It’s getting louder and louder in the Arctic marine areas. This is because, on the one hand, shipping traffic is increasing more and more due to people’s growing interest in the Arctic as a supplier of raw materials, a transport route and a place to spend the holidays. On the other hand, the increasingly warmer water probably also transmits the sounds further and faster. This is the conclusion of a study by Italian researchers.
In their study, the research team from the National Institute of Oceanography and Applied Geophysics in Trieste found out that if ocean temperatures continue to rise, sound in certain regions of the North Atlantic and Arctic will propagate up to 25 meters per second faster than under current conditions. According to the team, the depths most affected are those where most of the biodiversity occurs, that is, between 50 and 500 meters.
Furthermore, the results show that there are large regional differences and that the colder regions are more affected. This is likely due to the physical conditions in the regions, as the team examined how temperature, depth, and salinity would evolve in a high-emission scenario. “The major impact is expected in the Arctic, where we know already there is amplification of the effects of climate change now,” explains co-author Stefano Salon. “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.” In particular, the Greenland Sea, the area between Greenland and Svalbard, the Barents Sea and the Bering Sea area are among the Arctic regions where sound will travel faster. In the eastern part of the Southern Ocean, too, the results of the study show that sound propagation is likely to accelerate, at least in the upper 50 meters.
Many people know the songs of humpback whales, the clicking sounds of orcas or the whistling sounds of belugas. Numerous Arctic marine mammals use the fact that sound is better transported in water than in air to orient themselves or communicate with conspecifics. Especially in mating, this plays an important role, as this is how the sexes find each other in the first place. Sound usually travels at about 1,450 meters per second in polar regions. On the one hand, the faster dispersal due to warming could lead to the marine mammals’ calls spreading faster and further than before. Using the example of northern right whales, which occur in the “sound hotspots” identified by the researchers, it was calculated that transmission loss would actually decrease in warmer waters, allowing marine mammals to hear each other farther away. This would be of great importance for marine mammals, which are already threatened, as their numbers are already so low that it is becoming difficult for bulls and cows to find each other, not least because of the noise created by shipping and underwater resource extraction.
But this is exactly another negative aspect that warming of the Arctic (and Antarctic) waters would bring: sound from noise sources would also travel faster and farther than before, and it would not only affect marine mammals. This is also what the Italian scientists say: “We chose to talk about one megafauna species,” says Alice Affatati, the lead author of the study. “But many trophic levels in the ocean are affected by the soundscape or use sound, not just whales.” Previous studies had already shown that fish also use sound to communicate and perceive their environment and are negatively affected by increasing underwater noise. Add to this the already known direct physiological and ecological effects of warming, and the stress on Arctic marine life is likely to increase. But data on this are still lacking, and the team of authors calls for more study of the combination of stressors, including different approaches. “With complicated problems like climate change, to combine different approaches is the way to go,” Chiara Scaini, the third author, says. What is certain is that the polar underwater world, which is actually perceived as quiet, is likely to get even hotter in the future, and not just in terms of temperature.
Dr Michael Wenger, PolarJournal
Contributed image: Screenshot underwater explosion (C)Youtube Turtle Pictures
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