700 Fathoms Under the Sea: The Deep Sound Channel

This post is part of the STEM Story Project series.

Jacques Cousteau called it the “silent world.” Let’s just say he got that one wrong.

Something unusual happens 700 fathoms under the sea. Ocean physics create a special zone where sound travels for hundreds, even thousands of miles.

David Schulman gives us a preview of the ocean’s Deep Sound Channel in his PRXSTEM story:

You can think of the Deep Sound Channel this way: sound gets bent (refracted) by layers of pressure and depth in ocean water just as light gets refracted in a prism. Scientists discovered this “sound channel” in 1944. Whales use it to communicate across oceans — and during the Cold War the Navy secretly used it to track nuclear subs. This 1948 graphic shows sound traveling on an axis 700 fathoms down in the Atlantic.

When asked about how he got the idea for this piece, Schulman says, “I got talking with Bill McQuay (audio person for Cornell Ornithology Lab, sound designer, and former team member on NPR’s “Sound Expeditions”), a brilliant and imaginative sonic polyglot…[He] mentioned that the general field of anthropogenic noise — human-made sound — and its effect on other species and habitats, is an area where research is accelerating rapidly.” This eventually led to Schulman connecting with Chris Clark, whom you hear in the piece.

Ewing and Worzel 1948 report #2


Ewing and Worzel 1948 report


(above) Morris Ewing and J. Lamar Worzel discovered the deep sound channel in 1944, and published their results in 1948 in a paper titled “Long-Range Sound transmission.” In this image from their report, it’s possible to see the reading recorded on paper by one of their hydrophones just after an explosion set off 800 miles away in the sound channel. Photo credit: Maurice Ewing and J. Lamar Worzel

In every radio story, there’s at least one things that doesn’t make the final cut. Schulman points out one outtake he wishes he could have included:

“In early April 1944, a destroyer called the Buckley (also knows as DE-51) assisted in the experiments that, for the first time, proved the existence of the deep sound channel — and set the course for Naval intelligence for three decades of the Cold War. The crew of the Buckley set off charges that traveled through the sound channel, and were recorded more than 800 miles away by Maurice Ewing and J. Lamar Worzel aboard the USS Saluda. These tests were by far the longest transmission of human sounds recorded to that date.” (You can read more about that history here.)



Bioacoustic researcher Chris Clark by the San Francisco Bay. Photo credit: Michael Johnson

We asked Schulman what he hopes listeners get from this piece: “A sense of the power and extraordinary reach of the sound channel operates. And a dawning sense of how human activity may be changing the fundamentals of undersea life, through the noises we are making.”

Spoken like a true science storyteller, he adds, “This is as good as going to Mars.”