Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1305-1313, 2017
https://doi.org/10.5194/bg-14-1305-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Technical note
15 Mar 2017
Technical note: Coupling infrared gas analysis and cavity ring down spectroscopy for autonomous, high-temporal-resolution measurements of DIC and δ13C–DIC
Mitchell Call1,3, Kai G. Schulz2, Matheus C. Carvalho2, Isaac R. Santos3, and Damien T. Maher1,3 1School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
2Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
3National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, NSW, 2450, Australia
Abstract. A new approach to autonomously determine concentrations of dissolved inorganic carbon (DIC) and its carbon stable isotope ratio (δ13C–DIC) at high temporal resolution is presented. The simple method requires no customised design. Instead it uses two commercially available instruments currently used in aquatic carbon research. An inorganic carbon analyser utilising non-dispersive infrared detection (NDIR) is coupled to a Cavity Ring-down Spectrometer (CRDS) to determine DIC and δ13C–DIC based on the liberated CO2 from acidified aliquots of water. Using a small sample volume of 2 mL, the precision and accuracy of the new method was comparable to standard isotope ratio mass spectrometry (IRMS) methods. The system achieved a sampling resolution of 16 min, with a DIC precision of ±1.5 to 2 µmol kg−1 and δ13C–DIC precision of ±0.14 ‰ for concentrations spanning 1000 to 3600 µmol kg−1. Accuracy of 0.1 ± 0.06 ‰ for δ13C–DIC based on DIC concentrations ranging from 2000 to 2230 µmol kg−1 was achieved during a laboratory-based algal bloom experiment. The high precision data that can be autonomously obtained by the system should enable complex carbonate system questions to be explored in aquatic sciences using high-temporal-resolution observations.

Citation: Call, M., Schulz, K. G., Carvalho, M. C., Santos, I. R., and Maher, D. T.: Technical note: Coupling infrared gas analysis and cavity ring down spectroscopy for autonomous, high-temporal-resolution measurements of DIC and δ13C–DIC, Biogeosciences, 14, 1305-1313, https://doi.org/10.5194/bg-14-1305-2017, 2017.
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The conventional method for determining dissolved inorganic carbon (DIC) and it carbon stable isotope ratio (δ13C–DIC) can be a laborious process which can limit sampling frequency. This paper presents a new approach to autonomously determine DIC & δ13C–DIC at high temporal resolution. The simple method requires no customised design. Instead it uses two commercially available instruments and achieved a sampling resolution of 16 mins with precision and accuracy comparable to conventional methods.
The conventional method for determining dissolved inorganic carbon (DIC) and it carbon stable...
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