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| Titel |
Dynamics of particulate organic carbon flux in a global ocean model |
| VerfasserIn |
I. D. Lima, P. J. Lam, S. C. Doney |
| 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 ; 11, no. 4 ; Nr. 11, no. 4 (2014-02-27), S.1177-1198 |
| Datensatznummer |
250117249
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| Publikation (Nr.) |
 copernicus.org/bg-11-1177-2014.pdf |
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| Zusammenfassung |
| The sinking of particulate organic carbon (POC) is a key
component of the ocean carbon cycle and plays an important role in the
global climate system. However, the processes controlling the fraction of
primary production that is exported from the euphotic zone (export ratio)
and how much of it survives respiration in the mesopelagic to be
sequestered in the deep ocean (transfer efficiency) are not well
understood. In this study, we use a three-dimensional, coupled
physical–biogeochemical model (CCSM–BEC; Community Climate System Model–ocean
Biogeochemical Elemental Cycle) to investigate the processes
controlling the export of particulate organic matter from the euphotic zone
and its flux to depth. We also compare model results with sediment trap
data and other parameterizations of POC flux to depth to evaluate model
skill and gain further insight into the causes of error and uncertainty in
POC flux estimates. In the model, export ratios are mainly a function of
diatom relative abundance and temperature while absolute fluxes and
transfer efficiency are driven by mineral ballast composition of sinking
material. The temperature dependence of the POC remineralization length
scale is modulated by denitrification under low O2 concentrations
and lithogenic (dust) fluxes. Lithogenic material is an important control
of transfer efficiency in the model, but its effect is restricted to
regions of strong atmospheric dust deposition. In the remaining regions,
CaCO3 content of exported material is the main factor affecting
transfer efficiency. The fact that mineral ballast composition is
inextricably linked to plankton community structure results in correlations
between export ratios and ballast minerals fluxes (opal and CaCO3),
and transfer efficiency and diatom relative abundance that do not
necessarily reflect ballast or direct ecosystem effects, respectively. This
suggests that it might be difficult to differentiate between ecosystem and
ballast effects in observations. The model's skill in reproducing sediment
trap observations is equal to or better than that of other
parameterizations. However, the sparseness and relatively large
uncertainties of sediment trap data makes it difficult to accurately
evaluate the skill of the model and other parameterizations. More POC flux
observations, over a wider range of ecological regimes, are necessary to
thoroughly evaluate and test model results and better understand the
processes controlling POC flux to depth in the ocean. |
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