The ocean is alive with noise!! From the surface you would never know it, but underwater there is a symphony of sound. Noise is created underwater by boats, surf, wind, fish, marine mammals, crustaceans and more! When the first underwater microphone (called a hydrophone) was dropped into the ocean, scientists were astounded by the noise levels. The study of sound in the ocean is called underwater acoustics. On this page, you will learn how sound works underwater and about all the acoustically amazing animals that are part of the underwater orchestra!!
Click on the titles below!
Sources of sound
Echolocation - how do they do it?
Song of the Humpback Whale
Killer Whale Dialects
Out of this World Weddell Seals
Introduction to Underwater Sound
What is sound?
Sound is mechanical wave of energy that changes the pressure of its medium (air or water) as it moves. These changes of pressure are detected by our sense of hearing and transmitted to our brains for interpretation. Sound waves are described by their wavelength, amplitude and frequency and intensity (in decibels).
How do we hear?
Sound waves enter our ear and strike our ear drum
(the tympanic membrane) and this vibrates our ear bones
in the middle ear. These vibrations are transmitted to
the fluid of the inner ear. In turn, this fluid vibrates
the hair cells that line the inner ear. These hair cells
are connected by neurons to the auditory nerve. The auditory
nerve carries the signal to our brain where the sound
is translated into information. The volume of the sound
is determined by the number of hair cells stimulated
and the pitch is determined by the distribution pattern
of stimulated cells.
How does sound travel through water?
Water is an ideal medium for the transmission of
sound. The speed of sound in water is 5 times faster
than it is in air. Sound travels 334 meters per second
(m/s) in air and approximately 1500m/s in water. This
speed can be altered depending on the salinity, temperature
and depth of the water. Early marine scientists were
not aware of this property of water and originally the
ocean was considered a vast and silent realm. However,
when the first hydrophone was dropped in the water, they
realized the level of ambient noise underwater was incredible.
As water is such an efficient transmitter of sound, many
marine animals have adapted to use sound as a tool.
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Sources of Sound
in the ocean come from many different sources, both
natural and anthropogenic (made by humans). Humans
create underwater sound mostly through boat traffic,
especially the large shipping freighters. Other human
noise contributors include: industrial activity such
as drilling and mining and military surveillance
operations that use sonar (sound navigation and ranging).
Natural noise sources include: Earthquakes, underwater
landslides, rainstorms on the surface, wind, ice
bergs breaking off and last but certainly not least
Humans create sounds by expelling lots of air over our vocal cords.
Aquatic animals do not have the luxury of wasting so much oxygen.
Therefore, animals in the marine environment have developed a way
to create amazing repertoires of sounds with minimal use of air.
Shrimp and other crustaceans create sound through cavitation. They
close their claws at extremely high speed producing air bubbles
that POP! and create intense amounts of sound.
There are thought to be over 280 species of fish that make sounds.
They do so by vibrating the air in their swim bladders. Seals and
sea lions produce great underwater growls and roars by moving their
larynx to create sound. However, the most acoustically accomplished
of all the animals is the ocean, must be the cetaceans (whales
and dolphins)! The sounds that cetaceans can produce underwater
include echolocation clicks, whistles, chirps and songs! Keep reading
to find out how they do it!
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Continue on to Echolocation!
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