Coastal monitoring: Results from 34 samples, collected in December – March, did not find any of the Fukushima fingerprint isotope, 134Cs (2 year half-life), in coastal waters. Low levels of 137Cs (~30 year half-life) were present in all of the samples. These new data continue to lie along the increasing trend which indicates that the leading edge of the Fukushima plume is in BC’s coastal waters.
The above trend is clear and shows a steady rise that would predict that the average sample will have double the initial background concentrations of 137Cs by this coming summer. While still far below the 10,000 Bq m-3 level of concern for cesium radionuclides in drinking water, these more contaminated samples should also more regularly contain the Fukushima fingerprint isotope, 134Cs.
While the increasing 137Cs trend is clear for the whole coast, it is also evident that each region is telling the story of how ocean waters circulate in coastal British Columbia.
Looking at this regional graph and focusing on the period from August 2015 – February 2016, we see the highest concentrations of 137Cs shift from appearing on the west coast of Vancouver Island northward to Haida Gwaii. (Note: Since the results from March 2016 are incomplete with more samples to be run, I will not interpret findings for that period.) This northward shift of the highest concentrations may indicate that the bifurcation of the North Pacific Current (NPC), the current transporting Fukushima contamination, shifted northward during that period.
As you can see in the figure, the NPC splits into the California Current and the Alaska Current when it hits North America. The exact location of this bifurcation may vary widely from southeast Alaska to central Oregon depending on the prevailing winds. Regardless of where the bifurcation occurs, the Alaska Current receives ~60% of the water from the NPC with the rest heading south along the coast in the California Current. If the bifurcation shifted northward during the last 6 months of 2015, the core of the Fukushima plume would have been pushed with it to the north as well resulting in the increasing values from Haida Gwaii. This may mean that samples from more southerly stations will increase at a slower rate. Validation of this proposed shift in the current bifurcation will require further investigation into satellite data which proved unavailable prior to publication.
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