High-accuracy measurements of total dissolved inorganic carbon in the ocean: comparison of alternate detection methods

Abstract

High-accuracy measurements of total dissolved inorganic carbon in the ocean are currently performed using an automated coulometric system based on that described by Johnson et al. (1987). These measurements require highly-trained technicians and the manipulation of expensive and hazardous chemicals. We tested an alternate detection method based on non-dispersive infra-red analysis. All of the dissolved carbonate species from a seawater sample were extracted as CO 2 gas by acidification and nitrogen stripping. The CO 2 gas was then quantitatively detected with either a coulometric system or an infra-red analyzer. The reproducibility of the two detection methods is similar. Although the infra-red system requires further testing, it holds promise as an alternative to coulometry. The detection of the CO 2 gas by infra-red analysis presents several advantages over coulometric detection: it simplifies and reduces the cost of the measurements, shortens the analysis time, reduces the sample size requirement by at least a factor of five, and allows us to consider complete automation of the system for underway surface seawater measurements.