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| Titel |
Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident |
| VerfasserIn |
M. A. Charette, C. F. Breier, P. B. Henderson, S. M. Pike, I. I. Rypina, S. R. Jayne, K. O. Buesseler |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 3 ; Nr. 10, no. 3 (2013-03-28), S.2159-2167 |
| Datensatznummer |
250018177
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| Publikation (Nr.) |
 copernicus.org/bg-10-2159-2013.pdf |
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| Zusammenfassung |
| Radium has four naturally occurring isotopes that have proven useful in
constraining water mass source, age, and mixing rates in the coastal and
open ocean. In this study, we used radium isotopes to determine the fate and
flux of runoff-derived cesium from the Fukushima Dai-ichi Nuclear Power Plant (FNPP).
During a June 2011 cruise, the highest cesium (Cs) concentrations were found along
the eastern shelf of northern Japan, from Fukushima south, to the edge of
the Kuroshio Current, and in an eddy ~ 130 km from the FNPP
site. Locations with the highest cesium also had some of the highest radium
activities, suggesting much of the direct ocean discharges of Cs remained in
the coastal zone 2–3 months after the accident. We used a short-lived Ra
isotope (223Ra, t1/2 = 11.4 d) to derive an average water mass
age (Tr) in the coastal zone of 32 days. To ground-truth the Ra age
model, we conducted a direct, station-by-station comparison of water mass
ages with a numerical oceanographic model and found them to be in excellent
agreement (model avg. Tr = 27 days). From these independent Tr
values and the inventory of Cs within the water column at the time of our
cruise, we were able to calculate an offshore 134Cs flux of
3.9–4.6 × 1013 Bq d−1. Radium-228 (t1/2 = 5.75 yr) was used to derive
a vertical eddy diffusivity (Kz) of 0.7 m2 d−1 (0.1 cm2 s−1); from this Kz and 134Cs inventory, we estimated a
134Cs flux across the pycnocline of 1.8 × 104 Bq d−1 for the
same time period. On average, our results show that horizontal mixing loss
of Cs from the coastal zone was ~ 109 greater than
vertical exchange below the surface mixed layer. Finally, a mixing/dilution
model that utilized our Ra-based and oceanographic model water mass ages
produced a direct ocean discharge of 134Cs from the FNPP of 11–16 PBq
at the time of the peak release in early April 2011. Our results can be used
to calculate discharge of other water-soluble radionuclides that were
released to the ocean directly from the Fukushima NPP. |
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