5. Summary
The comprehensive analysis of the quality of the carbon data of the twenty-three cruises shows general good agreement and high quality. This is testament to the care that was taken in gathering and reducing the data. Extensive use of CRMs facilitated consistency of the DIC and TAlk data sets. Internal consistency calculations for cruises on which three or more carbon system parameters were measured suggest that the pH and, in particular, fCO2 measurements on the cruises were consistent and of high quality as well. Based on the extensive analyses, we suggest that the DIC and TAlk of two cruises (A06 and A07) not be considered as appropriate for this synthesis. In addition, the TAlk values of A1E are significantly different from neighboring cruises and are not recommended for use, either. A23 has inconsistent DIC data, so these data are also not included in this synthesis. Of the lines that have repeat occupations, we recommend that the later (repeat) cruises be used as the primary data set. This is because the data are more consistent with the other data, in part, because of improved analysis techniques and because they often are closer in time to the other cruises, thus minimizing the effects of anthropogenic and natural variability. No specific adjustments in DIC are recommended. Although crossover analyses often show systematic differences in DIC greater than the assumed precision of 2 µmol/kg, the differences either are not systematic for each crossover or do not show up in the regional multilinear analysis. TAlk values show greater inconsistency for some cruises, and adjustments of +14 µmol/kg and - 7 µmol/kg are suggested for TAlk values on A01W and A09, respectively.
The caveats in the analysis and recommendations should be borne in mind. The purpose of the exercise was to create a mutually consistent data set of TAlk and DIC for the Atlantic Ocean based on data obtained on different cruises in the 1990s. This data set will be used to create gridded fields of DIC and TAlk for model validation and to determine basin-scale quantities such as anthropogenic CO2 inventories, carbonate saturation levels, and other relevant large-scale phenomena. The analysis of consistency is primarily focused on deep-water quantities with the assumption that these values are invariant on the decadal timescale. In the well-ventilated Atlantic Ocean, where large-scale natural changes manifest themselves through much of the water column, this is not always the best assumption. Moreover, in this analysis we assume that there are no systematic differences with depth. No comparisons in the upper water column were made, both because of seasonal variability in the upper ocean and because the anthropogenic perturbations are most noticeable there.
