Abstract
Accurate and rapid determination of inorganic carbon constituents in ocean environments is important for understanding the carbon cycle, especially in the context of ocean-acidification research. A microsensor capable of directly measuring carbonate ion (CO3 2–) concentrations would be desirable. In this study, a carbonate microsensor with a polymeric liquid membrane was fabricated, and two calibration methods were used to evaluate its performance. The first method was based on continuous titration. Small increments of HCl were added to seawater or Na2CO3 solution to adjust the total alkalinity and pH values and thus obtain a series of carbonate concentrations. The second method used a series of discrete standards. Varying amounts of HCl or NaOH were added to separate seawater aliquots, and the CO3 2– concentration of each standard was calculated from the resulting total alkalinity and total dissolved inorganic carbon. Both methods were found to be adequate for achieving accurate calibration of the CO3 2– sensor, and both are suitable for field work. The discrete standards method, however, is more convenient and may provide a better linear range at low CO3 2– concentrations (detection range: 2–300 μmol/kg) than the continuous titration method in seawater (detection range: 10–250 μmol/kg). This CO3 2– microsensor can be used for 5–7 d and detects changes in carbonate concentration as low as 2 μmol/kg in the inorganic carbon constituents of the environments where marine calcareous organisms grow. The CO3 2– microelectrode was further assessed by applying it to the measurement of pore-water CO3 2– concentration profiles in a marine sediment core.
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Acknowledgments
This study was supported by the US National Science Foundation (no. EF1041070 to Cai); the Youth Foundation for Marine Science of State Oceanic Administration, Public Research Institutes (Second Institute of Oceanography, State Oceanic Administration, PRC, under contract no. 2013529). We are most grateful to Prof. C. Chen and Dr. X. Hu for helping to review and revise the paper and to Prof. Y. Zhang and Dr. Q. Zhao for providing helpful suggestions. We thank Prof. Nakhyun Nam for providing the carbonate ionophore and Charles Schutte for providing the sediment core. This work was also supported by the China Scholarship Council. Under this sponsorship, the first author (Han) was a visiting student in Cai’s laboratory at the University of Georgia while this work was accomplished.
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Han, C., Cai, WJ., Wang, Y. et al. Calibration and evaluation of a carbonate microsensor for studies of the marine inorganic carbon system. J Oceanogr 70, 425–433 (2014). https://doi.org/10.1007/s10872-014-0243-7
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DOI: https://doi.org/10.1007/s10872-014-0243-7