Acoustic map of underwater noise pollution made by the crew of the Fleur de Passion

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The boat has spent four and a half years sailing around the world. Image: Fondation Pacifique

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Researcher Michel André, director of the LAB. Image by Fondation Pacifique

The Ocean Mapping Expedition, which has returned to Seville after a four-year world tour aboard the Fleur de Passion sailing boat, mapped acoustic pollution in the ocean. The research project was led by the UPC’s Laboratory of Applied Bioacoustics (LAB).

Sep 17, 2019

The Laboratory of Applied Bioacoustics (LAB) of the Universitat Politècnica de Catalunya · BarcelonaTech (UPC), linked to the Polytechnic School of Engineering of Vilanova i la Geltrú (EPSEVG). The project is directed by the researcher of the same university, Michel André, has joined efforts with Fondation Pacifique to undertake 20,000 Sounds under the Sea, the first project that aims to sensitise the world’s population to the alarming issue of ocean noise by building up a noise map of the ocean around the world, continuously recording sounds, identifying marine organisms, measuring noise levels and automatically transmitting the data to shore.

Aboard the Fleur de Passion, the Ocean Mapping Expedition sailing vessel, a cutting-edge bioacoustics technology consisting of an array of towed hydrophones (microphones adapted to water that are capable of recording audible sounds but also infra- and ultrasounds from any biological or human-generated source) and computers using artificial intelligence techniques automatically process the data. The acoustic data of the four years of expedition can be consulted at: http://omexpedition.listentothedeep.com

The sea environment has always been filled with noise from animals and physical processes, although the last hundred years have seen the introduction of many anthropogenic sources that are currently contributing to the general noise budget of the oceans. The extent to which noise in the sea impacts and affects marine ecosystems has become a topic of considerable concern to the scientific community and to society at large. Anthropogenic noise, including the acoustic signals necessary to study the marine environment, can interfere with the natural use of sound by sea organisms and have chronic effects that may affect the long-term ability of marine animals to carry out their normal activities, reproduce, and maintain sustainable populations, or acute effects that can cause direct physical harm to them and may compromise their short-term ability to survive.

While deep-sea observatories have been playing a key role in the assessment and monitoring of ocean acoustic changes, no effort had yet been made to provide a global picture of underwater noise based on in situ measurements at sea from a moving platform.

Four years following the wake of Magellan
The initiative took place in the framework of the Ocean Mapping Expedition, a multidisciplinary scientific, artistic and social programme that undertook a four-year expedition around the world following Magellan’s route, which is ending in Seville on 4 September, five hundred years after the departure of Magellan.   
 
     Mapa acústic oceànic

To build the acoustic map and make accurate predictions of the levels and characteristics of the background noise caused by shipping, the contributions of individual ships crossed by the Fleur de Passion in the area were taken into account. Information on the distribution, density, and acoustic characteristics of the ships was obtained through the Automatic Identification System (AIS, an automatic tracking system aboard every vessel).

In addition, information on sound-speed profiles, bathymetry, and seafloor properties was used to calculate how sound travels from the location of each ship in the area to the location at which the background noise level was computed.

Maritime transport, the most polluting source
The data gathered has contributed to our understanding of the acoustic load of the oceans by providing essential knowledge on how artificial noise is distributed on large temporal and spatial scales. The route of the Fleur de Passion has crossed areas of our planet, particularly in the South Pacific, where shipping noise or other noises from human activities have not yet reached critical levels and that could be considered “a zero level of pollution”, below 70 dB re 1 microPa2/Hz, probably encountered before the industrialisation of the exploitation of ocean resources started a century ago, when ocean noise was only produced by marine organisms.

Commercial ships carrying a wide variety of cargo travel the world’s oceans and are a major contributor to ocean noise. Ships’ propulsion systems and other machinery generate underwater noise at low frequencies (20–500 Hz). 20,000 Sounds under the Sea measured broadband source levels (20–1000 Hz) as high as 189 dB re 1µPa @ 1 m from modern commercial ships (~50,000 gross ton container ships travelling at speeds of 20 knots) along the Fleur de Passion’s route across Southeast Asia, constituting the loudest noise levels recorded during the whole expedition.

Although the data provided by a moving platform must be considered acoustic snapshots, they will help to build models to predict future changes in the marine environment, in particular in the Arctic and Antarctic regions, where the ice is still preventing the massive introduction of anthropogenic noise from industrial operations that will inevitably look for the planet’s last unexploited resources.