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| Titel |
Modelling carbon overconsumption and the formation of extracellular particulate organic carbon |
| VerfasserIn |
M. Schartau, A. Engel, J. Schröter, S. Thoms, C. Völker, D. Wolf-Gladrow |
| 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 ; 4, no. 4 ; Nr. 4, no. 4 (2007-07-02), S.433-454 |
| Datensatznummer |
250001846
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| Publikation (Nr.) |
 copernicus.org/bg-4-433-2007.pdf |
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| Zusammenfassung |
| During phytoplankton growth a fraction of dissolved inorganic carbon (DIC)
assimilated by phytoplankton is exuded in the form of dissolved organic carbon
(DOC), which can be transformed into extracellular particulate organic carbon
(POC). A major fraction of extracellular POC is associated with carbon of
transparent exopolymer particles (TEP; carbon content = TEPC) that form from
dissolved polysaccharides (PCHO). The exudation of PCHO is linked to an
excessive uptake of DIC that is not directly quantifiable from utilisation of
dissolved inorganic nitrogen (DIN), called carbon overconsumption. Given these
conditions, the concept of assuming a constant stoichiometric carbon-to-nitrogen
(C:N) ratio for estimating new production of POC from DIN uptake becomes
inappropriate. Here, a model of carbon overconsumption is analysed, combining
phytoplankton growth with TEPC formation. The model describes two modes of
carbon overconsumption. The first mode is associated with DOC exudation during
phytoplankton biomass accumulation. The second mode is decoupled from algal
growth, but leads to a continuous rise in POC while particulate organic nitrogen
(PON) remains constant. While including PCHO coagulation, the model goes beyond
a purely physiological explanation of building up carbon rich particulate
organic matter (POM). The model is validated against observations from a
mesocosm study. Maximum likelihood estimates of model parameters, such as
nitrogen- and carbon loss rates of phytoplankton, are determined. The
optimisation yields results with higher rates for carbon exudation than for the
loss of organic nitrogen. It also suggests that the PCHO fraction of exuded DOC
was 63±20% during the mesocosm experiment. Optimal estimates are obtained
for coagulation kernels for PCHO transformation into TEPC. Model state estimates
are consistent with observations, where 30% of the POC increase was attributed
to TEPC formation. The proposed model is of low complexity and is applicable for
large-scale biogeochemical simulations. |
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