Research Article Received: 26 October 2011
Revised: 6 December 2011
Accepted: 21 December 2011
Published online in Wiley Online Library
Rapid Commun. Mass Spectrom. 2012, 26, 639– 644 (wileyonlinelibrary.com) DOI: 10.1002/rcm.6143
ISO-CADICA: Isotopic – continuous, automated dissolved inorganic carbon analyser Adrian M. Bass1*, Michael I. Bird1, Niels C. Munksgaard2 and Christopher M. Wurster1 1 2
Department of Earth and Environmental Science, James Cook University, Cairns Campus, Queensland, Australia Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Northern Territory, Australia
RATIONALE: Quantifying the processes that control dissolved inorganic carbon (DIC) dynamics in aquatic systems is essential for progress in ecosystem carbon budgeting. The development of a methodology that allows high-resolution temporal data collection over prolonged periods is essential and is described in this study. METHODS: A novel sampling instrument that sequentially acidifies aliquots of water and utilises gas-permeable ePTFE tubing to measure the dissolved inorganic carbon (DIC) concentration and d13CDIC values at sub-hourly intervals by Cavity Ring-down spectrometry (CRDS) is described. RESULTS: The minimum sensitivity of the isotopic, continuous, automated dissolved inorganic carbon analyser (ISOCADICA) system is 0.01 mM with an accuracy of 0.008 mM. The analytical uncertainty in d13CDIC values is proportional to the concentration of DIC in the sample. Where the DIC concentration is greater than 0.3 mM the analytical uncertainty is 0.1 % and below 0.2 mM stability is < 0.3 %. The isotopic effects of air temperature, water temperature and CO2 concentrations were found to either be negligible or correctable. Field trials measuring diel variation in d13CDIC values of coral reef associated sea water revealed significant, short-term temporal changes and illustrated the necessity of this technique. CONCLUSIONS: Currently, collecting and analysing large numbers of samples for d13CDIC measurements is not trivial, but essential for accurate carbon models, particularly on small scales. The ISO-CADICA enables on-site, high-resolution determination of DIC concentration and d13CDIC values with no need for sample storage and laboratory analysis. The initial tests indicate that this system can offer accuracy approaching that of traditional IRMS analysis. Copyright © 2012 John Wiley & Sons, Ltd.
Dissolved inorganic carbon (DIC) is a significant component of the global carbon cycle. It is the largest pool of carbon in the ocean and is significant in terms of both stocks and fluxes in the terrestrial aquatic carbon cycle.[1] The stable isotopic value of DIC (d13CDIC) provides information on the source of DIC, as well as subsequent biogeochemical processes that alter the composition of an existing pool. For example, d13CDIC values have been used to track changes in the autochthonous/allochthonous source of DIC during flood events in a temperate peatland catchment,[2] to delineate diel heterotrophic/autotrophic balance in rivers[3] and to trace the source of intermediate waters in the North Pacific.[4] Increasing interest in both the oceanic and the terrestrial aquatic carbon cycles now places more significance on access to higher resolution data both spatially and temporally. Until recently stable isotope analysis (SIA) of DIC has been a relatively expensive, lab-based technique. Current methodologies involve the determination in the laboratory via acidification and quantification of the pCO2 liberated into a headspace via isotope ratio mass spectrometry (IRMS).[2,5,6]
Rapid Commun. Mass Spectrom. 2012, 26, 639–644
Copyright © 2012 John Wiley & Sons, Ltd.
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* Correspondence to: A. M. Bass, Department of Earth and Environmental Science, James Cook University, Cairns Campus, Queensland, Australia. E-mail:
[email protected]
This has severely limited the potential for long-term, hightemporal resolution studies of DIC dynamics using SIA. Cavity Ring-down Spectrometry (CRDS) instruments are now commercially available and offer significantly improved field portability as well as precision approaching that of IRMS (e.g., d13C
