[M-IS18] Drilling Earth Science

[MIS18-03] IODP proposal for re-drilling in the East China Sea to understand the millennial-scale variability of the Asian monsoon during the Quaternary

★Invited Papers

*Yoshimi Kubota¹, Ken Ikehara², Kenji Matsuzaki³, Saki Ishino², Ayanori Misawa², Makoto Otsubo², Masataka Kinoshita⁴, Katsura Kameo³, Chiori Tamura³, Ryuta Arai⁵, Tomohiro Toki⁶, Yuki Mitsutome⁶, Zhirong Cai⁷, Keiko Takehara⁸, Kato Koudai⁸, Daisuke Kuwano⁹, Koshiro Matsuo¹⁰, Keita Suzuki¹¹, Misaki Horiuchi¹¹, Yohei Katayama¹², Satoshi Okumura¹³, Ryuji Tada¹⁴, Tomohisa Irino¹⁵, Kohsaku Arai², Takahiko Inoue², Takuya Sagawa¹⁶, Minoru Ikehara⁸, Yusuke Okazaki¹⁰, Keiji Horikawa¹⁷ (1.National Museum of Nature and Science, 2.National Institute of Advanced Industrial Science and Technology, 3.Atmosphere and Ocean Research Institute, The university of Tokyo, 4.Earthquake Research Institute, University of Tokyo, 5.Japan Agency for Marine-Earth Science and Technology, 6.University of the Ryukyus, 7.Kyoto University, 8.Kochi University, 9.China University, 10.Kyusyu University, 11.Nippon Marine Enterprises, Ltd., 12.Marine Works Japan, Ltd., 13.MOL Marine Co., Ltd., 14.Hokkaido University, 15.Graduate School of Science, The Univeristy of Tokyo, 16.Kanazawa University, 17.Toyama University)

Keywords:Asian monsoon, IODP, East China Sea, Quaternary, Millennial-scale, Speleothem

Understanding and predicting how monsoons respond to global climate change is a critical scientific and societal issue since monsoonal rainfall provides the water supply for more than half of the world's population and sometimes leads to natural catastrophes such as floods and droughts. The East China Sea (ECS) is a marginal basin located on the rim of the western North Pacific, receiving massive runoff from the Yangtze (Changjiang) River; the discharge accounts for ~90% of the total river discharge to the ECS, making surface salinity well-correlated with basin-wide summer precipitation in southern China. IODP Expedition 346 was held in 2013 to understand the long-term millennial-scale variability of the East Asian monsoon during the Quaternary. During IODP Expedition 346, we drilled the proposed sites to ~200 mbsf at Site U1429 in the northern ECS. Site U1429 recovered a continuous record of hemipelagic sediments for the last 400 ky with a high sedimentation rate of 30–70 cm/ky. The advantage of using the marine core is the oxygen isotope (δ¹⁸O) of calcite from planktic foraminifers preserved in nearshore marine sediments can be quantitatively partitioned into sea surface temperature and δ¹⁸O of seawater (δ¹⁸O_w), a function of sea surface salinity (a proxy of the monsoonal rainfall), using well-established methods of paired Mg/Ca and δ¹⁸O. Results from Site U1429 show that the δ¹⁸O_w marks the detectable millennial-scale variability, which correlates to the Chinese speleothem δ¹⁸O for the last 400 ky. The remarkable correlation between the ECS and the Chinese speleothem demonstrates that the ECS is a great candidate of a benchmark for the Asian monsoon record, especially for the early part of the Quaternary.
Here we propose to extend this excellent sediment archive through the last 1.5 Ma to reveal the underlying mechanism of the millennial-scale monsoon variability. In this presentation, we also report our recent progress on the site survey (KH-21-3) for re-drilling in the northern ECS.