Variation of Zr/Rb ratios in the Chinese loess deposits during the past 1.8 Myr and its implication for the change of East Asian monsoon intensity

Authors

  • Lianwen Liu,

    1. Institute of Surficial Geochemistry, State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing, China
    2. Laboratory of Marine Geology, Tongji University, Shanghai, China
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  • Jun Chen,

    1. Institute of Surficial Geochemistry, State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing, China
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  • Junfeng Ji,

    1. Institute of Surficial Geochemistry, State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing, China
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  • Yang Chen,

    1. Institute of Surficial Geochemistry, State Key Laboratory of Mineral Deposit Research, Department of Earth Sciences, Nanjing University, Nanjing, China
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  • William Balsam

    1. Department of Geology, University of Texas at Arlington, Arlington, Texas, USA
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Abstract

Most of our knowledge concerning the evolution of the East Asian monsoon (EAM) comes from the Chinese loess-paleosol sequence. Variations in the EAM, as recorded in loess, are highly correlated to the marine δ18O record and show a strong 100 kyr cyclicity during the past 800 kyr. This conclusion is based on both weathering and pedogenesis intensity changes as well as grain size variation in loess-paleosol sequences which usually serves as a proxy for winter monsoon variation. However, grain size distributions are subject to modification by pedogenic processes. In this paper we used the Zr/Rb ratio from the Lingtai section on the Loess Plateau in central China to trace variations in the East Asian winter monsoon for the past 1.8 Myr. Long-term Zr/Rb variations in the Lingtai section exhibit a similar amplitude and frequency to those of mean grain size in bulk samples over the past 1.8 Myr. Comparing the Zr/Rb record and mean grain size record between L1 and L9 shows that a good linear relationship exists in the glacial age loess samples, whereas paleosol samples usually deviate from the linear relationship because of intense pedogenesis during the relatively warm and humid interglacial intervals. Our results indicate that the Zr/Rb ratio reflects the original eolian grain size and may serve as a proxy for the strength of the East Asian winter monsoon. In the Lingtai section over the past 1.8 Myr, the Zr/Rb ratio record displays a very strong 41 kyr obliquity periodicity from 1.8–1.2 Myr B.P., implying that variations of the winter monsoon during this interval are controlled by high-latitude climate. However, during the past 0.8 Myr the Zr/Rb ratio exhibits a stronger precession cycle influence, suggesting a possible low-latitude control on the East Asian monsoon regime during this interval.

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