How do temperature, salinity, and pressure affect the speed of sound in seawater?

The speed of sound in seawater is determined by the water's elasticity and density, both of which are influenced by temperature, salinity, and pressure. Because seawater is only slightly compressible, it possesses a high degree of elasticity, allowing it to conduct sound rapidly.1

The speed of sound generally ranges between 1,450 and 1,570 metres per second and is affected by these three variables as follows:

• Temperature: The speed of sound increases by approximately 4.5 metres per second for every 1 °C rise in temperature. In the upper layers of the open ocean, temperature typically exerts a greater influence on sound speed than salinity.1
• Salinity: An increase in salinity raises the speed of sound by about 1.3 metres per second for each 1 psu increase.1
• Pressure: Increasing pressure also raises the speed of sound, at a rate of about 1.7 metres per second for every 100 metres of depth.1

While temperature and salinity are the primary factors in the upper ocean, pressure becomes the dominant controlling factor at greater depths. At approximately 1,000 metres, these factors combine to create a zone of minimum sound speed known as the SOFAR channel.12