Study lead author and NIOZ oceanographer Luca Possenti noted that in some places, by the end of this century, the sound of ships, for example, will be five times as loud. “That will interfere with the behavior of many species of fish and marine mammals.”
“Since the industrial revolution, oceans have become substantially noisier. The noise increase is mainly caused by increased shipping, resource exploration, and infrastructure development affecting marine life at multiple levels, including behavior and physiology,” wrote the researchers.
“Together with increasing anthropogenic noise, climate change is altering the thermal structure of the oceans, which in turn might affect noise propagation.”
The study was based on mathematical modeling conducted in collaboration with Utrecht University. The researchers used moderate to extreme climate scenarios provided by the UN climate panel IPCC, exploring the effects of water temperature and acidity on underwater sound propagation.
The ongoing release of greenhouse gases is causing seawater to become more acidic. When combined with rising ocean temperatures, these factors are anticipated to allow underwater sounds to travel farther in the majority of ocean regions.
Possenti explained that as warmer surface water supply to the northern Atlantic Ocean decreases, this will cause changes in temperature layers throughout the ocean.
“As a result of this, a separated ‘sound channel’ in the upper part of the North Atlantic may be formed. This will act as a kind of tunnel, which will carry sounds much further,” said Possenti.
Consequently, under a moderate climate scenario, the underwater sound level in this part of the oceans is expected to increase by seven decibels by the end of the century.
Although a 7 dB increase may seem minimal, it represents nearly a fivefold increase in underwater noise energy. Sounds from marine traffic and other sources, such as air guns utilized for seismic surveys, will be significantly amplified.
With an expected increase in marine traffic contributing to the total underwater noise, the impact of these changes is poised to be substantial, even under moderate climate scenarios.
The implications of this noise increase are profound for marine life, which relies heavily on sound for communication due to limited underwater visibility.
Possenti emphasized the critical importance of sound for these species, noting that increased human-generated noise will undoubtedly affect marine ecosystems.
“In the absence of good visibility underwater, fish and also marine mammals communicate mainly through sounds,” said Possenti. “If fish can no longer hear their predators, or if whales have a harder time communicating with each other, this will affect the entire ecosystem.”
Possenti and his colleagues from TNO and MARIN are actively measuring underwater sounds. Using glass spheres that break at great depths, they generate and record sounds used by marine mammals, capturing these noises from tens to hundreds of kilometers away.
This combination of theoretical and experimental research aims to provide a comprehensive understanding of the challenges posed by increased underwater noise, offering crucial insights for the protection of marine life.
“Much is still unknown about the exact effects of underwater conditions on the speed of sound. But because of the potentially profound effects on the ecosystem, that knowledge is essential if we want to understand what the changing climate may do to marine life,” said Possenti.
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