[M-IS04] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS04-01] Orbital- to millennial-scale variability of the East Asian monsoon and the Kuroshio Current during periods of low orbital eccentricity and precessional change in the Pleistocene

★Invited Papers

*久保田 好美¹、羽田 裕貴²、亀尾 浩司³、板木 拓也²、林 広樹⁴、紫谷 築⁴、泉 賢太郎⁵、Head Martin⁶、菅沼 悠介⁷、岡田 誠⁸ (1.国立科学博物館、2.産業技術総合研究所地質調査総合センター 、3.千葉大学理学研究科地球科学、4.島根大学総合理工学部 、5.千葉大学教育学部、6.ブロック大学、7.国立極地研究所、8.茨城大学理学部理学科 )

キーワード：アジアモンスーン、黒潮、千葉複合セクション、更新世、千年スケール、Marine Isotope Stage (MIS) 19

Marine Isotope Stages (MIS) 20–18, along with MIS 12–10, are the closest astronomical analogues of the present interglacial and last glacial period (MIS 2–1). Comparing MIS 20–18 with MIS 2–1 provides an excellent opportunity to investigate natural climate variability and constrain future climate change predictions in East Asia. A previous study on the Chinese Loess Plateau shows that the grain-size-inferred intensity of the East Asian winter monsoon (EAWM) remains weak during MIS 20 and 18 likely due to the less-severe summer insolation and resulting suppressed snow accumulation and weak Siberian High. Here, we reconstruct the paleoceanography of MIS 20–18 through multiple proxies including microfossil assemblage data, planktonic foraminiferal isotopes (δ¹⁸O and δ¹³C), and foraminiferal Mg/Ca-based temperature records, from the Chiba composite section (CbCS) exposed on the Boso Peninsula, east-central Japan to compare with the East Asian monsoon proxies. The boundary between the warm Kuroshio and cold Oyashio currents is presently situated just east of the Boso Peninsula. The fluctuating position of the boundary between the Kuroshio and Oyashio currents in the mid-latitude western North Pacific affects both heat transport and air–ocean interactions and has significant consequences for the East Asian climate. We use principal component analysis (PCA) to capture dominant patterns of the temporal variation in these marine records, and show that MIS 19b and 19a are represented by millennial-scale stadial/interstadial oscillations. The northerly positions for the gyre boundary during late MIS 19c, early MIS 18, and the interstadials of MIS 19a are inferred from the leading mode, which is consistent with a weak EAWM and consequent mild winter climate in East Asia. Glacial MIS 20 had significantly more mild winters than MIS 2. For the interglacial MIS 19 and following glacial MIS 18, the onset of winter cooling in East Asia lagged the summer/annual climate by 30–40 kyr, which is also seen in the leading mode of the CbCS marine proxies.