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"Sea Train" is the name given to a distinctive underwater sound recorded on March 5, 1997, by the U.S. National Oceanic and Atmospheric Administration (NOAA) using its Equatorial Pacific Ocean autonomous hydrophone array. [1] This sound is characterized by its rise to a quasi-steady frequency, typically around 32–35 Hz. [2]
The origin of the Sea Train sound has been attributed to a specific natural phenomenon. NOAA researchers, based on the arrival azimuth of the sound, concluded that it was most likely generated by a very large iceberg that had become grounded in the Ross Sea, near Cape Adare in Antarctica. [2] [3] The sound itself is believed to be produced as this massive iceberg slowly moves and drags its keel along the seafloor. [2] This friction between the ice and the seabed creates the characteristic "rub of train wheels against tracks" sound that led to its naming. [3]
The Sea Train is one of several formerly unidentified sounds detected by NOAA's hydrophone arrays that have since been explained by natural processes, particularly those related to glacial movements and ice activity in the Antarctic region. [4] Other similar sounds, such as "Slow Down" and "Julia," have also been linked to large icebergs grounding or fracturing. [3] The hydrophone arrays, originally developed during the Cold War as the Sound Surveillance System (SOSUS) to detect Soviet submarines, have proven invaluable for monitoring various marine environmental phenomena, including undersea seismicity, ice noise, and marine mammal populations. [5] The recorded signal of the Sea Train, like other NOAA sound files, was sped up by a factor of 16 to increase its intelligibility and shift its frequency from infrasound to a more audible range for analysis.
