Thousands of kilometers of fiber-optic cables lie on the ocean floor. They carry internet traffic, but the cables themselves sense the slightest vibrations in the water and the seabed. If you listen closely to such a cable, you can hear a blue whale singing or the ground trembling thousands of kilometers away.
Scientists hooked a device to a cable in Monterey Bay to record these vibrations. The result was a data stream like a continuous audio recording of the ocean. Sorting it by hand is impossible: there's too much noise. So they built a neural network called DASNet that learns to recognize different signal types, much as a person picks out voices in a noisy room.
The network heard local earthquakes, as well as sound waves from distant underwater volcanoes and earthquakes in the southwestern Pacific. It noticed seasonal changes in whale songs that matched recordings from conventional hydrophones. It even tracked the movement of ships near the cable.
It's as if an ordinary city telephone wire suddenly became a stethoscope listening to the planet's breath. The ocean is no longer mute — now we have a cheap way to hear its whisper.
The blue whale is the loudest animal on the planet: its songs can travel hundreds of kilometers underwater.
In Arthur C. Clarke's novel "The Deep Range," people use the ocean's sound channels to communicate over vast distances.