[M-IS15] Paleoclimatology and Paleoceanography

[MIS15-P21] Variation in planktic and benthic foraminiferal oxygen isotopes in a sediment core obtained from the Okinawa Trough’s the continental slope in the East China Sea.

*Reo Murakawa¹, Yusuke Okazaki¹, Mahsa Saeidi², Yoshimi Kubota² (1.Kyushu University, 2.National Museum of Nature and Science)

Keywords:Foraminifera, East China Sea

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.