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| Titel |
Potential impact of DOM accumulation on fCO2 and carbonate ion computations in ocean acidification experiments |
| VerfasserIn |
W. Koeve, A. Oschlies |
| 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 ; 9, no. 10 ; Nr. 9, no. 10 (2012-10-05), S.3787-3798 |
| Datensatznummer |
250007320
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| Publikation (Nr.) |
 copernicus.org/bg-9-3787-2012.pdf |
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| Zusammenfassung |
The internal consistency of measurements and computations of components of
the CO2-system, namely total alkalinity (AT, total dissolved
carbon dioxide (CT), CO2 fugacity (fCO2) and pH, has
been confirmed repeatedly in open ocean studies when the CO2 system had
been over determined. Differences between measured and computed properties,
such as ΔfCO2 (= fCO2 (measured) –
fCO2 (computed from AT and CT)) / fCO2 (measured) × 100), are usually below 5%.
Recently, Hoppe et al. (2012) provided evidence of significantly larger
ΔfCO2 in some experimental setups. These observations are
currently not well understood. Here we discuss a case from a series of
phytoplankton culture experiments with ΔfCO2 of up to about
25%. ΔfCO2 varied systematically during the course of these
experiments and showed a clear correlation with the accumulation of dissolved
organic matter (DOM).
Culture and mesocosm experiments are often carried out under high initial
nutrient concentrations, yielding high biomass concentrations that in turn
often lead to a substantial build-up of DOM. In such experiments, DOM can
reach concentrations much higher than typically observed in the open ocean.
To the extent that DOM includes organic acids and bases, it will contribute
to the alkalinity of the seawater contained in the experimental device. Our
analysis suggests that whenever substantial amounts of DOM are produced
during the experiment, standard computer programmes used to compute CO2
fugacity can underestimate true fCO2 significantly when the
computation is based on AT and CT. Unless the effect of
DOM-alkalinity can be accounted for, this might lead to significant errors in
the interpretation of the system under consideration with respect to the
experimentally applied CO2 perturbation. Errors in the inferred
fCO2 can misguide the development of parameterisations used in
simulations with global carbon cycle models in future CO2-scenarios.
Over determination of the CO2-system in experimental ocean acidification
studies is proposed to safeguard against possibly large errors in estimated
fCO2. |
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