Death Song of an Iceberg

January 17, 2011

credit: National Science Foundation

Last year, University of Washington oceanographer Seelye Martin and his colleagues reported the discovery of an iceberg graveyard: a previously unreported underwater shoal near the Antarctic coast on which large icebergs occasionally run aground and break apart. One notable victim was B-15A, a Rhode Island-size iceberg that was the largest remnant of a far larger, 1000-foot thick berg that had split from the Ross Ice Shelf in March 2000. In October 2005, as B-15A was cruising past Antarctica’s Cape Adare, it stopped, rotated slightly, and then, in just five hours, shattered into several pieces. Subsequent sonar surveys by Martin revealed a six-mile long underwater ridge, which they’ve named Davey Shoal, squarely in the path of coastal currents.

Needless to say, B-15A did not go quietly. Martin has just released a recording of the megaberg’s dying moments, which were picked up at the time by seismic equipment at the South Pole, several hundred miles away. According to the University of Washington website,

The wind-like, whistling sounds are the harmonics created as the iceberg sticks and slips over the shoal. Listen as the cracking sounds build – that’s probably fractures propagating through the iceberg like an ice cube fracturing when put in a glass of water – and then a sharp shot. The eerie moaning sounds are probably from the resulting pieces of ice rubbing against each other.

Seelye compressed the sound file by a factor of 200 so the iceberg’s death song can be heard in less than two minutes. Scientists have been recording iceberg sounds for some years now, using seismometers and other equipment that sit (and travel) directly on the bergs themselves; the video below, from New Scientist, includes the noises made in 2003 by B-15A as it and another iceberg, C-16, “grind against each other with the daily tides.”

A recent post by The Biology Files offers a nice primer on the mechanics of iceberg sounds. As a related sonic experience, don’t miss “Dispersion of Sound Waves of Ice Sheets,” a field recording made by composer and sound artist Andreas Bick of a frozen lake in Germany.

Martin, S., Drucker, R., Aster, R., Davey, F., Okal, E., Scambos, T., & MacAyeal, D. (2010). Kinematic and seismic analysis of giant tabular iceberg breakup at Cape Adare, Antarctica Journal of Geophysical Research, 115 (B6) DOI: 10.1029/2009JB006700

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