| Summary: | NOAA/GML Global Monitoring Annual Conference, May 24-28, 2021 We are moving towards an era of autonomous measurements, with pH and fCO2 being the only two variables of the seawater carbonate system that can be currently measured autonomously. However, corresponding discrete measurements or derived calculations based on the internal consistency of the seawater carbonate system (i.e., the agreement between measurements and thermodynamic calculations) are needed to correct biases and drifts in the sensor-based data and for our understanding of ocean acidification. In this work, we evaluate the internal consistency of the seawater carbonate system using cruises available in GLODAPv2.2020 that have paired measurements of discrete water column fCO2 and at least two of the three remaining measurable carbonate system variables, total dissolved inorganic carbon (DIC), total alkalinity (TA), and pH (using unpurified dye). We exploit the discrete fCO2 data to gain new insights into the causes of the remaining inconsistencies in the seawater carbonate system. We use a database of over 20,000 samples from the Atlantic, Pacific, and Southern Oceans, with fCO2 ranging 189–2,806 μatm. We found that fCO2 measurements are consistent with DIC, TA, and pH measurements, within the expected uncertainties for internal consistency, highlighting the good quality of the measurements produced by the community. However, inconsistencies between DIC, TA, fCO2, and pH corrected to be consistent with DIC and TA stand out, pointing towards the need for a detailed re-evaluation of the carbonic acid dissociation constants at high fCO2 values and probably methodological issues in the pH measurements or TA referencing No
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