Geochemical characteristics of deposits from the 2011 Tohoku‐oki tsunami at Hasunuma,Kujukuri coastal plain,Japan |
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| Authors: | Tetsuya Shinozaki Yuki Sawai Junko Hara Minoru Ikehara Dan Matsumoto Koichiro Tanigawa |
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| Institution: | 1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan;2. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan;3. Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan |
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| Abstract: | We examined the geochemical characteristics and temporal changes of deposits associated with the 2011 Tohoku‐oki tsunami. Stable carbon isotope ratios, biomarkers, and water‐leachable ions were measured in a sandy tsunami deposit and associated soils sampled at Hasunuma, Kujukuri coastal plain, Japan, in 2011 and 2014. At this site, the 2011 tsunami formed a 10–30 cm ‐thick layer of very fine to medium sand. The tsunami deposit was organic‐poor, and no samples contained any detectable biomarkers of either terrigenous or marine origin. In the underlying soil, we identified hydrocarbons and sterols derived from terrestrial plants, but detected no biomarkers of marine origin. In the samples collected in 2011, concentrations of tsunami‐derived water‐leachable ions were highest in the soil immediately beneath the tsunami deposit and then decreased gradually with depth. Because of its finer texture and higher organic content, the soil has a higher water‐holding capacity than the sandy tsunami deposit. This distribution suggests that ions derived from the tsunami quickly penetrated the sand layer and became concentrated in the underlying soil. In the samples collected in 2014, concentrations of water‐leachable ions were very low in both soil and sand. We attribute the decrease in ion concentrations to post‐tsunami rainfall, seepage, and seasonal changes in groundwater level. Although water‐leachable ions derived from seawater were concentrated in the soil beneath the tsunami deposit following the tsunami inundation, they were not retained for more than a few years. To elucidate the behavior of geochemical characteristics associated with tsunamis, further research on organic‐rich muddy deposits (muddy tsunami deposits and soils beneath sandy tsunami deposits) as well as sandy tsunami deposits is required. |
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| Keywords: | 2011 Tohoku‐oki tsunami tsunami deposit stable carbon isotope ratio biomarker water‐leachable ions Kujukuri Japan 水 溶 性 イ オ ン バ イ オ マ ー カ ー 日 本 九 十 九 里 炭 素 安 定 同 位 体 比 津 波 堆 積 物 2011年 東 北 沖 津 波 |
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