What happens to sound velocity with increasing depth in water?

Sound velocity in water generally increases with increasing depth due to a combination of factors, primarily temperature, salinity, and pressure. At greater depths, the pressure on the water column increases significantly, which contributes to a rise in sound speed.

As pressure increases, the density of the water also increases but at a lesser rate compared to the increase in bulk modulus, leading to an increase in sound velocity. Furthermore, temperature plays a crucial role; while temperature typically decreases with depth in the ocean, the effect of increased pressure has a more pronounced impact, particularly in deeper waters where temperature changes are less influential.

Salinity also influences sound speed; as the salinity of seawater increases, the sound velocity also increases. However, the dominating factor in the deep ocean is pressure. Therefore, the overall trend shows that as you go deeper into the water column, the velocity of sound increases due to these combined influences, making the correct answer the increase in sound velocity with depth.