[M-IS18] 古気候・古海洋変動

[MIS18-10] Deep Water Circulation in the Low Latitude Western Pacific Since the Last Glacial Maximum

*Wei-Cheng Hsiung¹、Hui-Ling Lin¹、Horn-Sheng Mii²、Ken Ikehara³、Takuya Itaki³、Toshiya Kanamatsu⁴、Yuan-Pin Chang¹ (1.Department of Oceanography, National Sun Yat-sen University, Taiwan, R.O.C.、2.Department of Earth Sciences, National Taiwan Normal University, Taiwan, R.O.C.、3.Geological Survey of Japan, AIST、4.Japan Agency for Marine-Earth Science Technology)

Global deep water circulation is important in regulating long-term carbon storage in the ocean and atmosphere. Basically, downwelling deep water in high latitude areas of both hemispheres has been considered as one of the major sources of sinking carbon dioxide. On the other hand, the eastern Pacific is considered as a carbon source to release the deep water reserved carbon dioxide to the atmosphere. It is reported that the present deep water circulation rate in the Pacific was quite different from that of the glacial periods, especially the Last Glacial Maximum (LGM) and during deglaciation. The deep water circulation rate of LGM was slower than that of the present. Meanwhile, the northwestern Pacific has been considered as a carbon sink because the glacial intermediate water mass formed down to 2000 m deep during the glacial periods. This phenomenon then has been considered as an important mechanism to constrain the global deep water circulation rate then decrease the atmospheric carbon dioxide concentration during glacial. There are only few paleo-records related to the deep water masses reported in the low latitude of the western Pacific. In this study, we provide ocean ventilation ages using the sediment core YK15-01 PC13 (23.5°N 124.24°E, southeast of Ishigaki Island) conducted in the western Pacific low latitude with water depth around 2520 m. The deep water ventilation ages are estimated by the difference of coexisting planktonic and benthic foraminifera radiocarbon ages plus the surface ocean reservoir ages. These results might contribute to filling the lack of deep water ventilation age records in the low-latitude western Pacific. Ventilation ages reconstructed by PC13 and reference cores in the mid-latitude western Pacific were increased from around 1000 years to around 2000 years when entering the LGM and remained in a less changed pattern until the present. This scenario does not match the ventilation age records which decreased since the LGM in the Atlantic. Thus, the Atlantic and the western Pacific may have different deep water ventilation trends from the deglaciation to the present. In addition, two ventilation age decreasing events occurred during the Heinrich event 1 (H1) and Younger Dryers (YD) with an amplitude of 500 years. This phenomenon might be related to the deep water forming in the northwestern Pacific caused by the cool climate conditions.