Radiation concentrations in the ocean surface offshore of Fukushima have been dropping. The latest validation work of the University of Toulouse’s SIROCCO model shows the spatial distribution of sampled and modeled surface radiation levels. Validation plots are averaged over 7 days. The station average is shown by the colored circle, with more observations (1, at Kodaka; up to 14, at Fukushima) shown as a larger circle.
The extension of the ocean radiation plume to the northeast is still evident below. But values at the Fukushima plant for the week ending May 2 (below right) are reduced by about a factor of 2 relative to those from the week ending April 11. For the week ending April 25 (below left) transport immediately adjacent to the Fukushima plant was more southward than in prior or successive weeks.
This movement was caused by a southward wind-driven flow that occurred for a several day period during the simulation time, as shown below in a snapshot for April 19.
Meanwhile, measurements of the seabed are picking up high radiation values. Samples taken 3 km & 15 km offshore at 20-30 m deep showed elevated levels. And scientists are calling for more marine life monitoring, and more multi-agency assessments.