Upsweep
As Upsweep a sound is called, which since 1991 by hydrophones from the National Oceanic and Atmospheric Administration using the Equatorial Pacific Ocean autonomous hydrophone array of US Navy in the Pacific Ocean is registered. The place of origin is roughly with 54 ° S, 140 ° W indicated. Seismic activity of volcanic origin is known in this area.
The sound lasts a few seconds and is repeated. Its volume is sufficient to be measured in the entire Pacific. The intensity is subject to seasonal fluctuations with maxima in spring and autumn.
The cause of this noise is so far unknown.