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Underwater noise


Marine sound propagation. Chart: A. Blöcker | [+] zoom

The figure shows a schematic representation of the propagation of sound waves in the sea. Chart: A. Blöcker

The underwater world is never silent. Sounds made by the wind, waves, currents and rain along with those emitted in the communication of many underwater species create a natural, permanent backdrop that can differ greatly in intensity from place to place. Add to this the sounds made by man. This mostly undesired form of underwater sound is described as noise as soon as it reaches a volume that many species find disturbing. Anthropogenic underwater noise is seen as one of the key pressures on the marine environment and marine life (OSPAR 2009). Underwater noise has doubled with every decade in the past 35 years.

Marine sound

Due to the physical properties of water, sound created under water spreads some 4.5 times faster than in the air. And because the dampening effect of water can differ depending on the frequency involved, deeper frequency sounds can be heard over vast distances.
Sound can be categorised into
 continuous sound and
impulse sound, each of which have different  effects on marine life. Underwater noise thus poses a serious threat for marine mammals that use sound to communicate, navigate and search for prey.

Sources of marine noise

There are many sources of man-made noise. Coastal waters are especially affected by  shipping. But seismic surveying to detect  oil and gas,  military sonar equipment, localised explosions (such as those used to destroy old ammunition),  sand and gravel extraction, and hydro-acoustic mapping of the sea bed all produce considerable noise. And with the expansion of  offshore wind farming, the problem is only exacerbated.

The Federal Agency for Nature Conservation (BfN) is highly committed to minimising underwater noise in the North and Baltic Sea.

Research on underwater noise

As part of a broad-based research project conducted in the Exclusive Economic Zone (EEZ), a range of studies look at underwater noise in the North and Baltic Seas. The aim of these studies is to develop verifiable standards for use in assessing the impact of underwater noise on marine life – especially harbour porpoises and grey seals, but also fish. To enhance available information on marine noise, underwater microphones were used to create a noise map for the Natura 2000 protected areas in the North and Baltic Seas.

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