The ocean, once perceived as a quiet realm, is increasingly filled with sound. Ocean noise refers to the pervasive presence of acoustic energy in marine environments. This phenomenon stems from both natural processes and human activities, creating a complex soundscape that influences marine life. Understanding the characteristics and origins of this noise is important for assessing its impact on ocean ecosystems.
Natural and Human-Generated Ocean Noise
Sounds in the ocean originate from various natural sources, including crashing waves, the patter of rain on the surface, the movement of ice, and seismic activity like underwater earthquakes and volcanic eruptions. Marine animals also contribute to natural soundscapes, using vocalizations for communication, foraging, and navigation.
Human-generated, or anthropogenic, noise has become a prominent component of the underwater soundscape. This distinct category of noise, which has grown substantially over the last two centuries, is the primary concern regarding ocean noise.
Major Sources of Noise Pollution
Commercial shipping is the most significant contributor to human-generated ocean noise. The primary source is propeller cavitation, where rapid pressure changes around a ship’s propeller cause vapor bubbles to form and violently collapse. This implosion generates considerable noise, often described as sounding like gravel hitting the hull. Engine noise and hull vibrations also add to the low-frequency sound that travels vast distances underwater.
Seismic surveys, conducted for oil and gas exploration, produce some of the loudest human-made sounds. These surveys use airgun arrays that release powerful, pressurized blasts of air into the seafloor, generating intense, low-frequency sound pulses. These blasts are highly repetitive, occurring every 10 to 15 seconds for days or months, and can be detected thousands of miles from their source.
Military sonar, used for submarine detection and navigation, is another major source of intense underwater noise. Active sonar systems emit high-intensity sound pulses or “pings” that bounce off objects and return as echoes. These powerful sound waves, particularly mid-frequency and low-frequency active sonar, can travel hundreds of miles underwater.
Offshore construction activities also contribute substantially to ocean noise, particularly through pile driving. This technique, used for installing foundations for structures like wind farms and oil rigs, involves repeatedly striking large piles into the seabed. The impact generates strong, impulsive underwater noise with peak sound pressure levels that can exceed 200 decibels at distances of 750 meters, often detectable over tens of kilometers.
Impacts on Marine Life
Ocean noise profoundly affects marine organisms by interfering with their fundamental biological and physiological functions. Many marine species, including whales, dolphins, fish, and invertebrates, rely on sound for essential activities like communication, navigation, foraging, and avoiding predators. Noise can disrupt these acoustic cues, leading to negative consequences.
One significant impact is the disruption of communication, known as masking. Anthropogenic noise can overlap with the frequencies used by marine animals, making it difficult for them to detect, recognize, or understand sounds vital for their survival. Whales and dolphins may alter vocalizations, such as increasing volume or changing frequencies, to be heard over shipping noise. This can impair their ability to find mates, coordinate group activities, or warn others about threats.
Noise pollution also causes behavioral changes in marine life. Animals may exhibit stress responses, including elevated stress hormone levels, and alter swimming or diving behaviors. Noise can force animals to abandon important feeding or breeding grounds, alter migration routes, or cause them to flee an area. In extreme cases, this disorientation can lead to stranding events, particularly for whales and dolphins exposed to military sonar.
Intense noise exposure can also result in physical injury to marine organisms. This includes temporary or permanent hearing loss, which can severely compromise an animal’s ability to perform life functions. Very loud sounds, such as those from seismic surveys or naval sonar, can cause internal injuries like tissue damage, hemorrhaging around organs, or even lead to decompression sickness if animals ascend too rapidly in panic.
Efforts to Address Ocean Noise
Addressing ocean noise pollution involves a multi-faceted approach, combining technological advancements, regulatory measures, and ongoing research. Technological solutions focus on designing quieter maritime equipment and operations. Advancements in ship design, such as optimizing propeller shape and adding more blades, can reduce noise from cavitation. Developing alternative seismic survey methods that produce less intense sound, or using non-seismic mapping techniques, are also being explored.
Regulatory measures and policy development help manage noise levels. These include implementing speed restrictions for vessels in sensitive marine habitats, as slower speeds reduce propeller cavitation noise. Designated quiet zones in biologically important areas provide sanctuaries for marine life. International bodies are also developing guidelines for noise reduction from shipping and other activities.
International collaboration and continued research efforts are crucial for a better understanding of ocean noise and its impacts. Scientists use passive acoustic monitoring to track changes in ocean soundscapes and study marine animal responses. Research identifies specific noise sources, their propagation characteristics, and long-term effects on marine populations. This knowledge informs the development of effective mitigation strategies and policies to reduce the acoustic footprint of human activities in the ocean.