Extended Data Fig. 4: This study’s ~1 Ma samples fall in different stages of the glacial–interglacial cycles, and δ11B-pH core top calibration used in this study recreates observed ambient pH.
From: Pliocene decoupling of equatorial Pacific temperature and pH gradients
a, b, High-resolution sea surface temperature records from western equatorial Pacific site ODP 806 G. ruber-derived Mg/Ca data116 (a) and eastern equatorial Pacific ODP Site 846 alkenone (UK′37) data117 (b). In both panels the ages of the ~1 Ma samples in this study are overlain as green lines, falling at different points in the glacial–interglacial cycles. c, Core top, net tow, and sediment trap d11B data36,109,110 converted to pH using the calibration of Henehan et al.36 shows good agreement with reported in situ pH. For the odd point to the far right (dark orange, x), Raitzsch et al109. calculated in situ pH using an anomalous low value of alkalinity (~200 μmol kg−1 lower than alkalinity for the location reported in datasets such as GLODAPv266. Recalculating pH using the same in situ temperature and salinity as Raitzsch et al. but an alkalinity value derived from GLODAPv2 (2,325 μmol kg−1) brings the point in agreement with the other data (empty dark orange circle). For the odd point in the lower part of the figure (dark green, x), Guillermic and colleagues110. report an unrealistic value for temperature at this site: ~18 °C whereas the same site (in the central Indian Ocean) appears to be closer to ~26 °C on average according to GLODAPv2. When we re-calculate δ11B-pH derived pH using GLODAPv2’s 26 °C, this brings the point into better agreement with the other data (empty dark green circle). The line of best fit and 2σ shading was calculated with the original odd data points, however, and note that the core top data is still in good agreement with reported in situ pH following this calibration.
