The ocean has a layer that acts like a whispering corridor. Depending on where you are in the world, it is located about 3,000 feet below the surface, and sound can do almost unbelievable things there. It moves. Thousands of them, not just a few miles, bounced between the pressure boundary below and the thermal ceiling above, moving forward like a hand-to-hand message across a pitch-black room.
It is referred to by scientists as the SOFAR channel or the Deep Sound Channel. The U.S. Navy was highly interested in it during the Cold War. Originally intended to detect Soviet submarines, they constructed an underwater listening network with hydrophones stretched over large areas of the Atlantic and Pacific. Inadvertently, they managed to capture something much older. Whale tunes. Traveling over 10,000 miles through ocean basins, they are low, slow, and nearly architectural in their structure. Before the military gear made it impossible to ignore, it’s possible that no one had ever fully realized how far those sounds were traveling.
The conversation was altered by that discovery, but not instantly or loudly. It demonstrated that the ocean had a complex, multi-layered acoustic life that operated on frequencies and distances that are incompatible with human intuition. Throughout the entire ocean basin, blue whales and fin whales—species whose calls are just barely audible to humans—had been communicating. There’s a feeling that, without realizing it, we’ve been living next to a massive ongoing conversation.
More recently, scientists from Oregon State University and NOAA lowered a ceramic hydrophone into Challenger Deep, the Mariana Trench’s lowest point, which is about 36,000 feet below the surface. For the instrument to withstand the pressure, it had to descend at a precisely regulated speed. Scientists anticipated that the recordings would support the long-held belief that the Earth’s deepest regions would be silent and nearly sterile.
The recordings seemed to indicate otherwise. From somewhere far above came the sound of baleen whale groans. The low mechanical hum of container ships was abandoned in the water. The channel was affected by the seismic tremor of an underwater earthquake. Additionally, a Category 4 typhoon that was raging on the surface of the earth sent its roar all the way to the bottom.
The precise amount of this acoustic complexity that science has yet to fully map is still unknown. An additional layer of strangeness is added to the entire scene by the ocean’s scattering layer, a dense biological mass of fish, squid, and zooplankton that migrates vertically with the light cycle, rising at night and sinking by day. Sonar operators reported seeing a false ocean floor that appeared to move during World War II. Life was what they were pinging off. Sound is reflected back up to the surface by millions of organisms moving together. A living acoustic mirror migrates at midnight.
The scope of what has been happening without human awareness is what makes all of this worthwhile. The sea is active. It simultaneously transmits biology, geology, history, and weather, converting them all into sound and transferring that sound over distances that make most human communication seem localized. Somewhere in the South Pacific, a weakened but undamaged whale call made close to Iceland might eventually reach its destination.
It’s difficult to ignore the fact that we treated the deep ocean for decades as a kind of emptiness, a blank area on the map of significant events. A different story is revealed by the sounds that kept coming up in research hydrophones, Navy recordings, and ceramic instruments that were carefully lowered into crushing pressure. The entire time, the ocean has been speaking. How much of it we’ve already missed is the only question worth asking at this point.
