[U-03] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia

[U03-P11] Radiocarbon and uranium profiles in marine gastropods around the Japanese archipelago

*平林 頌子¹、阿瀬 貴博¹、宮入 陽介¹、菅 浩伸²、横山 祐典¹ (1.東京大学大気海洋研究所、2.九州大学浅海底フロンティア研究センター)

キーワード：U/Th年代測定、放射性炭素年代測定、貝

In this study, we investigate the distribution of radiocarbon and uranium in the calcified opercula of Turbo sp. collected from Ryukyu region and Chiba, Japan, to explore the potential of U/Th dating using of mollusks around the Japanese archipelago. We acquired high-resolution radiocarbon and uranium concentration measurements using singlestage accelerator mass spectrometry and laser-ablation–inductively coupled plasma–mass spectrometry at Atmosphere and Ocean Research Institute, The University of Tokyo. Our results show that uranium in opercula of modern Turbo sp. is unevenly distributed at concentration 1000 times less than those in coral skeletons. Radiocarbons presented in the calcified opercula samples are reflected the radiocarbon values in ambient seawater as well as corals. Uranium in the calcified opercula of the Holocene Turbo marmoratus was also unevenly distributed but its area of concentration within the opercula was found to be different from that of modern samples, suggesting uranium exchange after death. Uranium distributions in fossil samples can affect U/Th ages by up to 800 years in case of 1 ka-old samples. Our results suggest variable uptake of uranium isotopes into mollusk shells, and highlights that it is important to define criteria for choosing mollusks species for U/Th dating around Japan.