Yes, sound can be heard underwater, but its behavior differs significantly from how it travels through air. Water is an efficient conductor of sound, allowing it to propagate over much greater distances and at faster speeds than in air. This difference influences how both humans and marine animals perceive and use sound in aquatic environments.
The Behavior of Sound in Water
Sound travels faster in water than in air. While sound moves at approximately 340 meters per second in air, it propagates at about 1500 meters per second in water, making it nearly 4.5 times quicker. This increased speed is due to water’s higher density and lower compressibility compared to air. Sound also travels much further in water with less energy loss over distance, allowing detection from afar.
Despite efficient transmission, sound underwater is less directional, making it challenging to pinpoint the source. The disparity in acoustic impedance between air and water also plays a role. Acoustic impedance, which represents a medium’s resistance to sound wave propagation, is thousands of times higher in water than in air. This impedance mismatch explains why sound transfers poorly between air and water, often becoming heavily attenuated or reflected at the surface.
How Humans Hear Underwater
When humans submerge, they can still perceive sound, though the experience is often muffled and disorienting. This altered perception occurs because the usual pathway for hearing in air, involving sound vibrations through the ear canal to the eardrum and middle ear bones, becomes less effective. Instead, underwater sound largely bypasses these structures and is perceived through bone conduction.
In bone conduction, sound vibrations directly stimulate the skull bones, which then transmit these vibrations to the inner ear. This mechanism allows humans to detect a wider range of frequencies underwater, potentially up to 200,000 hertz, far exceeding the 20 to 20,000 hertz range audible in air. However, because sound reaches both ears almost simultaneously due to its rapid speed and direct bone conduction, the brain struggles to process the subtle time differences needed for sound localization, making direction difficult to determine.
How Marine Animals Use Sound
Marine animals have evolved specialized adaptations to navigate and thrive in an environment where sound is often the dominant sense. Many marine mammals, such as whales and dolphins, possess specialized auditory systems to produce and receive sound underwater. For example, toothed whales use a melon on their forehead to focus outgoing sound waves and fatty tissues in their lower jaw to receive echoes. Fish rely on internal ear structures called otoliths and often a gas-filled swim bladder, which helps them detect particle motion and pressure changes.
Sound is important for communication among marine species. Many animals use distinct vocalizations for long-distance communication related to mating, warning signals, and maintaining social group structures. Beyond communication, some marine animals employ sound for navigation and hunting through echolocation. Dolphins and sperm whales, for instance, emit high-frequency clicks and interpret returning echoes to form a detailed acoustic map, allowing them to locate prey and avoid obstacles where vision is limited. This reliance on sound underscores its importance for survival.