Which factor is the biggest influence on the speed of sound in water?

• A. Temperature
• B. Salinity
• C. Pressure
• D. Depth

Answer: (A)

Sound speed in water is set by how easily a pressure disturbance propagates through the medium, which depends on how stiff the water is and how dense it is. Temperature has the biggest effect because warming water makes the molecules more active and changes the density and elastic response in ways that most strongly speed up the transmission of the wave. In practical terms, when the water gets warmer, the speed increases more than it does from changing salinity or from the pressure associated with depth. Salinity and depth do matter, but their influence is smaller across typical ocean conditions, so temperature is the dominant factor shaping how fast sound travels.