New ideas such as using bubbles to dissipate underwater noise pollution caused by offshore energy may have a profound impact for marine life as offshore energy ventures continuously increase in number.
The impact offshore energy sounds have on marine life is a topic that has been debated about for a while, and gains importance as offshore drilling increases and other alternative energy methods such as wind farms, begin to venture offshore as well.
Some of the most powerful offshore noises are emitted during seismic surveys used to map the sea floor. The Interior Department’s Minerals Management Service has assured that precautions have been taken to reduce the impact these sounds have on marine life. A few of these precautions include increasing the sound slowly to give marine life a chance to leave the area and employing a full time observer who looks for whales or dolphins within a certain radius (if a whale or dolphin is seen entering the activity would be called to a halt). However, according to Michael Stoker, director of the nonprofit group Ocean Conservation Research, these measures seem like “a token gesture that’s fairly meaningless.” [1] I have to agree with him that having someone looking for whales at 1,000 meters seems rather pointless. He also points out that although the slow increase of sound makes some common sense, there has not been any actual data showing that this helps, and that marine life that has formed habitats in these areas is unlikely to leave them despite gradually increasing noises.
The use of bubble curtains to dissipate offshore noise pollution is still in the experimental and optimization phases, with the first application being a new wind farm currently under construction in the North Sea. [2] These bubble curtains would dissipate underwater sound because sound travels faster through water than it does through air. The sound would travel from the source, hit these air bubbles which would cause them to compress, and travel through them allowing them to expand again. This process would cause loss of energy in the sound, altering the way that it travels from short pulses with higher peaks (louder noise) to longer waves with lower peaks. Although the exact amount of energy lost in the process is still under debate, the application has been found to lower sound by around 10 decibels.
Although bubble curtains seem promising, there are several issues with the technology. Firstly, air bubbles are sensitive to tide currents and although studies conducted at The University of Texas Applied Research Laboratory concluded that the optimal size air bubble for reducing sound compares to a softball size, bubbles of this size quickly break into many smaller bubbles once released from the source. Also the technology remains expensive and relatively ineffective with noise reduction at lower frequencies and when using monopole foundations (use of a single large-diameter foundation to support the entire load of an above surface structure).
An alternative to bubble curtains, Hydro Sound Dampers (HSD), uses fishing nets and foams to dampen noise pollution. This looks promising because it may be able to reduce sound more effectively, up to 20 decibels, compared to the bubble curtains 10 decibel reduction. Also this idea would not need a compressed air supply and is not affected by tide currents while remaining less expensive than bubble curtains. [3] This application is newer than bubble curtains and is still in the early testing and optimization stages, although it seems to be a competitive alternative to bubble curtains.
Although some argue that there are issues more pressing than offshore noise pollution that should be dealt with first, I think any advance in the right direction is a good one. This issue could be one that is easily helped before it becomes pressing. A proactive attitude is the right attitude to have when it comes to our energy issues, and maybe if we developed solutions to things before they became big issues, we wouldn’t be facing incoming crises consistently.
1) http://news.nationalgeographic.com/news/2010/04/100407-energy-undersea-sound/
2) http://news.nationalgeographic.com/news/energy/2012/02/120207-bubble-curtains-to-protect-whales/
3) http://www.bsh.de/de/Das_BSH/Veranstaltungen/Cetacean_Society/Elmer.pdf
