Distribution and fate of 129I and 236U in the German GEOTRACES expedition to the Arctic Ocean in 2015

Michiel.Rutgers.v.d.Loeff [ at ] awi.de


The GEOTRACES section (GN04, TransArc-II) on board the German R/V Polarstern covered a full transect in the Arctic Ocean from the Barents Sea to the Makarov Basin, crossing the Nansen and Amundsen basins. The distributions of 129I concentrations and 236U/238U atomic ratios obtained from more than 300 seawater samples are consistent with different water masses. Atlantic Waters flowing into the Arctic Ocean bring the signal of the two European nuclear reprocessing plants of Sellafield and La Hague, with the highest 129I concentrations (> 1500 x107 at·kg-1) and 236U/238U ratios (> 3000 x10-12) in the Norwegian shelf, where the Norwegian Coastal Current penetrates into the Barents Sea. Lowest 129I concentrations (< 5 x107 at·kg-1) and 236U/238U ratios (< 10 x10-12) were observed in the deep and bottom waters of the Makarov Basin, proving the long-term isolation of these waters. The combination of 129I/236U and 236U/238U atomic ratios can be used as a dual tracer to understand sources of artificial radionuclides to the Arctic Ocean [1]. This dataset confirms that global fallout and reprocessing plants are the main suppliers of 129I and 236U to the Arctic Ocean, while Siberian rivers would be minor contributors [2]. Different from previous assumptions, results show that the Barents Sea Branch Water (BSBW) has a higher 129I/236U atom ratio than expected from the mixed signal of Sellafield and La Hague. This high 129I/236U ratio suggests that the contribution of La Hague relative to Sellafield is larger than expected in this water mass. Together with the data from other GEOTRACES cruises, a synoptic distribution of 129I and 236U in the Arctic Ocean will be available soon, which will help understanding major water circulation patterns in the Arctic Ocean. [1] M. Christl, N. Casacuberta, C. Vockenhuber, E. C., P. Bailly du Bois, J. Herrmann, H.A. Synal, Reconstruction of the 236U input function for the Northeast Atlantic Ocean: Implications for 129I/236U and 236U/238U-based tracer ages, Journal of Geophysical Research: Oceans, (2015). [2] N. Casacuberta, P. Masque, G. Henderson, M.R. van der Loeff, D. Bauch, C. Vockenhuber, A. Daraoui, C. Walther, H.A. Synal, M. Christl, First 236U data from the Arctic Ocean and use of 236U/238U amd 129I/236U as a new dual tracer, Earth and Planetary Science Letters, 440 (2016) 127-134.

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ASLO Ocean Sciences Meeting, 26 Feb 2017 - 03 Mar 2017, Honolulu, Hawaii.
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Casacuberta, N. , Vockenhuber, C. , Castrillejo, M. , Masqué, P. , Synal, H. A. and Rutgers v. d. Loeff, M. (2017): Distribution and fate of 129I and 236U in the German GEOTRACES expedition to the Arctic Ocean in 2015 , ASLO Ocean Sciences Meeting, Honolulu, Hawaii, 26 February 2017 - 3 March 2017 .

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