Abstract
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.
Highlights
Dissolved inorganic carbon (DIC) is an important component of the evolving global carbon cycle, with ∼ 26 % of yearly anthropogenic carbon dioxide (CO2) emissions stored as DIC in the global ocean (Le Quéré et al, 2015)
This paper presents an alternative approach to autonomously determine concentrations of DIC and δ13C–DIC
Accuracy was tested by comparing AIRICA– Cavity Ring-down Spectrometer (CRDS) δ13C–DIC values to isotope ratio mass spectrometry (IRMS)-measured values from discrete samples collected during the bloom experiment
Summary
Dissolved inorganic carbon (DIC) is an important component of the evolving global carbon cycle, with ∼ 26 % of yearly anthropogenic carbon dioxide (CO2) emissions stored as DIC in the global ocean (Le Quéré et al, 2015). Whilst a variety of methods to autonomously measure DIC concentrations have been developed (Bandstra et al, 2006; Fassbender et al, 2015; Huang et al, 2015; Liu et al, 2013), the conventional method for determining δ13C-DIC requires discrete samples to be collected and stored prior to acidification and analysis in a laboratory by isotope ratio mass spectrometry (IRMS). The permeablemembrane-based equilibration system autonomously measured DIC and δ13C–DIC at 15 min intervals to a precision of ± 10 μmol kg−1 and ± 0.2 ‰ respectively, and has been shown to be sufficient for identifying spatial and short-term temporal variability in DIC concentrations in a variety of aquatic systems (Bass et al, 2013, 2014a, b). Using only a small sample volume (2 mL), the method achieves high precision and accuracy comparable to traditional IRMS techniques
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
