Abstract
Two salts cause significant sound absorption in the ocean, small concentrations of magnesium sulfate ion pairs and boric acid. Below 100 kHz, MgSO4 produces sound absorption ∼30 times greater than that of pure water. For boric acid below 1 kHz, the excess absorption in the Atlantic over pure water is ∼300 times and in the Pacific ∼150 times, the difference being lower pH at the sound axis in the Pacific than in the Atlantic (7.7 vs 8), the borate concentration being the same. For MgSO4, a four state dissociation model of Eigen and Tamm provides an explanation of sound absorption at 1 ATM from 10 kHz to 300 MHz. Remarkably, at 1000 ATM, this same model accounts for the observed large decrease in sound absorption (−66%) and the small increase in electrical conductance (+10%). For boric acid, Simmons explained absorption in terms of a three state ion pair model involving a configurational change of the B(OH)4 ion from a tetrahedral to a planar trigonal structure B(OH)3 involving a large volume change of 36 cm/mole. The discovery, some history and the current status of these once ‘‘anomalous’’ absorptions will be discussed. [Work supported by ONR and NSF.]
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