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| Titel |
Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen |
| VerfasserIn |
V. Sanial, P. van Beek, B. Lansard, M. Souhaut, E. Kestenare, F. d'Ovidio, M. Zhou, S. Blain |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 5 ; Nr. 12, no. 5 (2015-03-05), S.1415-1430 |
| Datensatznummer |
250117845
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| Publikation (Nr.) |
 copernicus.org/bg-12-1415-2015.pdf |
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| Zusammenfassung |
| The Southern Ocean is known to be the largest high-nutrient, low-chlorophyll
(HNLC) region of the global ocean due to iron limitation. However, a large
phytoplankton bloom develops annually downstream of the Kerguelen Islands, a
bloom which is sustained partly by iron released from the sediments
deposited onto the shelves. In the framework of the KEOPS-2 project, we used
radium isotopes (224Ra, T1/2 = 3.66 d; 223Ra,
T1/2 = 11.4 d; 228Ra, T1/2 = 5.75 yr) to provide
information on the origin of iron fertilization and on the timescales of the
transfer of sediment-derived inputs (including iron and other
micronutrients) towards offshore waters. Significant 224Ra and
223Ra activities were found in the near vicinity of the Kerguelen
Islands, in agreement with the short half-lives of these isotopes.
Significant 224Ra and 223Ra activities were also detected up to
200 km downstream of the islands and more unexpectedly in offshore waters
south of the polar front. These observations thus clearly indicate (i) that
the sediment-derived inputs are rapidly transferred towards offshore waters
(on timescales on the order of several days up to several weeks) and (ii)
that the polar front is not a physical barrier for the chemical elements
released from the sediments of the Kerguelen Plateau. The Ra data set
suggests that iron and other micronutrients released by the shelves of the
Kerguelen Islands may contribute to fueling the phytoplankton bloom downstream
of the islands, despite the presence of the polar front. However, the
heterogeneous distribution of the 224Ra and 223Ra activities in
surface waters suggests that this supply across the front is not a
continuous process but rather a process that is highly variable in space
and time. |
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