Potential impact of DOM accumulation of fCO2 and carbonate ion computations in ocean acidification experiments

Koeve, Wolfgang and Oschlies, Andreas (2012) Potential impact of DOM accumulation of fCO2 and carbonate ion computations in ocean acidification experiments Biogeosciences (BG), 9 . pp. 3787-3798. DOI 10.5194/bg-9-3787-2012.

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Supplementary data:

Abstract

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), there are usually below 5%. Recently, Hoppe et al. (2010) provided evidence of significantly larger ΔfCO2 in 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 carbon (DOC).

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 of 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 seawater 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 when the computation is based on AT and CT. Alternative explanations for large ΔfCO2, e.g. uncertainties of pKs, are explored as well, but are found to be of minor importance. Unless the effect of DOC-alkalinity is accounted for, this might lead to significant errors in the interpretation of the system under consideration to the experimentally applied CO2 perturbation, which could misguide the development of parameterisations used in simulations with global carbon cycle models in future CO2-scenarios.

Document Type: Article
Additional Information: WOS:000310471800006
Keywords: Biogeochemistry; ocean acidification; DISSOLVED ORGANIC-CARBON; TOTAL INORGANIC CARBON; HIGH CO2 OCEAN; DISSOCIATION-CONSTANTS; PHYTOPLANKTON BLOOMS; MARINE-PHYTOPLANKTON; COASTAL SEAWATER; SARGASSO SEA; ACID; ALKALINITY
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-9-3787-2012
ISSN: 1726-4170
Projects: BIOACID, Future Ocean
Date Deposited: 20 Jul 2012 07:48
Last Modified: 11 Feb 2014 13:09
URI: http://oceanrep.geomar.de/id/eprint/14871

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