A pressure-tolerant, miniature ocean-sensing tag with acoustic telemetry for real-time CTD monitoring.

Real-time ocean monitoring enables instantaneous oceanographic analysis and supports maritime operations. However, conventional sensors require metallic housings to withstand high hydrostatic pressure, increasing their weight and power demand. Soft electronics offer a promising alternative, but their functionality and commonly used electromagnetic communication are ineffective underwater. Here, we present a pressure-tolerant, miniaturized ocean-sensing tag that seamlessly integrates soft conductivity, temperature, and depth (CTD) sensors with acoustic transducers for in situ monitoring and underwater data transmission. Measuring 17 mm by 20 mm by 7.5 mm and weighing 4.90 g, the tag maintains reliable performance under hydrostatic pressures of up to 15 MPa, corresponding to a depth of approximately 1,500 m, and achieves underwater transmission ranges of up to 492.7 m. Field testing in the Salish Sea demonstrates wireless, real-time CTD monitoring with measurement accuracy comparable to commercial sensors and reliable acoustic telemetry (87.34% detection efficiency and 100% accuracy over evaluated transmission distances). This ocean sensing platform enables energy-efficient deployment on diverse platforms and significantly advances next-generation ocean observation and deep-sea exploration.