Post-Pliocene establishment of the present monsoonal climate in SW China: evidence from the late Pliocene Longmen megaflora

Y.-J. Huang,Z.-K. Zhou,F. M. B. Jacques,T. Su,R. A. Spicer,Y.-W. Xing,Y.-S. Liu

doi:10.5194/cp-9-1911-2013

Abstract

Abstract. The paleoclimate of the late Pliocene Longmen flora from Yongping County located at the southeastern boundary of the Qinghai-Tibet Plateau was reconstructed using two leaf-physiognomy-based methods, i.e., leaf margin analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP), to understand the paleoclimate condition and geographical pattern of monsoonal climate in southwestern China during the late Pliocene. The mean annual temperatures (MATs) estimated by LMA and CLAMP are 17.4 ± 3.3 °C and 17.4 ± 1.3 °C, respectively, compared with 15.9 °C at present. Meanwhile, the growing season precipitation (GSP) estimated by CLAMP is 1735.5 ± 217.7 mm in the Longmen flora, compared with 986.9 mm nowadays. The calculated monsoon intensity index (MSI) of the Longmen flora is significantly lower than that of today. These results appear consistent with previous studies on the late Pliocene floras in western Yunnan based on the coexistence approach (CA), and further suggest that there was a slightly warmer and much wetter climate during the late Pliocene than the present climate in western Yunnan. We conclude 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 intensification of the eastern Asian winter monsoon, both occurring concurrently in the post-Pliocene period.

Highlights

The modern Asian monsoon system is divided into the EastAsian monsoon and thTehSoeutCh Arsyiaons(Ipndhiaenr)emonsoon (Molnar et al, 2010)
The sediment of Longmen in this study belongs to the Sanying Formation (Ge and Li, 1999), which is assigned to the late Pliocene based on several lines of evidence, such as local geological structure (Compiling Group of the Regional Stratigraphic Table of Yunnan (CGRSTY), 1978; BGMRYP, 1990), stratigraphic correlations (Ge and Li, 1999), and fossil record (Tao and Kong, 1973; WGCPC, 1978; Zong et al, 1996; Su et al, 2011)
We recalculated the paleoclimate of the late Pliocene Tuantian flora in western Yunnan from a published account of Xie et al (2012; site 5 in Fig. 1) using the same calibration dataset in the present study

Summary

Introduction

The modern Asian monsoon system is divided into the East. Asian monsoon and thTehSoeutCh Arsyiaons(Ipndhiaenr)emonsoon (Molnar et al, 2010). They differ in precipitation terms, both are characterized by wet summers and dry winters The Asian monsoon has attracted great attention on its evolution, variability and forcing mechanisms (Sun and Wang, 2005; Wang et al, 2008; Han et al, 2012). While most work has focused on short-term fluctuations in monsoon behavior, study of the variations in the Asian monsoon in deep time is crucial to contextualize and understand the driving mechanisms underpinning monsoon changes

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