People enjoy the sunset over Stinson Beach in California on Nov. 29, 2024.
San Diego, California – In a study spanning 15 years of underwater recordings, researchers from Scripps Institution of Oceanography at the University of California San Diego have uncovered how the ocean has quietly captured the effects of climate change and human activity. Using data collected by six seafloor microphones installed off the coast of Southern California in 2008, scientists have pieced together a detailed acoustic history of the region’s waters — one that reveals the movements of whales, the rise and fall of global shipping noise, and even the economic reverberations of the 2008 financial crisis.
Published June 5 in the Journal of the Acoustical Society of America, the study is the longest-running acoustic timeseries on the California coast. It highlights how listening to the ocean can provide insights into the health of marine ecosystems and the far-reaching impacts of human behavior. By focusing on specific frequency ranges, researchers were able to isolate the calls of fin and blue whales, noise from commercial ships, and even wind-generated sounds. These acoustic fingerprints were then compared with climate data, shipping records, wind patterns, and economic events.
The findings are striking. During the marine heatwave of 2014–2016 — an event nicknamed “the Blob” — whale calls decreased by up to 50% in southern sites while increasing farther north, suggesting that whales followed cooler waters along the California Current. Similarly, ship noise dropped by over 40% during the 2008–2009 recession and had not fully returned to pre-crisis levels even by 2023. Researchers also detected daily “rush hours” at sea, with ship noise peaking as vessels moved in and out of the Ports of Los Angeles and Long Beach.
The study uncovered a clear link between whale vocalizations and the Pacific Decadal Oscillation (PDO), a long-term climate cycle in the North Pacific. Fin whale calls, for example, were found to be 30% more frequent during the PDO’s cool phase than its warm phase — a key finding that connects animal behavior to broader climate patterns.
These insights illustrate how ocean soundscapes can serve as real-time indicators of environmental change. For marine life, especially species like whales that spend most of their lives underwater, sound is often the only reliable signal researchers can track over vast distances.
As marine heatwaves and climate shifts grow more frequent, scientists argue that acoustic monitoring is essential. Yet long-term data collection remains vulnerable to funding disruptions. Without consistent support, researchers warn, the opportunity to observe and respond to deep, structural changes in the ocean could be lost.
