A row of microphones has been listening for almost 70 years somewhere off the coast of California, past the point where the continental shelf plunges into icy black water. None of this was ever intended for them. The Navy’s SOSUS hydrophones, built during the Cold War to detect the slow churn of Soviet submarines, sat on the seafloor, wired back to quiet stations onshore, waiting for the wrong kind of propeller. Instead, they captured the ocean conversing with itself.
The operators recorded moans, clicks, deep booms, and long repeating tones that didn’t match anything in their classified catalogs for decades. The majority of the printed waterfall displays were dismissed by the men who read them as “biologicals,” background life with no strategic significance. Most of the time, they were probably correct. Mostly whales. Shrimp are snapped. The rock was occasionally rocked by an earthquake. However, not all of those recordings were given names, and the researchers have never been able to stop being bothered by some of them.
Listening to bioacoustic researchers speak gives me the impression that the public has only ever been given a small portion of the sea, which is louder and much stranger than most of us imagine. Up until 1991, when a dual-use campaign in Washington forced the military’s tapes to be made available for civilian research, the entire archive remained closed. Geologists were able to locate volcanoes that were erupting beneath the surface, and biologists were able to hear blue whale songs that could travel a thousand miles. For the scientists who were invited inside, it was like entering a war room from a vintage film. Genuine, covert, humming with sound.
The calls that no one could explain were hidden in all that data. The most well-known is a 1997 signal known as the “Bloop,” which was so loud it registered on sensors thousands of kilometers apart. It was picked up a few more times that summer before disappearing forever. It is still listed as having an unknown origin. Nowadays, the majority of researchers focus on ice, a vast Antarctic shelf that is grinding and cracking. It’s a neat explanation. Quietly, not everyone agrees with it either.
The puzzle has changed, particularly off the West Coast. The more recent mystery is a silence rather than a roar. According to a six-year study conducted in the waters off the coast of California, blue whales become eerily silent during marine heat waves, and the warming water scatters the food web that the animals sing across. On top of that is a phenomenon known to researchers as auditory masking, in which the precise low frequencies whales use to locate one another are obscured by the continuous grind of cargo ships. A boat’s engine can be heard from ten kilometers away using a hydrophone. Just picture yourself as a whale attempting to be heard over that.
Therefore, the more difficult question isn’t always what’s causing an unexplained call. It’s whether we’re hearing a real animal at all or some strange combination of geology, machinery, and water acting like water. For twenty years, researchers have been unable to separate one voice from the chorus because the incoming signals could originate from any number of nearby creatures. The uncomfortable part is that. The catalog of the known has expanded significantly after fifty years of listening, while the margin of the unknown has obstinately refused to shrink.
It’s difficult to look at that without feeling humbled. The moon’s far side is more precisely mapped than the ocean floor. We’ve trained machines to use the turbine’s rhythm to determine the make and model of a submarine. Even so, the top experts in the field lean back and acknowledge they’re not quite sure when the recorders play a sound off a coastline dotted with surf shops and container ports.
Perhaps it’s a whale that we haven’t yet adequately described. Perhaps the planet itself is changing. For the time being, the truth is that the microphones continue to listen, the files continue to grow, and something continues to make an inappropriate noise somewhere beyond the breakers. The fact that we finally bothered to hear it at all may be more important than whether we ever give it a name.
