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Iceberg Grounding on Seafloor (Slow Down)

bloop spectrogramThis sound was recorded May 19, 1997 on the eastern equatorial Pacific Ocean autonomous hydrophone array. The origin time and source location are 15:30 GMT near 62°S, 60°W. This is an area off the Antarctic Peninsula with numerous islands and shoals and it is highly probable that this sound was produced by a large iceberg as it became grounded. The sound slowly descends in frequency over about 7 minutes as the drifting iceberg slows to a stop once it comes in contact with the seafloor, however it was of sufficient amplitude to be heard on three sensors at 110W, and 8S, 0, and 8N, at a range of nearly 5,000 km. The South American continent blocked the great circle path from this location to the three eastern sensors located along the 95° longitude line. This type of signal has been recorded numerous times as large icebergs run aground (MacAyeal et al., 2008). Often, after a “slowdown” occurs, a “speedup” follows an aseismic eye of no seismicity associated with local slack tide. This has been interpreted to reflect the acoustic energy of the grounded iceberg responding to the changing tides.

Click on spectrogram for full-sized image.

 

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