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

[U03-P04] Radiocarbon Dating of Historical Tsunami Deposits from Kiri-Kiri, Iwate Prefecture, Northeast Japan

*Jessica Biddle¹, Yusuke Yokoyama^1,2, Takashi Ishizawa³, Ren Tsuneoka², Yosuke Miyairi², David Heslop¹ (1.Australian National University, 2.University of Tokyo, 3.Tohoku University)

Keywords:Tsunami Deposit, Radiocarbon Dating, Pollen, Sedimentary Environment

Tsunamis are a series of large ocean waves caused by seafloor deformation, primarily triggered by large earthquakes, landslides, and volcanic eruptions. Japan experiences high seismic activity due to its location on and near plate tectonic boundaries. Large tsunami events greatly erode sea floors and terrestrial soils, resulting in sediments being mixed, transported, and deposited. This movement of material results in the formation of tsunami deposits, which can be identified within sedimentary records. These deposits contain critical information that can, if correctly understood provide insights into a tsunami’s inundation extent, flow conditions, number of backwash flows, magnitude, and chronology. This study aims to develop an in-depth understanding of historic tsunamis at Kiri-Kiri located on the Sanriku Coast, Iwate Prefecture, Northeast Japan. Previous attempts to bulk radiocarbon (¹⁴C) date three peat cores from this region resulted in failure to correlate the tsunami deposits between cores. This study will focus on achieving higher resolution bulk radiocarbon dating throughout the same three cores. Furthermore, chemical analysis of the sediment will be used to aid correlation and a new chronological approach based on radiocarbon dating of pollen will be tested. Specifically, when applying ¹⁴C dating on terrestrial sediments with plant cover, bulk sediment radiocarbon results can be inaccurate. This occurs due to the intrusion of ¹⁴C via plant roots, causing bulk dates to be spuriously young. Pollen only interacts with the ambient atmosphere and is, therefore not affected by new carbon intrusion. As a result, radiocarbon ages from pollen should be more accurate than bulk sediment dates. However, the accuracy of pollen dating is determined by the purity of the pollen collected from the sediment. Techniques are currently under development with various studies use of a cell sorter and flow cytometry (Cadd et al., 2022; Kron et al., 2021; Tunno et al., 2021; Zimmerman et al., 2019) to extract pollen. Hence, the aim of this study is to determine the viability of utilising a cell sorter to obtain a pure concentration of pollen to achieve more accurate radiocarbon dates of historical tsunamis, alongside understanding the historic tsunamis that have occurred at Kiri-Kiri, Sanriku Coast.