[M-IS17] 古気候・古海洋変動

[MIS17-23] 40万年間の東シナ海のMg/Ca水温および酸素同位体比に基づく東アジア夏季モンスーン変動

*久保田 好美¹、脇坂 恵都子²、Clemens Steven³、Holbourn Ann⁴、Lee Kyung Eun⁶、Ziegler Martin⁷、堀川 恵司²、木元 克典⁵ (1.国立科学博物館、2.富山大学、3.Brown University、4.Christian-Albrechts-University、5.海洋研究開発機構、6.Korea Maritime University、7.Utrecht University)

キーワード：モンスーン、東シナ海、ミランコビッチ サイクル、Mg/Ca古水温、酸素同位体比

The East Asian summer monsoon (EASM) system is involved in the hydrological cycle and in latent heat and energy transport, and thus plays a crucial role in the regional and global climate system. Modern summer sea surface salinity in the northern part of the East China Sea (ECS) is mainly controlled by the discharge of the Yangtze River, which reflects East Asian summer monsoon (EASM) precipitation in the drainage area of the Yangtze River. Site U1429 was drilled by Integrated Ocean Drilling Program (IODP) Expedition 346 in the northern part of the ECS to reconstruct the Yangtze River discharge in high temporal resolution (~100 year resolution). A ~200 m long sediment succession was recovered, which covers the last 400 ky based on a benthic foraminiferal oxygen isotope. A record of oxygen isotope of seawater (δ¹⁸O_w) was reconstructed, based on high-resolution Mg/Ca and oxygen isotope measurements of the planktic foraminifera Globigerinoides ruber. The δ¹⁸O_w shows variations that have been in concert with Chinese spleothem oxygen isotope records on millennial to orbital scales. However, comparison with a global mean δ¹⁸O_w reveals that the δ¹⁸O_w of U1429 follows the global mean except from MIS 7.3 to MIS 6.4 and from MIS 5.4 to MIS 4, when the δ¹⁸O_w of U1429 was higher than the global mean during MIS 7.2, 6.4, 5.4, 5.2, 4 and lower during MIS 7.3, 7.1, 6.5, 5.3, 5.1. These intervals correspond to higher eccentricity periods during the last 400 ky. During these time periods, the amplitude variations of the regional δ¹⁸O_w increased, suggesting that the 23 ky amplitude of the EASM precipitation was also enhanced. These results suggest that the 23 ky amplitude of the EASM precipitation has been modulated by the eccentricity.