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Redistribution of energy available for ocean mixing by long-range propagation of internal waves

Abstract

Ocean mixing, which affects pollutant dispersal, marine productivity and global climate1, largely results from the breaking of internal gravity waves—disturbances propagating along the ocean's internal stratification. A global map of internal-wave dissipation would be useful in improving climate models, but would require knowledge of the sources of internal gravity waves and their propagation. Towards this goal, I present here computations of horizontal internal-wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2,3. Analysis of the two most energetic frequency ranges—near-inertial frequencies and semidiurnal tidal frequencies—reveals that the fluxes in both frequency bands are of the order of 1 kW m-1 (that is, 15–50% of the energy input) and are directed away from their respective source regions. However, the energy flux due to near-inertial waves is stronger in winter, whereas the tidal fluxes are uniform throughout the year. Both varieties of internal waves can thus significantly affect the space-time distribution of energy available for global mixing.

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Figure 1: Hydrographic profiles, mode structure and instrument depths for a typical mooring.
Figure 2: Typical near-inertial time series.
Figure 3: Source terms and energy-flux vectors.

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Acknowledgements

I thank E. D'Asaro, E. Kunze and C. Garrett for insights and discussions, and M. Whitmont for quality control and preparation of the mooring data. This work was supported by the Office of Naval Research Young Investigator award.

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Correspondence to Matthew H. Alford.

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Alford, M. Redistribution of energy available for ocean mixing by long-range propagation of internal waves. Nature 423, 159–162 (2003). https://doi.org/10.1038/nature01628

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