There are several natural causes of underwater noises that can be mistaken for sounds from a submersible or underwater vehicle. Here are a few examples:
Marine Mammals: Whales, dolphins, and other marine mammals are known for producing a variety of sounds underwater. These include clicks, whistles, and songs. The low-frequency vocalizations of whales, in particular, can carry over long distances and may be mistaken for mechanical sounds.
Fish and Invertebrates: Some fish species, such as the croaker, produce drumming sounds by vibrating their swim bladder or specialized muscles. Invertebrates like snapping shrimp create loud snapping or popping sounds through a rapid closing of their claws. These biological noises can sometimes be mistaken for man-made sounds.
Geological Activities: Underwater geological activities, such as volcanic eruptions, underwater earthquakes, and shifting tectonic plates, can generate significant noise. These natural events produce rumbling, cracking, and grinding sounds that can be similar to the sounds produced by submersibles.
Hydrothermal Vents: Hydrothermal vents are underwater geysers that release hot, mineral-rich fluids into the ocean. The chemical reactions and bubbling of gases associated with these vents can produce distinctive sounds, including hissing and bubbling noises.
Ocean Waves: The crashing of ocean waves against rocks or other underwater formations can generate sounds that resemble mechanical noise. Especially during storms or turbulent conditions, the powerful forces of waves can create loud and persistent sounds.
It's important to note that while these natural causes can produce sounds that may resemble those of a submersible or underwater vehicle, their characteristics and patterns usually differ from the consistent and rhythmic sounds produced by machinery. Additionally, experienced listeners, such as trained sonar operators or marine biologists, can often differentiate between natural and artificial sounds based on their unique characteristics.