Abstract : Using a combination of sound absorption data from a large spherical resonator and relaxation frequency data from the temperature jump technique, it has been demonstrated that there is an increased sound absorption in sea water below approximately 1 kHz. The absorption mechanism has been traced to a chemical relaxation of boric acid. Observed and calculated data are in general agreement when a two step, three state boric acid ionization reaction is postulated. The observed sound absorption is attributed to the unimolecular second step of this reaction, with the faster bimolecular first step being of low sound absorption step being of low sound absorption magnitude and under diffusion control. The magnitude of the observed sound absorption is approximately nine times greater than the absorption calculated by considering only the contribution from the high frequency magnesium sulfate effect. There is an effect of bicarbonate on the low frequency absorption presumably through the buffering effect on the hydroxyl ion.