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| Titel |
14C-age tracers in global ocean circulation models |
| VerfasserIn |
W. Koeve, H. Wagner  , P. Kähler, A. Oschlies |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 8, no. 7 ; Nr. 8, no. 7 (2015-07-16), S.2079-2094 |
| Datensatznummer |
250116454
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| Publikation (Nr.) |
 copernicus.org/gmd-8-2079-2015.pdf |
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| Zusammenfassung |
| The natural abundance of 14C in total CO2 dissolved in seawater
(DIC) is a property applied to evaluate the water age structure and
circulation in the ocean and in ocean models. In this study we use three
different representations of the global ocean circulation augmented with
a suite of idealised tracers to study the potential and limitations of using
natural 14C to determine water age, which is the time elapsed since
a body of water has been in contact with the atmosphere. We find that,
globally, bulk 14C-age is dominated by two equally important components,
one associated with ageing, i.e. the time component of circulation, and one
associated with a "preformed 14C-age". The latter quantity exists
because of the slow and incomplete atmosphere–ocean equilibration of
14C particularly in high latitudes where many water masses form. In the
ocean's interior, preformed 14C-age behaves like a passive tracer. The
relative contribution of the preformed component to bulk 14C-age varies
regionally within a given model, but also between models. Regional
variability in the Atlantic Ocean is associated with the mixing of waters
with very different end members of preformed 14C-age. Here, variations
in the preformed component over space and time mask the circulation component
to an extent that its patterns are not detectable from bulk 14C-age.
Between models, the variability of preformed 14C-age can also be considerable (factor of
2), related to the combination of physical model parameters, which influence
circulation dynamics or gas exchange. The preformed component was found to be
very sensitive to gas exchange and moderately sensitive to ice cover. In our
model evaluation, the choice of the gas-exchange constant from within the
currently accepted range of uncertainty had such a strong influence on
preformed and bulk 14C-age that if model evaluation would be based on
bulk 14C-age, it could easily impair the evaluation and tuning of
a model's circulation on global and regional scales. Based on the results of
this study, we propose that considering preformed 14C-age is critical
for a correct assessment of circulation in ocean models. |
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