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| Titel |
The potential impact of DOM accumulation on computed fCO2, carbonate ion concentrations, and omega in ocean acidification experiments |
| VerfasserIn |
Wolfgang Koeve, Hyun-cheol Kim, Kitack Lee, Andreas Oschlies |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056330
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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, e.g. ΔfCO2 (=fCO2meas – fCO2(AT+CT))/ fCO2meas*100), there
are usually below 5%. Recently, Hoppe et al. (2010, Biogeosciences Discussions)
provided evidence of significantly larger ΔfCO2 in experimental setups. These
observations are currently not well understood. Here we provide additional examples from
phytoplankton culture and mesocosm experiments of ΔfCO2 of up to 40%. ΔfCO2 varied
systematically during the course of these experiments. In one set of experiments a clear
correlation with the accumulation of dissolved organic carbon (DOC) is evident.
Culture and mesocosm experiments are often carried out under very high initial
nutrient concentrations, yielding high biomass concentrations that in turn often
lead to a substantial build-up DOC. DOC can reach concentrations much higher
than typically observed in the open ocean. To the extent that DOC includes organic
acids and bases, it will contribute to the alkalinity of the sea water contained in the
experimental device. Our analysis suggests that whenever substantial amounts of DOC are
produced during the experiment, standard computer programs used to compute CO2
fugacity can underestimate true fCO2 significantly. Alternative explanations for large
ΔfCO2, e.g. uncertainties of pKs, are explore as well, but are found to be of minor
importance. |
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