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EPSL: Centennial-scale hydro-climate changes in the middle reaches of the Yangtze River in the past two millennia and their teleconnection mechanisms with EAP and ENSO

        The team of Professor Yongjin Wang from the Isotope Laboratory of the Academy of Geological Sciences of Nanjing Normal University has made the latest research progress in the study of stalagmites and paleoclimate. The result was published in the journal "Earth and Planetary Science Letters" of Nature Index with the title "Modulation of centennial-scale hydroclimate variations in the middle Yangtze River Valley by the East Asian-Pacific pattern and ENSO over the past two millennia" .

        The middle and lower reaches of the Yangtze River is a typical Meiyu area, which is significantly affected by ENSO and the West Pacific Subtropical High. Based on instrumental data, Chinese meteorologists pointed out that the abnormal drought and flood in the middle and lower reaches of the Yangtze River are related to the seasonal advancement of the East Asian summer monsoon. When the tropical western Pacific is colder, the El Niño event occurs, and convective activity around the Philippines is weak, the position of the Western Pacific Subtropical High is westward and southward, which is conducive to the long-term maintenance of the Meiyu front in the Yangtze River Basin and strong precipitation. The East Asia-Pacific type (EAP) teleconnection and its theory of the northern hemisphere summer atmospheric circulation anomaly affecting the summer droughts and floods in the Yangtze River Basin are proposed (Huang and Sun, 1992). EAP telecorrelation is embodied as a seesaw-type inverse correlation between precipitation in the tropical western Pacific and precipitation in the Yangtze River Basin; At the same time, the tropical western Pacific precipitation is teleported in reverse phase with the tropical eastern Pacific precipitation through the Walker Circulation. Therefore, ENSO and EAP modes are considered to be the main sources of summer precipitation predictability in the middle and lower reaches of the Yangtze River. However, due to the relatively short records of modern instruments in my country, it is still uncertain whether the EAP teleconnection mechanism will be established on a longer time scale.

        This study is based on the high-resolution stalagmite oxygen isotope records of Heizhugou Cave in Sichuan Province, Monshang Cave and Luoshui Cave in Hubei Province. Using principal component analysis, the history of Asian summer monsoon precipitation changes in the middle reaches of the Yangtze River was reconstructed in the last two thousand years (Figure 1A). The comparison results show that on a hundred-year scale, the monsoon precipitation records in the middle reaches of the Yangtze River and the western Pacific warm pool have a significant anti-phase relationship (Figure 1A and B). It reveals that on a hundred-year scale, the monsoon precipitation changes in the middle reaches of the Yangtze River may also be controlled by the tuning of the EAP teleconnection mechanism. Based on the hydro-climate records of the middle reaches of the Yangtze River and the Western Pacific Warm Pool, this paper reconstructs the EAP index records with a resolution of about 5 years in the last two millennia (Figure 1C). At the same time, there is a strong correlation between the hydrological and climate records of the middle reaches of the Yangtze River and the Western Pacific Warm Pool, as well as the EAP index and the Southern Oscillation Index (Figure 1), indicating that ENSO may modulate monsoon precipitation changes in the middle and lower reaches of the Yangtze River through EAP teleconnection. 

        The first author of this paper is Zhang Jingwei, a doctoral student in our school, and the corresponding author of the paper is Associate Professor Zhao Kan. The research was completed under the careful guidance of Professor Yongjin Wang and Professor Kong Xinggong of our school, Professor R. Lawrence Edwards from the University of Minnesota, and Professor Cheng Hai from Xi’an Jiaotong University. Under the guidance of Associate Professor Shao Qingfeng, the work of chronology was mainly completed in the isotope laboratory of the Academy of Geological Sciences of our school. This research was funded by the National Natural Science Foundation of China (42071105, 41931178, 41702180, 41672164, 41172314), the Disciplinary Innovation and Talent Introduction Program of Chinese Colleges and Universities (D19002), and the National Natural Science Foundation of China (1702816).
        Link to the paper: https://doi.org/10.1016/j.epsl.2021.117220