Millennial-scale Shifts in Summer Monsoon Front Position in East Asia during the late Holocene deduced from Provenance Changes of the Yangtze River Suspended Particulate Matter

Monday, June 15, 2015: 11:30 AM
Ryuji Tada1, Ke Wang2, Keita Saito1, Yoshimi Kubota3 and Hongbo Zheng4, (1)University of Tokyo, Department of Earth and Planetary Science, Bunkyo-ku, Japan, (2)Hokkaido University, Faculty of Environmental Earth Science, Sapporo, Japan, (3)National Museum of Nature and Science, Ibaraki, Japan, (4)Nanjing Normal University, College of Geographic Science, Nanjing, China
Abstract:
Reconstruction of spatiotemporal changes in summer monsoon precipitation in East Asia on centennial to millennial timescale during the Holocene is critical to understand the pattern and magnitude of natural variability of East Asian summer monsoon (EASM) precipitation and its potential impact on the cultural evolution in the East Asia. However, the effort was not so successful because there is no good proxy for summer monsoon precipitation, and it is not easy to attain high spatial coverage with high time resolution and precision. The Yangtze River drainage occupies a major part of South China, thus its water discharge quantitatively reflects EASM precipitation. In addition, the river runs oblique to the EASM front direction. Consequently, in the seasonal march of EASM front toward NW, the rain belt migrates from the lower reach through middle reach to the upper reach. It is also known that more than 90% of the sediment discharge from the Yangtze River is in the form of suspended particulate matter (SPM) with the modal size of 10-20 mm, and over 70% of the sediment discharge occurred during summer. Thus, it is possible to reconstruct changes in EASM front position by examining the provenance of fine silt fraction (4-16 mm) of the sediments discharged from the Yangtze River. We used two sediment cores retrieved from offshore Yangtze Delta and mud belt to the southwest of the Yangtze River mouth to examine the provenance changes of the Yangtze River SPM. We also attempted to reconstruct temporal changes in freshwater discharge from the Yangtze River during the middle to late Holocene based on d18Osw estimation using planktonic foraminifera (Kubota et al., 2015). When the two results are combined, we will be able to reconstruct spatiotemporal changes in EASM precipitation. The preliminary result of our attempt will be presented.

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