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Julia was an ultra-low-frequency sound recorded on March 1, 1999, by the U.S. National Oceanic and Atmospheric Administration (NOAA) using its Equatorial Pacific Ocean autonomous hydrophone array. [1] The sound was loud enough to be detected across the entire array, lasting approximately 2 minutes and 43 seconds. Its origin was narrowed down to a region between the Bransfield Straits and Cape Adare, off the coast of Antarctica. [2] [ unreliable source ] [3]
Initially, the sound was unidentifiable and eerily resembled the voice of a human, leading to its nickname "Julia". [2] [ unreliable source ] [3] This human-like quality, combined with its remote origin and massive range, captivated public imagination and led to various speculations, including theories of alien activity or deep-sea monsters. [3] However, NOAA researchers later determined that the most likely source of the sound was a large iceberg that had run aground off Antarctica. [2] [ unreliable source ] [1] [3] This explanation aligns with similar previously unidentified sounds, such as the "Bloop," which was also attributed to icequakes. [3] Icequakes, which are massive icebergs cracking off glaciers or scraping the ocean floor, can generate sounds of significant amplitude that travel vast distances. [3] The "Slow Down" and "Sea Train" sounds, also recorded by NOAA, were similarly attributed to grounded icebergs. The scientific community has largely accepted the iceberg grounding theory for Julia, recognizing that the sound of a continent's ice fracturing against the seafloor can be profoundly impactful. [3] With increasing glacial melt due to climate change, such ice-generated rumbles are becoming more common and are frequently detected by hydrophones around Antarctica. [3]