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| Titel |
Biology and air-sea gas exchange controls on the distribution of carbon isotope ratios (δ13C) in the ocean |
| VerfasserIn |
A. Schmittner, N. Gruber, A. C. Mix, R. M. Key, A. Tagliabue, T. K. Westberry |
| 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 ; 10, no. 9 ; Nr. 10, no. 9 (2013-09-04), S.5793-5816 |
| Datensatznummer |
250085320
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| Publikation (Nr.) |
 copernicus.org/bg-10-5793-2013.pdf |
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| Zusammenfassung |
| Analysis of observations and sensitivity experiments with a new
three-dimensional global model of stable carbon isotope cycling elucidate
processes that control the distribution of δ13C of dissolved
inorganic carbon (DIC) in the contemporary and preindustrial ocean.
Biological fractionation and the sinking of isotopically light δ13C organic matter from the surface into the interior ocean leads to low
δ13CDIC values at depths and in high latitude surface
waters and high values in the upper ocean at low latitudes with maxima in the
subtropics. Air–sea gas exchange has two effects. First, it acts to
reduce the spatial gradients created by biology. Second, the associated
temperature-dependent fractionation tends to increase (decrease) δ13CDIC values of colder (warmer) water, which generates
gradients that oppose those arising from biology. Our model results suggest
that both effects are similarly important in influencing surface and interior
δ13CDIC distributions. However, since air–sea gas
exchange is slow in the modern ocean, the biological effect dominates spatial
δ13CDIC gradients both in the interior and at the
surface, in contrast to conclusions from some previous studies. Calcium
carbonate cycling, pH dependency of fractionation during air–sea gas
exchange, and kinetic fractionation have minor effects on
δ13CDIC. Accumulation of isotopically light carbon from
anthropogenic fossil fuel burning has decreased the spatial variability of
surface and deep δ13CDIC since the industrial revolution
in our model simulations. Analysis of a new synthesis of δ13CDIC measurements from years 1990 to 2005 is used to quantify
preformed and remineralized contributions as well as the effects of biology
and air–sea gas exchange. The model reproduces major features of the
observed large-scale distribution of δ13CDIC as well as
the individual contributions and effects. Residual misfits are documented and
analyzed. Simulated surface and subsurface δ13CDIC are
influenced by details of the ecosystem model formulation. For example,
inclusion of a simple parameterization of iron limitation of phytoplankton
growth rates and temperature-dependent zooplankton grazing rates improves the
agreement with δ13CDIC observations and satellite
estimates of phytoplankton growth rates and biomass, suggesting that δ13C can also be a useful test of ecosystem models. |
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