In the aftermath of an earthquake and tsunami on 11 March 2011 considerable amounts of radioactive materials were accidentally released into the sea off Fukushima-Daiichi, Japan. This study uses a three-dimensional eddy-resolving oceanic general circulation model to explore potential pathways of a tracer, similar 5 to 137 Cs, from the coast to the open ocean. Results indicate that enhanced concentrations meet a receding spring bloom offshore and that the area of enhanced concentrations offshore

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... is strongly determined by surface mixed layer dynamics. However, huge uncertainties remain. Among them are the realism of the simulated cross-shelf transport and apparently inconsistent estimates of the particle reactivity of 137 Cs which 10 are discussed in a brief literature review. We argue that a comprehensive set of 137 Cs measurements, including sites offshore, could be a unique opportunity to both evaluate and advance the evaluation of oceanic general circulation models. We expect that, driven by concerns about radiation in seafood, a large dataset of radiation measurements in seawater will be collected and be available to the scientific community in the near future. Such a dataset could be a unique opportunity to benchmark the exchange, or interconnection, between the shelf sea and the open ocean as modeled with todays oceanic general circulation models. We feel that such a bench-5 mark would be an important step towards a more comprehensive understanding of global biogeochemistry as expressed in models because the shelf seas host a significant fraction of oceanic primary production and carbon burial even though their surface area make up less than 10 % of the ocean's surface (e.g., Muller-Karger et al., 2005) . Also, there is some evidence that large open-ocean regions are influenced by nutrients 10 OSD 8, Circulation model We use the MOM4p0d (GFDL Modular Ocean Model v.4, Griffies et al., 2005) zcoordinate, free surface ocean general circulation model. The model region covers the entire global ocean with an enhanced meridional and zonal resolution around Japan. 5 OSD 8, Abstract An intercomparison of modeled tracer distribution with climatological surface chlorophyll concentrations observed from space (calculated from SeaWiFS level Abstract 8, Abstract Tracer distribution off Japan H.