AUDIO-003 Acoustic Record Documented

Julia

A slow-descending acoustic signal lasting nearly 15 seconds, recorded in March 1999 by NOAA's hydrophone network. Detected across a broad area of the Pacific. Source unconfirmed. Not repeated.

Signal Record — AUDIO-003
Julia — Pacific Hydrophone Network
March 1999  ·  ~15 s descending  ·  NOAA PMEL
Original signal at frequencies near the lower limit of human hearing. This recording is presented at native speed.
Julia was named informally by NOAA staff. Unlike Upsweep, it did not recur. Unlike the Bloop, it did not peak dramatically — it descended. Its detection across a wide geographic area implies a large source or unusually efficient propagation. No source has been confirmed.

Signal Description

Julia was recorded on March 1, 1999 by NOAA's Equatorial Pacific autonomous hydrophone array. The signal descends slowly over approximately 15 seconds, with a characteristic profile that distinguishes it from other catalogued Pacific anomalies. Detection occurred across multiple stations simultaneously, indicating a geographically broad source or a signal with exceptional long-range propagation efficiency through the SOFAR channel.

The most likely proposed origin is a large iceberg grounding against the ocean floor near Antarctica — a known mechanism for generating extended low-frequency acoustic signals. However, no specific grounding event has been confirmed to match Julia's location, timing, and spectral profile precisely. The classification remains probable but unverified.

Technical Parameters

Acoustic record IDAUDIO-003 / "Julia"
Detection dateMarch 1, 1999
NetworkNOAA PMEL equatorial hydrophone array
Duration~15 seconds
Frequency profileSlowly descending, low-frequency
Detection rangeBroad Pacific coverage
Proposed sourceAntarctic iceberg grounding — unconfirmed
RecurrenceNone confirmed
Official classificationProbable iceberg-related — unverified
AudioAvailable