This record is being processed for inclusion into GeoRef. It may not yet have been indexed, given a translated title, or checked by a GeoRef editor.

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

Saved in:
Online Access: Get full text
doi: 10.5194/bg-15-5545-2018
Authors:Castrillejo, Maxi; Casacuberta, Núria; Christl, Marcus; Vockenhuber, Christof; Synal, Hans-Arno; García-Ibáñez, Maribel I.; Lherminier, Pascale; Sarthou, Géraldine; Garcia-Orellana, Jordi; Masqué, Pere
Author Affiliations:Primary:
ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland
Uni Research Climate, Bjerknes Centre for Climate Research, Norway
Université Brest, Ifremer, CNRS, IRD, Laboratoire d' Océanographie Physique et Spatiale, France
Laboratoire des Sciences de l'Environnement Marin, France
Universitat Autònoma de Barcelona, Institut de Ciència i Tecnologia Ambientals, Spain
Volume Title:Biogeosciences
Source:Biogeosciences, 15(18), p.5545-5564. Publisher: Copernicus GmbH on behalf of the European Union, Katlenburg-Lindau, International. ISSN: 1726-4170
Publication Date:2018
Note:In English. 82 refs.; illus., incl. 1 table, sketch maps
Summary: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 tracers 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 129I and 236U 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 north-western European coastal waters by the Sellafield and La Hague nuclear reprocessing plants (NRPs). As a result, 129I concentrations and 236U/238U atom ratios and 129I/236U atom ratios display a wide range of values: (0.2-256) × 107 at kg-1 (40-2350) × 10-12 and 0.5-200, respectively. The signal from NRPs, which is characterised by higher 129I concentrations and 129I/236U 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 236U/238U and 129I/236U dual tracer approach further serves to discern Polar Intermediate Water (PIW) of Canadian origin from that of Atlantic origin, which carries comparably higher tracer levels due to NRPs (particularly 129I). The cascading of these waters appears to modify the water mass composition in the bottom of the Irminger and Labrador seas, which are dominated by Denmark Strait Overflow Water (DSOW). Indeed, PIW-Atlantic, which has a high level of 129I compared to 236U, appears to contribute to the deep Irminger Sea increasing the 129I concentrations in the realm of DSOW. A similar observation can be made for 236U for PIW entering through the Canadian Archipelago into the Labrador Sea. Several depth profiles also show an increase in 129I concentrations in near bottom waters in the Iceland and the West European basins that are very likely associated with the transport of the NRP signal by the Iceland-Scotland Overflow Water (ISOW). This novel result would support current modelling studies indicating the transport of ISOW into the eastern SPNA. Finally, our tracer data from 2014 are combined with published 129I data for the deep central Labrador Sea between 1993 and 2013. The results obtained from comparing simulated and measured 129I concentrations support the previously suggested two major transport pathways for the AWs in the SPNA, i.e. a short loop through the Nordic seas into the SPNA and a longer loop, which includes recirculation of the AWs in the Arctic Ocean before it enters the western SPNA.
Subjects:Actinides; Halogens; I-129; Iodine; Isotope ratios; Isotopes; Mathematical models; Metals; Models; Radioactive isotopes; Transportation; U-238/U-234; Uranium; Water; Arctic region; Atlantic Ocean; Canada; Eastern Canada; English Channel; Europe; Great Britain; Greenland; Labrador; Labrador Sea; Newfoundland and Labrador; North Atlantic; Scotland; United Kingdom; Western Europe
Coordinates:N400000 N800000 W0600000 E0200000
Record ID:843181-3
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute. Reference includes data from Copernicus Gesellschaft, Katlenburg-Lindau, Germany
Tags: Add Tag
No Tags, Be the first to tag this record!