Meet Julia. Julia is a 15-second recording made by the National Oceanic and Atmospheric Association (NOAA) on March 1, 1999. Julia is a sound of unknown origin, but was sufficiently loud enough to be heard over the entire Equatorial Pacific Ocean Autonomous Hydrophone Array (that’s very loud… the array consists of 12 hydrophones stretched out over hundreds of miles in the Pacific Ocean). The array was originally designed to detect Soviet submarines during the Cold War, but has since been re-purposed for scientific study (mainly studying seismic movements under the ocean floor). Julia is one of many sounds recorded by the array that have no discernible origin. Her friends include Whistle, Train, Slowdown, Upsweep, and of course, the infamous Bloop. Most of these sounds are thought to be ice calving (when ice breaks away from glaciers or slides off of land), but that does not stop the imagination from running wild. All kinds of theories have been put forth to explain the origins of these unusual sounds, from massive sea creatures to underwater alien civilizations.

All those sounds are fine and dandy, but none quite compare to the Bloop. The Bloop is the name of an unexplained sound, recorded by the array several times during the summer of 1997. It hasn’t been heard since, and no source for the sound was ever discovered (although the general location of the sound was traced to about 3,000 miles away from the array, off of the southern tip of South America). NOAA’s official stance was the same as pretty much all of the unexplained sounds profiled in this article: ice calving. However, after Christopher Fox (a lead oceanographer with NOAA) was paraphrased as “having a hunch” that the Bloop was caused by “some sort of animal” in a 2002 issue of New Scientist (“Calls From The Deep”), all bets were off. The Bloop has since been used as a major plot device in movies, books, and TV shows. Some even speculate that the sound might have been emitted by Cthulu. What is so striking about the sound is that it’s acoustic profile seems to fall in line with other sea creatures, yet the sound was so loud that no known creature (not even the mighty Blue Whale) could possibly have been the source. When you hear the sound, does it call to mind the monstrous nature of the deep that it does for so many others?

Imagine that you’re diving off of the coast of South America, a colorful reef full of fish and eels writhes beneath you. You’re not very deep, maybe 40 feet, but you quickly drift farther from the shore and deeper than you thought. Perhaps you loaded your weight belt with a few too many pounds, perhaps you were breathing too shallowly to maintain buoyancy, but before you know it, the Continental Shelf drops out from beneath you like a trap door under a brightly-lit stage. You suddenly realize that you are completely surrounded by absolute darkness. With nothing but the fading shafts of light coming from the surface to give you any sense of direction, you begin to swim upward, only to be stopped almost immediately by extreme pain in all of your joints. You remember your certification classes, and realize that all of the liquids in your body have been filled with tiny, expanding bubbles, and you’ve been paralyzed by decompression sickness. Just rise slowly, you think. Take a break every few meters, get to the surface and you can find the boa–you’re cut off mid-thought as a deep, thunderous sound vibrates through your bones. You snap your body in all directions, desperately looking for the source of the unearthly sound, only to find yourself in complete darkness. As the sound rises from the depth’s below you again, scattering what few fish you could see around you like windshield glass in a car accident, it dawns on you that during your agonizing ordeal with decompression sickness, you weren’t able to move your legs, and you’d sunken below the point where any light could penetrate the dense ocean. You’ve lost the surface, your tank is quickly running out of air, and you can feel currents of water ripple around you as something very large surges toward you…

For part 2, we’ll get up–and over–sea level.