Sound absorption in seawater involves relaxations of magnesium sulfate, boric acid, and magnesium carbonate. Absorption varies with both region and depth, due mainly to the pH dependence of the boric acid relaxation. The nominal seawater pH range is 7.7–8.3 and magnitudes can vary over nearly a factor of 4 at low frequencies. A global model for World Ocean prediction has been developed, employing contour charts of the pH factor at several depths. Profiles for integration of loss along ray paths are generated by algorithm. The pH range in the Arctic is nominally 8.0–8.3 and similar contour charts are provided for the pH factor in these regions. Although long-range propagation is generally limited by under-ice scattering, absorption can be the dominant loss mechanism under ice-free conditions and for ranges less than 50 km at sonar frequencies with an ice cover. Predicted absorption spectra are presented and compared with the limited data available. [Work supported by NUSC/NL.]