Post-Pliocene Establishment of the Present Monsoonal Climate in SW China
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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Open Access Clim. Past Discuss., 9, 1675–1701, 2013 Climate www.clim-past-discuss.net/9/1675/2013/ Climate CPD doi:10.5194/cpd-9-1675-2013 of the Past of the Past Discussions © Author(s) 2013. CC Attribution 3.0 License. 9, 1675–1701, 2013 Open Access Open Access Earth System This discussion paper is/hasEarth been System under review for the journal Climate of the Past (CP). Post-Pliocene Please refer to the correspondingDynamics final paper in CP if available. Dynamics Discussions establishment of the present monsoonal Open Access Post-PlioceneGeoscientific establishment ofGeoscientific the Open Access climate in SW China Instrumentation Instrumentation T. Su et al. present monsoonalMethods and climate in SWMethods China: and Data Systems Data Systems Discussions Open Access evidence from the lateOpen Access Pliocene Longmen Title Page Geoscientific Geoscientific megaflora Model Development Abstract Introduction Model Development Discussions Conclusions References T. Su1,3, F. M. B. Jacques1, R. A. Spicer4,5, Y.-S. Liu6, Y.-J. Huang2, Y.-W. Xing7, Open Access 1,2 Open Access and Z.-K. Zhou Hydrology and Hydrology and Tables Figures 1Key Laboratory of TropicalEarth Forest System Ecology, Xishuangbanna TropicalEarth Botanical System Garden, Chinese Academy of Sciences,Sciences Mengla, 666303, China Sciences J I 2Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany,Discussions Chinese Open Access Open Access Academy of Sciences, Kunming, 650204, China J I 3 Ocean Science State Key Laboratory ofOcean Paleobiology Science and Stratigraphy, Nanjing Institute of Geology and Back Close Paleontology, the Chinese Academy of Sciences, Nanjing, 210008, China Discussions 4Environment, Earth and Ecosystems, Centre for Earth, Planetary, Space and Astronomical Full Screen / Esc Open Access Research, The Open University, Milton Keynes,Open Access MK7 6AA, UK 5 Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, ChinaSolid Earth Printer-friendly Version 6 Solid Earth Department of Biological Sciences, P.O. Box 70703, East Tennessee StateDiscussions University, Johnson City, Tennessee, 37614-1710, USA Interactive Discussion 7Institute of Systematic Botany, University of Zurich, Zurich, 8008, Switzerland Open Access 1675 Open Access The Cryosphere The Cryosphere Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Received: 16 January 2013 – Accepted: 25 January 2013 – Published: 2 April 2013 Correspondence to: Z.-K. Zhou ([email protected]) CPD Published by Copernicus Publications on behalf of the European Geosciences Union. 9, 1675–1701, 2013 Post-Pliocene establishment of the present monsoonal climate in SW China T. Su et al. Title Page Abstract Introduction Conclusions References Tables Figures J I J I Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 1676 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract CPD The paleoclimate of the late Pliocene Longmen flora from Yongping County located at the southeastern boundary of the Qinghai-Tibet Plateau was reconstructed us- 9, 1675–1701, 2013 ing two leaf physiognomy based methods, i.e. Leaf Margin Analysis (LMA) and Cli- 5 mate Leaf Analysis Multivariate Program (CLAMP), to understand the paleoclimate Post-Pliocene condition and geographical pattern of monsoonal climate in southwestern China dur- establishment of the ing the late Pliocene. The mean annual temperatures (MATs) estimated by LMA and present monsoonal ◦ ◦ ◦ CLAMP are 17.4 ± 3.3 C and 17.4 ± 1.3 C, respectively, compared with 15.9 C at climate in SW China present. Meanwhile, the growing season precipitation (GSP) estimated by CLAMP is 10 1735.5 ± 217.7 mm in the Longmen flora, compared with 986.9 mm nowadays. The T. Su et al. calculated monsoon index (MSI) of the Longmen flora is significantly lower than that of today. These results appear consistent with previous studies based on the coexistence approach (CA), and further suggest that there was a slightly warmer and much wetter Title Page climate during the late Pliocene than the present climate in western Yunnan. We con- Abstract Introduction 15 clude that the significant change of the monsoonal climate might have been resulted from the continuous uplift of mountains in western Yunnan, as well as the intensifica- Conclusions References tion of eastern Asian winter monsoon, both occurring concurrently in the post-Pliocene Tables Figures period. J I 1 Introduction J I 20 The modern Asian monsoon system is divided into the East Asian monsoon and the Back Close South Asian (Indian) monsoon (Molnar et al., 2010). Although they differ in precipita- tion terms, both are characterized by wet summers and dry winters (B. Wang, 2006). Full Screen / Esc Approximately 60 % of the world’s population lives in the regions directly affected by the monsoon system, and therefore its fluctuation can greatly impact human activities Printer-friendly Version 25 worldwide as well as the local economy (B. Wang, 2006). The Asian monsoon has attracted great attention on its evolution, variability and forcing mechanisms (Sun and Interactive Discussion 1677 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Wang, 2005; Wang et al., 2008; Han et al., 2012). While most work has focused on short term fluctuations in monsoon behaviour, study of the variations in the Asian mon- CPD soon in deep time is crucial to contextualise and understand the driving mechanisms 9, 1675–1701, 2013 underpinning monsoon changes. 5 Western Yunnan, located at the southeastern boundary of the Qinghai-Tibet Plateau, uniquely experiences both the East Asian monsoon and the Indian monsoon (Y. Wang, Post-Pliocene 2006). The uplift and east-west extension of the Qinghai-Tibet Plateau has created establishment of the a series of north-south oriented mountains such as Mt. Gaoligong and Mt. Nu in west- present monsoonal ern Yunnan (Ge and Li, 1999). These high mountains form geographical barriers for climate in SW China 10 the convergence of these two monsoons (Hao et al., 2008) and result in a special re- gional monsoonal climate (Kou et al., 2006). Consequently, western Yunnan is an ideal T. Su et al. region for exploring the evolution of the Asian monsoon climate in deep time. Fossil flo- ral assemblages have been widely used as a proxy for paleoclimate reconstructions Title Page due to their direct interaction with the past surrounding environment (Wolfe, 1979, 15 1993; Mosbrugger and Utescher, 1997; Greenwood, 2005; Jordan, 2011). Thus, the Abstract Introduction abundance of Neogene floras in western Yunnan (Writing Group of Cenozoic Plants of China – WGCPC, 1978; Bureau of Geology and Mineral Resources of Yunnan Province Conclusions References – BGMRYP, 1990; Ge and Li, 1999) provides important materials for understanding the Tables Figures evolution of monsoonal climate. 20 The Pliocene is a key period for the global climate change with a transition from J I the warmer Miocene to the cooler Pleistocene (McKay et al., 2012). However, our un- derstanding of the Pliocene climate in the Qinghai-Tibetan Plateau is poor. Although J I paleoclimates derived from several Pliocene floras in western Yunnan have been re- Back Close constructed and have provided important information on the character of the monsoon 25 during the Pliocene (Xu et al., 2004; Yao et al., 2012; Supplement Table 1), most of Full Screen / Esc these paleoclimatic studies of the Pliocene floras are based on the coexistence ap- proach (CA) and one type of fossil material, namely palynological material (Kou et al., Printer-friendly Version 2006). The principle of CA is based on the climate interval of the nearest living rela- tives of each taxon in the flora (Mosbrugger and Utescher, 1997). Although CA clearly Interactive Discussion 1678 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | produces coherent climate trends that match other proxies such as those based on iso- topes (Mosbrugger et al. 2005), the climatic range encompassed by the co-existence CPD interval can be large in some circumstances, and when this occurs, the resolution of 9, 1675–1701, 2013 the technique appears low. An alternative approach is based on the leaf physiognomic 5 spectrum displayed by leaves of woody dicots (Wolfe, 1993; Greenwood, 2005). Meth- ods of this kind only need to classify fossil leaves in a flora into morphotypes without Post-Pliocene taxonomic identification (Wolfe, 1993). The Tuantian flora, being on the western side establishment of the of Mt. Gaoligong and Mt. Nu, is the only Pliocene fossil flora in western Yunnan with present monsoonal palaeoclimate reconstructions based on leaf physiognomy (Xie et al., 2012; Fig. A1a). climate in SW China 10 Here, we examine the late Pliocene Longmen flora on the eastern side of Mt. Gaoligong and Mt. Nu in western Yunnan. The aims of this paper are: (1) to recon- T.