It is no secret that human activity in the oceans has been disrupting wildlife. Our foray into water has come in different forms, producing noise with it. Noise created in the ocean is significant sound travels 4.5 times faster in water than on land, and 60 times further than in air (WWF, 2017). Hence, any disturbances produced underwater will be heard with a greater reach and more immediately by marine creatures.
Research has also attributed the increase in noise in the ocean to commercial shipping activity as a result of global economic growth (Frisk, 2012). From 1950 to 2007, low-frequency, ambient noise levels in the open ocean increased by approximately 3.3 dB.
So, what kinds of noise are we making underwater?
According to the World Wildlife Fund (WWF, 2017), there are 7 major sources of underwater noise.
For the purpose of the blog, I will be covering mainly commercial shipping, oil drilling, and submarine (sonar) sources in my posts.
For ships and tankers, vessel noise is a mechanical noise that arises from drag from poor hull maintenance, bow/stern thruster, the engine, or any onboard machinery and the propeller. Cavitation, is a fluid phenomenon where vapour bubbles are formed in a liquid due to low pressure (Britannica, 2018). Cavitation occurs where the liquid has been accelerated to high velocities such as in centrifugal pumps, water turbines, and machine propellers. Cavitation produces extensive erosion of rotating blades, noise from resultant knocking, and vibrations when the vapour bubbles collapse, as well as a reduction in efficiency.
You may be wondering, why is noise pollution by shipping a concern?
Shipping is highly pervasive today. 90% of all goods travel by ship, with 60,000 commercial tankers and container ships on the sea at any given time. Moreover, shipping traffic is expected to expand, with the Arctic traffic projected to quadruple by 2025, facilitated by opening routes in the Arctic (WWF, 2017). Hence, it is only a matter of time before the ocean becomes noisier and noisier.
To combat this, the International Maritime Organisation has also adopted regulations on noise levels on ships, which are reviewed following developments in ship design and technology (IMO, n.d.). This way, noise generated by ships are not too disruptive for marine creatures.
References
Frisk, G.V. (2012). Noiseonomics: The relationship between ambient noise levels in the sea and global economic trends. Scientific Reports, 2(1).
International Maritime Organisation (n.d.). Ship noise. [online] www.imo.org. Available at: https://www.imo.org/en/MediaCentre/HotTopics/Pages/Noise.aspx.
The Editors of Encyclopedia Britannica (2018). Cavitation | physics. In: Encyclopædia Britannica. [online] Available at: https://www.britannica.com/science/cavitation.
World Wildlife Fund (2017). Infographic: Underwater noise. [online] Arcticwwf.org. Available at: https://arcticwwf.org/newsroom/the-circle/underwater-noise/infographic/.