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.

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 δ¹³C_DIC values at sub-hourly intervals by Cavity Ring-down spectrometry (CRDS) is described.

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 δ¹³C_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 CO₂ concentrations were found to either be negligible or correctable. Field trials measuring diel variation in δ¹³C_DIC values of coral reef associated sea water revealed significant, short-term temporal changes and illustrated the necessity of this technique.

Currently, collecting and analysing large numbers of samples for δ¹³C_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 δ¹³C_DICvalues 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.