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Article Dans Une Revue Biogeosciences Année : 2018

Tracing water masses with 129I and 236U in the subpolar North Atlantic along the GEOTRACES GA01 section

Résumé

Pathways and timescales of water mass transport in the subpolar North Atlantic Ocean (SPNA) have been investigated by many studies due to their importance for the meridional overturning circulation and thus for the global ocean. In this sense, observational data on geochemical trac-ers provide complementary information to improve the current understanding of the circulation in the SPNA. To this end, we present the first simultaneous distribution of artificial 129 I and 236 U in 14 depth profiles and in surface waters along the GEOVIDE section covering a zonal transect through the SPNA in spring 2014. Our results show that the two tracers are distributed following the water mass structure and that their presence is largely influenced by the global fallout (GF) and liquid effluents discharged to northwestern European coastal waters by the Sellafield and La Hague nuclear reprocessing plants (NRPs). As a result, 129 I concentrations and 236 U/ 238 U atom ratios and 129 I/ 236 U atom ratios display a wide range of values: (0.2-256) ×10 7 at kg −1 (40-2350) ×10 −12 and 0.5-200, respectively. The signal from NRPs, which is characterised by higher 129 I concentrations and 129 I/ 236 U atom ratios compared to GF, is transported by Atlantic Waters (AWs) into the SPNA, notably by the East Greenland Current (EGC)/Labrador Current (LC) at the surface and by waters overflowing the Greenland-Scotland passage at greater depths. Nevertheless, our results show that the effluents from NRPs may also directly enter the surface of the eastern SPNA through the Iceland-Scotland passage or the English Channel/Irish Sea. The use of the 236 U/ 238 U and 129
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Dates et versions

hal-02322755 , version 1 (21-05-2020)

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Maxi Castrillejo, Núria Casacuberta, Marcus Christl, Christof Vockenhuber, Hans-Arno Synal, et al.. Tracing water masses with 129I and 236U in the subpolar North Atlantic along the GEOTRACES GA01 section. Biogeosciences, 2018, 15 (18), pp.5545-5564. ⟨10.5194/bg-15-5545-2018⟩. ⟨hal-02322755⟩
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