[U-13] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia:

[U13-P04] High-resolution marine surface Δ¹⁴C reconstructions using marine organisms produced carbonate attached to tetrapod ashored by high-wave in northern Pacific Coast of Japan.

*Kai Leggett¹, Yusuke Yokoyama¹, Yosuke Miyairi¹, Ota Kosuke¹, Yoshiki Shirahama² (1.Atmosphere and Ocean Research Institute, University of Tokyo, 2.Advanced Industrial Science and Technology, Geological Survey of Japan, Research Institute of Earthquake and Volcano Geology, Active Fault Research Group)

Keywords:ΔC-14, Radiocarbon analysis, Hydroides Elegans, Aerial photographs, Accelerator Mass Spectrometer, Sanriku

Radiocarbon is produced in the upper atmosphere and distributed on the surface of the Earth via carbon cycles and has been used for radiometric dating and as a tracer of Earth surface processes including ocean current. Due to global ocean circulation, apparent radiocarbon ages ranging from ca. 400 to 2,000 years (eg., Servettaz et al., 2019), known as marine reservoir ages. Thus, continuous monitoring of radiocarbon concentrations, Δ¹⁴C, has been conducted commonly using annual bands of coral skeletons to reconstruct local oceanography (eg., Hirabayashi et al., 2019). Though, it has mainly been restricted in low latitude since warmer water (higher than 18 degrees C) is required to live for corals. One of the few studies that reconstruct the Δ¹⁴C values in higher latitude, such as the Tohoku region, in Japan, Kubota et al. (2018) reported the Δ¹⁴C values in the inner bay of the Otsuchi area using M.stimposoni shells. Yet the records could not cover recent Δ¹⁴C variations. Additionally, the M.stimposoni samples used in this study are mostly collected from 20 m deep from the sea surface, only one sample collected from shallow water at around 5 m water depth thus more information at shallow water is needed. Ota et al. (2019) also reported high-resolution Δ¹⁴C records using abalone shells. However, habitat differences for individual tests could not provide the reference of local marine water Δ¹⁴C. In this study, we reconstruct the Δ¹⁴C of the sea surface by analyzing the calcium carbonate calcareous tubes of Hydroides elegans, which lives at ambient sea level. The samples were obtained from Iwate Prefecture and the carbonate tubes are found on tetrapods at an elevation of 7~8 m and were 30 m away from the nearest group of wave-dissipating blocks. According to the aerial photographs, we identified the exact timing when the tetrapods were dislodged. Eighteen samples of carbonate tubes of Hydroides elegans have filled the gap of the dataset previously published by Kubota et al. (2018). The oceanographic condition also seems to be overprinted to the signal and we will discuss it during the presentation.