These sounds were recorded by the US National Oceanic and Atmospheric Administration (NOAA) and were conditionally divided by scientists into 2 groups.
The first group includes …
Upsweep
The unknown sound was recorded in equatorial waters in 1991 by the Pacific Marine Research Laboratory using the SOSUS sound recording system. The sound is different from those that can make sea currents, and the nature of its origin is unknown. The sound appears in spring and autumn. The source is located at approximately 54 ° S 140 ° W. Every year the sound is heard fainter.
Whistle
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The sound was recorded on July 7, 1997 with an autonomous hydrophone. The source of origin could not be determined.
And here are examples from the second group …
Bloop
Extremely powerful ultra-low frequency sound recorded by the National Oceanic and Atmospheric Administration in 1997 in the Equatorial Pacific Ocean. Presumably, it appeared as a result of the shaking of the ice fields during collision and compression, the melting of ice in the sea and the breaking off of blocks from glaciers.
Julia
Sound recorded on March 1, 1999. Its source, most likely, was an iceberg that ran aground near Antarctica between Bransfield Strait and Cape Adair. The sound was heard throughout the equatorial Pacific.
Slow Down
The source of the sound recorded on May 19, 1997 is also believed to be a stranded iceberg or ice movement in Antarctica. The sound lasted about 7 minutes.
Train
The sound was recorded on March 5, 1997, and is believed to be an iceberg somewhere in the Ross Sea.