We don't usually think of oceans as being filled with sound.

But that's exactly what oceanographer Kate Stafford studies -- the underwater soundscapes of the world's oceans, which are filled with noises from waves crashing to ice screeching to whales singing. She also studies migratory patterns and geographic variation of marine mammals, and in a recent Tedx Talk, Stafford discussed how climate change is changing the sonic landscape of oceans. Using the Arctic Ocean as a case study, she explained how the human impact on climate could have unknown consequences for marine life which rely on listening to sounds in the ocean for survival.

As Stafford explains, there are three main ways climate change and the resulting retreat of sea ice, particularly in the Arctic, are affecting the soundscapes of the ocean. First, is the role that sea ice plays in creating sounds. Although in the dead of winter, when ice covers the ocean, ambient noise is almost nonexistent, when the weather warms and ice starts to melt and move, "The ice, too, makes sounds," says Stafford. "It screeches and cracks and pops and groans, as it collides and rubs when temperature or currents or winds change."

Humans rely on sight most heavily of all the senses, but underwater mammals rely on sound, as visibility underwater is poor and sound travels better through water and so can be heard over great distances. It is important for mammals, who need to come up to the surface to breathe, to know where there is ice on the surface of the water. They use sounds to communicate with each other and to detect changes in their environment, such as by using echoes.

Humans are directly impacting the soundscape of the Arctic Ocean through more shipping activity. Due to the considerable decrease in seasonal sea ice, which in turn is also an increase in the "open water season," the Arctic is navigable to ships. Not only does decreasing sea ice reduce wildlife habitat and erode coastal villages, but it also allows humans to use bigger ships more frequently, which create loud noises in the water. A cruise ship crossed the Northwest Passage between Europe and the Pacific during the summer of 2016, and shipping routes are made for commercial transportation of oil and and gas exploration and extraction. These human-made sounds may interfere with communications among whales or be painful to their sensitive ears.

Due to warmer waters and less sea ice, Stafford and scientists are seeing other species of whales and mammals moving further north. The reason most Arctic Ocean whales like bowhead whales do not have dorsal fins is that they are not conducive to swimming with ice. However scientists are now seeing more "subarctic" whales with dorsal fins such as humpbacks and killer whales. This may mean competition for food among Arctic whales, or the potential for introducing new parasites or bacteria to the Arctic animals.

There are still many unanswered questions about the impact of human-induced climate change on the soundscape of the world's oceans, but it is clear that they are getting noisier. Studying underwater sounds is yet another perspective on the sensitivity of marine life and humanity's relationship to the world's oceans.