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| Titel |
The transient distributions of nuclear weapon-generated tritium and its decay product 3 He in the Mediterranean Sea, 1952-2011, and their oceanographic potential |
| VerfasserIn |
W. Roether, P. Jean-Baptiste, E. Fourré, J. Sültenfuss |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 9, no. 5 ; Nr. 9, no. 5 (2013-10-08), S.837-854 |
| Datensatznummer |
250085244
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| Publikation (Nr.) |
 copernicus.org/os-9-837-2013.pdf |
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| Zusammenfassung |
| We present a comprehensive account of tritium and 3He in the
Mediterranean Sea since the appearance of the tritium generated by the
atmospheric nuclear-weapon testing in the 1950s and early 1960s, based on
essentially all available observations. Tritium in surface waters rose to
20–30 TU in 1964 (TU = 1018 × [3H]/H]), a factor of
about 100 above the natural level, and thereafter declined 30-fold up to
2011. The decline was largely due to radioactive tritium decay, which
produced significant amounts of its stable daughter 3He. We present the
scheme by which we separate the tritiugenic part of 3He and the part
due to release from the sea floor (terrigenic part). We show that the
tritiugenic component can be quantified throughout the Mediterranean waters,
typically to a ± 0.15 TU equivalent, mostly because the terrigenic
part is low in 3He. This fact makes the Mediterranean unique in
offering a potential for the use of tritiugenic 3He as a tracer. The
transient distributions of the two tracers are illustrated by a number of
sections spanning the entire sea and relevant features of their
distributions are noted. By 2011, the 3He concentrations in the top few
hundred metres had become low, in response to the decreasing tritium
concentrations combined with a flushing out by the general westward drift of
these waters. Tritium-3He ages in Levantine Intermediate Water (LIW)
were obtained repeated in time at different locations, defining transit
times from the LIW source region east of Rhodes. The ages show an upward
trend with the time elapsed since the surface-water tritium maximum, which
arises because the repeated observations represent increasingly slower
moving parts of the full transit time spectrum of LIW. The transit time
dispersion revealed by this new application of tritium-3He dating is
considerable. We find mean transit times of 12 ± 2 yr up to the
Strait of Sicily, 18 ± 3 yr up to the Tyrrhenian Sea, and 22 ± 4 yr up into the Western Mediterranean. Furthermore, we present
full Eastern Mediterranean sections of terrigenic 3He and
tritium-3He age in 1987, the latter one similarly showing an effect of
the transit time dispersion. We conclude that the available tritium and
3He data, particularly if combined with other tracer data, are useful
for constraining the subsurface circulation and mixing of the Mediterranean
Sea. |
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