Effect of pressure on sound absorption in seawater at 0°C

Earlier measurements of the effect of pressure on sound absorption by magnesium sulfate in seawater by Hsu at 0 °C in the laboratory were limited to pressures of just over 300 bars. The pressure was limited by the strength of the 100‐liter titanium sphere, a spare ballast tank from the Woods Hole submarine ALVIN. To obtain data at higher pressures at 0 °C, measurements were recently made in 0.5 M magnesium sulfate solutions in a cylindrical reesonator. Because the magnesium sulfate relaxation frequency is independent of pressure, measurements are necessary at only one frequency. This was done in the 100‐kHz region and a sodium sulfate solution was used to correct for wall losses in the cylinder. Mode interference problems as well as a shutdown in the building air circulation system, which gave rise to temperature control problems, degraded the data. Nevertheless, enough data were obtained at higher pressures (600 to 1300 bars) to be useful in assessing the effect of pressure on seawater sound absorption at 0 °C as has been done with earlier work by Fisher at 25 °C on 0.5 molar magnesium sulfate solutions. These results will be incorporated with those of Hsu at lower pressures into an equation for absorption in seawater at 0 °C covering the whole pressure range. Predictions using this equation will be compared with those from the Garrlson‐Francois and Fisher‐Simmons equations for sound absorption in seawater. [This work was supported by Office of Naval Research.]