Bronte Wells
Underwater noise pollution is a significant issue that threatens marine ecosystems and wildlife. It is caused by human activities such as global shipping, oil and gas exploration, construction, and naval exercises, which introduce excessive and unnatural sounds into the ocean environment. These activities generate continuous low-frequency noise, impulsive noise from construction and explosions, and high-intensity sound waves from sonar systems. The Arctic Ocean, for instance, is increasingly affected by underwater noise as climate change warms temperatures and melts sea ice. Marine mammals, such as whales, dolphins, and porpoises, are particularly vulnerable to underwater noise pollution as they rely on sound for critical activities like communication, navigation, foraging, and avoiding predators. The impact of noise pollution on these species can lead to behavioural and physiological changes, hearing loss, injury, and even death. Addressing this issue requires coordinated efforts from governments, industries, and conservationists to implement regulations, adopt quieter technologies, and protect noise-sensitive habitats.
| Characteristics | Values |
|---|---|
| Sources of Underwater Noise Pollution | Ships, seismic surveys, explosions, construction, sonar devices, wind farms, oil rigs, naval exercises, pile driving, drilling, machinery operations |
| Regions Affected by Underwater Noise Pollution | Arctic Ocean, Europe's seas, North Atlantic |
| Marine Animals Affected by Underwater Noise Pollution | Whales, dolphins, porpoises, beluga whales, narwhals, blue whales, fish, invertebrates |
| Impact of Underwater Noise Pollution on Marine Animals | Behavioural changes, physiological changes, increased stress, habitat loss, hearing loss, injury, death |
| Mitigation Measures for Underwater Noise Pollution | Quieter ship designs, slower ship speeds, bubble curtains during offshore construction, declaring noise-sensitive habitats as Marine Protected Areas (MPAs) |
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What You'll Learn
Commercial shipping
The total carrying capacity of the global fleet nearly quadrupled between 1996 and 2020, with new and larger ships added to match the growing global economy. This trend is expected to continue, with underwater noise emissions predicted to double every 11.5 years. The largest contributors to shipping noise emissions are container ships, dry bulk vessels, and liquid tanker vessels, which emit 75% of underwater shipping noise source energy.
Underwater noise from commercial shipping has been shown to cause elevated stress in marine mammals, affecting their reproduction, immunity, foraging, and overall health. For example, studies have found increased stress hormones in critically endangered North Atlantic right whales, reduced foraging by Southern Resident orcas, and poorer body condition in Atlantic cod.
To reduce underwater noise pollution, ships can slow down. For each 1-knot reduction in speed, a ship's noise is reduced by 1 decibel. Slowing down the global fleet by 10% could reduce total sound energy from shipping by around 40%. For example, the Vancouver-Fraser Port Authority in British Columbia asks ships to slow down to either 11 or 14.5 knots as they approach the port to protect the endangered Southern Resident orca population.
In addition to speed, reducing the number of ships can also help lower underwater noise pollution. For example, cruise ship arrival times can be synchronized to decrease the cumulative amount of time that marine life is exposed to ship noise and create quiet periods that may benefit whale communication and behavior.
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Oil exploration
Seismic blasts, a common method used in oil and gas exploration, involve the repeated use of air guns blasting pressurised air into the ocean depths. These air guns produce extremely loud noises, with sound waves that penetrate deep into the ocean and are picked up by hydrophones to create three-dimensional maps of potential oil and gas deposits. The noise from these blasts can be detected 4,000 kilometres away and has been linked to hearing damage and even the death of marine creatures, including giant squid and zooplankton.
In addition to seismic blasts, other human activities associated with oil exploration also contribute to underwater noise pollution. Drilling machinery, propellers, thrusters, and the placement of offshore structures generate significant noise that can reach high intensities and affect marine life. The construction of infrastructure and the use of sonar by vessels searching for new oil and gas sources further add to the noise levels in the ocean.
The Arctic Ocean, for example, is facing increasing noise pollution from oil and gas exploration, shipping, and infrastructure development due to the melting of sea ice caused by the climate crisis. This region is particularly sensitive to noise pollution, and the increased human activity in the area is expected to have significant impacts on the behaviour and communication of marine mammals, especially whales.
To address the issue of underwater noise pollution from oil exploration, several measures have been proposed. These include implementing quieting technology on ships, transitioning to low-noise renewable energy sources, and regulating the use of seismic surveys. It is important to adopt precautionary regulations backed by scientific research to safeguard marine life and ecosystems from the detrimental effects of noise pollution caused by oil exploration activities.
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Seismic surveys
The use of seismic air guns has been found to severely damage the internal organs of giant squid and cause hearing loss in sea turtles. It can also kill zooplankton within a 1.2-kilometre radius of each blast. Furthermore, the loud noises generated by seismic surveys can trigger escape responses in seals and whales, causing them to ascend too quickly and leading to decompression sickness and skin damage from gas bubble lesions.
To reduce the impact of seismic surveys on underwater noise pollution, emerging quieter technologies such as 'marine vibroseis' are being proposed as alternatives to airguns. Slowing down ships involved in the surveys can also help reduce noise levels.
The negative impacts of noise pollution from seismic surveys and other sources have been documented for at least 150 marine animal species, highlighting the urgent need for regulations and the adoption of noise-reducing solutions to protect marine life and ecosystems.
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Offshore wind turbine installation
Ocean noise pollution is a form of environmental pollution caused by human activities such as commercial shipping, oil exploration, seismic surveys, offshore wind turbine installation, and military sonar. Marine life, particularly marine mammals, are impacted by this noise, which can interfere with their natural behaviours and ability to communicate.
Offshore wind energy is a renewable and clean source of electricity that can help reduce greenhouse gas emissions and fossil fuel dependence. However, the installation of offshore wind turbines can generate underwater noise that affects marine species. The main sources of this noise are the installation of monopile foundations using pile driving and dynamic positioning systems. Pile driving involves hammering steel or concrete piles into the seabed to provide a foundation for the wind turbine, creating loud, high-energy acoustic waves that radiate out through the water.
The size of wind turbines has increased significantly over the years, and with their increased height, the distance from the noise source in the nacelle to the water also becomes larger. As a result, it is challenging to predict changes to the underwater noise as turbine sizes increase. The underwater sounds from wind turbines can be characterized as continuous sound sources with both broadband and tonal components, all below 1,000 Hz. While the sound source level of a wind farm is equivalent to that of a large commercial ship, the wind farm is stationary and constantly adds a variable noise level due to changing wind speeds.
The installation of offshore wind turbines can cause marine mammals to exhibit behavioural changes, such as avoidance, displacement, changes in vocalization, swimming speed, and diving patterns. These behavioural changes may impact their vital functions, including feeding, breeding, resting, and migrating. Additionally, marine mammals and fish may experience physiological stress, increased heart rate, blood pressure, or cortisol levels. Hearing impairment, such as temporary or permanent threshold shifts, and injuries, such as haemorrhage or rupture of auditory cells, may also occur due to the noise exposure during monopile foundation installation.
To mitigate the underwater noise and protect marine fauna during offshore wind turbine installation, several methods can be employed, including source reduction, propagation reduction, receptor protection, and alternative foundations. Source reduction aims to decrease the sound pressure level or frequency by using low-noise vessels, such as electric or hybrid vessels. Propagation reduction techniques, such as bubble curtains, aim to reduce sound transmission or reflection. Receptor protection involves strategies like excluding vulnerable species from the area during installation. Lastly, alternative foundations can be explored to reduce noise impacts, such as using jacket or tripod systems instead of monopile foundations.
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Military sonar
Sonar systems were first developed by the US Navy to detect enemy submarines. Military sonar devices emit high-intensity sonar pings that can travel long distances and create a pervasive noise field, affecting a wide range of marine species. These sound waves can reach up to 235 decibels, far exceeding the volume of the loudest rock bands, and can retain an intensity of 140 decibels as far as 300 miles from their source.
The impact of military sonar on marine life has been a subject of debate and concern. Research has shown that certain species of whales and dolphins are sensitive to mid-frequency active sonar and exhibit avoidance behaviours, such as rapidly changing their depth, which can lead to physical injuries and even beach themselves to escape the sonar sounds. In one notable incident in 2005, 34 whales from three different species died after stranding along North Carolina's Outer Banks during nearby Navy sonar training.
Environmental groups and organisations like the Natural Resources Defense Council (NRDC) have campaigned to ban or restrict the use of military sonar in waters rich in marine wildlife. They argue that the use of sonar harms marine mammals and interferes with their basic biological functions, such as feeding and mating. Some groups have suggested implementing quieter technologies and regulatory measures to reduce the impact of sonar on marine life.
While the US Navy has faced legal challenges and criticism, they continue to use sonar for national security reasons. The Navy defines its mitigation requirements and argues that some mitigation measures suggested by civilian agencies could have disastrous effects on training and readiness. The use of sonar by the military highlights the complex balance between national security needs and the protection of marine ecosystems.
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Frequently asked questions
Underwater noise pollution happens wherever human activities, such as commercial shipping, oil exploration, seismic surveys, offshore wind turbine installation, and military sonar, generate unnatural and excessive sound underwater.
Marine mammals rely on sound to communicate, locate mates and prey, navigate, and defend their territories. Underwater noise pollution can interfere with these key life functions, causing behavioural and physiological changes, increased stress, habitat loss, and even death.
The major sources of underwater noise pollution include cargo vessels, seismic surveys, explosions, construction, and sonar devices. Cargo ships can emit noise levels of up to 190 decibels, which is much louder than a plane taking off.
To reduce underwater noise pollution, governments, industries, and conservationists must work together. This includes adopting quieter ship designs, implementing noise-reducing technologies during offshore construction, declaring noise-sensitive habitats as Marine Protected Areas (MPAs), and transitioning to low-noise renewable energy sources.
