Measurements of Carbonate System in the Ocean

Abstract

This paper summarizes the current status of measurement technology for the four measurable parameters of the ocean carbonate system: pH, pCO₂, total inorganic carbon, and total alkalinity. They are keys to the future of global warming and its mitigation. The technology should be improved from batch measurement of water samples in the laboratory to in-situ measurement by sensors and automatic measurement deployed on buoys and floats: from point and line observations to three-dimensional and temporal observations. The best accuracy for practical measurements is 0.002 pH, 2-5 μatm, 2-4 μmol kg⁻¹, and 2-3 μmol kg⁻¹ for pH, pCO₂, total inorganic carbon, and alkalinity, respectively. Automatic measurement of pH and pCO₂ is now practical, but since both are extremely small components of the carbonate system and change synchronously, determining the carbonate system from these two parameters results in a large uncertainty. The combination of pH and total alkalinity provides the smallest error, and thus to develop an automatic measurement system for pH-total alkalinity is anticipated. All the parameters can be determined by equilibrating the sample and the solution or by measuring the pH after adding acid, so the key is to develop a stable pH measurement technique even in high-pressure deep seawater.