Bronte Wells
Ocean noise pollution is a growing concern, with human activities such as commercial shipping, sonar use, exploration, construction, and seismic surveys causing a significant rise in noise levels. These anthropogenic noises are detrimental to the marine ecosystem, impacting the ability of marine mammals, fish, and invertebrates to communicate, navigate, and perform other critical activities. The constant underwater noise generated by vessels, airguns in the petroleum industry, and military activities has been likened to an acoustic fog, disrupting marine life and endangering species that rely on sound to survive. With shipping increasing over the years, ocean noise pollution has doubled in many marine areas, affecting both protected and unprotected species. Scientists are studying the effects of these noises on marine life and working towards reducing noise emissions, with guidelines expected to be issued in 2023.
| Characteristics | Values |
|---|---|
| Commercial shipping | Propeller cavitation, hull vibrations, diesel engines, and vessel speed |
| Military activities | Active sonar systems, seismic air guns |
| Oil and gas activities | Drilling, offshore structures, production |
| Marine dredging | Channel deepening/widening, seabed mining |
| Seismic surveys | Geophysical surveys, hydrocarbon deposit identification |
| Recreational boating | |
| Energy exploration | |
| Naval surveillance sonars | |
| Construction and industrial activities | |
| Explosives | |
| Aircraft sonic booms | |
| Natural sources | Fish sounds, biological choruses |
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What You'll Learn
Commercial shipping
The underwater noise generated by vessels can be imagined as a kind of "acoustic fog". It is known to cause so-called "masking" of communication, for example, of marine mammals. Fin whales stop singing when the noise levels from ships drown them out. Vessel noise leads to increased stress levels in right whales, impacting their reproduction and immunity. It has also been observed to change important behaviours in marine life, such as singing to mates, and their ability to navigate, find food, and avoid predators.
The noise from commercial shipping is caused primarily by a ship's propeller cavitation, which is the bubbles that are generated and implode due to excessive propeller speed. Another big source of ocean noise pollution produced by ships is hull vibrations and the vessel's diesel engines. Ships produce a low-frequency sound that goes from 10 Hz up to 1 kHz. As ocean traffic is not evenly distributed, some areas are more frequented than others, such as commercial routes and ports, which will experience a significant increase in sound levels when a vessel passes by.
The International Maritime Organization (IMO) has recognized the issue of underwater noise and its impact on marine life and has issued guidelines to reduce noise pollution in the seas. The Marine Environment Protection Committee (MEPC 82) approved revised guidelines for the reduction of underwater noise from commercial shipping to address adverse impacts on marine life. The guidelines aim to further prevent and reduce underwater radiated noise from ships and will be reviewed and revised as necessary over time.
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Military sonar
There are two types of sonar systems: passive and active. Passive sonar systems listen for underwater sounds, while active sonar systems emit sounds to detect and locate objects using the returning echo. The active sonar systems used by the military are the primary source of noise pollution. They operate within low and mid-frequency ranges and emit signals with an intensity of up to 240 decibels.
The use of military sonar has been shown to have negative impacts on marine life, particularly whales and dolphins. The loud and unnatural noises can interfere with the vocalizations that many marine animals use to communicate and navigate. This can cause disorientation, disrupt hunting and feeding behaviours, and make it difficult for animals to find mates. For animals that rely on echolocation, like dolphins and toothed whales, excessive noise can completely disrupt their signals.
In addition to the behavioural impacts, military sonar has also been linked to physical injuries and even deaths in marine wildlife. Exposure to sonar noise can cause decompression sickness, skin damage, and bleeding from the eyes and ears. In some cases, animals may panic and try to escape the noise too quickly, leading to stranding or haemorrhaging to the heart and brain. Environmental groups have been lobbying the government to curtail testing and restrict the use of sonar, especially during peacetime, to give marine wildlife a chance to flee affected areas.
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Seismic surveys
The impact of seismic surveys is not limited to marine mammals but also extends to other species. For example, seismic survey airgun operations have been found to negatively impact zooplankton. Additionally, the noise from these surveys can propagate into deep oceans, affecting marine life in these regions as well.
The use of seismic surveys for identifying new oil and gas deposits has been a subject of debate. While these surveys can provide valuable information about offshore resources, there are concerns about their impact on the marine environment. Environmental organizations and researchers have called for stricter environmental impact assessments and, in some cases, a ban on seismic activities in certain regions to protect marine species and conserve the wider marine ecosystem.
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Marine dredging
The impact of marine dredging on marine life, including marine mammals, is a significant concern. While collisions between dredgers and marine mammals are possible, they are unlikely due to the slow speed of dredgers. The broadband noise emitted by dredging has most of its energy below 1 kHz and is unlikely to cause damage to marine mammal auditory systems. However, masking and behavioural changes in marine mammals are possible due to the interfering nature of anthropogenic noise.
Dredging can also affect benthic, epibenthic, and infaunal communities through entrainment, habitat degradation, noise, contaminant remobilization, suspended sediments, and sedimentation. Seagrass beds, which are an essential part of marine ecosystems, can be impacted by dredging activities, leading to changes in primary productivity, nutrient cycling, and sediment stabilization. The survival of juvenile marine organisms that depend on seagrass beds for shelter can be affected by smothering, burial depth, sediment type, nutrient load, and the presence of pollutants in the sediment.
The noise generated by marine dredging can have both direct and indirect effects on marine life. Direct effects include masking, where the polluting noise is so loud that biologically important sounds are drowned out or distorted, resulting in reduced or no communication. If the noise intensity is high enough, hearing organs can be damaged, either temporarily or permanently. Indirect effects of noise pollution can have wider implications, including stress, increased vulnerability to predation, reduced foraging, reduced fertility and breeding success, and loss of direction when migrating.
Overall, marine dredging is a significant source of ocean noise pollution, and its impacts on marine life and ecosystems are a cause for concern. While some research suggests that dredging-related impacts on seagrasses have declined in recent years compared to the past, the complex and far-reaching effects of noise pollution on marine organisms and their habitats underscore the importance of understanding and mitigating the noise generated by marine dredging activities.
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Oil and gas drilling
The use of air guns in oil and gas exploration has been linked to changes in the behavior of marine animals, including whales and dolphins. The loud noises can cause whales to change their diving habits, leading to a dangerous condition called "the bends," where nitrogen bubbles become trapped in their bodies. Noise pollution from oil and gas drilling can also disrupt migration, reproduction, and the ability of sea creatures to communicate with their own species.
In addition to air guns, other equipment used in oil and gas drilling, such as drilling machinery, propellers, and thrusters, also contribute to underwater noise pollution. These activities, mainly located on the continental shelf, can generate sounds of up to 135 dB re 1µPa @ 1 m and intensities peaking at 40 to 100 Hz. This level of noise pollution can have significant impacts on marine life, as it falls within the frequency range used by whales, which varies from 10 to 31 Hz depending on the species.
The continued use of seismic activities and air guns for oil and gas exploration has raised concerns among environmentalists and scientists. There are calls for stricter regulations and assessments of the environmental impact of these activities to protect marine species and conserve the wider marine ecosystem. Some lawsuits have even been filed against industries and governments regarding the growing problem of ocean noise pollution.
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