[M-IS34] 古気候・古海洋変動

[MIS34-19] 大阪湾堆積物コアの花粉記録から見た海洋酸素同位体ステージ11の気候変化

*中野 恒佑¹、北場 育子²、兵頭 政幸³、加藤 茂弘⁴ (1.神戸大学理学研究科地球惑星科学専攻、2.立命館大学古気候学研究センター、3.神戸大学　自然科学系先端融合研究環　内海域環境教育研究センター、4.兵庫県立人と自然の博物館自然・環境評価研究部)

キーワード：海洋酸素同位体ステージ11, 古気候, 古植生, 花粉分析, 大阪湾堆積物

Climate of marine isotope stage (MIS) 11 has been investigated by many researchers, regarded as an analogue for the Holocene. MIS 11 is a super-interglacial characterized by its high sea-level and long duration. To reveal millennial to centennial scale climate changes of this interglacial in comparison with sea-level variations shown by diatoms, pollen analyses were conducted on a 1700-m core of Osaka Bay over a depth range from 162 m to 222 m. The core has an average sedimentation rate of about 60 cm/ka, dated with a linear age model based on the orbital tuning, reinforced by tephrostratigraphy and magnetic polarity stratigraphy. Cold climate shown by dominance of coniferous tree taxa in the latest stage of MIS 12 was replaced by cool climate dominated by deciduous tree taxa mainly composed of Fagus, a cool proxy, in the earliest MIS 11. The vegetation in MIS 11 was gradually dominated by deciduous tree taxa. The proportion of Quercus (Cyclobalanopsis), a warm proxy, increased with sea-level rise and reached its maximum at sea-level highstand of MIS 11.3. After the thermal maximum, Quercus (Cyclobalanopsis) gradually decreased with fluctuations and coniferous tree taxa such as Cryprtomeria and Sciadopitys increased, both indicating cooling and wetting. After MIS 11.3, the climate shows clear precession-related signals correlated with changes in the diatom sea-level proxies. Pollen taxa, especially Alnus and non-arboreal pollen, also show environmental changes. From the latest stage of MIS 12 to the earliest MIS 11, a marsh environment was dominant during the post-glacial sea-level rise. In the early stage of MIS 11, the post-glacial warming is clearly shown by the rapid increase of Quercus (Cyclobalanopsis), and the warming is interrupted by a short-term cooling that ranges in age from about 416 ka to 413 ka based on the linear age model. The temporal cooling almost coincides with the sea-level fall or stagnation suggested by the diatom sea-level proxies. A similar cooling event has been reported from Europe, Lake Baikal and the Antarctic. Therefore, the cooling event in the early MIS 11 may be global and accompanied by an ice volume increase.