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| Titel |
Distribution of the Fukushima-derived radionuclides in seawater in the Pacific off the coast of Miyagi, Fukushima, and Ibaraki Prefectures, Japan |
| VerfasserIn |
S. Oikawa, H. Takata, T. Watabe, J. Misonoo, M. Kusakabe |
| 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. 7 ; Nr. 10, no. 7 (2013-07-25), S.5031-5047 |
| Datensatznummer |
250018360
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| Publikation (Nr.) |
 copernicus.org/bg-10-5031-2013.pdf |
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| Zusammenfassung |
| The activities of artificial radionuclides in seawater samples collected off
the coast of Miyagi, Fukushima, and Ibaraki Prefectures were measured as part
of a monitoring program initiated by the Japanese Ministry of Education,
Sports, Science and Technology immediately after the Fukushima Dai-ichi
Nuclear Power Plant accident. The spatial and temporal distributions of those
activities are summarized herein. The activities of strontium-90, iodine-131,
cesium-134 and -137 (i.e. 90Sr, 131I, 134Cs, and 137Cs)
derived from the accident were detected in seawater samples taken from areas
of the coastal ocean adjacent to the power plant. No 131I was detected
in surface waters (≤ 5 m depth) or in intermediate and bottom waters
after 30 April 2011. Strontium-90 was found in surface waters collected from
a few sampling stations in mid-August 2011 to mid-December 2011. Temporal
changes of 90Sr activity in surface waters were evident, although the
90Sr activity at a given time varied widely between sampling stations.
The activity of 90Sr in surface waters decreased slowly over time, and
by the end of December 2011 had reached background levels recorded before the
accident. Radiocesium, 134Cs and 137Cs, was found in seawater
samples immediately after the accident. There was a remarkable change in
radiocesium activities in surface waters during the first 7 months (March
through September 2011) after the accident; the activity reached a maximum in
the middle of April and thereafter decreased exponentially with time.
Qualitatively, the distribution patterns in surface waters suggested that in
early May radiocesium-polluted water was advected northward; some of the
water then detached and was transported to the south. Two water cores with
high 137Cs activity persisted at least until July 2011. In subsurface
waters radiocesium activity was first detected in the beginning of April
2011, and the water masses were characterized by σt (an indicator
of density) values of 25.5–26.5. From 9–14 May to 5–16 December 2011, the
depths of the water masses increased with time, an indication that deepening
of the isopycnal surfaces with time can be an important mechanism for the
transport of radiocesium downward in coastal waters. During 4–21 February
2012, the water column became vertically homogeneous, probably because of
convective mixing during the winter; the result was nearly constant values of
radiocesium activity throughout the water column from the surface to the
bottom (~200 m depth) at each station. |
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