North Pacific distribution andbudget of radiocesium releasedby the 2011 Fukushima nuclear
accident
Michio Aoyama, Mizuo Kajino, Taichu Y. Tanaka,
111Tsuyoshi Thomas Sekiyama,1 Daisuke Tsumune,2 Takaki
Tsubono,2 Yasunori Hamajima,3 Toshitaka Gamo,4Mitsuo Uematsu,4 Takeshi Kawano,5 Akihiko Murata,5Yuichiro Kumamoto,5 Masao Fukasawa,5 Chino
Masamichi6
1.Meteorological Research Institute2.Environmental Science Research Laboratory, Central Research Institute of ElectricPower Industry
3.Kanazawa University
4.Atmosphere and Ocean Research Institute , The University of Tokyo
5.Japan Agency for Marine-Earth Science and Technology
6.Japan Atomic Energy Agency

Objectives• To reveal temporal and spatial distributionof radiocaesium released from Fukushima
in the North Pacific Ocean• To estimate total amount of radiocaesium
released from Fukushima NPP accident
including atmospheric release and directdischarge

我々の研究の特徴
北太平洋全域での観測結果から出発し、変動の大きい事故サイト周辺を除く北太平洋で積分した人工放射能総量を推定し使用した。また大気および海洋の輸送モデルも最先端のものを使用している。
外国の研究も含めて先行研究の弱点：複数のモデルや気象条件の解析から判っていることは、放出された人工放射能の2/3以上は北太平洋に降下したことである。
しかし、大気への放出量を推定しているすべての研究は陸上（日本および諸外国）での観測値のみに依っている。
従ってそれらの推定の不確かさが必然的に大きくなる。
得られた成果の自己評価：現時点で最も真実に近い数字を得た。

Temporal and spatial
distribution of radiocaesium
released from Fukushima in theNorth Pacific Ocean
Sampling summary and other data source•NYK ships 7 cruises more than 150
samples, 79 samples done, 2 liters surface
only until end of May 2011.
•NYK ships 10 cruieses from Aug. 2011Now•Tansei-maru, Hakuho-maru and Keifu-maru
surface and vertical samples

放射性セシウムの高精度分析と不確かさ• 収率99%程度で安定した抽出（Aoyama andHirose 2008)事実上の世界標準法• 金沢大学尾小屋地下測定室での測定：総量で1mBq以下まで測定可能• 137Csは表面水すべての値を決定：核実験起源分と整合• 134Csは0.4mBq L-1以下を下限値以下：福島事故由来分を正しく評価できたTable S2. Radiocaesium activity in the North Pacific Ocean in April/May 2011134Cs
Depth Latitude Longitude
Datedbar
Bq m-3
NYK11-043
034.95ºN 143.86ºE 20110331 135 ± 10
NYK11-001
035.68ºN 143.77ºE 20110401 507 ± 33
NYK11-003
036.60ºN 147.60ºE 20110401 1000 ± 71
NYK11-044
035.07ºN 146.44ºE 20110401
34 ± 2.6
NYK11-007
038.18ºN 154.97ºE 20110402 17.7 ± 1.6
NYK11-009
038.08ºN 158.58ºE 20110402
1.9 ± 0.5
NYK11-046035.12ºN 154.14ºE 20110402
9.5 ± 1.1
NYK11-047034.89ºN 158.76ºE 20110402
6.6 ± 0.8
NYK11-048034.76ºN 161.27ºE 20110402
2.6 ± 0.5
NYK11-085033.85ºN 141.31ºE 20110402
ND
NYK11-049
034.09ºN 173.28ºE 20110403
3.4 ± 0.6
NYK11-086
034.33ºN 144.68ºE 20110403 158 ± 11
NYK11-087
034.51ºN 148.40ºE 20110403 98.4 ± 6.6
NYK11-050
035.09ºN 173.38ºE 20110404
0.7 ± 0.4
NYK11-089
034.81ºN 153.51ºE 20110404 10.2 ± 1.1NYK11-090
034.98ºN 156.16ºE 20110404
2.7 ± 0.7
NYK11-091
035.15ºN 158.93ºE 20110405
3.4 ± 0.7
NYK11-092
035.32ºN 161.70ºE 20110405
3.4 ± 0.6
NYK11-095
036.35ºN 178.99ºE 20110406
1.1 ± 0.6
NYK11-021
041.12ºN 167.75ºW 20110407
ND
NYK11-023
042.33ºN 159.88ºW 20110408
0.6 ± 0.3
NYK11-025
043.00ºN 151.95ºW 20110409
ND
NYK11-055
033.46ºN 154.15ºW 20110409
ND
NYK11-098
036.84ºN 163.23ºW 20110409
ND
NYK11-027
043.62ºN 143.57ºW 20110410
0.7 ± 0.3
NYK11-056
032.52ºN 146.59ºW 20110410
ND
NYK11-100035.88ºN 151.92ºW 20110410
ND
NYK11-125033.29ºN 142.20ºE 20110410
3.1 ± 0.6
NYK11-029
038.18ºN 134.97ºW 20110411
ND
NYK11-057
031.32ºN 140.20ºW 20110411
ND
NYK11-101
034.97ºN 146.43ºW 20110411
ND
NYK11-127035.36ºN 147.57ºE 20110411
2.2 ± 0.5
NYK11-102033.92ºN 141.12ºW 20110412
ND
NYK11-103032.50ºN 135.86ºW 20110412
ND
NYK11-129
039.01ºN 152.70ºE 20110412
1.9 ± 0.4NYK11-058
028.94ºN 130.73ºW 20110413
ND137Cs

StationLatitude Longitude

Date

Bq m-3150 ± 8546 ± 281080 ± 60
36.8 ± 2.1
21.5 ± 1.3
3.6 ± 0.4 134
11.3 ± 0.8
6.7 ± 0.6
3.6 ± 0.4
1.7 ± 0.2
6.1 ± 0.5
181 ± 9118 ± 62.4 ± 0.3
12.5 ± 0.8
6.1 ± 0.6
7.5 ± 0.6
5.3 ± 0.4
2.4 ± 0.4
1.8 ± 0.2
1.9 ± 0.2
1.8 ± 0.2
1.4 ± 0.2
1.9 ± 0.2
2.3 ± 0.2
1.8 ± 0.2
1.8 ± 0.2
3.5 ± 0.41.4 ± 0.2
1.9 ± 0.2
2 ± 0.2
3.3 ± 0.4
2 ± 0.2
1.8 ± 0.2
3.6 ± 0.3
1.6 ± 0.2

Example of results

36.60ºN 147.60ºE

20110401

Cs
Bq m-31000 ±7136.35ºN 178.99ºE
41.12ºN 167.75ºW

20110406
20110407

1.1 ± 0.6
ND
Fuksuhima

137Cs

Bq m-31080 ± 60
2.4 ± 0.4
1.8 ± 0.2
Fukushima+ bomb

134Cs:137Cs activity ratioof Fukushima radioactivity
0.99 +- 0.02
Buesseller et al., 2011

NYK11 137Cs April 2011

NYK11 137Cs May 2011

NYK11 134Cs April 2011

Blue: Bq m-3
Green: less than 0.4 Bq m-3

NYK11 134Cs May 2011

Blue: Bq m-3
Green: less than 0.4 Bq m-3

134Cs (left) and 137Cs(right) in April-May 2011

NYK ships : Brown
MR11-03: light blue , Honda et al., 2011(11:00 today)
KT11-06：Blue

1000 Bq m-3

137Cs distribution before Fukushima

Fig. S1. 3-D 137Cs in the Pacific Ocean before Fukushima accident in 2011

137

Area 2Cs / Bq m-3

1001010.11950 1960 1970 1980 1990 2000 2010
Year137Cs trend in the subtropical gyre in the western North PacificOcean.( Aoyama, M., Hirose, K. , TheScientificWorldJOURNAL,4, 200-215, 2004 and update)Past and present
TEPCO: Tokyo Electric Power Company, TEPCO News Press
Releases 2011
http://www.tepco.co.jp/en/press/corp-com/release/30km offshore: Ministry of Education, Culture, Sports,
Science and Technology- Japan (MEXT). Readings of Sea
Area Monitoring at Post Out of Fukushima Dai-ichi NPP
http://www.mext.go.jp/english/radioactivity_level/detail/13041
92.htmHistorical: Aoyama, M., Hirose, K. ,TheScientificWorldJOURNAL, 4, 200-215, 2004 and update
Fukushima: http://www.pref.fukushima.jp/j/kaisui1115.pdf
MEXT:http://radioactivity.mext.go.jp/ja/monitoring_around_Fuku/shimaNPP_sea

NYK: This study

Radiocaesium activity in 4 regions

Fig. S3 Region of interest A, B, C and D

Fig S4. 137Cs and 134Cs activity in region A: eastern
North Pacific Ocean

Fig S5. 137Cs and 134Cs activity in region B: western
North Pacific Ocean

Slow decrease

Fig S6. 137Cs and 134Cs activity in region C:
35ºN−39ºN, 140.7ºE−144ºE

Slow decrease

Fig S7. 137Cs and 134Cs activity in region D: close tothe FNPP1 siteSummary of temporal and spatial
distribution of
Fukushima radiocaesium• Fukushima radiocaesium deposited onwide area in the North Pacific Ocean,
especially in western part of subarctic gyreand subtropical gyre.
• In the eastern North Pacific Ocean,maximum 134Cs activity was ca. 10 Bq m-3
in April/May 2011.
• Detected 134Cs was Fukushima origin and137Cs was Fukushima+ pre-existing bombi i

8 steps to estimate total amount of
released radiocaesium fromFukushima NPP accident
We already have direct discharge estimation.
(3.5±0.7 PBq, Tsumune et al., 2011,presentation 14:45 today)
Step 1: prepare first guess of source term
scenario of atmospheric release. (8.8 PBq)
Step 2: Three atmospheric transport models tosimulate daily deposition
Step 3: Pass daily deposition to an ocean
model in the North Pacific Ocean.

Step 4: simulate radiocaesium activity in thesea
Step 5: Compare simulated activities andobserved activities to evaluate model
simulations.
Step 6: Calculate inventory based on theocean observations (8.1±2.8 PBq) and in themodels.
Step 7: Compare observed inventory andmodel simulated inventories to havecorrection factors of the first guess of thereleased scenario.(factors were 1.7-2.3)
Step 8: Evaluate land portions and ocean

Step 5Figure 3 Model results vs. observation results compariso

Step 6 calculate inventory in the ocean

Fig S10. 10 deg mesh for integration of radiocaesium in
Bq m-2Black dots show observation location.

Table S7. Estimation of total amount in the North Pacific Ocean
Longitude

Latitude

Area
km2

170
150
150200160210160180160
190
170220130230

4040304040403040504030302020

875218758595101156287522387521187522310115628752236112438752231011562101156211167111116920

Total

134

Cs surface
Bq m-3

57
25.5
7.4
7.05
6.8
4.4
3.4
3.3
33
1.7
1.5
0.7
0.6

Inventory
Bq m-2

4275
1913
555
529
510
330
255
248
225
225
128
113
53
45

Total amount in a grid
PBq

3.7
1.5
0.6
0.5
0.4
0.3
0.3
0.2
0.1
0.2
0.1
0.1
0.06
0.05
8.1 +-2.8

Our assumption to estimate inventory

Summary of budget of137Cs• Global fallout as of 1970
290 ±30PBq a• Observed inventory as of 2002
85 PBq b• Estimated inventory as of 2011
69 PBq b• Fukushima direct discharge to the North
Pacific Ocean
3.5 ±0.7 PBq c• Fukushima atmospheric release15 - 20PBq d• Fukushima deposition on land
3.8 – 6.6
PBq d
a: Aoyama, M., Hirose, K., Igarashi, Y., J. ENVIRON. MONITOR., 8, 431-438, 2006
• Aoyama
Totalunpublishedreleasedata
fromFukushimaca.
Cs 19 – 24b:estimeted
3-D dostribution of 137
c: Tsumune
PBq det al., 2011,
d: this studye• IAEA,(Chernobylreleasein 1986
85Apr.
PBqe:
Proceeding ofglobal
an InternationalConference,Vienna, 8-121996 )Our study

Our results are added to Ken’sslide from his presentation(11:30 today)

Conclusions
1. Temporal and spatial distributions of radiocaesium fromFukushima were clearly observed in the North Pacific
Ocean and coupled atmospheric/ocean models simulate
the activity of radiocaesium well.
2. Total amount of the atmospheric deposition in the North
Pacific Ocean from Fukushima was 12 – 15 PBq for both
134Cs and 137Cs. Newly added 12 – 15 PBq by atmosphericdeposition and 3.5 ± 0.7 PBq of direct discharge made the22-27 % increase of total 137Cs inventory in the North
Pacific Ocean.
3. Our study also gives us that total amount of released
radiocaesium from the Fukushima NPP1 accident to the air
was about 15 – 20 PBq for both 134Cs and 137Cs. Total
deposition on land might be around 3.4 – 6.2 PBq whichcorresponds to 23 -33% of total amount to the air.

Acknowledgements
Seawater sampling: Nippon Yusen Kaisha, theNYK Group's corporate social responsibility ,Captains and crew of NYK ships
Sample treatments: Mr. Tomita at KANSO ,Japan
Ocean model: Ms. Taguchi at DCC, Japanpossible pathway ofradiocaesium

Fig. S2 Possible pathway of 137Cs in the Pacific
Ocean