Speed of sound in seawater at high pressures

The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single-transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) -UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) - (UO−UOH2O) =AS (°/oo)+BS (°/oo)3/2 +CS (°/oo)2, where U and UH20 are the speeds of sound in seawater and pure water, respectively; superscripts P and O are used to denote applied pressure P and O (1 atm); A, B, and C are temperature- and pressure-dependent parameters; S (o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high-pressure pure-water sound-speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1-atm seawater sound-speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1 over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1 (maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1 (maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure-water data.