[H-QR03] 第四紀：ヒトと環境系の時系列ダイナミクス

[HQR03-P10] Reassessment of Lagoon-Specific Marine Reservoir Effects in Tongatapu, Kingdom of Tonga, over the Past 3000 Years

*福與 直人¹、Geoffrey Clark³、横山 祐典² (1.産業技術総合研究所　地質調査総合センター、2.東京大学　大気海洋研究所、3.オーストラリア国立大学　アジア太平洋学部)

キーワード：放射性炭素、海水準変動、南太平洋

Lagoon-specific local marine reservoir effects (ΔR_lagoon) were introduced as a novel proxy to estimate the radiocarbon (¹⁴C) activity change in the lagoon freshwater proportion in Fukuyo et al. (2020). In Tongatapu island, ΔR_lagoon values increased linearly between ~2.6 and 0.4 ka, which suggested that ΔR_lagoon value increase was caused by the near-closure of the Fanga ‘Uta Lagoon. However, these values still presented large errors. Here, we present 10 new Δ¹⁴C and 16 new ΔR_lagoon values from G. tumidum combined with the previously published values and a ΔR_lagoon value recalculated using Marine20. Moreover, we examined whether the ¹⁴C value of G. tumidum reflected that of the dissolved inorganic carbon in the lagoon water. Although the new ΔR_lagoon values were similar between 0.4 ka and 1.2 ka, the values increased from 2.6 ka to 1.2 ka. This timing was consistent with geophysical comparisons reported in our previous study and archaeological studies.