1. The document discusses the distribution of cesium-137 (137Cs) in the ocean derived from nuclear weapons testing and the Fukushima Daiichi nuclear accident. 2. It estimates that 3.6-7 PBq of 137Cs entered the ocean from Fukushima through atmospheric deposition and direct release, with more than 99% transported offshore and into the ocean interior. 3. Sampling between 2011-2012 showed the Fukushima-derived 134Cs moving eastward and subducting into the ocean interior, indicating it has started traveling southwest into the ocean interior along the same pathway as previously observed for weapons testing 137Cs.

1. Fukushima derived radionuclides in the ocean
Michio Aoyama
Meteorological Research Institute, Japan
Talk Outline
1. Global cesium distribution and mass balance
- pre Fukushima
2. Fukushima cesium
- mass balance of 137Cs
- surface transport and subduction to the ocean interior
IAEA Scientific Forum 17-18 September 2013 Vienna, Austria

2. Decay corrected accumulative fallout of 137Cs
derived from atmospheric weapons tests as of 1970
Michio Aoyama, Katsumi Hirose and Yasuhito Igarashi, Re-
construction and updating our understanding on the global
weapons tests 137Cs fallout, Journal of Environmental
Monitoring, 8, 431-438, 2006.
In Northern Hemisphere
765±79 PBq 1970
In the North Pacific Ocean
290±30 PBq 1970
69±7 PBq 2011
Chernobyl accident 1986
85 PBq

3. A pathway of weapons tests derived
137Cs in the North Pacific Ocean,
tracer of sea water movement
Fig. S2 Possible pathway of 137Cs in the Pacific Ocean based on 3-D
observations of 137Cs in 2000s (Aoyama et al., 2013)
We can expect that Fukushima
origin radiocaesium should go
same pathway

4. Pathways of Fukushima derived
radionuclides to the Ocean
• Atmospheric deposition
• Direct release
• Groundwater discharge
• River runoff
TEPCO Press release
137Cs : 1.8E+12 Bq/m3
Simulated atmospheric deposition of
137Cs (Bq m-2) (by Masingar II of MRI)
(Aoyama et al., in preparation)
4

5. Boiling Water Reactor Systems "Nuclear
Reactor Concepts" Workshop Manual,
U.S. NRC
3.6±0.7 PBq to the ocean
(Tsumune et al., 2013)
14–17 PBq to the atmosphere
700 PBq was in the three core 140 PBq in stagnant water
(Nishihara et al.,, 2011) (Nishihara et al., 2011)
140 PBq in stagnant water
12 - 15 PBq to the ocean
137Cs mass balance

6. More than 99% of released radioaesium to the ocean
was transported offshore, then to the ocean interior
30 GBq day-1
Revised estimation

7. R/V Mirai
NYK AQUARIUS
凌風丸
R/V Hakuho Maru
NYK Heijin
Sampling locations during the period from
March 2011 to Oct. 2012

8. 10 Bq m-3
Aoyama, M. et al., Biogeosciences, 10, 3067-3078, 2013.
10 Bq m-3
Aoyama, M. et al., Biogeosciences, 10, 3067-3078, 2013.
134Cs in surface water in Oct. – Dec. 2011 134Cs in surface water in Jan. – Mar. 2012
(Aoyama et al., BG 10 3067-3078, 2013)
Apr-Jun
2011
Jul-Sep
2011
Oct-Dec
2011
Jan-Mar
2012
Surface speed of contaminated water ca. 7 km day-1
8
X

9. 0 5 10 15 20 250
100
200
300
400
500
600
700
800
at 40N, 165E on 12 Oct. 2011 Stn KS1109-3101
and
at 39N, 165E on 11 June 2012 stn RF1205-4418
KS1109-3101
RF1205-4418
134
Cs / Bq m
-3
Depth/m
Oxygen maximum
Sigma0=26.3
Station 3101 4418
Year 2011 2012
Month 10 6
Bq m
-2
Bq m
-2
134Cs
inventory
2710+-210 2350+-190
0 - 200 m 2150 520
Deeper than
200 m 520 1830
Oct. 2011
Over time, Cs moves east and subducted in the ocean interior
June 2012

10. Bq m-3
137Cs cross section along 165 ºE in June 2012
Start of travel into ocean interior
N

11. Possible pathway of Fukushima derived
radionuclides in the North Pacific Ocean
Fig. S2 Possible pathway of 137Cs in the Pacific Ocean
We found start of travel of Fukushima derived
radioactivity in the ocean interior.

12. Summary of budget of 137Cs
for pre- and after the Fukushima accident
Main portion of Fukushima derived radioactivity
already subducted into the ocean interior and is
moving to southwest ward.