Who pollutes the ocean with noise?
It’s getting louder and louder in the oceans. Ocean noise emissions can be kind of constant or continuous, as generated by vessels, or impulsive (kind of explosive), as by airguns used by the petroleum industry when searching for fossil fuels in the seabed, or in military activities. It is difficult for us humans to even imagine what is happening acoustically below the surface. We need to bear in mind that sound travels almost five times as fast in seawater as it does in the air. The impacts to marine life are tremendous.
Let’s take a look at who and what the ocean noise generating activities are:
Ships emit noise into the ocean mainly because of cavitation generated by the propeller. In simple terms, the basic rule is: the bigger and faster a ship, the louder it is. Globally, just about 15% of the global fleet account for half of the noise emissions into the ocean caused by shipping. With shipping increasing massively in recent decades – up to 90% of internationally traded goods are now transported by sea – ocean noise pollution in many marine areas has doubled every decade since the 1960s. In European waters, noise levels even doubled within just 5 years between 2014 and 2019.
This constant underwater noise generated by vessels can be imagined as a kind of «acoustic fog». It is known to cause so-called «masking» of the communication, e.g. of marine mammals. Fin whales stop singing when the noise levels drown them out. Vessel noise lead to increased stress levels in right whales. But it’s not «just» marine mammals affected, but also fish and invertebrates.
The simplest and quickest way to reduce underwater noise from shipping is to reduce the ship’s speed. Russell Leaper, IFAW consultant and noise expert, has calculated that reducing the speed of the global shipping fleet by 10 or 20% would reduce noise emissions by 40 or 67% respectively. Such a measure would also have other positive environmental benefits, such as reducing CO2 emissions as well as other air pollutants and lowering the risk of collisions with whales significantly. Currently, the International Maritime Organization (IMO) is working on the revision of the guidelines for the reduction of noise emissions from shipping. Technical innovations and adaptations in shipbuilding are also being taken into account. The revised guidelines are expected to be issued in the summer of 2023.
The so-called impulsive and thus most dangerous ocean noise sources include:
Seismic activities - oil & gas exploration
Just imagine being jolted out of bed by a bang a million times louder than a jackhammer. This gives you a rough idea of what it feels like for a whale when seismic activities searching for oil and gas are being conducted in its habitat. The industry employs extensively such impulsive technology within geophysical surveys discover sources within the seabed and find hydrocarbon deposits. In order to map an area, 12 to 48 compressed air guns are towed behind a ship generate deafening noise pulses of up to 260 decibels every 10 to 15 seconds around the clock for weeks or even months.
This generates sound waves that travel hundreds or even thousands of metres through the water column of the ocean before penetrating up to more than a hundred kilometres deep into the seabed. The echo provides information about the composition of the seabed and clues to oil and gas deposits. Such seismic activities are extremely dangerous, can drive away or even kill marine animals, and can increase normal levels of background noise by a factor of a hundred over a radius of up to 300,000 km².
The continuation of seismic activities in the ocean for the purpose of identifying new oil and gas deposits must be banned both for tackling the climate crisis, but also for protecting marine species and conserving the wider marine ecosystem. General scientific geophysical research activities should be subject to strict environmental impact assessments prior to receiving a licence.
Military activities, along with the activities of the oil industry and shipping, are among the biggest noise polluters in the ocean. Referring to national security interests, the navies usually do not consider themselves bound by environmental and species protection regulations.
Active sonar systems: Navies are using powerful active sonar systems operating within low and mid frequencies, which emit signals with an intensity of up to 240 decibels for the purpose of detecting submarines. They screen and sonify whole ocean areas. The usage of active sonar systems has in the past decades been linked to numerous atypical whale strandings. These strandings, however, are only the tip of the iceberg in terms of impacts caused by this dangerous technology.
Detonations: Numerous military activities – even in peacetime – lead to explosions of various kinds: weapon tests, detonations of old ammunition lying on the seabed, firing during manoeuvres, material tests or testing the durability of new ships. The explosions generate extremely powerful noise in a wide range of frequencies.
Military activities should not be exempt from requirements arising from marine protection regulation.
Pile driving during construction of offshore windfarms
The construction of offshore wind turbines generates intense noise emissions when steel piles are driven into the seabed. The setting of noise thresholds in some countries has led to companies investing large sums into the development of noise reduction measures or alternative construction methods or even floating platforms.
The extraction of raw materials in the context of deep-sea mining would lead to numerous noise-generating activities. These include machinery that would be used to mine the seabed as well as seismic surveys and the use of multibeam echo sounders, etc.
Other intense noise generating activities are port construction work, setting up and operating offshore oil and gas drilling platforms, fisheries as well as employing fisheries’ acoustic devices which are used to scare away marine mammals from nets as well as fish farms.
Since 2004, OceanCare has been actively campaigning in numerous regional and international bodies to reduce noise emission in the ocean. In recognition of its engagement, the organisation was granted UN Special Advisor Status for Ocean Issues in 2011.