The pCO2, SAL, and SST values from the LDEOv2009 climatology (Takahashi et al., 2010), and calculated TA values described below were buy PD98059 used with CO2SYS (Van Heuven et al., 2009) to estimate TCO2 and Ωar. The carbonic acid dissociation constants of Millero et al. (2006) were used for the calculation as the estimated errors for these thermodynamic constants are considered to be smaller compared to other published constants (Millero et al., 2006). For the calculation of Ωar (Eq. (1)), the concentration of dissolved calcium ions in μmol kg− 1 is estimated from salinity using [Ca2 +] = 2.934 × 10− 4SAL
(Culkin and Cox, 1976). The concentration of carbonate ion [CO32 −] is a function of TA and TCO2 at a given SST and SAL, and K⁎sp
is a function of SST and SAL. This section describes the updated TA–SAL relationship, and then focuses on the estimation, variability and distribution XL184 chemical structure of TA, TCO2, and Ωar for the Pacific study area. The seasonal variability of pCO2, SST and SAL has been documented for the region in previous studies (Bingham et al., 2010, Johnson et al., 2002 and Takahashi et al., 2009). For the Pacific Ocean study region, the GLODAP and CLIVAR TA and SAL data (http://cchdo.ucsd.edu/pacific.html) were used to derive the following relationship: equation(2) TAcalc=(2300.0±0.2)+(66.3±0.4)×(SAL−35).TAcalc=2300.0±0.2+66.3±0.4×SAL−35. The standard error of the fit is ± 6 μmol kg− 1 and the coefficient of determination R2 = 0.98. An SST term in (2) reduced the residuals by only 0.1%, and was not included in the equation. The TA–SAL relationship is compared to earlier relationships (Chen and Pytkowicz, 1979, Christian et al., 2008 and Lee et al., 2006) in Fig. 3. The TA residuals in Fig. 3 are the difference between the measured TA values for surface samples from the GLODAP and CLIVAR/CO2 section data and the derived TA values. The variance of the residuals is indicated by the slope of the lines. The range of the residuals should be small and the variance constant (i.e. little unless or no gradient) if the relationship is a good predictor of TA. Comparison of
the measured and calculated TA from (2) shows the residuals range from − 20 to 20 μmol kg− 1. Most of the surface samples used to calculate the TA–SAL relationship are from nutrient-poor, oligotrophic waters in the Pacific study area. The effect of dissolved nitrate on TA (Brewer and Goldman, 1976) was estimated using surface (< 10 dbar) data from the CLIVAR/CO2 Pacific Ocean sections P06 and P21. These cruise data were collected after 2008 and were not used to calculate the relationship in Eq. (2). The TA residuals average − 5.8 ± 3.9 μmol kg− 1 (n = 117) for leg 1 of P06 along 30°S, and − 3.2 ± 6.0 μmol kg− 1 (n = 8) for leg 2 of P21 between 17°S and 25°S. The surface nitrate concentrations for the TA samples used were less than 5 μmol kg− 1.