[H-QR03] Quaternary, Diachronic dynamics of human-environment interactions

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

*Naoto Fukuyo¹, Geoffrey Clark³, Yusuke Yokoyama² (1.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 2.Atmosphere and Ocean Research Institute, University of Tokyo, 3.College of Asia and the Pacific, The Australian National University)

Keywords:radiocarbon, sea level change, South Pacific

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.