It is a common known fact that noise travels about five times more quickly in the sea. But did you know that there are conditions where sound can travel similar to light in a fiber-optic cable?

High frequencies attenuate more quickly than low frequencies, so deep notes go farther especially in the ocean where noise drops off less quickly. Some of the great wales communicate over hundreds or even thousands of miles using this kind of low frequency rumbles we hear from recordings.

Sounds underwater go farthest of all if animals take advantage of a strange property of the sea:
Between the warm lighter layer at the surface and the cool dense water below there is a narrow region where sounds travel in a similar way to light in a fiber-optic cable. Differences in density across this boundary – the “thermocline” – keep soundwaves produced in a narrow channel, where they lose little energy as they travel.

Before the days of satellite beacons the U.S. Navy issued pilots with an explosive charge. If they had to ditch their plane and land in the sea, they were to lower the charge on a string and explode it in this acoustic pipeline. The sound would carry to sensors thousands of miles away in places like California, Hawaii and Panama that could then work out where the pilot was by triangulation.

Several species of whales are known to use this aquatic telephone to broadcast calls over hundreds of thousands of square miles under the sea. Their voices are well adapted to be heard from far away.
Blue whales are the largest and loudest animals on this planet and they can bellow at over 190 decibels.

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