28 Aug 2013

Multi-decadal projections of surface and interior pathways of the Fukushima Cesium-137 radioactive plume (ScienceDirect/EurekAlert, abstract, edited)

[Source: Science Direct, full page: (LINK). Abstract, edited. Via EurekAlert.]

Deep Sea Research Part I: Oceanographic Research Papers, Volume 80, October 2013, Pages 37–46

Multi-decadal projections of surface and interior pathways of the Fukushima Cesium-137 radioactive plume

Vincent Rossia, b, Erik Van Sebilleb, c, Alexander Sen Guptab, c, Véronique Garçond, Matthew H. Englandb, c

a IFISC (Institute for Cross-Disciplinary Physics and Complex Systems), CSIC-UIB, Palma de Mallorca, 07122 Spain; b Climate Change Research Centre, University of New South Wales, Sydney 2052, Australia; c ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney 2052, Australia; d Laboratoire d’Etude en Géophysique et Océanographie Spatiales, CNRS/UPS/IRD/CNES, 14 av. E. Belin, Toulouse 31400, France

Received 8 February 2013 - Revised 16 May 2013  - Accepted 29 May 2013  - Available online 15 June 2013

 

Highlights

  • Cs-137 plume strongly diluted by July 2011, reaches American coast by 2014.
  • Mode water formation and persistent upwelling affect Cs-137 concentrations.
  • Cs-137 enters the deep ocean and exits the North Pacific in the next 30 years.
  • Sensitivity to uncertainties in the source function and to interannual variability.

 

Abstract

Following the March 2011 Fukushima disaster, large amounts of water contaminated with radionuclides, including Cesium-137, were released into the Pacific Ocean. With a half-life of 30.1 years, Cs-137 has the potential to travel large distances within the ocean. Using an ensemble of regional eddy-resolving simulations, this study investigates the long-term ventilation pathways of the leaked Cs-137 in the North Pacific Ocean. The simulations suggest that the contaminated plume would have been rapidly diluted below 10,000 Bq/m3 by the energetic Kuroshio Current and Kurushio Extension by July 2011. Based on our source function of 22 Bq/m3, which sits at the upper range of the published estimates, waters with Cs-137 concentrations >10 Bq/m3 are projected to reach the northwestern American coast and the Hawaiian archipelago by early 2014. Driven by quasi-zonal oceanic jets, shelf waters north of 45°N experience Cs-137 levels of 10–30 Bq/m3 between 2014 and 2020, while the Californian coast is projected to see lower concentrations (10–20 Bq/m3) slightly later (2016–2025). This late but prolonged exposure is related to subsurface pathways of mode waters, where Cs-137 is subducted toward the subtropics before being upwelled from deeper sources along the southern Californian coast. The model suggests that Fukushima-derived Cs-137 will penetrate the interior ocean and spread to other oceanic basins over the next two decades and beyond. The sensitivity of our results to uncertainties in the source function and to inter-annual to multi-decadal variability is discussed.

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