The rate at which sound energy moves through a medium. In sea water this is between 1400 and 1550 m/s. In sea water, the speed of sound is a function of temperature, salinity, and pressure due to depth. At a salinity of 34.85‰ and a temperature of 0 °C, the speed of sound is 1445 m/s. It increases by approximately 4 m/s for each degree Celsius rise in temperature, by 1.5 m/s for each 1‰ increase in salinity, and by 18 m/s for each 1000 m increase in depth. It is calculated by a = √(γ‎RT), where a is the speed of sound, γ‎ is the ratio of specific heats (= 1.4 for air at standard temperature and pressure), R is the gas constant (286 m²/s²/K for air), and T is the temperature in kelvins. In air at 20 °C the speed of sound is approximately 343 ms⁻¹.