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Ocean Bottom Boundary Layer Turbulence Scaling From the Vibrations of a Subsea Cable With Long-range Fiber-optic Sensing

Description: 

Bottom boundary-layer (BBL) turbulence is a key sink of ocean kinetic energy and a major control on the boundary-interior exchanges that shape large-scale circulation. Yet, turbulence and bottom-drag parameterizations remain poorly constrained at basin scales. We use vibrations of an operational Ireland-Iceland subsea telecommunication cable, measured with long-range fiber-optic interferometric sensing, to recover near-bed velocity fluctuations and infer turbulence scaling. Where the cable is locally unburied, vortex-induced vibrations (VIV) generate narrow spectral peaks in fiber-sensing data whose dominant frequencies map to flow speed via the Strouhal relation, following Mata-Flores et al. (2023).

Although repeater-spaced sensing averages strain over ~100-km spans, VIV peaks remain resolvable because vibration amplitudes are large. We detect and track peaks to form vibrational frequency time-series, convert frequency to velocity with the Strouhal relation, and analyze the resulting velocity fluctuations. Using Taylor’s frozen-turbulence hypothesis to map frequency to wavenumber, we find that velocity spectra follow the classic k^-5/3 scaling of Kolmogorov (1941) for isotropic turbulence. We then fit an inertial-subrange spectral model over length scales of ~100-10 m to estimate time-dependent and location-dependent variability in turbulence parameters.

VIVs are strongest over rough shelf bathymetry. Some spans shows continuous, tidally-modulated frequency wandering with multiple simultaneous peaks, consistent with several exposed segments responding to evolving near-bed flow. Other spans exhibit intermittent, tidally-gated quasi-stationary peaks with overtones, suggestive of episodic lock-in (vortex shedding frequencies matching or exceeding cable vibrational modes, which may inhibit flow velocity estimation). Inferred values for turbulence intensity and dissipation rate are physically reasonable, demonstrating that existing telecom infrastructure can provide sustained, basin-scale constraints on BBL turbulence relevant to ocean circulation models.

Session: Fiber-Optic Sensing Applications in Seismology and Environmental Science - V

Type: Oral

Date: 4/17/2026

Presentation Time: 05:00 PM (local time)

Presenting Author: Ethan F. Williams

Student Presenter: No

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