Dynamic control on grain-size distribution of terrigenous sediments in the western South China Sea: Implication for East Asian monsoon evolution |
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Authors: | GuoCheng Chen HongBo Zheng JianRu Li Xin Xie Xi Mei |
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Institution: | (1) State Key Laboratory of Marine Geology, Tongji University, Shanghai, 200092, China |
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Abstract: | High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China
Sea (SCS), was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density,
fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate (TMAR) was obtained, which
is 4.9–6.0 g cm−2 ka−1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9–5.0 g cm−2 ka−1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis
of grain size distribution of all the samples, two main control factors (F1 and F2) were obtained, which are responsible for
about 80% variance of granularity. The contents of grain size population 1.26–2.66 μm% and 10.8–14.3 μm% which are sensible
to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15°N. They exhibit a distinct cyclicity
with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24–7.42 μm%
and 30.1–43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations
of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations
of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer
monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with
precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing
of the East Asian winter monsoon but with less important insolation forcing.
Supported by the National Natural Science Foundation of China (Grant No. 40676033), the National Key Basic Research Special
Foundation Project of China (Grant No. 2007CB815906) and the Funds for Creative Research Groups of China (Grant No. 40621063) |
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Keywords: | South China Sea late Quaternary terrigenous sediments grain size East Asian monsoon |
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