Noise pollution: Why the sea needs more peace

What may look like a calm and still ocean from shore is anything but. From the magical song of whales to the clicking of dolphins and chattering of crustaceans, the sea hosts a symphony of sounds. Here animals use sound to communicate, navigate, find mates or prey. Sound is essential for the survival of almost all sea creatures. Clownfish, which you might now from the animation film “Finding Nemo,” set in Australia’s Great Barrier Reef, make it clear who is boss by clacking with their jaws. Small shrimp advertise their services to reef fish by flapping their fins.

And some coral fish listen carefully when choosing the right reef. The ocean sounds inform them if the reef is healthy enough to provide for their offspring. But in reality, oceans are being infiltrated by alien sounds that have intruded an ancient underwater symphony. Global waters are noisier today than ever before. It’s disastrous for a wide range of marine life. Some sea creatures are being exposed to noise levels that could deafen or even kill them. “It’s like walking around in a fog,” Lindy Weilgart, a marine biologist for the non-governmental organization Ocean Care and Dalhousie University in Canada, told DW. For underwater life, undue noise affects “foraging, protection from predators, awareness of surroundings, reproduction,” Weilgart explained.

But it doesn’t have to be that way. Ocean noise can be reduced in numerous ways. More efficient ships are better for the climate and noise levels. Ship noise is generated primarily by the ship’s propeller — an effect called cavitation. Container ships that are used to conduct 90% of global trade are the main source of this noise pollution. Over the last 50 years, noise along major shipping routes is estimated to have increased 32-fold. In response, more efficient container ship propellers can make the sea quieter while also saving polluting fuel. Max Schuster, who advises shipping companies on how to reduce underwater acoustic noise at the consulting firm DW-ShipConsult, explains how rapid propeller movement is to blame for all the racket.

As the propeller churns through the water the “pressure is extremely low in some places,” which causes the water to boil and form “vapour bubbles that grow, shrink and collapse,” he said. The noise level caused by collapsing bubbles during ship propeller cavitation is comparable to that of a rock concert. Less cavitation would not only mean less noise but less fuel consumption — and cost — which would also be a win for the climate and balance sheets.

In 2017, the Danish company Maersk retrofitted the engines and propellers on five of its cargo ships to save fuel. However, noise levels also dropped by 75%. Retrofits are not cheap, however, and shipping companies are rarely required to do them. Incentives for shipping operators have, however, been provided by the Port of Vancouver. Ships that are proven to be quieter pay only half the port fees.

As a rule, the less man intervenes in the marine ecosystem, the less disturbing the noise.

However, if noise does occur, such as during the installation of wind turbines, so-called bubble curtains can help. Offshore wind energy is an important part of the energy transition to limit climate change. To meet our climate targets, we need to install 150,000 new offshore wind turbines worldwide by 2050.

“This generates noise underwater that is more or less comparable to an airplane taking off on land,” said Michael Bellmann of the Institute of Technical and Applied Physics (ITAP). Bubble curtains, whereby compressed air flows through tubes on the seafloor, can help reduce this noise. When installed, the tubes sit around the turbine pylons and allow air bubbles to rise to the surface and form an insulating veil. Fewer sound waves can pass through this curtain of bubbles, with noise reduced by up to 90%.