People mistakenly believe that the ocean is a quiet place. Quite the contrary, there are lots of sounds that can be picked up even by the noisiest scuba divers: catfish, sea horses and grunts are just three of the talky organisms that you can find in the deep. But what about the deepest deep, where life and light is a little less prevalent??
Scientists wanted to develop a baseline for noise levels under the sea in order to track the increase in noise pollution from humans. By dropping a hydrophone into the Challenger Deep, a trough in the Mariana Trench that is more than 36,000 feet below sea level, they were able to test their hypothesis about current noise levels.
Getting the hydrophone down was no easy feat: previously, the deepest a hydrophone had been placed was one mile under the surface. NOAA worked to create a hydrophone designed to withstand 16,000 pounds per square inch, and to descend at a rate of no more than 15 feet per second, at the risk of cracking the structure from too sudden a pressure change. It took 6 hours total to descend.
Finding the right time to drop mattered also; the location was quite exposed to the elements. When conditions permitted, the hydrophone was placed. After 21 days, the memory card was filled with sounds, but retrieving the hydrophone needed to be timed properly as well, as conditions in the ocean made it difficult to return. So, while placed in July 2015 and full of information after 21 days, scientists weren’t able to retrieve the device until November 2015, when the stars aligned (figuratively).
Here’s what they found:
The hydrophone picked up on fish, baleen whales, and a very conveniently passing category 4 typhoon. There was also …
“… a loud magnitude 5.0 earthquake that took place at a depth of about 10 kilometers (or more than six miles) in the nearby ocean crust,” Dziak said. “Since our hydrophone was at 11 kilometers, it actually was below the earthquake, which is really an unusual experience. The sound of the typhoon was also dramatic, although the cacophony from big storms tends to be spread out and elevates the overall noise for a period of days.”
Matsumoto said the hydrophone also picked up a lot of noise from the surface of the ocean – some seven miles above – including waves and winds disturbing the surface.
“Sound doesn’t get as weak as you think it does even that far from the source,” he said.”
Next step? Drop the hydrophone again…this time with a video camera, to see what we are hearing.
ps want to hear?
(baleen whale call)