Upsweep is a sound detected by the U.S. National Oceanic and Atmospheric Administration's (NOAA) equatorial autonomous

hydrophone A hydrophone () is a microphone designed for underwater use, for recording or listening to underwater sound. Most hydrophones contains a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a ...

arrays. The sound was recorded in August, 1991, using the Pacific Marine Environmental Laboratory's underwater sound surveillance system,

SOSUS Sound Surveillance System (SOSUS) was the original name for a submarine detection system based on passive sonar developed by the United States Navy to track Soviet Navy, Soviet submarines. The system's true nature was classified with the name a ...

, and is loud enough to be detected throughout the entire

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. By 1996, early speculations that the sound originated from a biological source was dismissed. The sound consists of a long train of narrow-band upsweeping sounds that occur in intervals of several seconds each. Upsweep occurs and changes

seasonally A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and polar ...

, and is therefore speculated by NOAA scientists to originate from areas of underwater volcanic activity.

Sound profile

The sound's source is roughly located at , in a remote region of the Pacific Ocean between

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and approximately 2,500 miles due west of the southern tip of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. The sound varies seasonally, usually reaching peaks around spring and

fall Autumn, also known as fall (especially in US & Canada), is one of the four temperate seasons on Earth. Outside the tropics, autumn marks the transition from summer to winter, in September (Northern Hemisphere) or March ( Southern Hemispher ...

, but it is unclear whether this is due to changes in the source or seasonal propagation changes in the sound's environment. The sound consists of a long sequence of repeating vertical "sweeps" from low to high frequency lasting for roughly three seconds each and was loud enough to be heard by the entire Equatorial Pacific Ocean autonomous hydrophone array system. Upsweep is characterized by its anomalous reverberating tone, such as those from an

ambulance An ambulance is a medically-equipped vehicle used to transport patients to treatment facilities, such as hospitals. Typically, out-of-hospital medical care is provided to the patient during the transport. Ambulances are used to respond to ...

or siren. The sound was heard by a system of

hydrophones A hydrophone () is a microphone designed for underwater use, for recording or listening to underwater sound. Most hydrophones contains a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a ...

operated by the NOAA's Sound Surveillance System (SOSUS) program for monitoring the northeast Pacific Ocean for low-level seismic activity and detection of

volcanic activity Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

along the northeast Pacific spreading centers. Researchers initially attributed the sound to

Fin whales The fin whale (''Balaenoptera physalus''), also known as the finback whale or common rorqual, is a species of baleen whale and the second-longest cetacean after the blue whale. The biggest individual reportedly measured in length, wi ...

, however, this theory was dismissed after it was argued there was not enough variation in the tone for the sound to be biological. Scientists have traced the source's origins near the location of inferred volcanic

seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 194 ...

. Since 1991, the Upsweep's level of sound (volume) has been declining, but it can still be detected on NOAA's hydrophone arrays.

Volcanic origin

A leading theory behind the origins of Upsweep are attributed to underwater volcanic and seismic activity. Submarine volcanic eruptions are characteristic of the formation of rift zones found in all of the Earth's major ocean basins. These are also known as seafloor spreading centers, where the SOSUS program was established by the NOAA to monitor seafloor earthquake and volcanic activity. The

Monterey Bay Aquarium Research Institute The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foun ...

described the acoustic characteristics of these phenomena as: The source's approximate location has led scientist to infer its source was near an area of underwater volcanic seismicity, however, the sound's exact location is unknown.

Notes

References

{{reflist

External links

Acoustics Monitoring Program - Upsweep
1991 in science Pacific Ocean Oceanography Unidentified sounds Underwater

Sound profile

Volcanic origin

See also

Notes

References

External links