Navy Scientists Find New "Channel" In Beaufort Sea Where Sound Travels 4X Farther Than Normal
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As the drone sank, it traveled through the three key layers of water. The first, a slightly warmer layer from about 50 to 80 meters depth, has long existed in summer months. But thanks to climate change, this layer is now permanent and warmer than before. “The ice has been melting more in the summer, the waters are being exposed to the atmosphere, and the solar heating warms them up,” explains John M Toole, an oceanographer at Woods Hole Oceanographic Institution.
The second was a cold layer from 100 to 200 meters. The third was another warm layer centered around 200 meters deep. This layer was also created by climate change, and is the result of heat flowing into the Arctic Ocean from the Pacific through the Bering Strait (among other factors), says Mary-Louise Timmermans, an oceanographer at Yale University.
As ongoing research has shown, these three layers have created a channel in the ocean—sometimes called the Beaufort Lens—through which sound waves travel particularly well. The sound waves travel in the coldest middle layer, and the surrounding warmer layers keep the sound waves contained. This happens because of a particular quirk of how sound waves interact with water of different temperatures.
At low water temperatures, such as those in the Arctic, sound waves propagate most slowly through the very coldest water. Sound waves also bend toward the places where they travel slowest. So when a sound wave reaches the buffering warmer layers, it bends back toward the colder layer in the middle. The result is that sounds that used to peter out after 100 kilometers can now be detected 400 kilometers away. The navy is learning how the Beaufort Lens works acoustically, but they still don’t know exactly where it extends geographically—a map that is probably changing every year because of ocean warming. Unfortunately, Schmidt and his drone weren’t able to give them all the information they need.
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https://www.hakaimagazine.com/article-short/global-warming-changing-how-ocean-carries-sound