since 2016, the past sand dune mobility history recorded by aeolian sand deposition, the team, Dr. Xu Zhiwei, and the team of Professor Xu chi from Nanjing University Academy of Sciences, in collaboration with scholars from the United States, the Netherlands, Israel and many domestic universities, have formed a multidisciplinary team, aiming at the main sandy land (including Maowusu Sandy Land and hunshandaksha) in the semi-arid area of northern China 144 aeolian sand deposits in DIHE and Horqin sandy land were reconstructed and integrated based on process analysis. Using more than 500 strata independent age data and paleoclimate reconstruction simulation data, the environmental change history (resolution of 500-1000 years) of these sandy land in the past 12000 years was obtained. The bistability of sand dunes and the change of Aeolian environment in the past 12000 years in the north of China
It is found that in the past 12000 years, the mobile sand dunes and fixed sand dunes coexist in the north of China, and the area of mobile sand dunes is the least around 6000 years ago. Influenced by the change of monsoon precipitation, the change of local dune state (flowing or fixed) occurs in a short time, showing obvious mutation characteristics, but the time node of mutation occurrence has significant asynchronous characteristics, and its evolution track also has distinct spatial heterogeneity. The formation and state mutation of dune bistable pattern are mainly related to various positive feedback effects among vegetation, soil and aeolian activities, and regulated by the internal process of ecosystem. The reconstruction results on the whole scale show that the evolution of the overall state of these sands is gradual because the local spatial heterogeneity characteristics cancel each other, and there is a clear quantitative relationship with monsoon precipitation (but there is still a lag phenomenon).
Response and lag of sandy environment in northern China to climate change in the past 12000 years
This research result is helpful to understand the mechanism of environmental change and predict the trend of regional environmental change. This study highlights the importance of considering the interaction between spatial scale and surface layer in the study of geomorphic development and environmental change in arid areas, and provides an important reference for clarifying the historical process and mechanism of environmental mutation and gradual change in other arid areas in the world, such as the Sahara desert.
Paper information: Xu, Z., Mason, J.A., Xu, C., Yi, S., bathyany, S., yizhaq, H., & Lu, H. (2020). Critical transitions in Chinese cities during the past 12000 years. Science advances, 6 (9), eaay8020. Paper link: https://advances.sciencemag.org/content/6/9/eaay8020.abstract review of previous articles 2020, 01, 02, 03, 042019, January, February, March, April, may, July, August, September, October, November, December
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