Climate change is making oceans louder

Climate change is expected to significantly alter how sound travels underwater, potentially affecting natural soundscapes as well as accentuating human-generated noise. That’s according to a study in the journal Earth’s Future that identified future ocean ‘acoustic hotspots’, which could impact essential activities of marine life.

The ocean soundscape is a cacophony of vibrations produced by living organisms, natural phenomena like waves and cracking ice, and ship traffic and resource extraction. In warmer water, soundwaves propagate faster and last longer before dying away — this means the speed of sound at 50 m depth ranges from 1450 m/s in the polar regions to 1520 m/s in equatorial waters.

Many marine animals use sound to communicate with each other and navigate their underwater world. Changing the sound speed could thus impact their ability to feed, fight, find mates, avoid predators and migrate, the study authors said.

“We calculated the effects of temperature, depth and salinity based on public data to model the soundscape of the future,” said lead author Alice Affatati, from the Memorial University of Newfoundland. Temperature, pressure with increasing depth and salinity all affect how fast and how far sound travels in water, so the researchers focused on hotspots where the climate signal stood out clearly from the model uncertainty and was larger than seasonal variability.

Two hotspots, in the Greenland Sea and a patch of the north-western Atlantic Ocean east of Newfoundland, can expect the most change at 50 and 500 m depths, the study projected. The average speed of sound is likely to increase by more than 1.5%, or approximately 25 m/s in these waters from the surface to depths of 500 m, by the end of the century, given continued high greenhouse gas emissions (RCP8.5).

“The major impact is expected in the Arctic, where we know already there is amplification of the effects of climate change now,” said study co-author author Stefano Salon, from the National Institute of Oceanography and Applied Geophysics in Italy. “Not all the Arctic, but one specific part where all factors play together to give a signal that, according to the model predictions, overcomes the uncertainty of the model itself.”

The study also found a 1% sound speed increase — more than 15 m/s — at 50 m in the Barents Sea in the north-western Pacific, as well as in the Southern Ocean (between 0 and 70E), and at 500 m in the Arctic Ocean, Gulf of Mexico and southern Caribbean Sea.

The study also modelled common vocalisations, under the projected future conditions, of the North Atlantic right whale, a critically endangered species inhabiting both north Atlantic acoustic hotspots. The whales’ typical ‘upcall’ at 50 Hz is likely to propagate further in a warmer future ocean, the researchers found.

“We chose to talk about one megafauna species, but many trophic levels in the ocean are affected by the soundscape or use sound,” Affatati said. “All these hotspots are locations of great biodiversity.”

Future work will combine the global soundscape with other maps of anthropogenic impacts in the oceans to pinpoint areas of combined stressors, or direct needed observational research.

Image credit: ©stock.adobe.com/au/jamesteohart

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