Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers |
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| Authors: | Yoshiyuki Nakano Hideshi Kimoto Shuichi Watanabe Koh Harada Yutaka W Watanabe |
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| Institution: | (1) Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan;(2) Kimoto Electric Co., Ltd., Osaka 543-0024, Japan;(3) Japan Marine Science and Technology Center, Yokosuka 237-0061, Japan;(4) National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8569, Japan |
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| Abstract: | 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). |
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| Keywords: | In situ measurement pH CO2 spectrophotometric measurement |
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