This data set provides the pH values obtained for discrete water samples collected from the CTD+Rosette assembly at the water levels sampled during the Iberia-Forams cruise along the western and southwestern Iberian margin in September 2012. For pH measurement 250 ml of water were collected from the Rosette bottle and the bottle closed tightly. In the lab, the respective pH value was obtained by inserting a WTW (Wissenschaftlich-Technische Werkstaetten GmbH) pH meter 3110 into the bottom half of each bottle. Before the measurement, the pH probe was calibrated with pH solutions of 4.01 and 7.00 (accuracy of ≤ 0.005 pH ± 1 digit). Listed pH values are generally the mean of two measurements.