I’m actually quite heartened that they found today a source of the radiation leak into the ocean. In a post last week I mentioned how the high radiation values several kilometers upstream of the Fukushima site were indicative of more widespread contamination. Actually identifying a source for the leak is a big step forward in addressing the issue. However there may be still as yet unidentified sources of contamination draining directly into the ocean. Here is more information on the marine monitoring being done in the area.
For Wednesday March 30 the global data-assimilating forecast models (~6-10 km resolution) run by the Naval Research Laboratory that I discussed in my prior post on this topic both showed a local ~40-60 km ocean eddy south of the release site (see images below). This eddy was adjacent to the waters of the fast Kuroshio current and rotating in opposite directions in the two models (HYCOM and NCOM). This type of local eddy likely acts to trap radiation in the near-coast realm, which is especially evident in the HYCOM map. While NCOM is run in nowcast mode, HYCOM forecasts out 5 days. So we turn to the HYCOM results that predict for Tuesday April 5 more direct feeding of the flow from near the release site into the swift northeastward Kuroshio current.
The ocean is a very efficient mixer and so any radiation effects should remain relatively local. Unlike for meteorological models, point source tracer release is not generally a capability in ocean models. A very interesting and highly applicable approach is to map the stable and unstable manifolds that determine horizontal stirring using tools from dynamical systems (chaos) theory. I was a co-author on a recent paper on this subject.