Monitoring deep‐ocean temperatures using acoustic ambient noise

Measuring temperature changes of the deep oceans, important for determining the oceanic heat content and its impact on the Earth's climate evolution, is typically done using free‐drifting profiling oceanographic floats with limited global coverage. Acoustic thermometry provides an alternative and complementary remote sensing methodology for monitoring fine temperature variations of the deep ocean over long distances between a few underwater sources and receivers. We demonstrate a simpler, totally passive (i.e., without deploying any active sources) modality for acoustic thermometry of the deep oceans (for depths of ~ 500–1500 m), using only ambient noise recorded by two existing hydroacoustic stations of the International Monitoring System. We suggest that passive acoustic thermometry could improve global monitoring of deep‐ocean temperature variations through implementation using a global network of hydrophone arrays.