Preprints
https://doi.org/10.5194/essd-2022-374
https://doi.org/10.5194/essd-2022-374
 
28 Nov 2022
28 Nov 2022
Status: this preprint is currently under review for the journal ESSD.

Evaluating the transport of surface seawater from 1956 to 2021 using 137Cs deposited in the global ocean as a chemical tracer

Yayoi Inomata1 and Michio Aoyama2 Yayoi Inomata and Michio Aoyama
  • 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)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2022-374', Fabio Conte, 13 Jan 2023 reply
  • AC1: 'Comment on essd-2022-374', Yayoi Inomata, 23 Jan 2023 reply
    • RC2: 'Reply on AC1', Fabio Conte, 23 Jan 2023 reply
      • AC2: 'Reply on RC2', Yayoi Inomata, 24 Jan 2023 reply
    • EC1: 'Reply on AC1', Dagmar Hainbucher, 25 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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Short summary
Behavior of 137Cs in surface seawater in the global ocean was analyzed by using the Historical Artificial radioactivity database in Marine environment. Approximately 32 % of 137Cs existed in the surface seawater in 1970. The 137Cs released into the North Pacific Ocean by large scale nuclear weapons tests transported to the Indian Ocean and then Atlantic Ocean with 4-5 decadal, whereas 137Cs released from nuclear reprocessing plants transported northward in the Arctic Ocean with decadal scale.