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 δ 13C DIC 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 (ISO-CADICA) system is 0.01 mM with an accuracy of 0.008 mM. The analytical uncertainty in δ 13C DIC 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 CO 2 concentrations were found to either be negligible or correctable. Field trials measuring diel variation in δ 13C DIC 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 δ 13C DIC 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 δ 13C DIC 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.