The Bloop

NOAA detected an ultra-low frequency sound in 1997 that matched no known animal or geological phenomenon

In the summer of 1997, an array of underwater microphones operated by the National Oceanic and Atmospheric Administration (NOAA) detected an extremely powerful ultra-low-frequency sound originating from a remote point in the South Pacific Ocean west of South America, and the sound, which was nicknamed "the Bloop" because of the blooping noise it made when sped up to be audible to human ears, was so loud that it was detected on sensors over 3,000 miles apart, making it the loudest underwater sound of unknown origin ever recorded, and the frequency pattern and characteristics of the Bloop did not match any known geological phenomena like volcanic activity or earthquakes, but intriguingly it did show characteristics similar to sounds produced by living creatures, specifically matching the frequency profile of sounds made by marine animals, though the Bloop was many times louder than the loudest sounds produced by the largest known animal, the blue whale, leading to speculation that it might have been generated by an enormous unknown marine animal far larger than any creature known to science.

The sound was recorded on multiple occasions during the summer of 1997 by NOAA's Equatorial Pacific Ocean autonomous hydrophone array, a system of underwater microphones that was originally deployed during the Cold War to track Soviet submarines but was later used for scientific research including monitoring underwater volcanic activity, tracking whales, and studying ocean acoustics, and the sensitivity and geographic distribution of these microphones meant they could detect sounds across vast expanses of ocean and triangulate the approximate location where sounds originated. The Bloop's source was triangulated to a remote area of the South Pacific approximately 1,750 kilometers west of the southern tip of South America, an area of deep ocean far from any major shipping lanes or human activity, and the fact that the sound was detected by sensors thousands of miles apart indicated it was extraordinarily powerful, far louder than any known biological or geological source.

THE SOUND CHARACTERISTICS AND BIOLOGICAL HYPOTHESIS

When NOAA scientists analyzed the frequency spectrum and pattern of the Bloop, they noticed that it rose rapidly in frequency over about one minute before fading away, a pattern that is characteristic of sounds made by marine animals rather than geological events which typically produce more sustained sounds with different frequency characteristics, and this similarity to biological sounds led some researchers to speculate that the Bloop might have been produced by a living creature, though one far larger than any animal currently known to exist. Blue whales, the largest animals ever to live on Earth reaching lengths over 100 feet and weights over 200 tons, produce loud low-frequency calls that can travel hundreds of miles through the ocean, but the Bloop was substantially louder and lower in frequency than the loudest blue whale calls, and simple scaling calculations suggested that if the Bloop was indeed produced by an animal, that animal would need to be many times larger than a blue whale, potentially hundreds of feet long, a size that seems biologically implausible given the physiological constraints on animal size and the lack of any evidence for such creatures.

The idea of an unknown massive marine animal producing the Bloop captured public imagination and spawned countless theories about undiscovered giant squids, ancient marine reptiles that somehow survived to the present day, or even more fantastical creatures from mythology or fiction like the Cthulhu creature from H.P. Lovecraft's stories, and the fact that the Bloop's source location was relatively close to the fictional coordinates of Lovecraft's sunken city of R'lyeh where Cthulhu was said to sleep added a creepy coincidence that fueled speculation though of course this was purely coincidental as Lovecraft's coordinates were entirely fictional. More seriously, marine biologists pointed out that the deep ocean remains one of the least explored environments on Earth, with only a small fraction of the ocean floor having been mapped in detail and even less having been directly observed by humans or cameras, and that new species of marine animals are discovered regularly including large species like new whale species discovered as recently as the 2000s, so the possibility of unknown large animals existing in the deep ocean cannot be entirely dismissed even if creatures large enough to produce the Bloop seem implausible.

THE ICEQUAKE EXPLANATION

In 2005, NOAA released a statement offering a natural explanation for the Bloop and similar mysterious underwater sounds that had been detected, concluding that these sounds were most likely produced by icequakes, the sounds created when large ice shelves or icebergs fracture and break apart, and they noted that the frequency and pattern of the Bloop were consistent with sounds that would be produced by a very large iceberg cracking or a section of ice shelf calving into the ocean, events that can release enormous amounts of energy and create extremely loud sounds that propagate across vast distances through the water. The source location of the Bloop, while not directly adjacent to Antarctica, was within range of where icebergs from Antarctica could drift, and the timing in the middle of Antarctic winter was consistent with when ice fracturing events would be most likely to occur, and subsequent analysis of other mysterious sounds detected by the hydrophone array, sounds with names like "Upsweep," "Julia," and "Slow Down," concluded that most of them could also be explained by ice-related phenomena rather than requiring biological or other exotic explanations.

The icequake explanation was accepted by most scientists as the most parsimonious account that fit the available evidence without requiring the existence of unknown giant animals or unusual geological activity, and NOAA's expertise in ocean acoustics and their familiarity with sounds produced by both marine life and geological processes gave their conclusion substantial credibility, but some critics of this explanation noted that it was presented without detailed acoustic modeling showing exactly how an icequake would produce the specific frequency pattern observed in the Bloop, and that the triangulated source location was quite distant from the nearest ice shelves, requiring that an iceberg had drifted substantially north from Antarctica, which while possible is not definitively proven. The debate over whether the icequake explanation fully accounts for all characteristics of the Bloop continues in some corners of the marine science and cryptozoology communities, with most mainstream scientists considering the question resolved while some researchers and enthusiasts argue that the mystery has not been completely closed and that the biological hypothesis, while unlikely, has not been definitively ruled out.

OTHER MYSTERIOUS UNDERWATER SOUNDS

The Bloop was just one of several mysterious sounds detected by NOAA's hydrophone array during the 1990s, and the fact that multiple different unexplained sounds were recorded suggested either that the ocean contains various unknown acoustic phenomena or that our understanding of natural sounds produced by geological and environmental processes was incomplete, and the investigation of these sounds provided valuable scientific insights into ocean acoustics regardless of whether they ultimately turned out to have exotic or mundane explanations. The sound nicknamed "Julia," detected in 1999, was sufficiently loud to be picked up by the entire Equatorial Pacific hydrophone array spanning thousands of miles, and like the Bloop it had characteristics that some analysts thought were consistent with biological sources, though it too was later attributed to icequake activity, specifically to the sound of a large iceberg running aground on the seafloor or breaking apart.

Another sound called "Upsweep," which was first detected in 1991 and was recorded seasonally for several years before fading away, consisted of a long series of narrow-band upsweeping sounds that occurred repeatedly, and this sound was ultimately attributed to volcanic or seismic activity, possibly related to an uncharted seamount or underwater volcanic area, and the seasonal variation in the sound was thought to be related to how ocean temperature and salinity changes with seasons affect sound propagation rather than indicating seasonal variation in the source itself. The sound nicknamed "Slow Down," detected in 1997 around the same time as the Bloop, had frequency characteristics that slowly decreased over about seven minutes, and it too was eventually explained as likely being produced by ice shelf or iceberg activity, and the pattern of these various sounds being detected in the late 1990s and then decreasing or disappearing in subsequent years was thought to possibly relate to climate change effects on Antarctic ice, with warming temperatures potentially causing increased ice fracturing and calving during that period.

THE CONTINUING SEARCH FOR UNKNOWN MARINE LIFE

While the Bloop has been officially explained as an icequake, the broader question of whether large unknown animals might exist in the deep ocean remains a topic of legitimate scientific interest, and the history of marine biology includes numerous examples of large species that were unknown to science until relatively recently, including the giant squid which was considered legendary until the first specimen was scientifically documented in the 1870s and which was not photographed alive until 2002, and the colossal squid which was first described from fragmentary remains and was not observed complete until 2007, and the megamouth shark which was completely unknown to science until 1976 when one was accidentally captured in a ship anchor, demonstrating that even very large marine species can remain undiscovered because of the vast size and depth of the ocean. The deep sea environment, particularly the ocean depths below 1,000 meters where sunlight does not penetrate and pressure is enormous, remains one of the least explored frontiers on Earth, with more detailed maps existing of the Moon's surface than of most of the ocean floor, and new species are discovered regularly in deep sea expeditions including some species that challenge our understanding of the limits of animal size and the environmental conditions where life can exist.

The search for unknown large marine animals continues through various research programs including the Census of Marine Life which conducted extensive surveys of ocean biodiversity and discovered thousands of new species between 2000 and 2010, and through acoustic monitoring programs that continue to listen for whale calls and other marine animal sounds while simultaneously watching for unexplained acoustic phenomena that might indicate unknown species, and while most marine biologists consider the likelihood of undiscovered animals large enough to produce sounds like the Bloop to be very low, the possibility cannot be entirely excluded given how much of the ocean remains unobserved and how limited our acoustic data from most regions of the ocean actually is. The development of new technologies including autonomous underwater vehicles, deep-sea cameras, and satellite tracking of large marine animals has significantly expanded our ability to study the ocean and its inhabitants, but even with these tools the deep ocean remains largely unexplored, and the possibility of discoveries that challenge our current understanding remains real even if the specific mystery of the Bloop has been reasonably explained through icequake phenomena.

THE CULTURAL IMPACT AND SCIENTIFIC VALUE

The Bloop achieved cultural status far beyond its scientific significance, becoming one of the most famous examples of unexplained natural phenomena and inspiring countless documentaries, fictional stories, and internet discussions about unknown creatures in the ocean's depths, and the sound's association with the Lovecraftian mythology of the sleeping monster Cthulhu gave it a particularly creepy cultural resonance that persists even after the icequake explanation has been officially accepted. The fascination with the Bloop reflects broader human psychology about the unknown and the undiscovered, our tendency to find mystery and potential danger in phenomena we do not immediately understand, and our enduring interest in the possibility that Earth still contains secrets and unknown creatures despite our technological capabilities and scientific knowledge, and the ocean serves as a particularly potent source of these mysteries because its depths remain genuinely unexplored and because its vastness and darkness evoke primal fears and fascinations.

From a scientific perspective, the investigation of the Bloop and other mysterious sounds detected by NOAA's hydrophone array provided valuable research opportunities for understanding ocean acoustics, for improving our ability to distinguish between different types of natural sounds, and for demonstrating the power of distributed sensor networks for monitoring large-scale phenomena across vast areas of ocean, and the fact that relatively mundane explanations involving ice dynamics ultimately accounted for these sounds does not diminish their scientific value as case studies in how to investigate unexplained observations using rigorous methodology and multiple lines of evidence. The Bloop remains a reminder that the ocean contains phenomena we do not fully understand, that unusual observations deserve serious scientific investigation before being dismissed or sensationalized, and that the process of moving from mystery to understanding requires careful analysis, multiple observations, and willingness to consider various hypotheses while following the evidence toward the most parsimonious explanation, even when that explanation is less exciting than the possibilities that initially captured our imagination.