The Bloop is the name given to an ultra-low frequency and extremely powerful underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) several times during the summer of 1997. The source of the sound remains unknown.
According to the NOAA description, it "rises rapidly in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 km." NOAA's system ruled out its origin as any known man-made sound, such as a submarine or bomb, or familiar geological sounds such as volcanoes or earthquakes. While the audio profile of the bloop does resemble that of a living creature, the system identified it as unknown because it was far too loud for that to have been the case: it was several times louder than the loudest known biological sound (that of the blue whale).
So, uh, Cthulhu rising?...
Given that we really haven't explored the ocean depths much at all, it is highly plausible and possible that we're looking at a completely new species, monster even.
It is also highly suspect and unusual why, if it is a monster, we have not heard more from it; however, even whales and dolphins do not telegraph or advertise their presence much at all. Some scientists are of the opinion that the sound produced by the Bloop more than resembles an organic signature. IIRC, a scientist who initially speculated that the sound could be that of an ice calving has apparently reframed his opinion to that of 'animal in origin.'
H.P. Lovecraft also appears to have been psychic...
50° S 100° W (a remote point in the south Pacific Ocean west of the southern tip of South America)
47° 9 S 126° 43 W 47.15° S 126.717° W / -47.15 ; -126.717 in the southern Pacific Ocean
49° 51 S 128° 34 W / 49.85° S 128.567° / -49.85 ; -128.567
Pacific pole of inaccessibility 48° 52.6 S 123° 23.6 W / ;48.8767° S 123.3933° W / -48.8767 ; -123.3933