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Large-scale impacts of the mesoscale environment on mixing from wind-driven internal waves

Nature Geoscience (2018) | Download Citation

Abstract

Oceanic mesoscale structures such as eddies and fronts can alter the propagation, breaking and subsequent turbulent mixing of wind-generated internal waves. However, it has been difficult to ascertain whether these processes affect the global-scale patterns, timing and magnitude of turbulent mixing, thereby powering the global oceanic overturning circulation and driving the transport of heat and dissolved gases. Here we present global evidence demonstrating that mesoscale features can significantly enhance turbulent mixing due to wind-generated internal waves. Using internal wave-driven mixing estimates calculated from Argo profiling floats between 30° and 45° N, we find that both the amplitude of the seasonal cycle of turbulent mixing and the response to increases in the wind energy flux are larger to a depth of at least 2,000 m in the presence of a strong and temporally uniform field of mesoscale eddy kinetic energy. Mixing is especially strong within energetic anticyclonic mesoscale features compared to cyclonic features, indicating that local modification of wind-driven internal waves is probably one mechanism contributing to the elevated mixing observed in energetic mesoscale environments.

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Acknowledgements

The authors are grateful for the support of NSF OCE-1259573 and for valuable comments from K. Polzin and E. Kunze.

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Affiliations

  1. Applied Physics Laboratory, University of Washington, Seattle, WA, USA

    • C. B. Whalen
  2. Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA

    • J. A. MacKinnon
    •  & L. D. Talley

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C.B.W conceived of the study, conducted the analysis, and wrote the manuscript. Both J.A.M and L.D.T. contributed to the analysis and writing of the manuscript.

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The authors declare no competing interests.

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Correspondence to C. B. Whalen.

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https://doi.org/10.1038/s41561-018-0213-6