As well as being the largest animals alive today, blue whales are also the loudest. The call of the blue whale can reach up to 188 decibels, louder than a jet engine's 140 decibels. Only the male of the species sings to attract a female mate, and scientists believe that blue whales can hear one another over distances of up to 1,600 km. It is thought that these vocalizations also help the blue whale to navigate their way around the dark ocean depths.
An unidentified sound, known as the Bloop, was recorded in a remote point in the Pacific Ocean during the summer of 1997. The low-frequency sound was detected by the U.S. National Oceanic and Atmosphere Administration (NOAA) and was loud enough to be recorded by several sensors at a range of over 5,000 km. The Bloop was said to "rise rapidly in frequency over about one minute" and was several times louder than the call of the blue whale.
Earthquakes in the deep ocean are known to generate significant acoustic signals called T-phases, which have been compared to man-made explosions. These T-phases can exceed 200 decibels and last for several minutes, although geophysicists from the Woods Hole Oceanographic Institute (WHOI) have discovered that many underwater earthquakes are much smaller than anticipated.
Ship traffic accounts for the majority of manmade ocean noise. The large ocean-going vessels such as supertankers and cruise ships that are needed to support the global economy generate noise from engines and propellers. Other underwater sounds come from drilling operations carried out by the oil and gas industry.
