[M-IS14] Paleoclimatology and paleoceanography

[MIS14-P22] The East China Sea subsurface water temperature indicating steady Kuroshio path since the last glacial period

Reo Murakawa¹, *Yusuke Okazaki¹, Takuya Sagawa², Yoshimi Kubota³, Mahsa Saeidi Ortakand³, Yusuke Yokoyama⁴, Yosuke Miyairi⁴ (1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, 2.Institute of Science and Engineering, Kanazawa University, 3.National Museum of Science and Nature, 4.Atmosphere and Ocean Research Institute, University of Tokyo)

The Kuroshio Current is a western boundary current flowing in the surface and subsurface in the North Pacific Gyre. It transports warm and high salinity water from the Western Pacific Warm Pool to the mid-latitudes in the western North Pacific, playing an important role in the climate of Northeast Asia. The part of the Kuroshio enters the South China Sea from the south of Luzon Strait and flows out from the north of Luzon Strait. Therefore, the Kuroshio water in the Okinawa Trough is mixed with water masses from the western Philippine Sea and the South China Sea. Although a number of previous studies have reconstructed the glacial Kuroshio path, the subsurface water records are sparse. This study aims to reconstruct the subsurface water temperature in the Okinawa Trough since the last glacial period based on Mg/Ca ratios of planktonic foraminiferal subsurface species P. obliquiloculata and N. dutertrei in the piston core KS22-4 PC05 (28°56.7341’N, 127°13.7761’E, 563.85 m water depth). The reconstructed subsurface Mg/Ca temperatures of both species were consistent with each other, showing small changes ~1°C colder during the last glacial period than during the Holocene. The subsurface water temperature cooling during the last glacial period (1°C) was lower than the surface water temperature cooling (~3°C) during the Holocene. On the contrary, the intermediate water temperature during the last glacial period was warmer (~6°C) than during the Holocene. These results suggest that the glacial thermocline was weak in the Okinawa Trough. Such glacial temperature gradient was consistent with the South China Sea, whereas inconsistent with the western Philippine Sea. Thus, the glacial Kuroshio water was likely to be mixed with water masses from the western Philippine Sea and the South China Sea.