3b. Analyses of Certified Reference Solutions:

For the purpose of quality control of total CO2 determinations, SIO Reference Solutions (Batches # 12 and 13) were determined 758 times during the expeditions using the coulometer. Our shipboard analyses agreed with the SIO manometric values within 1.2 µmol/kg. Based upon this observation and the consistency of the results of this investigation and our previous expeditions, the overall precision of our total CO2 data is estimated to be about ±2 µmol/kg. The results of our coulometric determinations of the total CO2 concentration in the SIO Reference solutions are summarized and compared, in Fig. 3 and Table 2, with those of the manometric determinations made by C. D. Keeling of SIO. The difference between the mean values for these two independent sets of measurements ranges between -1.4 and +0.2 µmol/kg. The shipboard TCO2 measurements listed in this report have not been corrected for the differences to conform to the SIO manometric values.

Table 2. Results of Analyses for the SIO Reference Solutions

WOCE sections No. of SRM bottles and batch no. No. of analyses (N) LDEO-Shipboard TCO2 analyses (µmol/kg) SIO-manometric TCO2 analyses (µmol/kg) Difference (µmol/kg)
P-16S/P-17A 73 (batch #12) 166 1983.0±1.5 1984.3±0.7 (N=7) -1.3
P-17E/P-19S 90 (batch #13) 233 2013.7±2.1 2015.1±0.6 (N=7) -1.4
P-19C 97 (batch #13) 359 2015.3±1.9 2015.1±0.6 (N=7) +0.2
Total 260 758   Mean Difference = -0.8

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