Dziak, R.P., J.H. Haxel, H. Matsumoto, T.-K. Lau, S. Heimlich, S. Nieukirk, D.K. Mellinger, J. Osse, C. Meinig, N. Delich, and S. Stalin (2017): Ambient sound at Challenger Deep, Mariana Trench.Oceanography, 30 (2), doi:10.5670/oceanog.2017.240.
You might imagine the bottom of the ocean’s deepest point, seven miles down, to be a very quiet place. However, NOAA and partner scientists, making the first recordings from the Challenger Deep trough in the Mariana Trench in the Pacific Ocean, found something remarkably different: a wide variety of human-caused and natural sounds, including the hum of ship propellers, active sonar, earthquakes, baleen whales, and a category 4 typhoon passing near the sensor.
Human-generated noise has increased steadily over the past several decades. This project, which was funded by the NOAA Office of Ocean Exploration and Research, was designed to establish a baseline for ambient noise in the deepest part of the Pacific Ocean. The collection of these first recordings will allow scientists to detect changes in future noise levels and determine how such changes might affect marine animals that use sound to communicate, navigate, and feed, such as whales, dolphins, and fish.
For three weeks, a titanium-encased hydrophone recorded ambient noise from the ocean floor at a depth of more than 36,000 feet in the Challenger Deep trough in the Mariana Trench near Micronesia. The team of researchers from the NOAA Pacific Marine Environmental Laboratory, Oregon State University, and the U.S. Coast Guard were surprised by how much they heard. Along with the hydrophone, the researchers also included a high-precision pressure sensor on the mooring to measure the ocean depth. The sensor returned a value of 10,854.7 m, providing only the fourth direct measurement of ocean depth made at Challenger Deep since the first measurement taken there in 1960.
A paper recently published in Oceanography (Dziak et al., 2017) offers a closer look at these sources of sound and their impact on the ambient soundscape of this deep-ocean ecosystem, as well as the cutting-edge ocean technology developed to make these unique measurements.