There have been many strange and wonderful noises from the ocean which have baffled scientists over the years. Some have been solved using modern technology, while others remain a mystery. One of these is the strange and recurring noise called the Upsweep Sounds.
What are Upsweep Sounds?
The Upsweep Sounds refer to an unidentified sound that has existed since the Pacific Marine Environmental Laboratory (PMEL) began recording Sound Surveillance System (SOSUS) in August 1991. PMEL is an underwater sound surveillance system with listening stations worldwide.
The name given to this phenomenon came from the fact that the sounds repeatedly sweep upwards from low to high frequency. To the human ears, the upsweep sounds resemble an ambulance wail or a howl from an unearthly creature. They consist of a long train of narrow-band sounds that last for about 3 seconds each. On the spectrogram, the repeating sequence of upsweep sounds is represented as vertical loops, which get taller occasionally.
Upsweep sounds are one of the first sounds captured using NOAA's equatorial autonomous hydrophone arrays. Interestingly, the phenomenon changes throughout the year, reaching peaks in fall and spring. However, whether that trend is due to changes in the source or seasonal changes in the propagation environment is unclear.
The location of the source is difficult to identify. Still, it was captured in a remote region of the Pacific Ocean, far away from land, around the halfway point between Australia and South America. Its source level is high enough to be recorded throughout the Pacific Ocean.
The source can be roughly traced near the location of inferred volcanic seismicity, but the origin of the sound remains unresolved. Although the overall source level has declined since 1991, the sound can still be detected on NOAA's hydrophone.
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What Causes These Unexplained Sounds?
Scientists have a plausible but unconfirmed explanation for this phenomenon. They believe the upsweep sounds are due to undersea volcanoes pouring out hot lava into cold water. Additionally, experts claim that there is not enough variation in the tone of the sound for it to come from something biological. Over the years, significant progress has been made in narrowing down the potential source regions, but pinpointing the exact location and cause of the Upsweep remains a challenge.
It might be tempting to go to the location where the Upsweep Sounds were first recorded to investigate its origin. However, several practical challenges and limitations need to be considered.
First, the coordinates where it was found are far from any inhabited land, so accessing such a remote and isolated location could pose logistical and safety challenges. Aside from this, the sounds were detected in deep regions of the ocean, so investigating their source would need advanced diving or submersible technology that can withstand extremely high pressures in the deep.
Upsweep sounds are also not continuous, but they occur intermittently. Experts must be at the right place and time to capture the mysterious sound. Lastly, ocean explorations are costly and require significant resources, like expert personnel, specialized equipment, and research vessels.
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