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| Titel |
A mechanistic modelling and data assimilation approach to estimate the carbon/chlorophyll and carbon/nitrogen ratios in a coupled hydrodynamical-biological model |
| VerfasserIn |
B. Faugeras, O. Bernard, A. Sciandra, M. Lévy |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 11, no. 4 ; Nr. 11, no. 4 (2004-11-12), S.515-533 |
| Datensatznummer |
250009332
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| Publikation (Nr.) |
 copernicus.org/npg-11-515-2004.pdf |
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| Zusammenfassung |
| The principal objective of hydrodynamical-biological models is to provide estimates of the main carbon fluxes such as
total and export oceanic production. These models are nitrogen based, that is to say that the variables are expressed
in terms of their nitrogen content. Moreover models are calibrated using chlorophyll data sets.
Therefore carbon to chlorophyll (C:Chl) and carbon to nitrogen (C:N) ratios have to be assumed.
This paper addresses the problem of the representation of these ratios. In a 1D framework at the DYFAMED station
(NW Mediterranean Sea) we propose a model which enables the estimation of the basic biogeochemical fluxes
and in which the spatio-temporal variability
of the C:Chl and C:N ratios is fully represented in a mechanical way.
This is achieved through the introduction of new state variables coming from the embedding of a phytoplankton
growth model in a more classical Redfieldian NNPZD-DOM model (in which the C:N ratio is assumed to be a constant).
Following this modelling step, the parameters of the model are estimated using the adjoint data assimilation method
which enables the assimilation of chlorophyll and nitrate data sets collected at DYFAMED in 1997.Comparing the predictions of the new Mechanistic model with those of the classical Redfieldian NNPZD-DOM model
which was
calibrated with the same data sets, we find that both models reproduce the reference data in a comparable manner. Both
fluxes and stocks can be equally well predicted by either model. However if the models
are coinciding on an average basis, they are diverging from a variability prediction point of view.
In the Mechanistic model biology adapts much faster to its environment giving rise to higher
short term variations. Moreover the seasonal variability in total production differs from
the Redfieldian NNPZD-DOM model to the Mechanistic model. In summer
the Mechanistic model predicts higher production values in carbon unit
than the Redfieldian NNPZD-DOM model. In winter the contrary holds. |
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