Bloop was an ultra-low-frequency, high amplitude underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. [1] By 2012, earlier speculation that the sound originated from a marine animal [2] was replaced by NOAA's description of the sound as being consistent with noises generated via non-tectonic cryoseisms originating from glacial movements such as ice calving, or through seabed gouging by ice. [1] [3] [4]
The sound's source was roughly triangulated to 50°S100°W / 50°S 100°W , a remote point in the South Pacific Ocean west of the southern tip of South America. The sound was detected by the Equatorial Pacific Ocean autonomous hydrophone array, [1] a system of hydrophones primarily used to monitor undersea seismicity, ice noise, and marine mammal population and migration. [5] : 284 This is a stand-alone system designed and built by NOAA's Pacific Marine Environmental Laboratory (PMEL) to augment NOAA's use of the U.S. Navy Sound Surveillance System (SOSUS), which was equipment originally designed to detect Soviet submarines. [5] : 255–256
According to the NOAA description, the sound "rose" in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 km (3,000 miles).
The NOAA Vents Program has attributed the sound to that of a large cryoseism (also known as an ice quake). [4] Numerous ice quakes share similar spectrograms with Bloop, as well as the amplitude necessary to detect them despite ranges exceeding 5,000 km (3,000 miles). This was found during the tracking of iceberg A53a as it disintegrated near South Georgia Island in early 2008. The iceberg(s) involved in generating the sound were most likely between Bransfield Strait and the Ross Sea; or possibly at Cape Adare, a well-known source of cryogenic signals. [1] Sounds generated by ice quakes are easily determined through the use of hydrophones since seawater, an excellent sound channel, allows the ambient sounds generated through ice activities to travel great distances. [6] : 5
In ice calving, variations result from a sound source's motion. [6] : 55 Icequakes, caused by the fracturing and movement of large ice masses, can produce powerful low-frequency sounds that propagate over vast distances in water. This mechanism could explain the Bloop's wide detection range and distinct acoustic signature. [7] As oceanographer Yunbo Xie explains, the alteration of waveforms from a detected sound "can also be caused by so-called angular frequency dependent radiation patterns associated with antisymmetric mode motion of the ice cover." [6] : 59
Two processes known as rubbing and ridging are responsible for acoustical emissions similar to those from ice calving. [8] Rubbing involves two or more areas of compacted glacial ice floes which are being forced together, inducing shear deformation at its edges and triggering horizontally-polarized shear waves, i. e. SH waves . [6] : 137 Ridging occurs when that ice bends or slides at the ridges. [6] : 121 According to Xie, both events will produce sound in the failure sequence (breakup) of an ice floe:
"A wave equation resulting from shear deformation will be defined in an ice floe with the rubbing effect coupled to the floe through its boundary with the adjacent ice," [6] : 137 while "ridging deformation(s) revealed by this event indicate that the failure process is associated with a crushing process that seals air or vacuous gaps between ice floes. The acoustical signals emitted by this failure process are similar to those emitted from a collapsing air bubble in a fluid." [6] : 121
NOAA's Christopher Fox, in an interview with CNN in 2001, stated that he believed Bloop to be ice calving in Antarctica. [9] In 2002, Fox was interviewed by David Wolman for an article in New Scientist , where he stated that he did not believe its origin was man-made, such as a submarine or bomb. Fox also stated that while the audio profile of Bloop does resemble that of a living creature, [2] the source was a mystery because it would be "far more powerful than the calls made by any animal on Earth." [10] Wolman reported in his article the following:
Fox's hunch is that the sound nicknamed Bloop is the most likely (out of the other recorded unidentified sounds) to come from some sort of animal, because its signature is a rapid variation in frequency similar to that of sounds known to be made by marine beasts. There's one crucial difference, however: in 1997 Bloop was detected by sensors up to 4,800 km (3,000 miles) apart. That means it must be far louder than any whale noise, or any other animal noise for that matter. Is it even remotely possible that some creature bigger than any whale is lurking in the ocean depths? Or, perhaps more likely, something that is much more efficient at making sound? [11] : 174–175
— David Wolman
According to author Philip Hayward, Wolman's speculations "amplified Fox's 'hunch' and—through the use of the word 'likely'—opened the door for subsequent speculation as to what such an 'efficient' noise-making entity might be. Over the last decade, consensus has supported the argument that the noise is produced by ice fracturing processes." [11] : 175
Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.
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 sound wave.
Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore wind farms, offshore oil exploration and drilling and related activities. Surveys may also be conducted to determine the route of subsea cables such as telecommunications cables, cables associated with wind farms, and HVDC power cables. Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities. The term hydrography is used synonymously to describe maritime cartography, which in the final stages of the hydrographic process uses the raw data collected through hydrographic survey into information usable by the end user.
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface. Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs undergo a significant yearly cycling in surface extent, a natural process upon which depends the Arctic ecology, including the ocean's ecosystems. Due to the action of winds, currents and temperature fluctuations, sea ice is very dynamic, leading to a wide variety of ice types and features. Sea ice may be contrasted with icebergs, which are chunks of ice shelves or glaciers that calve into the ocean. Depending on location, sea ice expanses may also incorporate icebergs.
Acoustic homing is the process in which a system uses the sound or acoustic signals of a target or destination to guide a moving object. There are two types of acoustic homing: passive acoustic homing and active acoustic homing. Objects using passive acoustic homing rely on detecting acoustic emissions produced by the target. Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target. The signal detected is then processed by the system to determine the proper response for the object. Acoustic homing is useful for applications where other forms of navigation and tracking can be ineffective. It is commonly used in environments where radio or GPS signals can not be detected, such as underwater.
A sonobuoy is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on the water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater.
Iceberg B-15 was the largest recorded iceberg by area. It measured around 295 by 37 kilometres, with a surface area of 11,000 square kilometres, about the size of the island of Jamaica. Calved from the Ross Ice Shelf of Antarctica in March 2000, Iceberg B-15 broke up into smaller icebergs, the largest of which was named Iceberg B-15-A. In 2003, B-15A drifted away from Ross Island into the Ross Sea and headed north, eventually breaking up into several smaller icebergs in October 2005. In 2018, a large piece of the original iceberg was steadily moving northward, located between the Falkland Islands and South Georgia Island. As of August 2023, the U.S. National Ice Center (USNIC) still lists one extant piece of B-15 that meets the minimum threshold for tracking. This iceberg, B-15AB, measures 20 km × 7 km ; it is currently grounded off the coast of Antarctica in the western sector of the Amery region.
The SOFAR channel, or deep sound channel (DSC), is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating. An example was reception of coded signals generated by the US Navy-chartered ocean surveillance vessel Cory Chouest off Heard Island, located in the southern Indian Ocean, by hydrophones in portions of all five major ocean basins and as distant as the North Atlantic and North Pacific.
Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can discharge material into the atmosphere during an eruption. The total number of submarine volcanoes is estimated to be over one million of which some 75,000 rise more than 1 kilometre above the seabed. Only 119 submarine volcanoes in Earth's oceans and seas are known to have erupted during the last 11,700 years.
A cryoseism, ice quake or frost quake, is a seismic event caused by a sudden cracking action in frozen soil or rock saturated with water or ice, or by stresses generated at frozen lakes. As water drains into the ground, it may eventually freeze and expand under colder temperatures, putting stress on its surroundings. This stress builds up until relieved explosively in the form of a cryoseism. The requirements for a cryoseism to occur are numerous; therefore, accurate predictions are not entirely possible and may constitute a factor in structural design and engineering when constructing in an area historically known for such events. Speculation has been made between global warming and the frequency of cryoseisms.
Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.
The Erebus Glacier Tongue is a mountain outlet glacier and the seaward extension of Erebus Glacier from Ross Island. It projects 11 kilometres (6.8 mi) into McMurdo Sound from the Ross Island coastline near Cape Evans, Antarctica. The glacier tongue varies in thickness from 50 metres (160 ft) at the snout to 300 metres (980 ft) at the point where it is grounded on the shoreline. Explorers from Robert F. Scott's Discovery Expedition (1901–1904) named and charted the glacier tongue.
Glacial earthquakes refer to a type of seismic event, with a magnitude of about 5, resulting from glacial calving events. The majority of glacial earthquake activity can be seen in the late summer and are found in Antarctica, Alaska, and Greenland. About 90% of these occur in Greenland. Glacial earthquakes occur most frequently in July, August, and September in Greenland. Seismographs are analyzed by scientists to identify and locate glacial earthquakes.
A Fessenden oscillator is an electro-acoustic transducer invented by Reginald Fessenden, with development starting in 1912 at the Submarine Signal Company of Boston. It was the first successful acoustical echo ranging device. Similar in operating principle to a dynamic voice coil loudspeaker, it was an early kind of transducer, capable of creating underwater sounds and of picking up their echoes.
Ice mélange refers to a mixture of sea ice types, icebergs, and snow without a clearly defined floe that forms from shearing and fracture at the ice front. Ice mélange is commonly the result of an ice calving event where ice breaks off the edge of a glacier. Ice mélange affects many of the Earth's processes including glacier calving, ocean wave generation and frequency, generation of seismic waves, atmosphere and ocean interactions, and tidewater glacier systems. Ice mélange is possibly the largest granular material on Earth, and is quasi-2-dimensional.
JASCO Applied Sciences provides scientific consulting services and equipment related to underwater acoustics. JASCO operates from 7 international locations and provides services to the oil and gas, marine construction, energy, renewable energy, fisheries, maritime transport and defence sectors. The head office is located in Halifax, NS Canada. JASCO employs acousticians, bioacousticians, physicists, marine mammal scientists, engineers, technologists, and project managers.
Radio acoustic ranging, occasionally written as "radio-acoustic ranging" and sometimes abbreviated RAR, was a method for determining a ship's precise location at sea by detonating an explosive charge underwater near the ship, detecting the arrival of the underwater sound waves at remote locations, and radioing the time of arrival of the sound waves at the remote stations to the ship, allowing the ship's crew to use true range multilateration to determine the ship's position. Developed by the United States Coast and Geodetic Survey in 1923 and 1924 for use in accurately fixing the position of survey ships during hydrographic survey operations, it was the first navigation technique in human history other than dead reckoning that did not require visual observation of a landmark, marker, light, or celestial body, and the first non-visual means to provide precise positions. First employed operationally in 1924, radio acoustic ranging remained in use until 1944, when new radio navigation techniques developed during World War II rendered it obsolete.
Seismic oceanography is a form of acoustic oceanography, in which sound waves are used to study the physical properties and dynamics of the ocean. It provides images of changes in the temperature and salinity of seawater. Unlike most oceanographic acoustic imaging methods, which use sound waves with frequencies greater than 10,000 Hz, seismic oceanography uses sound waves with frequencies lower than 500 Hz. Use of low-frequency sound means that seismic oceanography is unique in its ability to provide highly detailed images of oceanographic structure that span horizontal distances of hundreds of kilometres and which extend from the sea surface to the seabed. Since its inception in 2003, seismic oceanography has been used to image a wide variety of oceanographic phenomena, including fronts, eddies, thermohaline staircases, turbid layers and cold methane seeps. In addition to providing spectacular images, seismic oceanographic data have given quantitative insight into processes such as movement of internal waves and turbulent mixing of seawater.
Upsweep is an unidentified sound detected by the U.S. National Oceanic and Atmospheric Administration's (NOAA) equatorial autonomous hydrophone arrays. The sound was recorded in August, 1991, using the Pacific Marine Environmental Laboratory's underwater sound surveillance system, SOSUS. Loud enough to be detected throughout the entire Pacific Ocean, Upsweep remains one of the only detected sounds to have an unresolved origin. 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, and is therefore speculated by NOAA scientists to originate from areas of underwater volcanic activity.
