In the centre of the Pacific it’s continuously getting louder. Only during the last 40 years, the sound level has increased to the tenth, as has been shown by American scientists in a comparison of acoustical data from the deep sea.
published Deepwave Report 05
According to the scientists, the enormous increase may be mainly due to shipping. This way, not only their number but also their magnitude and performance have increased. What consequences this noise level will have for the animals in the oceans cannot be estimated exactly, the scientists say. For their analysis the scientists made use of two series of measurement which had been recorded in the depth of about 1000 meters off the Californian coast near the channel island San Nicolas. The first record dated from the years 1964 until 1966 and arose within the scope of the American Sound Surveillance System , an acoustical surveillance program with the purpose to track the movements of foreign submarines. The second data set was recorded during winter 2003/2004 at the same place using an automatic underwater microphone about 10 meters above seafloor.
Ten times the amount of noise
There was a clear difference between the two measurements: in the frequency range between 30 and 50 hertz, which is typical for shipping, the level of sound pressure on the average was higher by 10 db as compared to those taken earlier. This factor of 10 cannot only be caused by the numerical increase of the fleet size, which approximately doubled between 1965 and 2003 as has been calculated by the scientists. Rather, each single ship seemed itself to be louder than before. According to them, an increase in tonnage and in motor performance might be responsible for this fact. For example, the gross tonnage as well as the motor performance have increased by a factor of about four in the same period. In addition, the individual ships spend altogether more days on the seas than before because of shorter dispatch times. Though the data had been recorded in a single place only, they are representative for the whole area of the Northeastern Pacific according to the scientists John Hildebrand and his colleagues of Scripps. They are quite worried about the strong increase of noise pollution in the deep sea. There is an urgent need to investigate whether the increasing sound levels have consequences for the fauna and if this should be the case, then one should look for a possibility to protect the animals from the noise for example by relocating shipping routes.
Sources:
- John Hildebrand et al.: Journal of the Acoustical
- Society of America, Bd. 120, S. 711
- http://www.wissenschaft.de
- http://scrippsnews.ucsd.edu