[M-IS03] Evolution and variability of the Asian monsoon in Cenozoic global climate changes

[MIS03-07] 400,000 years millennial scale temperature and rainfall in East Asia deduced from paired Mg/Ca and oxygen isotope of planktic foraminifera from the East China Sea

★Invited Papers

*Yoshimi Kubota¹, Steven Clemens², Kyung-Eun Lee³, Ann Holbourn⁴, Etsuko Wakisaka⁵, Keiji Horikawa⁵, Ryuji Tada⁶, Katsunori Kimoto⁷ (1.National Museum of Nature and Science, 2.Brown University, 3.Korea Maritime and Ocean University, 4.Christian-Albrechts-University, 5.University of Toyama, 6.The University of Tokyo, 7.Japan Agency for Marine-Earth Science and Technology)

Keywords:Asian Monsoon, East China Sea, Millennial-scale climate variability, oxygen isotope, Mg/Ca, IODP Exp.346

Abrupt millennial-scale climate changes during the late Quaternary were widely recognized in the East Asian monsoon region from deep-sea sediments in the Japan Sea and more recently from oxygen isotope (δ¹⁸O) variability in Chinese speleothems (δ¹⁸O_sp). The finely ²³⁰Th-dating method on the speleothems enables comparison to climate records from other regions on millennial scale, and there is little doubt that the variability of these δ¹⁸O_sp records is synchronized with climate perturbation in the North Atlantic high latitude, known as Heinrich events and with Dansgaard-Oeschger (D-O) oscillations in Greenland. However, mechanisms of the climate response in East Asia remain unclear due to the lack of fundamental agreement on what the δ¹⁸O_sp climate signal represents. A primary impediment to interpreting the variability in δ¹⁸O_sp is the lack of the means to decompose δ¹⁸O_sp into constituent components. By contrast, the δ¹⁸O of calcite planktic foraminifers (δ¹⁸O_p) from nearshore marine sediments can be quantitatively partitioned into sea surface temperature (SST) and δ¹⁸O_w of seawater (δ¹⁸O_w), a function of sea surface salinity (SSS). In this study, millennial-scale climate variability in East Asia is investigated using 400,000-yr records of SST, δ¹⁸O_p, and δ¹⁸O_w from the East China Sea (IODP Site U1429). δ¹⁸O_w can be interpreted as reflecting SSS, hence rainfall, as the monsoonal runoff from the Yangtze River determines summer SSS in the northern East China Sea. As a result, SST and δ¹⁸O_w variability accounts for 58% and 35% of the total variability of δ¹⁸O_p and the rest (6%) is the ice volume component or noise; the primary contributor to δ¹⁸O_p variations is SST, and the secondary is δ¹⁸O_w. Foraminiferal δ¹⁸O_p shows the strongest similarly with Chinese δ¹⁸O_sp, indicating that δ¹⁸O_sp is best interpreted as the combination of changes in surface temperature and monsoon rainfall; it is not indicative of summer monsoon rainfall alone. Partitioning of variance between temperature and rainfall does not change on glacial-interglacial timescales indicating that the hemispheric teleconnection mechanism between the Atlantic and East Asia does not depend on the global climate background status (CO₂, ice volume). In comparison with the millennial scale Greenland temperature, the East China Sea SST decreases and δ¹⁸O_w increases (rainfall deceases) in most of the North Atlantic cold events (e.g., Heinrichs). However, SST and δ¹⁸O_w exhibit overall poor coherence, revealing that these climate parameters fundamentally behave differently on the millennial scale, but tend to respond in the manner described above (decrease in temperature and rainfall) once a severe cold event occurs in the North Atlantic.