[M-IS16] 古気候・古海洋変動

[MIS16-P18] 南東太平洋チリ沖コア試料中の有孔虫殻破片率・殻重量に基づく炭酸塩保存・溶解変動

*粕谷 拓人¹、岡崎 裕典²、岩崎 晋弥³、IODP Expedition 383 Scientific Party (1.九州大学　理学部　地球惑星科学科、2.九州大学 大学院理学研究院 地球惑星科学部門、3.ブレーメン大学 海洋環境科学センター (marum))

キーワード：炭酸塩保存・溶解、南大洋、MIS 5、浮遊性有孔虫

The Southern Ocean plays an important role in global climate change as a reservoir of heat and carbon. Glacial atmospheric carbon dioxide concentrations were 80-100 ppm lower than the interglacial level. Changes in CaCO₃ dissolution and preservation in the deep-sea particularly for the Southern Ocean is thought to be a key factor for glacial carbon reservoir. In this study, we investigated change in dissolution and carbonate preservation in Southern Ocean sediment for the last 140 kyrs based on two proxies, fragmentation index and size-normalized weight of planktic foraminiferal tests. Fragmentation index represents a ratio of the number of fragments to the intact planktic foraminiferal tests. Two planktic foraminiferal species, Neogloboquadrina pachyderma and Globigerina bulloides were employed. For size-normalized weight of planktic foraminiferal tests, Globigerina bulloides tests were picked up from the 212-250 µm, 250-300 µm, and 300-355 µm sieve fractions. Sediment core samples used in this study were obtained at Site U1543 (54°35.06’S; 76°40.58’W; 3864 m water depth) in the eastern South Pacific west of the Chile Trench during the International Ocean Discovery Program (IODP) Expedition 383 in 2019. At U1543, foraminiferal tests in the sediment have been preserved only during glacial terminations to early interglacials during the last 140 kyrs, which is consistent with expected deep-sea carbonate ion response to atmospheric CO₂ elevations during the glacial terminations. During the last interglacial period (marine isotope stage 5e), both fragmentation ratio and size-normalized weight of planktic foraminiferal tests suggested two carbonate dissolution events at millennial time-scale.