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| Titel |
Estimate of radiocaesium derived FNPP1 accident in the North Pacific Ocean |
| VerfasserIn |
Yayoi Inomata, Michio Aoyama, Takaki Tsubono, Daisuke Tsumune, Masatoshi Yamada |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150849
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| Publikation (Nr.) |
 EGU/EGU2017-15364.pdf |
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| Zusammenfassung |
| 134Cs and 137Cs (radiocaesium) were released to the North Pacific Ocean by direct discharge
and atmospheric deposition released from the TEPCO Fukushima Dai-ichi Nuclear Power
Plant (FNPP1) accident in 2011. After the FNPP1 accident, measurements of 134Cs and
137Cs were conducted by many researches. However, those results are only snapshots in order
to interpret the distribution and transport of the released radiocaesium on a basin scale. It is
recognized that estimation of the total amount of released 134Cs and 137Cs is necessary to
assess the radioecological impacts of their release on the environment. It was reported that the
inventory of 134Cs or 137Cs on the North Pacific Ocean after the FNPP1 accident
was 15.2-18.3 PBq based on the observations (Aoyama et al., 2016a), 15.3±1.6
PBq by OI analysis (Inomata et al., 2016), 16.1±1.64 PBq by global ocean model
(Tsubono et al., 2016). These suggest that more than 75 % of the atmospheric-released
radiocaesium (15.2-20.4 PBq; Aoyama et al., 2016a) were deposited on the North Pacific
Ocean.
The radiocaesium from the atmospheric fallout and direct discharge were expected to
mixing as well as diluting near the coastal region and transported eastward across the North
Pacific Ocean in the surface layer. Furthermore, radicaesium were rapidly mixed and
penetrated into the subsurface water in the North Pacific Ocean in winter. It was revealed that
these radiocaesium existed in the Subtropical Mode Water (STMW, Aoyama et al., 2016b;
Kaeriyama et al., 2016) and Central Mode Water (CMW, Aoyama et al., 2016b),
suggesting that mode water formation and subduction are efficient pathway for
the transport of FNPP1 derived radiocaesium into the ocean interior within 1-year
timescale. Kaeriyama et al. (2016) estimated the total amount of FNPP1 derived
radiocaesium in the STMW was 4.2 ± 1.1 PBq in October–November 2012. However,
there is no estimation of the amount of radiocaesium in the CMW. Therefore, it is
impossible to discuss about the mass balance of radiocaesium injected into the
North Pacific Ocean. In this study, we conducted the optimum interpolation (OI)
analysis to estimate the inventory of radiocaesium in the ocean interior as well as
surface sweater by using the measured activities. Furthermore, transport speed of
radiocaesium in the surface layer in the North Pacific Ocean were also estimated.
The data used in this study were derived from all of the available data reported
by such as the Tokyo Electric Power Company (TEPCO), the Japanese Ministry
of Education, Culture, Sports, Science and Technology (MEXT), and voluntary
cargo ships. The data analysis period was until December 2015 after the FNPP1
accident.
It was found that the radiocaesium across the North Pacific Ocean were reached to 180˚
E around 40˚ N latitude at July, 2012 by OI analysis. The transport speed was estimated to
8.5 cm s−1. These were reached to the coastal site of America continent and the activities
were increased after the year of 2014. The transport speed across 70˚ W (40˚ N latitude) was
decreased to 5.2 cm s−1.
We estimated the inventory of radiocaesium in the surface seawater (depth; 0-100m)
during the periods from August to December, 2012, based on the OI analysis. Amount of
134Cs inventory was estimated to 4.7 PBq with decay-corrected to 1 October 2012 (7.9 PBq
at the time on 11 March 2011). (In the case of 137Cs, the inventory was estimated to 12.5 PBq
with decay-corrected to 1 October 2012 and 13 PBq at the time on 11 March 2011 which
includes pre-Fukushima 137Cs derived from atmospheric weapons test conducted in late
1950s and eraly 1960s). These correspond to 43-53% of the injected 134Cs in the North
Pacific Ocean. It was reported that the 4.2±1.1 PBq of 134Cs were distributed in the STMW
(Kaeriyama et al., 2016), which corresponds to 22-28% of the injected 134Cs in
the North Pacific Ocean. Taking into account these estimation, FNPP1 derived
radiocaesium existed in the CMW in the North Pacific Ocean would be about 3-6
PBq.
(References)
Aoyama, M., Hamajima, Y., Hult, M., Uematsu, M., Oka, E., . 2016. 134Cs and 137Cs in
the North Pacific Ocean derived from the March 2011 TEPCO Fukushima Dai-Ichi Nuclear
Power Plant accident, Japan. Part one: surface pathway and vertical distributions. J.
Oceanogr. 72:53–65.
Aoyama, M., Kajino, M., Tanaka, T. Y., Sekiyama, T.T., Tsumune, D., Tsubono, T.,
Hamajima, Y., Inomata, Y., Gamo, T., .2016. 134Cs and 137Cs in the North Pacific Ocean
derived from the March 2011 TEPCO Fukushima Daiichi Nuclear Power Plant accident,
Japan. Part two: estimation of 134Cs and 137Cs inventories in the North Pacific Ocean. J.
Oceanogr. 72:53–65.
Inomata, Y., Aoyama, M., Tsubono, T., Tsumune, D., Hirose, K. 2016. Spatial and
temporal distributions of 134Cs and 137Cs derived from the TEPCOFukushima Daiichi
nuclear power plant accident in the North Pacific Ocean by using optimal interpolation
analysis. Environ. Sci. Process. Impacts 18:126–36.
Tsubono, T., Misumi. K., Tsumune, D., Bryan, F.O., Hirose, K., Aoyama, M. 2016.
Evaluation of radioactive cesium impact from atmospheric deposition and direct release
fluxes into the North Pacific from the Fukushima Daiichi nuclear power plant. Deep-Sea Res.
I. 115:10–21.
Kaeriyama, H., Shimizu, Y., Setou, T., Kumamoto, Y., Okazaki, M., Ambe, D., Ono, T.
2016. Intrusion of Fukushima-derived radiocaesium into subsurface water due to formation of
mode waters in the North Pacific. Sci. Report., 6:22010 | DOI: 10.1038/srep22010. |
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