In 1997, the U.S. National Oceanic and Atmospheric Administration (NOAA) recorded a strange sound deep in the South Pacific.
NOAA officials knew it was some kind of animal, because the sound started at ultra low frequencies and rose in pitch. Ice breaking or underground quakes don't have that kind of pattern -- they're abrupt and limited in frequency. And unlike ice cracking or ground shifting, the sound lasted nearly a minute. The pattern clearly matched what they'd expect from whale calls or other animal vocalizations. And it was detected across thousands of miles of ocean, again common for the low-frequency sounds made by marine animals, but rare for ice quakes. This noise was biological.
Researchers who heard the sound called it "amazing". But it was also disturbing. Because they didn't know what animal could make it. It was no whale. In fact, the amplitude was beyond what any currently known creature could make. It was extremely loud. Which suggested the animal was extremely big. Was there a giant roaming undiscovered in the deepest parts of the ocean?
It wasn't a one-off anomaly -- the sound kept happening. The mystery creature made the call several times, in a brief, concentrated series that was recorded and analyzed. Something was out there.
28 years later, we still don't know what it was. Since no known animal ever surfaced whose call matches the extremely low frequency, high volume pattern, NOAA now attributes it to ice quakes. But many hold onto the belief there is a hidden leviathan yet to be found, silently gliding through the depths of the Pacific.
Could such a creature roam the Earth's oceans undetected for all of human history? Seems unlikely. But a recent, ground-breaking study revealed how possible that may be -- and how little we know about the depths of our own oceans.
The study -- published last month -- was impressive in its scale. Led by Museums Victoria Research Institute, the work involved over 40 institutions around the world. The goal was simple. Researchers wanted to understand how marine species split and move between different parts of the ocean, and how unique communities of animals develop in oceans around the world. The DNA analyzed came from specimens collected during 332 research voyages, many undertaken decades ago, and preserved in institutions around the world. Lynley Crosswell, CEO and Director of Museums Victoria called it "science on a global scale."
The focus of this massive study was about as far from a giant sea creature as you can get: the brittle star. It's a relative of a starfish, with a round center three centimeters across. Turns out, this tiny animal is the perfect choice if you want to study differences in the same animal in every possible ocean, because brittle stars are everywhere, across all sea floors on Earth. In fact, they are everywhere in big numbers.
Brittle stars also offer a window into the past few other living creatures can match. By comparison, humans first appeared around 300,000 years ago. But brittle stars originated around 480 _million_ years ago, well before dinosaurs. Indeed, brittle stars are among the most ancient creatures living on Earth today, a living fossil that allowed researchers to investigate movement over evolutionary timescales.
The researchers expected to find different species of brittle stars restricted to different regions. It's how marine life is, generally -- different oceans tend to have their own communities. It's true, all the oceans are connected in some way, through narrow straits or passages. But there are barriers between them that make it hard or, in some cases, impossible for animals to move freely around. Some are physical land barriers, and some are seas so shallow the fish are literally stopped from crossing. And there are other major barriers as well. Stark differences in temperatures block the movement of some species from tropical to temperate or polar waters, for example. And certain dangerous currents also create natural barriers isolating populations. There should be distinct groups of brittle stars in every ocean.
But that's not at all what they found.
Turns out, on the sea floor where brittle stars live, there are different rules. Here, we are at the abyssal zone, 20,000 feet under. It's pitch dark, near freezing, and under extremely high pressure. The sea floor is mostly flat abyssal plains, with occasional trenches, ridges, and underwater mountains. You won't find as much life here as in shallower waters, but you will find the most stable and continuous habitat on Earth. Which is why the brittle stars could call it home for such a mind-boggling span of time, nearly half a billion years.
This new study of brittle star biogeography found the exact same species in vast, geographically distant areas and separate deep sea regions. Any barriers in the upper part of the ocean meant nothing to them. Genetic analyses showed that populations in different deep-sea biomes were closely related. They've been moving around the globe freely for generations.
The study showed the same biomes in northern Atlantic and southern Australian oceans -- opposite sides of the planet. Any barriers in temperatures or currents had no effect on the dispersal of the ancient animals. In the most dramatic example, the eastern Pacific-Indo-Pacific barrier, which is a major divider of biomes in the Pacific and Indian oceans was not at all evident in the abyssal data. It just didn't exist.
Simply put, they found a more extensive degree of deep-sea connectivity than was ever previously understood. At extreme depths, the ocean is truly a different world, an environment that is highly connected, or, as one of the study leads described it, "a superhighway." Under land barriers and shallow seas lies uninterrupted plains where animals can live undisturbed for millions of years.
We have yet to travel all the highways at these abyssal depths. But back in 1997, we may have already heard one of its creatures inviting us to try.