Why Are the World’s Oceans Getting Louder Each Year?

If you stand on a beach in California or Maine, the ocean can seem peaceful. You hear waves rolling in, maybe a distant boat engine, perhaps seabirds overhead. But beneath the surface, the ocean is alive with sound. Whales send deep calls across miles. Dolphins whistle and click. Fish produce grunts and pulses. Even shrimp create a steady crackling noise.

In water, sound travels about five times faster than it does in air and much farther. For marine animals, hearing is not optional. It is how they navigate, find food, locate mates, and stay together. In many ways, sound is their version of sight.

Over the past several decades, scientists have found that this underwater world has grown steadily louder. The change is not from storms or natural shifts. It is largely from us.


What the research shows

Commercial shipping is one of the biggest sources of low-frequency ocean noise. Large cargo vessels produce a constant rumble that travels long distances. A study published in Environmental Pollution found that global shipping noise emissions increased rapidly in recent years, doubling roughly every decade in some regions as maritime trade expanded.

Researchers track these changes using hydrophones, underwater microphones anchored to the seafloor or attached to buoys. Long-term acoustic records collected by oceanographic institutions show that in busy shipping lanes, sound levels below 100 hertz are significantly higher than in quieter waters. Low-frequency sound travels especially far, meaning noise from ships can affect areas hundreds of miles away.

The impact is not just theoretical. A study published in the Proceedings of the National Academy of Sciences examined North Atlantic right whales in the Bay of Fundy after shipping traffic declined following September 11, 2001. During that quieter period, researchers measured lower levels of stress hormones in the whales. When vessel traffic resumed, stress levels increased again. The findings offered rare biological evidence that noise can directly affect whale health.

During the early months of the COVID-19 pandemic, shipping activity temporarily slowed in parts of the world. Acoustic monitoring off the California coast recorded a measurable drop in low-frequency noise. The ocean, for a short time, became noticeably quieter.

Why noise matters to marine life

For baleen whales, whose calls are naturally low in frequency, ship noise overlaps directly with their communication range. When the background sound increases, their calls do not travel as far. This phenomenon, known as acoustic masking, reduces the distance over which whales can hear one another.

Imagine trying to call out to a friend across a park while a constant truck engine runs beside you. Now imagine that engine never stops.

Some species respond by changing their behavior. Research has shown that certain whales lengthen their calls or shift pitch in noisy conditions. That may help them be heard, but it can also require more energy. In other cases, marine mammals leave feeding or breeding grounds when sound levels rise.

The effects extend beyond whales and dolphins. A study published in Scientific Reports found that noise resembling shipping and construction sounds altered the behavior of bottom-dwelling invertebrates. Those small organisms play a key role in mixing sediment and recycling nutrients. Changes in their activity can influence entire marine ecosystems.

When sound becomes constant and widespread, it shrinks the effective acoustic habitat available to animals. The ocean may look unchanged from the shore, but its communication network is under strain.

Can the ocean be quieter?

Scientists are not simply documenting the problem. They are studying solutions.

Research shows that reducing ship speeds can significantly lower underwater noise. Even modest speed reductions can decrease acoustic output. Engineering improvements in propeller design and hull maintenance can also make vessels quieter.

Some researchers are exploring the idea of protecting acoustic refuges, areas where underwater noise remains relatively low. Just as marine protected areas safeguard coral reefs and fisheries, quieter zones could preserve critical communication space for marine species.

The ocean’s soundtrack has always included wind, waves, and animal voices. What is new is the constant mechanical layer that now fills much of the sea.

Science makes one thing clear. Sound is not a minor detail of ocean life. It is central to survival. As shipping and coastal development continue to grow, understanding and managing underwater noise will be essential to protecting the marine world that so many communities in the United States depend on.