Abrupt mid-Holocene decline in the Indian Summer Monsoon caused by tropical Indian Ocean cooling
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Abrupt mid-Holocene decline in the Indian Summer Monsoon caused by tropical Indian Ocean cooling Yongbo Wang1 · Ji Shen2 · Yong Wang3 · Xingqi Liu1 · Xianyong Cao4,5 · Ulrike Herzschuh6,7,8 Received: 20 January 2020 / Accepted: 6 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The evolution of the Indian Summer Monsoon (ISM) has been widely investigated and traditionally interpreted as consequences of orbital forcing change and the migration of the Intertropical Convergent Zone (ITCZ). The potential influence of sea-surface temperature (SST) on ISM variation at millennial time scales has been progressively proposed in recent studies. Towards a better understanding of Holocene evolution of ISM, especially the potential response to variations in SST, a 643 cm continuous sediment sequence covering the past 11.1 ka was recovered from Beihai Wetland in western Yunnan Plateau. Fossil pollen analysis revealed that evergreen broadleaved forest dominated the regional vegetation in the early Holocene, which represented a warm and humid period associated with strong ISM. Expansions of deciduous broadleaved forest and grassland from 5.2 cal. ka BP to the present, together with the appearance of abundant plant remains, indicate the formation of the wetland system. Ordination analysis of the pollen assemblages further confirmed the abrupt vegetation turnover at ca. 5.2 cal. ka BP, which is consistent with the abrupt decline in reconstructed mean annual precipitation (Pann, from ca. 1400 to 1100 mm), and indicates an abrupt decline in the summer monsoon. We performed a climate regime shift test on various records from the ISM domain and eastern Africa and found this phenomenon as well, which could not be explained by changes in solar insolation or the migration of the ITCZ. A mid-Holocene cooling was detected from the Indian Ocean, especially a decreased SST in the tropical Indian Ocean ca. 5.5 cal. ka BP. Cooling of the tropical Indian Ocean possibly caused the abrupt retreat of the summer monsoon by restraining the duration of the monsoonal season and the convergent process, which was supported by an abrupt monsoon decline based on results from a minimal concept model. Keywords Indian Summer Monsoon · Pollen · Holocene · Sea-surface Temperature · Yunnan Plateau
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05363-7) contains supplementary material, which is available to authorized users. * Yongbo Wang [email protected] * Ji Shen [email protected] 1
College of Resource Environment and Tourism, Capital Normal University, Beijing 100048, China
2
School of Geography and Ocean Science, Nanjing University, Nanjing 210093, China
3
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China
4
Alpine Paleoecology and Human Adaptation Group (ALPHA), Key Laboratory of Alpine Ecology, Institute of Tibetan Plateau Research, Chines
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