Julia was a very 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. The sound was loud enough to be heard all across the array and lasted about 2 minutes and 43 seconds. Its origin was traced to an area between the Bransfield Strait and Cape Adare, near the coast of Antarctica.

At first, the sound could not be identified and sounded like a person’s voice, which led to its nickname "Julia." This human-like quality, along with its distant location and long reach, sparked public interest and led to guesses about alien activity or deep-sea creatures. However, NOAA scientists later concluded that the most likely source was a large iceberg that had become stuck on the seafloor near Antarctica. This explanation matches other previously unexplained sounds, such as the "Bloop," which was also linked to icequakes. Icequakes occur when massive icebergs break away from glaciers or move along the ocean floor, creating loud sounds that can travel long distances. Other sounds, like "Slow Down" and "Sea Train," recorded by NOAA, were also attributed to grounded icebergs. Scientists now widely accept that Julia was caused by an iceberg breaking apart on the seafloor. As glaciers melt more frequently due to climate change, such ice-related noises are becoming more common and are often detected by hydrophones near Antarctica.