HR: 0800h
AN: PP11B-0527    [Abstracts]
TI: Rock magnetic records of Southeast Asian monsoon variability during the past 800 kyr
AU: * Suganuma, Y
EM: suganuma@eps.s.u-tokyo.ac.jp
AF: Department of Earth & Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
AU: * Suganuma, Y
EM: suganuma@eps.s.u-tokyo.ac.jp
AF: Geological survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AU: Yamazaki, T
EM: toshi-yamazaki@aist.go.jp
AF: Geological survey of Japan, AIST, Central 7, Higashi 1-1-1, Tsukuba, 305-8567, Japan
AU: Kanamatsu, T
EM: toshiyak@jamstec.go.jp
AF: IFREE, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15, Natsushima, Yokosuka, 237-0061, Japan
AB: Rock magnetic investigations were carried out on a sedimentary core taken from the Ninety-east ridge, the eastern equatorial Indian Ocean in order to reconstruct the South Asia monsoon variability during the past 800 kyr. A 10.2 m long piston core ÃÂ・#8216;Ã・#8216;‚Â・#202;Ã・œMR0503 -PC3ÃÂ・#8216;Ã・#8216;‚Â・#202;ï 4;¿Â½ was recovered in August 2005 during the R/V Mirai MR0503 cruise. The core site is located in the western flank of the Ninety-east ridge (1Ã・¹Ã・¡13.2'N, 88Ã・¹Ã・¡26.0'E), and water depth is 4400 m. In order to develop an age model for the MR0503-PC3 core, a relative paleointensity record (NRM30mT/IRM30mT) obtained from the core is correlated with the global stack of relative paleointensity records ÃÂ・#8216;Ã・#8216;‚Â・#202;Ã・œSint- 800ÃÂ・#8216;Ã・#8216;‚Â・#202;½ (Guyodo and Valet, 1999). Based on the developed age model, the age of the bottom of the MR0503-PC3 core is ca. 800 ka and an average sedimentation rate is 1.3 cm/kyr. A suite of rock magnetic parameters (Magnetic Susceptibility, IRM, ARM, Mrs/Ms, and S-ratio) was obtained from discrete samples collected from the half-split of the core. Magnetic Susceptibility, IRM, and ARM are used as proxies for the magnetic mineral flux. Mrs/Ms and S-ratio are used as proxies for mean grain size and magnetic mineralogical parameter, respectively. The results show that a magnetic mineral flux increases during warmer periods, whereas the flux decreases during colder periods. On the other hand, magnetic grain size increases during colder periods and decreases during warmer periods. These indicate that a supply of fine-grained magnetite (or maghemite), probably originated to pedogenesis, increases during warmer periods, suggesting intense precipitation related to the South Asian summer monsoon. During MIS 15 to 11, stepwise increases of the magnetic mineral flux accompanied with sudden drops of S-ratios are recognized. The sudden drop of S-ratio is related to intense inputs of coarse-grained hematite and maghemite, probably originated to the chemical weathering of the Himalaya-Tibet plateau. This feature suggests that intensification of the South Asian monsoon from MIS 15 to 11. This intensification of the South Asia monsoon may be related to the climate shift during the mid-Brunhes epoch observed from several regions of the western Eurasia (e.g., Chinese Loess plateau and Baikal lake).
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1512 Environmental magnetism
DE: 1521 Paleointensity
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 9340 Indian Ocean
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting