A team of researchers from Oregon State University has made the first-ever recordings of what the soundscape is like in the ocean’s deepest spot: the Challenger Deep.  This part of the Mariana Trench is more than 36,000 feet below the surface, but it’s not all that isolated from the normal cacophony of the seas.  As lead investigator Robert Dziak says,

“You would think that the deepest part of the ocean would be one of the quietest places on Earth. Yet there is almost constant noise. The ambient sound field is dominated by the sound of earthquakes, both near and far, as well as distinct moans of baleen whales, and the clamor of a category 4 typhoon that just happened to pass overhead.”

They also heard large ships coming in “loud and strong,” and even the calls of a smaller  toothed whale or dolphin relatively near the surface; you can listen to short sound clips here.  It may seem surprising that sound penetrates so deep.  But of course, seven miles is not really all that far in the ocean; whales routinely communicate over larger distances, and several human sounds sources are readily heard for tens of miles around (or hundreds when caught in a sound-reflecting layer).  What sets the ocean’s depths apart is the extreme density of the water, which can facilitate sound transmission.  Still, it’s a bit disconcerting to realize that no part of the sea is truly free of the acoustic footprints of man.