Upsweep Sound

Other

NOAA hydrophones have recorded Upsweep, a rising tone from the South Pacific, since 1991. Its source is unresolved, with undersea volcanism the leading idea.

1991 - Present
South Pacific Ocean

Upsweep is a mysterious sound recorded in the Pacific Ocean. It is a long train of narrow-band upsweeping tones, each lasting several seconds. It is real and well documented. Its cause is not settled.

Documented facts

According to the NOAA Pacific Marine Environmental Laboratory (PMEL), Upsweep was already present when the lab began recording the Navy’s SOSUS hydrophone arrays in August 1991. The sound is strong enough to be recorded across the whole Pacific. It seems to peak in spring and fall, but NOAA says it is unclear whether that reflects changes at the source or in sound propagation. The source can be roughly located at 54 degrees south, 140 degrees west, near an area of inferred volcanic seismicity. The origin is described as unresolved. The sound’s overall level has fallen since 1991, yet it can still be detected on NOAA’s equatorial arrays. NOAA hosts a spectrogram and a version sped up 20 times so people can hear it.

What it might be

Wikipedia says that an early biological idea, involving whales, was dismissed by 1996. The leading explanation is volcanic or seismic activity near the seafloor spreading zone of the south Pacific. No specific volcano has been shown to be the source.

Reading the mystery

Claims that Upsweep is a creature or a signal are speculation. The record shows an odd, persistent, declining sound that is probably geological, and the simplest answer is that NOAA’s location is only rough, so exact identification needs more data.

Sources

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