In 1956, a documentary by Jacques Cousteau won both the Palme d'Or and an Oscar award. This film was called, "Le Monde Du Silence," or, "The Silent World." The premise of the title was that the underwater world was a quiet world. We now know, 60 years later, that the underwater world is anything but silent.
Although the sounds are inaudible above water depending on where you are and the time of year, the underwater soundscape can be as noisy as any jungle or rainforest. Invertebrates like snapping shrimp, fish and marine mammals all use sound. They use sound to study their habitat, to keep in communication with each other, to navigate, to detect predators and prey. They also use sound by listening to know something about their environment.
Take, for an example, the Arctic. It's considered a vast, inhospitable place, sometimes described as a desert, because it is so cold and so remote and ice-covered for much of the year. And despite this, there is no place on Earth that I would rather be than the Arctic, especially as days lengthen and spring comes.
To me, the Arctic really embodies this disconnect between what we see on the surface and what's going on underwater. You can look out across the ice—all white and blue and cold—and see nothing. But if you could hear underwater, the sounds you would hear would at first amaze and then delight you. And while your eyes are seeing nothing for kilometers but ice, your ears are telling you that out there are bowhead and beluga whales, walrus and bearded seals. The ice, too, makes sounds. It screeches and cracks and pops and groans, as it collides and rubs when temperature or currents or winds change. And under 100 percent sea ice in the dead of winter, bowhead whales are singing.
And you would never expect that, because we humans, we tend to be very visual animals. For most of us, but not all, our sense of sight is how we navigate our world. For marine mammals that live underwater, where chemical cues and light transmit poorly, sound is the sense by which they see. And sound transmits very well underwater, much better than it does in air, so signals can be heard over great distances.
In the Arctic, this is especially important, because not only do Arctic marine mammals have to hear each other, but they also have to listen for cues in the environment that might indicate heavy ice ahead or open water. Remember, although they spend most of their lives underwater, they are mammals, and so they have to surface to breathe. So they might listen for thin ice or no ice, or listen for echoes off nearby ice.
Arctic marine mammals live in a rich and varied underwater soundscape. In the spring, it can be a cacophony of sound.
But when the ice is frozen solid, and there are no big temperature shifts or current changes, the underwater Arctic has some of the lowest ambient noise levels of the world's oceans. But this is changing. This is primarily due to a decrease in seasonal sea ice, which is a direct result of human greenhouse gas emissions. We are, in effect, with climate change, conducting a completely uncontrolled experiment with our planet.
Over the past 30 years, areas of the Arctic have seen decreases in seasonal sea ice from anywhere from six weeks to four months. This decrease in sea ice is sometimes referred to as an increase in the open water season. That is the time of year when the Arctic is navigable to vessels. And not only is the extent of ice changing, but the age and the width of ice is, too.
Now, you may well have heard that a decrease in seasonal sea ice is causing a loss of habitat for animals that rely on sea ice, such as ice seals, or walrus, or polar bears. Decreasing sea ice is also causing increased erosion along coastal villages, and changing prey availability for marine birds and mammals.
Climate change and decreases in sea ice are also altering the underwater soundscape of the Arctic. What do I mean by soundscape? Those of us who eavesdrop on the oceans for a living use instruments called hydrophones, which are underwater microphones, and we record ambient noise—the noise all around us. And the soundscape describes the different contributors to this noise field. What we are hearing on our hydrophones are the very real sounds of climate change. We are hearing these changes from three fronts: from the air, from the water and from land.
First: air. Wind on water creates waves. These waves make bubbles; the bubbles break, and when they do, they make noise. And this noise is like a hiss or a static in the background. In the Arctic, when it's ice-covered, most of the noise from wind doesn't make it into the water column, because the ice acts as a buffer between the atmosphere and the water. This is one of the reasons that the Arctic can have very low ambient noise levels. But with decreases in seasonal sea ice, not only is the Arctic now open to this wave noise, but the number of storms and the intensity of storms in the Arctic has been increasing. All of this is raising noise levels in a previously quiet ocean.
Second: water. With less seasonal sea ice, subarctic species are moving north, and taking advantage of the new habitat that is created by more open water. Now, Arctic whales, like this bowhead, they have no dorsal fin, because they have evolved to live and swim in ice-covered waters, and having something sticking off of your back is not very conducive to migrating through ice, and may, in fact, be excluding animals from the ice. But now, everywhere we've listened, we're hearing the sounds of fin whales and humpback whales and killer whales, further and further north, and later and later in the season. We are hearing, in essence, an invasion of the Arctic by subarctic species. And we don't know what this means. Will there be competition for food between Arctic and subarctic animals? Might these subarctic species introduce diseases or parasites into the Arctic? And what are the new sounds that they are producing doing to the soundscape underwater?
And third: land. And by land...I mean people. More open water means increased human use of the Arctic. Just this past summer, a massive cruise ship made its way through the Northwest Passage—the once-mythical route between Europe and the Pacific. Decreases in sea ice have allowed humans to occupy the Arctic more often. It has allowed increases in oil and gas exploration and extraction, the potential for commercial shipping, as well as increased tourism. And we now know that ship noise increases levels of stress hormones in whales and can disrupt feeding behavior. Air guns, which produce loud, low-frequency "whoomps" every 10 to 20 seconds, changed the swimming and vocal behavior of whales. And all of these sound sources are decreasing the acoustic space over which Arctic marine mammals can communicate.
Now, Arctic marine mammals are used to very high levels of noise at certain times of the year. But this is primarily from other animals or from sea ice, and these are the sounds with which they've evolved, and these are sounds that are vital to their very survival. These new sounds are loud and they're alien. They might impact the environment in ways that we think we understand, but also in ways that we don't. Remember, sound is the most important sense for these animals. And not only is the physical habitat of the Arctic changing rapidly, but the acoustic habitat is, too. It's as if we've plucked these animals up from the quiet countryside and dropped them into a big city in the middle of rush hour. And they can't escape it.
So what can we do now? We can't decrease wind speeds or keep subarctic animals from migrating north, but we can work on local solutions to reducing human-caused underwater noise. One of these solutions is to slow down ships that traverse the Arctic, because a slower ship is a quieter ship. We can restrict access in seasons and regions that are important for mating or feeding or migrating. We can get smarter about quieting ships and find better ways to explore the ocean bottom. And the good news is, there are people working on this right now. But ultimately, we humans have to do the hard work of reversing or at the very least decelerating human-caused atmospheric changes.
So, let's return to this idea of a silent world underwater. It's entirely possible that many of the whales swimming in the Arctic today, especially long-lived species like the bowhead whale that the Inuits say can live two human lives—it's possible that these whales were alive in 1956, when Jacques Cousteau made his film. And in retrospect, considering all the noise we are creating in the oceans today, perhaps it really was "The Silent World."