Internal consistency of marine carbonate system measurements and assessments of aragonite saturation state: Insights from two U.S. coastal cruises

Calculations of TA from (pH, DIC) and (fCO2, DIC) showed that internal consistency could be achieved if minor subtractions of TA (≤ 4 μmol kg− 1) were applied to samples of salinity < 35. The extent of thermodynamic consistency is also exemplified by the small offset between TA calculated from (DIC, pH) and that calculated from (DIC, fCO2): ~ 3 μmol kg− 1, which is similar to the accuracy of the TA measurements. Systematic trends can be detected in the offsets between measured and calculated parameters, but for this high-quality data set the magnitude of methodological improvements required to achieve exact thermodynamic consistency is quite small.