01 Nov Noisy Oceans
What do oil and gas exploration, Navy sonar exercises, and the shipping industry have in common? They’re all implicated in ocean noise pollution and its profound effect on marine life, and especially the daily life of marine mammals. That’s the message of Sonic Sea, the award-winning 2016 documentary produced by the Natural Resources Defense Council. I recently had a chance to see it at a meeting of the New Jersey Environmental Lobby – and I recommend it to you.
Whales and dolphins emit noise to communicate, navigate and find food. Meanwhile, human activities have introduced increasing levels of noise that is both acute and persistent. Repeated underwater air blasts are used in oil and gas exploration to “see” the profile of rock layers under the sea. And naval forces around the world conduct exercises with high-energy sonar to detect enemy submarines. These acute noises travel far and can be so powerful as to cause internal bleeding and force marine mammals out of the water. According to the film, multiple whale strandings have been linked to navy sonar exercises.
As world trade has increased, so has ship traffic. Pervasive and persistent noise pollution comes from two ship noise emitters. First, a ship’s engines are typically solidly mounted to the ship’s hull and vibrations are transferred from the hull into the water. Second, as propellers spin they create bubbles in a process known as “cavitation”. The bubbles are temporary vapor cavities in the water that collapse due to the surrounding water pressure – each collapse creating a micro-bang. The way lightning splits the air momentarily and creates thunder is not dissimilar. The result is a constant hiss filling the ocean, like static on the radio, that obscures marine mammal communication. Think of how difficult it is to have a conversation while standing alongside a busy highway and that’s the idea.
The offshore wind industry is a new ocean user and we must ensure that our presence does not add to ocean noise pollution. Noise emissions can come from ocean survey equipment used to map the seabed and sediment and rock layers beneath it, construction vessels and pile driving for turbine foundation installation, and vibrations from rotating machinery like gearboxes during turbine operations. In the summer of 2015, when the Block Island wind farm was under construction, contractors for the Bureau of Ocean Energy Management used hydrophones to listen to the sound of pile driving during foundation installation and found that the sound could be heard as far away as 25 miles.
Each of the wind farm noise emitters can be managed better. Concrete foundations that sit on the seabed using gravity to stay in place, for example, do not require pile driving and so eliminate that noise entirely. Sonic Sea shows us that many ocean users need to operate as better stewards of the world’s ocean life. Offshore wind can live up to that challenge.