Increase in shipping traffic will cause sound pollution

The National Oceanic and Atmospheric Administration’s 2021 Arctic Report Card was released last week and among reports documenting rising surface air and ocean temperatures and decrease in sea ice, one study stood out as to be of interest to coastal communities along the Bering Strait: The study of underwater sound.

K.M. Stafford, of the Applied Physics Laboratory at the University of Washington, wrote a paper for the report card titled “The changing Arctic marine soundscape.” In it, she points to three highlights of her research: “Less sea ice and increasing storminess are making Arctic waters louder during the open water season due to increased wind and wave noise; arctic marine mammals are changing their migratory patterns and subarctic visitors are heard for more of the year and further north as sea ice loss opens habitat for them; arctic shipping traffic between the Pacific and Atlantic Oceans continues to increase and with it, ambient noise levels are increasing in the frequency bands used by marine mammals.”

Sound waves move much faster through water than through air, but the actual speed depends on water temperature and pressure. As the waters of the ocean warm, the same sound wave will sound differently in a few years, due to warming waters. This simple fact of physics has potentially huge implications for marine mammals, and the people who rely on the sea for their life and livelihood.

Stafford’s paper is broken into three sections, for the three different types of sounds: geophony, the sounds of the earth, water, and wind; biophony, the sounds of plants and animals, such as whale song or walrus barks; and anthrophony, the sound of humans. Human noises can include those from natural resource extraction, shipping vessels, and even smaller, local boats.

In the geophony section, Stafford compares data which shows that wind speeds over open water leads to much higher sound levels than the same wind over heavy ice. Climate change is melting sea ice, and with it, the dampening effect the ice can have is eroded away. As periods of open water lengthen, sound levels in the Arctic will also rise.

Stafford’s study of biophony shows that marine mammals are the largest contributors to the soundscape. According to her research, “in the winter and spring, most Arctic species make reproductive displays that are more elaborate and cover a greater range of frequencies than signals they produce when migrating or feeding.” But if the sounds change due to the lengthening and shortening of seasons, this could also overlap with, and impact, the migration and mating seasons. This may have long-term impacts on marine mammal populations.

The anthrophony section of the paper is called “When ‘sound’ becomes ‘noise.’” During the press event at the launch of the Arctic Report Card last week, Stafford referred to her research as looking at underwater sound as a form of pollution. “We are hearing increasing human use of the Arctic,” she said.

Human behavior can have serious implications for animals living on and under the sea. “The most persistent, and growing source of anthrophony in the Arctic are cargo and

fishing vessels, most of which sail the Northern Sea Route,” Stafford writes. Because this is a new and evolving phenomenon, “Arctic species may have a lower tolerance of, and reach more strong to, such noise.”

Sound is the primary modality for marine mammals to find where they are going, food, or mates. But, Stafford writes, “many anthropogenic sources overlap in frequency with the sounds produced and received by marine mammals.” This means that the increased ship traffic through the Arctic and the Bering Strait can interfere with animals’ ability to “navigate, communicate, and reproduce.”