The latest ocean plume validation plots from the University of Toulouse’s SIROCCO model are averaged over 7 days and encapsulate more observations than before. In the week ending April 18 the radiation values were on the decline from the prior week. 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 also evident.
The latest predicted concentrations for April 21 are shown below and reveal transport turning toward the southeast below Oshika Peninsula. This interesting pattern has a mushroom shape at its tip – with embedded rotating vortices. These types of circulations are quite common in the coastal ocean and are frequently seen along with “squirts” and “filaments”. As the winds have been frequently northward or northeastward lately, it is expected that the northward ocean jet is associated with coastal upwelling. There would then exist relatively cooler and more nutrient-rich water inshore of the current that would attract organisms. The biological productivity in these waters should be sampled to assess the impact of the radiation on these regions of presumed higher productivity.
Meanwhile, retrospective assessments of the magnitude of the release into the ocean have appeared:
“…water with a radioactivity 20,000 times [4,700 terabecquerels] over the permissible annual limit entered the Pacific Ocean from leaks at the crisis-hit Fukushima No. 1 power plant…
…the concentration of radioactive substances [in 520 tons] that likely contaminated the sea from a cracked pit [of reactor 2] between April 1 and 6 was about 30,000 times higher than the low-level radioactive water Tepco deliberately dumped into the ocean between April 4 and 10. Tepco discharged around 10,000 tons of relatively low-level water to secure storage space for more dangerous water.” more details
Additional sources of radiation leaking to the ocean cannot be ruled out, but have not been identified so far. And underground barriers are being considered to protect the groundwater from more contamination. Flooding of the reactors to cool them continues.