Global warming is having a profound effect on the soundscape of the oceans and marine life.

The oceans are bearing the brunt of the impacts of climate change, in particular sea level rise, temperature and water acidification. The new study takes a closer look at other impacts that are too little talked about: the changing ocean soundscape and its impact on marine life.

Indeed, accelerating global warming is no longer a secret… The latest IPCC report gives goosebumps, and limiting global warming to nearly 1.5°C in temperature rise in the 21st century seems elusive. . As a reminder, current emissions policies and commitments put the world on a warming trajectory of around 2.3-2.7°C.

All of this has direct implications, sometimes visible or invisible to the naked eye, for the oceans, which have to deal with fundamental changes affecting ecosystems and marine life. However, we must not forget that the oceans are important sinks of carbon, they produce most of the oxygen we need to live, and they play an important role in climate regulation.

According to a new global study published in Earth’s Future (AGU’s journal of interdisciplinary research on the past, present and future of our planet and its inhabitants), climate change, and especially global warming, may adversely affect the speed of sound propagation under water. This environmental issue should be taken very seriously as these modifications can alter natural soundscapes and amplify man-made noise.

Currently, there are only a few studies on a global scale examining the vulnerability of marine mammals to global warming, but none of them have focused on changes in sound propagation under water. Thus, this is the first estimate of ocean sound speed under climate conditions expected in the future.

According to the researchers, it is important to analyze the soundscape of the ocean because much of life in the ocean depends on sound. For example, cetaceans have evolved a highly specialized auditory system and require a suitable acoustic environment to develop normally. Aquatic mammals, on the other hand, function largely through vocalization to show territorial hegemony, seek food, find mates, or alert other individuals to the presence of a predator.

Thus, the aim of the new study is to predict the future effects of climate change on marine life in order to mitigate them and prevent them from becoming irreversible. So the scientists identified the areas where the variations in the speed of sound were the strongest – “acoustic hot spots” – and where marine ecosystems may undergo significant changes.

Two areas of future acoustic hotspotshaving the greatest variations in the speed of sound, at depths of 50 and 500 meters, scientists have noticed: in the eastern part of the Greenland Sea and in the northwestern part of the Atlantic Ocean, in the east of Newfoundland.

The soundscape of the ocean…

“We calculated the effects of temperature, depth and salinity using publicly available data to model the soundscape of the future.”said Alice Affatati, bioacoustics researcher at Memorial University of Newfoundland and Labrador, Saint John, Canada, and lead author of the study.

in ocean soundscape corresponds to the cacophony of vibrations produced by living organisms, natural phenomena such as waves and cracking ice or maritime transport and resource extraction.

The speed of sound at a depth of 50 meters ranges from 1450 meters per second in the polar regions to 1520 meters per second in equatorial waters.

Sound is an essential tool for many animals to communicate and move. Therefore, changes in the speed of sound can affect their ability to feed, fight, mate, avoid predators, and ultimately migrate.

… in complete transformation

According to the study, the average speed of sound should increase by 1.5%, that is, about 25 meters per second in surface waters and up to 500 meters deep by the end of the 21st century in two “future acoustic hotspots” of the Greenland Sea and the Northwest Atlantic Ocean if high rates of greenhouse gas emissions continue until 2100. .

Researchers have pointed to other hotspots − hot Spots – or sound speed can increase by 1%or more than 15 meters per second: Barents Sea, Northwest Pacific Ocean and Southern Ocean, at a depth of 50 meters, or Arctic Ocean, Gulf of Mexico and Southern Caribbean Sea, at a depth of 500 meters.

“The main impact is expected in the Arctic, where we already know that there is currently an increase in the effects of climate change. Not the whole Arctic, but a specific part, where all the factors work together to give a signal that the model predicts, overcomes the uncertainty of the model itself.”said author Stefano Salon, a researcher at the National Institute of Oceanography and Geophysical Applications in Trieste, Italy.

The temperature, pressure associated with the increase in depth and salinity of ocean waters directly affect the speed and distance traveled by sound in water. Sound waves travel faster in warmer water and it takes more time to disappear.

Impact on North Atlantic right whale

Changing soundscapes in two future acoustic foci will have a strong impact on right whales in the North Atlantic (Eubalaena icy).

According to the Red List, in 2020 the North Atlantic right whale was listed as endangered. Between 2011 and 2020, its population has declined due to increased mortality rates (mainly due to entanglement in fishing gear or collisions with ships), as well as lower reproduction rates than the average in previous years.

The study simulated the vocalizations of southern right whales in warmer oceans, and their sound likely traveled farther. “We decided to talk about one species of megafauna, but many trophic levels in the ocean depend on soundscapes or use sound.”Affatati said. “All of these hotspots are places of great biodiversity..”

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