The whale’s voice reaches up to 300 miles away.
In the deep sea, there is a layer called SOFAR Channel.
This layer is several hundred meters thick and is located at a depth of about 4,000 ft.
Thanks to this SOFAR Channel, dolphin voices are said to reach up to 300 miles away.
In other words, whales in Tokyo and whales in Osaka can talk.
Normally, the lower the water temperature, the slower the movement of water molecules.
Then, the speed of the sound transmitted through the water will decrease.
Also, the higher the water pressure, the higher the density of water.
Then the speed of the sound will increase.
The deeper the sea, the harder it is for sunlight to reach, so the water temperature will drop accordingly.
However, if the depth exceeds 4,000 ft, the influence of sunlight will disappear, so the water temperature will not drop anymore.
In other words, the speed of sound gets already lowest in the layer.
Well, the main subject is from here.
Sound makes up a wave.
When sound waves generated in this layer try to leave this layer, they are reflected at the boundary with other layers.
This is because “waves are reflected when you try to go from a low speed to a high speed”.
In this way, the sound waves in this SOFAR Channel travel far away without escaping up or down.
The principle is similar to optical fiber.
– NOAA’s National Ocean Service: What is SOFAR?