Slowdown — NOAA PMEL equatorial hydrophone array
Speed-shifted ×16 for audibility. Original signal descended over ~7 minutes as iceberg grounded. NOAA PMEL recording, May 19, 1997.
What makes Slowdown unusual is its duration and systematic frequency descent over 7 minutes. The most accepted explanation is an iceberg decelerating as it grounds on the Antarctic seafloor. The sound diminishes in frequency as the object slows — hence the name. Audio file will be added from NOAA PMEL records.
A 7-minute gradually descending acoustic signal recorded May 19, 1997. Each segment slows in frequency over 7 minutes — as if something large was decelerating. Detected at 3 stations across 5,000 km. Classified as probable iceberg grounding.