日本地球惑星科学連合2023年大会

講演情報

[J] オンラインポスター発表

セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS15] 古気候・古海洋変動

2023年5月25日(木) 10:45 〜 12:15 オンラインポスターZoom会場 (22) (オンラインポスター)

コンビーナ:岡崎 裕典(九州大学大学院理学研究院地球惑星科学部門)、長谷川 精(高知大学理工学部)、山崎 敦子(名古屋大学大学院環境学研究科)、小長谷 貴志(東京大学大気海洋研究所)

現地ポスター発表開催日時 (2023/5/23 17:15-18:45)

10:45 〜 12:15

[MIS15-P21] 東シナ海沖縄トラフ陸棚斜面堆積物における浮遊性・底生有孔虫殻の酸素同位体比変動

*村川 怜央1岡崎 裕典1、サイディ マッソウ2久保田 好美2 (1.九州大学、2.国立科学博物館)

キーワード:有孔虫、東シナ海

The Kuroshio Current is a western boundary current in the North Pacific Gyre, flowing along the continental shelf edge of the Okinawa Trough in the East China Sea. A piston core KS22-4 PC05 was obtained from the continental slope of the Okinawa Trough (PC05, 28°56.7341′N, 127°13.7761′E, 563.85 m water depth). Foraminiferal shells’ oxygen isotope (δ18O) records seawater's ambient temperature, salinity, and δ18O. We measured δ18O of planktic foraminifera Globigerinoides ruber sensu stricto (G. ruber ss) and benthic foraminifera Uvigerina spp. In addition, δ18O of three G. ruber morphotypes (G. ruber ss; G. ruber sensu lato, G. ruber sl; and G. ruber subspecies with a small final chamber, G. ruber subsp) were compared to understand the δ18O differences in morphotypes. In PC05, G. ruber ss δ18O showed light values -2.02‰ and -2.97‰ at the two core top samples, whereas heavy values from -0.63‰ to -1.61 ‰ below 13.8 cm core depth. Comparing the G. ruber ss δ18O patterns with the neighboring piston core YK12-15 PC01 with radiocarbon dates, the Holocene interval of PC05 is suggested to be less than 24 cm thick. Uvigerina spp. δ18O in PC05 ranged from 2.66‰ to 3.84‰ but mostly between 3.2‰ and 3.6‰. At the two core top samples, Uvigerina spp. δ18O were 3.21‰ and 3.53‰, not showing light values. Holocene and Glacial Uvigerina spp. δ18O in Core MD01-2404 (26°38.84′N, 125°48.75′E, 1397 m water depth) were 2.5-3.0‰ and 4.0-4.5‰, respectively. We have estimated the Uvigerina spp. δ18O offset as ~1.1‰ due to the temperature differences at PC05 (564 m) and MD01-2404 (1397 m). The PC05 core top values of Uvigerina spp. δ18O (3.21‰ and 3.53‰) are likely equivalent to the glacial periods. δ18O of three G. ruber morphotypes showed different values: the lightest for G. ruber ss and the heaviest for G. ruber sl. G. ruber subsp δ18O showed intermediate values between G. ruber ss and G. ruber sl. This suggests that G. ruber subsp’s living depth is between the depths of habitats Globigerinoides ruber ss and G. ruber sl, or a mixture of values from the two morphotypes.