Evaluating the transport of surface seawater from 1956 to 2021 using 137Cs deposited in the global ocean as a chemical tracer
- 1Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, 920-1192, Japan
- 2Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, 305-8572, Japan
- 1Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, 920-1192, Japan
- 2Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba, 305-8572, Japan
Abstract. We analysed the spatiotemporal variations in the 137Cs activity concentrations in global ocean surface seawater from 1956 to 2021 using the HAMGlobal2021: Historical Artificial radioactivity database in Marine environment, Global integrated version 2021. The global ocean was divided into 37 boxes. The 0.5-yr average value of 137Cs in each box, except in the northern North Atlantic Ocean and its marginal sea, decreased exponentially in 1970–2010, immediately before the Fukushima Nuclear Power Plant (F1NPS) accident. The 137Cs inventory in the surface mixed layer in 1970 was estimated to be 187 ± 26 PBq. In 1975 and 1980, the 137Cs inventory increased to 201 ± 28 and 210 ± 12 PBq, respectively, due to direct discharge from the Sellafield and La Hague nuclear fuel reprocessing plants. In 2011, the 137Cs inventory in the global ocean mixed layer increased to 48.1±12.1 PBq compared to that before the F1NPS accident, in which the contribution from the accident was estimated to be approximately 15.5 ± 3.9 PBq. The distribution and variation in 137Cs in global surface seawater reflect basin-scale or global-scale transport. Mass balance analysis indicates that 137Cs deposited by the global fallout in the western North Pacific Ocean moves to the eastern North Pacific Ocean. Subsequently, 137Cs is transported southwards, followed by westwards transport in the subtropical and equatorial Pacific Ocean and inflow into the Indian Ocean via the Indonesian Archipelago. The longer apparent half residence times in the Indonesian Archipelago (36.7 years from 1973 to 1997), South Atlantic Ocean (37.0 years from 1973 to 2004), and Central Atlantic Ocean (43.5 years from 1993 to 2016) also support the interpretation of the global-scale transport of 137Cs from the western North Pacific Ocean to the Indian and Atlantic Oceans. In the northern North Atlantic Ocean and its marginal sea, 137Cs discharged from nuclear reprocessing plants is transported to the North Sea, Barents Sea and coast of Norway, and Arctic Ocean on a decadal scale. The dataset is available at http://dx.doi.org/10.34355/CRiED.U.Tsukuba.00085 (Aoyama, 2021), http://dx.doi.org/10.34355/Ki-net.KANAZAWA-U.00149 (Inomata and Aoyama, 2022a), http://dx.doi.org/10.34355/Ki-net.KANAZAWA-U.00150 (Inomata and Aoyama, 2022b), http://dx.doi.org/10.34355/Ki-net.KANAZAWA-U.00151 (Inomata and Aoyama, 2022c).
Yayoi Inomata and Michio Aoyama
Status: open (until 05 Mar 2023)
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RC1: 'Comment on essd-2022-374', Fabio Conte, 13 Jan 2023
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Dear Author,
The work is flowing and clear in the exposition. There are some graphical inaccuracies and greater attention to local processes such as in the Mediterranean and Black Sea.
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Please, correct the UNSCEAR quote which is incorrect in almost all of the text.
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line 56 the dissolved 137 Cs
line 490 Papucci
line 1850 Papucci, C., Salvi, S., Lorenzelli R.
line 1857 Papucci
please, define tap in a more explicit way: apparent half-life
please, define the start of half year because layering could affect the mixed layer
Correct the follow figure:fig 1 (a-b) unreadable labels and coordinates
fig 2 label, mediterranean
fig 5 b unreadable coordinates
fig 6 b unreadable coordinates
fig 7 (a-j) unreadable label
fig 8 (a-j) unreadable coordinates
fig 10 (a b) unreadable coordinates
fig 12 (a-j) unreadable labels and coordinates
fig 18 (b) unreadable coordinates
fig 19 (a-i) unreadable label
fig 20 (a-i) unreadable coordinates
line 480
the value that is almost equal to the value before Chernobyl accident demonstrates the importance of increased release from the rivers flowing through the area affected by the accident: in fact, in Mediterranean Sea, where this input is negligible, the value in 2002 were less than half pre-Chernobyl accident.Â
Thank you
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AC1: 'Comment on essd-2022-374', Yayoi Inomata, 23 Jan 2023
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Dear reader
I am now modified the manuscript by referee's comments.
I ask you a question.
After the manuscript opened as discussion paper, Prof. Pascal Bailly du Bois send me their data.
The data was measured in the North European Continental Shelf, Atlantic Ocean, English Channel, Irish Sea, North Sea, Barents Sea, Indian Ocean. There were 2046 record. Is it possible to use (include) these data for revised version? I think that contents of paper do not change. And estimated inventory with including additional data is almost same to the inventory in the discussion paper.Â
Best regards, Yayoi Inomata-
RC2: 'Reply on AC1', Fabio Conte, 23 Jan 2023
reply
Dear Author,
I think adding data to support existing ones can only make the work more robust, so I agree.
Best regards
Fabio Conte
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AC2: 'Reply on RC2', Yayoi Inomata, 24 Jan 2023
reply
Dear Prof. Fabio Conte
Thank you very much for ryour reply. IÂ inclued the data to the revised version. Best regards, Yayoi INOMATA
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AC2: 'Reply on RC2', Yayoi Inomata, 24 Jan 2023
reply
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EC1: 'Reply on AC1', Dagmar Hainbucher, 25 Jan 2023
reply
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Updates of data can be performed during or after the review process. However, the content of the manuscript should still be valid.
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RC2: 'Reply on AC1', Fabio Conte, 23 Jan 2023
reply
Yayoi Inomata and Michio Aoyama
Data sets
Histroical Artifial radioacitity database in Marine environmnet, Global2021 Aoyama, M. https://doi.org/10.34355/CRiED.U.Tsukuba.00085
137Cs measurement points in the surface seawater in the global ocean based in the HAM database2021 Inomata, Y. and Aoyama, M. https://doi.org/10.34355/Ki-net.KANAZAWA-U.00149
Temporal variations of 137Cs activity concentrations and these 0.5-yr average values in the surface seawater in the global ocean Inomata, Y. and Aoyama, M. https://doi.org/10.34355/Ki-net.KANAZAWA-U.00150
Dataset of 0.5-yr average values of 137Cs activity concentrations in the surface seawater in the global ocean during the period from 1957 to 2021 Inomata, Y. and Aoyama, M. https://doi.org/10.34355/Ki-net.KANAZAWA-U.00151
Yayoi Inomata and Michio Aoyama
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