The definitive answer emerged in the mid-2000s through long-term polar observation. Led by oceanographer Dr. Robert Dziak and researchers at NOAA’s PMEL Acoustic Program, scientists deployed targeted hydrophone arrays near the Antarctic continent between 2005 and 2012. Specifically, research arrays placed near the Bransfield Strait and the Drake Passage began capturing dozens of sounds identical to the 1997 anomaly.
The culprit was a cryoseism, commonly known as an icequake. When a colossal ice sheet fractures, calving an iceberg the size of a small island into the ocean, the structural failure unleashes tremendous potential energy. The sudden tensile break acts like a subterranean fault rupture, generating powerful acoustic shear waves that pass directly into the water column.
As massive icebergs scrape along the continental seafloor or crack clean in two under hydraulic pressure, they create long-duration, low-frequency sound profiles that rise and fall. NOAA confirmed that the 1997 signal was generated between the Palmer Peninsula and Cape Adare in Antarctica. The sound channel carried the low-frequency pulses north through the deep ocean trenches of the South Pacific basin, where the equatorial listening array detected it minutes later.
