While the levels of 137Cs in the affected region prior to the accident ranged from 0.68 to 1.7 Bq/kg (dry weight) (MEXT, 2011), values of several hundred Bq/kg are now common. The total inventory of 137Cs accumulated in the upper

3 cm of surface sediments off the Miyagi, Fukushima and Ibaraki prefectures has been estimated to be 3.78 × 1013 Bq (Kusakabe et al., 2013), which is 0.9–1.4% of the total 137Cs flux from the PD0325901 order plant to the ocean estimated by Tsumune et al. (2012). The distribution of 137Cs on the seafloor determined from samples obtained off Fukushima shows considerable spatial variability in concentration, exhibiting no obvious correlation with proximity to the F1NPP. While remobilization of surface layers and local heterogeneity in the physical CTLA-4 antibody and chemical characteristics of the sediments have been identified as potential causes for the variability seen (Otosaka and Kobayashi, 2013), it has been

pointed out that sediment mineralogy alone cannot completely account for the spatial distribution of 137Cs in the sediments (Kusakabe et al., 2013). Furthermore, since the information obtained through sampling is discrete, with points often separated by several tens of kilometers, it is possible that variations in concentration exist on spatial scales that have not been captured through sampling. While this is not a problem in areas where it has been demonstrated that the levels of seafloor radiation change gradually (Thornton et al., 2013), the local scale distribution of radioactive material on the seafloor

following the accident is largely unknown. The lack of information raises concerns regarding our ability to predict the effects of Florfenicol the accident on the marine ecosystem and limits our ability to form effective recovery strategies. In this work, we apply in situ measurement techniques to map the continuous distribution of 137Cs on the seafloor, and reveal the existence of a number of local 137Cs anomalies within 20 km of F1NPP. The size and distribution of these anomalies is closely related to meter scale features of the seafloor terrain, and the concentrations of 137Cs are often more than an order of magnitude higher than in the surrounding regions. The existence of these anomalies should be taken into account when planning future survey efforts, and when considering the potential effects of 137Cs on marine ecology. The instrument used in this work consists of a gamma ray spectrometer contained within a flexible rubber hose that is towed along the seafloor by a ship, as illustrated in Fig. 1 (Jones, 2001). The instrument, called the RESQ hose (RESQ: Radiometric Environment Survey and Quantification), is 8 m long with an external diameter of 0.145 m and weighs 135 kg in air and 115 kg in water.