Scientists have been mapping the changing sounds of the Arctic to improve global monitoring efforts, as the region undergoes significant transformation due to melting sea ice, new shipping routes, expanding resource development, and increasing geopolitical tensions. Researchers at Los Alamos National Laboratory have created one of the first long-term acoustic baselines for the Arctic's underwater soundscape. This effort helps in detecting and interpreting events of national security interest, such as earthquakes, underwater explosions, and ship traffic. "Before you can reliably detect something unusual, you have to understand what's normal," said Siobhan Niklasson, a scientist at Los Alamos National Laboratory and lead author of the study. "Long-term, continuous acoustic records from the Arctic are extremely rare. This dataset allows us to understand how the soundscape changes throughout the year and what kinds of events we can realistically detect under different conditions." The study, published in The Journal of the Acoustical Society of America, analyzed seven years of continuous recordings from a hydrophone placed 500 meters (1,640 feet) deep in the Beaufort Sea. The data were collected by one of 12 acoustic sensors in the National Oceanic and Atmospheric Administration's Ocean Noise Reference Station Network. The findings reveal how the Arctic's underwater soundscape changes with the seasons, and how these changes influence scientists' ability to detect important events. Unlike land and space, the world's oceans are sparsely instrumented and relatively poorly understood. Scientists have limited knowledge about how underwater background noise varies by location and season, which makes it difficult to determine how sensitive ocean-based monitoring systems can be. Hydrophones detect sound traveling through seawater, where sound can travel long distances under the right ocean conditions. Every measurement is influenced by factors such as underwater topography, waves, sea ice, wind, marine mammals, ships, and other human activities. The researchers found that the Arctic soundscape changes dramatically with the seasons. In the summer, ocean waves dominate the acoustic environment. In the winter, moving and deforming sea ice becomes the primary source of underwater noise. Seismic surveys that use air guns to map geology beneath the seafloor for scientific research and offshore resource exploration also contribute to the region's acoustic environment. Understanding these patterns helps scientists distinguish routine background sounds from signals that may require further investigation.