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.