The sea is lovely, dark and deep — but it’s not quiet. In recent decades, the explosive growth of manmade noise from ships, sonar activity and oil drilling has created a new class of worries for marine animals and the scientists who study them. In the United States, researchers and activists are renewing a long-stated concern that the noise from oil exploration may be too much to bear for the last remaining North Atlantic right whales.

In a few months, the U.S. Atlantic coast may get another layer in its cacophony of ocean noise: the dynamite-like blasts of seismic airguns, which are used to search for oil and gas deposits buried beneath the seabed…