Since the Industrial Revolution, the oceans have filled with noise from vessels ranging from small motorboats to gargantuan container ships, seismic exploration and oil drilling, and the building and running of various other forms of human infrastructure.
And it appears that climate change will make some parts of the ocean even noisier, according to a new study. The analysis suggests that these changes over the next century are likely occur even if strong action is taken to reduce carbon emissions.
“Climate change has an effect on the marine soundscape, especially in the North Atlantic and Arctic Oceans,” says study team member Luca Possenti, a postdoctoral researcher at the Royal Netherlands Institute for Sea Research in Texel. “This will make the region noisier affecting marine life.”
Both the temperature and the pH of seawater affect how easily sound travels through it. Possenti and his colleagues modeled the how the changes in these parameters predicted under different carbon emissions scenarios would alter how sound propagates through the ocean.
The study is the first to quantify the effect of climate change on the marine soundscape, Possenti says.
Some of the carbon dioxide released into the atmosphere from burning fossil fuels and other human activities gets dissolved in the ocean, lowering its pH—that is, making it more acidic. Ocean acidification tends to decrease the absorption of low-frequency sounds, enabling them to travel farther.
This mechanism will have relatively little impact on ocean noise, the researchers report in a paper published in PeerJ. Instead, the analysis shows that the main effect of climate change on the ocean soundscape will come from changes in ocean temperature.
The researchers modeled soundscape changes during winter and summer for six different locations around the world: two in the North Atlantic Ocean and one each in the North Pacific Ocean, Southern Ocean, Arctic Ocean, and Norwegian Sea. “We expected similar results between different regions but the results differ depending on the location you consider,” Possenti says.
Most dramatically, the researchers found that a “sound channel” will open up in the North Atlantic Ocean as climate change alters the stratification of the ocean resulting in colder surface water.
This sound channel will enable sounds to travel much farther, and produce an increase in underwater sound of 7 decibels if moderate carbon emissions continue. The decibel scale is logarithmic, so this represents a fivefold increase in the loudness of sound underwater.
The colder layer of surface water is a consequence of a slowdown in the Atlantic Meridional Overturning Current, the primary ocean current in the area, which brings warm water up from the tropics. The current is weakening as an influx of freshwater pours in from melting of the Greenland Ice Sheet, and is projected to continue to slow.
The researchers found that this sound channel will form regardless of the level of carbon emissions in the coming decades. “The results are similar between low and high CO2 emission scenarios, that means we are going to witness these changes [in ocean noise] even if we take action soon” to limit carbon emissions, Possenti adds.
The noisier ocean is likely to pose a problem for many marine species that rely on sound for communication, finding mates, and detecting prey. “It is hard to predict the effect on the marine species because a lot of research is still ongoing but probably the species most affected will be marine mammals, especially whales,” Possenti says.
Source: Possenti L. et al. “Predicting the contribution of climate change on North Atlantic underwater sound propagation.” PeerJ 2023.
Image: ©Anthropocene Magazine.