South Asian monsoon variability during the past 800 kyr revealed by rock magnetic proxies |
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| Authors: | Y Suganuma T Yamazaki T Kanamatsu |
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| Institution: | 1. Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan;2. Department of Chemistry, Biology, and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan;3. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan;4. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba 305-8568, Japan;5. Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo 060-0810, Japan;1. Institut für Chemie und Biologie des Meeres (ICBM), Carl von Ossietzky Universität Oldenburg, Postfach, Oldenburg, Germany;2. Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science Technology (JAMSTEC), Yokosuka, Japan |
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| Abstract: | A rock magnetic investigation was carried out on a sedimentary core taken from the distal portion of the Bengal Fan in order to reconstruct the South Asian monsoon variability during the past 800 kyr. The 10.2 m long piston core MR0503-PC3, recovered at a water depth of 4400 m, consists of clay to silty clay with minor amounts of nannofossils. An age model for the MR0503-PC3 core is established by correlating a relative paleointensity record of the core Suganuma Y., Yamazaki, T., Kanamatsu, T., Hokanishi, N., 2008. Relative paleointensity record during the last 800 kyr from the equatorial Indian Ocean: implication for relationship between inclination and intensity variations. Geochemistry, Geophysics, Geosystems. 9, Q02011. doi:10.1029/2007GC001723.] to the global paleointensity stack “Sint-800” Guyodo, Y., Valet, J.P., 1999. Global changes in intensity of the Earth's magnetic field during the past 800 kyr. Nature. 399, 249–252.]. The age model is consistent with the published ages of tephra layers intercalated in the core, and shows continuous sedimentation during the past 800 kyr.Temporal variations in rock magnetic proxies for the magnetic concentration (ARM, IRM, and HIRM), the grain size (Mrs/Ms), and the composition (S?0.3T and S?0.1T) show that the amount of fine-grained magnetite increased during interglacial stages, and then gradually decreased toward the following glacial maxima. This indicates that the supply of fine-grained magnetite probably originated from areal expansion and/or increased pedogenic activity in the Ganges and Brahmaputra Rivers catchment. Increases during warmer periods suggest intensification of the South Asian summer monsoon during interglacial stages. During marine isotope stages (MIS) 15–11, enhancement of fine-grained magnetite and increased hematite and maghemite contributions are observed. These suggest a significant intensification of the South Asian summer monsoon during this period. Our record and other paleoclimatic reconstructions mainly from the low and mid-latitudes suggest that a major climatic event possibly occurred prior to the mid-Brunhes event (MBE), but the timing is not synchronous. |
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