How does increasing pressure (depth) affect the speed of sound in water?

How does increasing pressure (depth) affect the speed of sound in water?

• A. Decreases
• B. Remains the same
• C. Increases
• D. Depends on salinity

Answer: (C)

Increasing depth raises pressure, which makes water less compressible (bulk modulus goes up). Since sound speed in a fluid is about the square root of the bulk modulus divided by the density, the stronger increase in stiffness with depth causes the speed to rise overall. Density also rises with depth, but the change in compressibility dominates enough to increase the speed. Temperature and salinity can tweak the exact value, but the general trend with depth is that sound travels faster in deeper water.

Increasing depth raises pressure, which makes water less compressible (bulk modulus goes up). Since sound speed in a fluid is about the square root of the bulk modulus divided by the density, the stronger increase in stiffness with depth causes the speed to rise overall. Density also rises with depth, but the change in compressibility dominates enough to increase the speed. Temperature and salinity can tweak the exact value, but the general trend with depth is that sound travels faster in deeper water.