Ambe Daisuke, Kaeriyama Hideki, Shigenobu Yuya, Fujimoto Ken, Ono Tsuneo, Sawada Hideki, Saito Hajime, Miki Shizuho, Setou Takashi, Morita Takami, Watanabe Tomowo
National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4, Fukuura, Kanazawa-ward, Yokohama, Kanagawa 236-8648, Japan.
National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4, Fukuura, Kanazawa-ward, Yokohama, Kanagawa 236-8648, Japan.
J Environ Radioact. 2014 Dec;138:264-75. doi: 10.1016/j.jenvrad.2014.09.007. Epub 2014 Sep 30.
The spatial distributions of radiocesium concentration in sea sediment to a core depth of 14 cm were investigated in the offshore region from the Fukushima Prefecture to the northern part of the Ibaraki Prefecture in February and July 2012, at a spatial resolution of 5 min of latitude and longitude. The concentrations in the area south of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) were generally higher than those in the area north of it. In the southern area, a band of especially high concentration with a width about 20 km was present in the region shallower than 100 m, and a narrow minimal concentration band was found along the 200-m isobaths. In more than half of all cases, the vertical core profiles of radiocesium concentration generally showed an exponential decreasing trend with depth. However, in the area north of the FDNPP, where the radiocesium concentrations tended to be very low, radiocesium concentrations that had similar or larger magnitude compared with those of the most-surface layer were often found in deeper layers. Relatively good correlations were found between radiocesium concentrations and grain sizes of the most-surface sediment. The vertical profile of radiocesium concentration also had a relationship with grain size. In other case, the radiocesium concentration in the sediment seems to have had a dependence on the radiocesium concentration in bottom seawater, suggesting that the quantity of radiocesium supplied and the grain size were major factors determining the spatial distribution pattern of the radiocesium concentration after the FDNPP accident.
2012年2月和7月，在从福岛县到茨城县北部的近海区域，以纬度和经度5分钟的空间分辨率，研究了海沉积物中放射性铯浓度在14厘米核心深度内的空间分布。福岛第一核电站（FDNPP）以南区域的浓度普遍高于其以北区域。在南部区域，在深度小于100米的区域存在一条宽度约20公里的特别高浓度带，并且在200米等深线沿线发现了一条狭窄的最低浓度带。在所有情况的一半以上，放射性铯浓度的垂直岩芯剖面通常显示出随深度呈指数下降趋势。然而，在FDNPP以北放射性铯浓度往往非常低的区域，在较深层中经常发现与最表层浓度相似或更大的放射性铯浓度。在最表层沉积物的放射性铯浓度与粒度之间发现了相对较好的相关性。放射性铯浓度的垂直剖面也与粒度有关。在其他情况下，沉积物中的放射性铯浓度似乎依赖于底层海水中的放射性铯浓度，这表明在FDNPP事故后，供应的放射性铯数量和粒度是决定放射性铯浓度空间分布模式的主要因素。
