Fiber-Optic Observations of Internal Waves and Tides
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1.
California Institute of Technology
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2.
University of Washington
Abstract
Although typically used to measure dynamic strain from seismic and acoustic waves, Rayleigh‐based distributed acoustic sensing (DAS) is also sensitive to temperature, offering longer range and higher sensitivity to small temperature perturbations than conventional Raman‐based distributed temperature sensing. Here, we demonstrate that ocean‐bottom DAS can be employed to study internal wave and tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. First, we show temperature transients up to about 4 K from a power cable in the Strait of Gibraltar south of Spain, associated with passing trains of internal solitary waves in water depth <200 m. Second, we show the propagation of thermal fronts associated with the nonlinear internal tide on the near‐critical slope of the island of Gran Canaria, off the coast of West Africa, with perturbations up to about 2 K at 1‐km depth and 0.2 K at 2.5‐km depth. With spatial averaging, we also recover a signal proportional to the barotropic tidal pressure, including the lunar fortnightly variation. In addition to applications in observational physical oceanography, our results suggest that contemporary chirped‐pulse DAS possesses sufficient long‐period sensitivity for seafloor geodesy and tsunami monitoring if ocean temperature variations can be separated.
Copyright and License
© 2023. American Geophysical Union. All Rights Reserved.
Acknowledgement
The authors acknowledge Red Electrica de España and CANALINK-Canarias submarine link S.L., part of group Instituto Tecnológico y de Energías Renovables (ITER) and Cabildo de Tenerife, for providing cable access and support during the DAS deployments. Funding for this project was provided through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S), the Spanish MCIN/AEI/10.13039/501100011033 and the European Union NextGenerationEU/PRTR Program under projects PSI ref. PLEC2021-007875 and TREMORS ref. CPP2021-008869, the Spanish MCIN/AEI/10.13039/501100011033 and FEDER Program under projects PID2021-128000OB-C21 and PID2021-128000OB-C22, and the European Innovation Council under Grant SAFE: ref. 101098992. E. F. W. was supported by a National Science Foundation Graduate Research Fellowship. M.C. was funded by the European Union (HORIZON-MSCA-2021-PF MOORING, grant agreement no. 101064423). M. R. F.-R. and H. F. M. acknowledge support from the MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR under Grants RYC2021-032167-I and RYC2021-035009-I, respectively. J. C. acknowledges support from the National Science Foundation (Grant OCE-2023161). K. B. W. acknowledges funding provided by the National Science Foundation (Grants OCE-2045399 and OCE-185076) and the U.S. Office of Naval Research (Grant N00014-18-1-2803). Z. Z. acknowledges support from the Moore Foundation and NSF under CAREER Award 1848166.
Contributions
Data curation: E. F. Williams, A. Ugalde, H. F. Martins, C. E. Becerril.
Formal analysis: E. F. Williams, A. Ugalde, H. F. Martins, M. Claret.
Methodology: H. F. Martins, M. R. Fernandez-Ruiz, M. Gonzalez-Herraez, S.
Martin-Lopez.
Software: K. B. Winters.
Supervision: A. Ugalde, J. Callies, M. Gonzalez-Herraez, S. Martin-Lopez, J. L.
Pelegri, K. B. Winters, Z. Zhan.
Writing – original draft: E. F. Williams.
Writing – review & editing: A. Ugalde, H. F. Martins, C. E. Becerril, J. Callies, M. Claret, M. R. Fernandez-Ruiz, M. Gonzalez-Herraez, S. Martin-Lopez, J. L. Pelegri, K. B. Winters, Z. Zhan.
Data Availability
All 4.5 days of DAS data from the Strait of Gibraltar necessary to reproduce Figure 2 and the 3 days of DAS data from Gran Canaria necessary to reproduce Figures 3 and 4 are available through the CaltechDATA repository (Williams et al., 2023). Figures were produced using GMT6 (Wessel et al., 2019).
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Additional details
- Fundación Carmen y Severo Ochoa
- CEX2019‐000928‐S
- Ministerio de Ciencia, Innovación y Universidades
- MCIN/AEI/10.13039/501100011033
- European Union
- PLEC2021-007875
- European Union
- CPP2021-008869
- Ministerio de Ciencia, Innovación y Universidades
- PID2021-128000OB-C21
- Ministerio de Ciencia, Innovación y Universidades
- PID2021-128000OB-C22
- HORIZON EUROPE European Innovation Council
- 101098992
- European Union
- 101064423
- European Union
- RYC2021-032167-I
- European Union
- RYC2021-035009-I
- National Science Foundation
- OCE‐2023161
- National Science Foundation
- OCE‐2045399
- National Science Foundation
- OCE‐185076
- Office of Naval Research
- N00014‐18‐1‐2803
- Gordon and Betty Moore Foundation
- National Science Foundation
- EAR-1848166
- Accepted
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2023-09-05Manuscript Accepted
- Available
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2023-09-20Available Online
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory
- Publication Status
- Published