Amazing.
I recall a show on the old network of submarine listening posts. At the end they said they were used for marine research, and they tracked pods of whales, etc. with them.
They are in some room with a marine biologist and he is playing recordings.
“That’s a Blue Whale at a depth of 100 feet off the coast of Maine.”
“That’s a Killer Whale off the coast of Washington.”
Then he played one that sounded half electronic and have biological, sounded like something straight out of an alien movie.
“We have NO idea what that is. It is in the Indian Trench at a depth of over a mile down!” (Not sure on the depth - but it was DEEP. And pretty sure it was the “Indian” something.
I have tried to find it on youtube - but no luck.
Let me know if you ever stumble upon it.
That was in 1997 and it was called the “Bloop.” Some scientists now believe it was the cracking of an ice shelf as it breaks up from Antarctica.