Passive acoustic monitoring of ambient noise in the Atlantic sector of the Southern Ocean

Ilse.van.Opzeeland [ at ]


Natural ambient noise in the ocean is generated by the interaction of wind, waves, ice and biological sound sources. This thesis investigates ambient noise and its dynamics at selected locations in the Atlantic sector of the Southern Ocean. The Southern Ocean provides an important habitat for marine mammals. Rising noise levels might negatively affect marine mammals, which rely on their acoustic senses for foraging, orientation and communication. Two autonomous underwater recorders were deployed on moorings at 66° S and 69° S along the zero meridian, they provided a quasi 3-year acoustic dataset which was analysed using Matlab TM . A set of good environmental status descriptors, as proposed under the European Union marine strategy framework directive, was used to evaluate low frequency continuous noise. The recorded ambient noise, varying strongly over time and frequency, was correlated to ice coverage, wind speed and solar radiation. Seasonal sound pressure level change of 4.25 dB re 1 µPa was caused by the annual change in sea ice coverage. On a Weekly to sub-diurnal scale, sound pressure level variation is caused mainly by changes in wind speed. Marine mammal choruses influence distinct parts of the noise spectrum. The low frequency chorus generated by blue whales is the loudest frequency band in the ambient noise. During Antarctic winter, signals of unknown origin dominate the mid frequency part of the spectrum. The chorus of this signals exhibits a circadian rhythm at the beginning of winter. Over the 3-year recording period, a low frequency noise increase of 0.36 db re 1 µPa 2 s −1 at 40 hz per was detected. These findings can be used as baseline for future passive acoustic monitoring in the Southern Ocean.

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Menze, S. (2012): Passive acoustic monitoring of ambient noise in the Atlantic sector of the Southern Ocean , Bachelor thesis, Hochschule Bremerhaven.

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