An inter-comparison of autonomous in situ instruments for ocean CO2 measurements under laboratory-controlled conditions

Qipei Shangguan, Adam Prody, Taylor S. Wirth, Ellen M. Briggs, Todd R. Martz, Michael D. DeGrandpre

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Observations of the marine CO2 system are important for understanding ocean acidification, air-sea CO2 fluxes and the marine carbon cycle in general. A variety of autonomous in situ instruments have been developed and used towards this end. There is, however, a lack of inter-comparison studies of currently available sensor technologies. In this study, a total of 10 instruments including commercially available pH, partial pressure of CO2 (pCO2), and total alkalinity (AT) sensors were tested and compared in a 5000 L seawater tank located at Scripps Institution of Oceanography (SIO), California, USA. The test took place over ~12 days (August 16 to 28, 2016) where conditions in the tank were artificially varied to encompass a wide range of AT, pH and pCO2 as well as temperature and salinity. To assess accuracy, independent measurements of pH, pCO2, dissolved inorganic carbon (DIC) and AT were made using benchtop instrumentation. We also evaluated internal consistency, comparing the measured parameter from the sensors with the calculated parameter, e.g. pCO2 calculated from AT and pH compared with directly measured pCO2. DIC can be precisely derived (within ±5 μmol/kg) over a wide range of conditions from measured pH or pCO2 paired with AT. Sensor accuracy established by discrete samples is sufficient for short-term and seasonal dynamical studies, but their ability in determining long-term (e.g. climate) variability could not be evaluated because of the brevity of the study. These results provide insights into sensor performance and strategies for data quality control for future studies of ocean acidification and carbon cycling.

Original languageEnglish
Article number104085
JournalMarine Chemistry
StatePublished - Mar 20 2022


  • Autonomous sensors
  • Internal consistency
  • Marine CO system
  • Ocean acidification
  • Sensor inter-comparison


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