This sound was recorded May 19, 1997 on the Equatorial Pacific Ocean autonomous hydrophone array. The sound slowly descends in frequency over about 7 minutes and was of sufficient amplitude to be heard on three sensors at 95W, and 8S, 0, and 8N, at a range of nearly 2,000 km. This type of signal has not been heard before or since. It yields a general location near 15^oS; 115^oW. The origin of the sound is unknown.  

Click on spectrogram for full-sized image.

283K wav file(The recorded signal has been sped up 16 times)