Observing coastal ocean and ice physics with seafloor distributed acoustic sensing

When distributed acoustic sensing (DAS) is applied to seafloor fiber optic cables, the observations of cable strain record oceanographic signals including acoustic waveforms in the water column and pressure variations from ocean waves. In comparison to other traditional sensors, such as seafloor moorings with pressure sensors and hydrophones, DAS provides much higher spatial resolution — up to 2-m spacing on 10s of kilometers of cable — with the trade-off of reduced signal-to-noise. Here, we particularly focus on what we can learn about ocean physics in seasonally sea ice-covered coastal oceans with seafloor DAS. Experiments have been completed on a variety of cable types and deployments ranging from seafloor telecommunication cables and scientific communication cables to purpose-deployed lightweight cables. Ocean surface waves can be observed in high resolution in a phase-resolved manner and converted to bulk statistics with the use of in situ calibration. In the presence of sea ice, the attenuation rate of surface waves can also be derived to provide additional insight into ice distribution and concentration. More bespoke deployments of fiber optic cables, such as on top of sea ice and vertically through the water column, can provide more targeted information on environments and processes of interest.