Constraining fiber-optic cable observations of internal waves with conventional oceanographic measurements

Ocean mixing plays a crucial role in the Earth’s climate, however quantifying it is challenging because energy enters the ocean at basin-scale but it dissipates at cm-scale over the vast ocean. Internal waves play an important role in the cascade of energy toward dissipative scales. Energy transfers to the internal wave field are greatly enhanced through flow interactions with topography. Observations of wave-topography interactions are, however, scarce. Distributed Acoustic Sensing (DAS) has recently opened a new door for exploring near-bottom wave dynamics using fibre-optic cables at unprecedented spatio-temporal resolution (meters and seconds) over long spatio-temporal scales (kilometers and months). DAS is particularly attractive as it can use telecommunication cables already in place so that it could potentially be implemented at global scale.

Here we present repeated DAS observations on the continental slope east of Gran Canaria island complemented with contemporaneous hydrographic and velocity data collected with bottom moorings for the first time. Results show that upslope propagation of internal tides is a permanent feature at this site. DAS-inferred tidal temperature oscillations of 2 K magnitude agree with direct temperature observations. Preliminary results showing spectral peaks at the M₂ tidal frequency and its harmonics is suggestive of wave-wave interactions. Finally, the potential of DAS to estimate lateral diffusion coefficients is considered.