Now we’re getting somewhere! (v.2.0)
Lower-noise-technology used to install monopile foundations at Gode Wind 3 in Germany
As stated in our last newsletter, unlike other ocean pollution issues – (plastic, chemical, and municipal sewage), once you remove the sources of noise pollution, it goes away!
But heretofore, given the acceleration of ocean industrialization, the prospect of eliminating noise pollution has been daunting. Trans-oceanic shipping alone has increased the base-level of broadband ocean noise by a factor of ten. And then there are all sorts of other industrial noises: seismic airgun surveys seeking oil and gas; pile driving for offshore wind farms and other marine construction; military and industrial sonar; various extraction industry noises; and more recently underwater digital communication networks.
But finally, after advancing this ocean noise conversation for 30 years, we are seeing some encouraging responses. Our last newsletter focused on curbing cavitation noise generated by vessel propellers – which theoretically might attenuate shipping noise contribution down to1960’s levels. But there are a few other improvements that also orbit around noise.
Probably most significant in terms of offshore development are construction piles driven into the benthic substrate by hydraulics rather than impacts. In this context, pile driving for offshore wind structures is growing into a serious source of ocean noise. While the end result of offshore wind power will result in improved CO2 atmospheric metrics, the actual noise from pile driving (and all of the other industrial wind-farm-associated noises) will likely have much more habitat impacts than the seismic surveys seeking offshore oil we managed to stop a few years ago.
This damage risk has to do with the rapid rise time of pile driving strikes, as opposed to the much slower rise time of of seismic airguns (the difference between a ‘clang!’ and a ‘boom’ – expressing noise qualities again). The quality difference here is between a continuous loud rumble of airguns for years on end, and a continuous clanging of metal-against-metal strikes of pile driving for years on end. And given that these piles are in some cases 10m (33ft.) across, the clanging will be extremely loud.
Currently the noise mitigation for pile driving involves “bubble curtains” wrapped around the pile driving operations. The objective of this is to have the “curtain of bubbles” create a acoustical compliance discontinuity between the pile driving strikes and the open ocean. The bubbles act as resonators that convert acoustical energy into physical vibrations, attenuating the noise between the inside of the curtain and the outside ocean. In theory.
This does work, but a little ocean current in one way or the other washes away the curtain between they noise and the protected animals. Additionally, it takes a lot of energy to pump air down a few hundred feet to a pipe system that releases the bubbles – being driven by diesel-fueled compressors. And the bubbles do little to protect benthic invertebrates inhabiting the mud into which the piles are being driven, which while they are not “protected,” are nonetheless an important link in the trophic pyramid.
Oersted’s hydrodynamic pile driving technology promises to significantly decrease the biological impacts of pile driving both above and below the sea floor, as offshore wind is advanced along the Atlantic Seaboard. I’m sure this takes a lot of energy as well. But the transfer energy is focused on getting the pile driving job done, not mitigating for the noise generated by an unruly and noisy industrial process.
