[M-IS18] 古気候・古海洋変動

[MIS18-P15] 後期鮮新世の北半球氷床発達にともなう北大西洋高緯度域の浮遊性有孔虫寒冷種の変化

村中 美樹¹、*岡崎 裕典¹、木元 克典³、林 辰弥² (1.九州大学大学院理学研究院地球惑星科学部門、2.九州大学大学院比較社会文化研究院環境変動部門、3.海洋研究開発機構地球表層システム研究センター)

キーワード：浮遊性有孔虫、北大西洋、鮮新世の北半球氷床発達

We investigated planktic foraminiferal assemblage in sediment samples from the North Atlantic during the intensification of the Northern Hemisphere glaciation between 2.5 and 2.7 Ma. Sediment cores used for this study were obtained at Site U1314 (56°21.9′N, 27°53.3′W, water depth 2820 m) in the southern Gardar Drift, subpolar North Atlantic by the Integrated Ocean Drilling Program (IODP) Expeditions 303/306. We picked up planktic foraminiferal specimens from >150 μm aliquots of the sediment samples. Neogloboquadrina pachyderma sinistral and Neogloboquadrina atlantica sinistral were the representative cold water species in the Pliocene North Atlantic. Relative abundances of the two cold-water species during 2.5-2.7 Ma were about 80% in glacials and 40% in interglacials, respectively. These planktic foraminiferal cold water species abundances showed almost consistent with benthic foraminiferal oxygen isotopes and ice-rafted debris at Site U1314. However, from the late marine isotope stage (MIS) 104 to 103 (~2.6 Ma), the lowest relative abundances of the cold water species were found at Site U1314 during the studied period. Considerable contribution of warm water species such as Neogloboquadrina pachyderma dextral and Neogloboquadrina atlantica dextral increased in the late MIS 104. Because the timing of the warm water species increasing was soon after the short-term IRD event, we speculate the event responding to the resumption of Atlantic meridional overturning circulation inferred by paleomagnetic properties and alkenone sea-surface temperature.