Journal of Oceanography

, Volume 62, Issue 1, pp 71–81 | Cite as

Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers

  • Yoshiyuki Nakano
  • Hideshi Kimoto
  • Shuichi Watanabe
  • Koh Harada
  • Yutaka W. Watanabe


We have developed new systems capable of profiling to >1000 m for measuring in situ pH and fugacity of CO2 (fCO2) in the ocean using spectrophotometric analysis (pH and CO2 profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO2 profiler analyzed in situ fCO2 by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 μM bromocresol purple (BCP) and 5 μM sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO2 profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 ± 0.005 pH (SE, n = 25) and −0.4 ± 3 μatm (SE, n = 31).


In situ measurement pH CO2 spectrophotometric measurement 


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Yoshiyuki Nakano
    • 1
  • Hideshi Kimoto
    • 2
  • Shuichi Watanabe
    • 3
  • Koh Harada
    • 4
  • Yutaka W. Watanabe
    • 1
  1. 1.Graduate School of Environmental Earth ScienceHokkaido UniversitySapporoJapan
  2. 2.Kimoto Electric Co., Ltd.OsakaJapan
  3. 3.Japan Marine Science and Technology CenterYokosukaJapan
  4. 4.National Institute of Advanced Industrial Science and TechnologyTsukubaJapan

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