Measured values of absorption coefficients in sea water below 1 kHz show a marked regional dependence; for example, the value in the North Atlantic is found to be about twice that in the North Pacific. Recent laboratory measurements have demonstrated that the absorption mechanism is a boric acid—borate relaxation. Since this boric acid reaction acts as a buffer in sea water, the absorption coefficient is strongly pH dependent. Over the range of pH values encountered in the oceans (7.5–8.2), the absorption is a monotonically increasing function of pH and has a range of values of roughly 4:1. Comparison of experimental absorption coefficients and predictions based on reported local pH values show reasonably good agreement. [Work supported by NUSC.]